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Help - another overboosting problem

60K views 336 replies 21 participants last post by  andrewk 
#1 ·
I've been lurking occasionally for quite a while, but I'm getting so fed up with the overboost issue on my 'Troll that I thought I'd see if any of you guys have a clue what's going on with my motor. I know there are lots of threads on here about overboosting and turbo problems and I've read most of them already.

The motor:

A (late) 2005 Nissan Patrol 3.0D GR (what you call a GU, I think) with a ZD30 engine. It is completely standard - no mods of any kind. It has done 50,000 miles (80,000Km) from new. It starts first time, performance is fine, it uses about as much fuel as Patrol's usually do. It doesn't make smoke or use more than a tiny amount of oil between services.


The problem:

Occasionally & usually up hill under load at 2500-2800rpm there is a sudden power loss. Pressing the loud pedal slowly to the floor achieves nothing. Lifting off restores performance. The ECM stores a 0905 error code (boost pressure)


What have I done so far:

1) Replaced MAF sensor (cheapie off Ebay). Tested new sensor with DMM and measured output volts against engine speeds. It's exactly as it should be (per workshop manual)

2) Replace MAP (boost) sensor. Done by Westway Nissan in Oldham. God those are expensive from Nissan!!! This seemed to cure the problem for about 8 or 9000 miles and nearly 12 months. Just before Xmas 2010, the problem returned.

3) Westway Nissan replaced the MAP sensor under warranty, as it seemed the most likely culprit. It didn't cure the problem. I still have the overboost error.

4) Today, I removed the vac hose from the VNT boost control solenoid, put it in my mouth and sucked hard. The turbo VNT rod moved smoothly to the full extent of its travel. I put my tongue on the end of the hose - and the VNT rod stayed exactly where it was. I gradually released the vacuum and the VNT level smoothly returned to its rest position.

5) I've bought a boost pressure gauge (electronic stepper motor type) but haven't yet fitted it.

What do I *think* I know:

* The MAF sensor is probably OK - I'll test it in the morning again to be sure
* The MAP (boost) sensor is *probably* OK - though I'll test that in the morning too.
* The turbo itself is probably fine - at least the vanes aren't stuck or sticky.
* The VNT actuator works and its diaphragm doesn't leak.
* The vacuum hose to the VNT actuator doesn't leak.
* I don't know how to test the VNT vac control solenoid. Any thoughts?

I know that some of the folks on the forum have cured boost problems by fitting a Dawes valve (whatever one of those is), but this motor has worked fine for over 40,000 miles from new and I'm determined that it's going to work fine again, without making any mods.

One possible option is to give the 'Troll to Westway Nissan in Oldham - and tell them to give it back to me only when they've fixed it. I'm more than a bit nervous of that - the last time they had their hands on it, they tried to clear the ECM error codes with a Consult III & didn't understand why that didn't work. I can just imagine them replacing bits at random until it stops generating the overboost error. No thanks .........

Am I missing something obvious here? Has anyone got any thoughts or suggestions about what I should do next?

Andrew
 
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#2 ·
Hi,

1) I would use a original MAF not some unknown brand.

2) The MAP sensor can become dirty with oil from intercooler so fit a catch can and clean sensor with some MAF spray (clean the old MAF too).

3) Install a boost gauge so you can check the pressure the turbo generates.

4) Fit an EGR plate, dawes valve and neddle valve to have manual boost

or you can take it to Ni$$an and pay...
 
#3 ·
Hi,

1) I would use a original MAF not some unknown brand.
Yes, so would I, usually. The calibration of this "unknown brand" is actually spot on.

2) The MAP sensor can become dirty with oil from intercooler so fit a catch can and clean sensor with some MAF spray (clean the old MAF too).
Yes, I'm sure it can - but this one is a geniune Nissan part and is new


3) Install a boost gauge so you can check the pressure the turbo generates.
Mmm ... I have just bought one


4) Fit an EGR plate, dawes valve and neddle valve to have manual boost
On balance, I think it's probably better to diagnose a fault *before* fixing it.

Any ideas what the problem might be?

Andrew
 
#4 ·
My car does the exact same thing. Your turbo is spooling up too quick. You need to adjust your VNT screw to slow the turbo down. Its free to do and can be found in the ZD30 reference document on this forum.

And you really should invest in a oil catch can and block that EGR before your engine starts to build up full of soot and goes kapoot!
 
#5 ·
My car does the exact same thing. Your turbo is spooling up too quick. You need to adjust your VNT screw to slow the turbo down. Its free to do and can be found in the ZD30 reference document on this forum.
Yes, I've read that document - but obviously, I need to install the gauge and see what's happening first.

I still have a problem with doing it anyway. This is a completely standard motor (no mods) and it has done 40,000 trouble free miles, so something must have changed. I rather think I should try to identify what that is. Fiddling with the VNT calibration feels like a kludge rather than a fix.

Andrew
 
#6 ·
Don't be mad at me!

I just wouldn´t risk a unknow brand MAF even if the idle voltage was correct, not with a zd30...

Try to borrow a friends MAF, that's what I would do before buying a new one.

Since I got my GU I never went to limp mode altough I tried several times, and I didn't had any overboost errors, but I made the mod's stated in Akniss ref document just as a precaution measure.

You can adjust the VNT screw as dan-O wrote.

To me one of the issues with overboost is the ECU doesn´t manage the turbo boost and EGR signals well so I prefer to manage it myself with a needle valve and EGR blocked.

Since I think this is a design error and Nissan didn´t come up with a ECU firmware upgrade I prefer to make the mods rather than rely on them...

Just trying to help,

Edu
 
#7 · (Edited)
Don't be mad at me!
Hey, I'm not. Sorry if I gave that impression. I'm grateful for any advice and help anyone can offer. :)

I just wouldn´t risk a unknow brand MAF even if the idle voltage was correct, not with a zd30...
I didn't test it just at idle. I tested it every 500 rpm between idle and 4000 rpm. It's very close to the correct voltages as in the factory workshop manual at all engine speeds to at least 3500rpm.

Maybe MAFs are cheaper in Oz than in the UK. The MAF I bought was manufactured in USA and looks (and measures) absolutely identical to original Nissan part.

Since I think this is a design error and Nissan didn´t come up with a ECU firmware upgrade I prefer to make the mods rather than rely on them...
I understand that but I still have difficulty getting my head around the fact that it ran perfectly fine for the first 40odd thousand miles of its existence, so something must have changed and I'd feel more comfortable if I could find out what that is and fix it. I just wish I could suss out what the change is ..........

Andrew
 
#8 ·
Don´t worry, no hard feelings :D

I understand you have the correct voltages at various rpm but you may have not the same reaction times to airflow changes (some mili seconds can make a difference), anyway are you sure your original MAF is bad? (I can´t assume from your first post)

I´m from Portugal and they charge about 160€+VAT for a MAF, this after we started giving them the reference 22680-AD21A, otherwise they would give the MAF with the tunnel box and that was 500€+VAT (Ni$$an is your friend).

Maybe some of the variable vanes of your turbo are not moving well, they can get stuck with the carbon giving overboost and the piston solenoid valve is good giving a false impression.

Other thing that can happen is some problem with the CAT converter, here when some of us replaced the cat with a direct conection most would start giving overboost error codes because of the missing "restriction" (we adjusted the VNT screw).

Here in Portugal when we try everything and it doesn´t work we take it to the witch!:evillaug:

Edu
 
#9 · (Edited)
I understand you have the correct voltages at various rpm but you may have not the same reaction times to airflow changes (some mili seconds can make a difference), anyway are you sure your original MAF is bad? (I can´t assume from your first post)
No, it may not be bad. Performance did definitely improve when I fitted a new one. I could probably clean the old one properly and refit it.

I´m from Portugal and they charge about 160€+VAT for a MAF
I think the UK Nissan dealer price is much higher than that. I did buy a Hitachi boost sensor from Nissan (because I couldn't find it anywhere else) and that was nearly £200 (about 235 euro).

Maybe some of the variable vanes of your turbo are not moving well, they can get stuck with the carbon giving overboost
They are mechanically linked, aren't they? Isn't it - one stuck, all stuck?? I can easily(?) push the VNT actuator rod up with my finger for its full travel. It moves smoothly with no stickiness

Andrew
 
#11 ·
If one vane is stuck, then none of them will move. They are mechanically interlocked, so if your actuator rod moves up and down and it moves the arm with it, your turbo vanes are working ok.
There are a number of causes for intake air pressure codes and it doesn’t necessarily mean that it’s over boosting. Firstly I would check the vacuum line with a vacuum gauge and make sure that you have at least 28 to 30”Hg. If that’s ok, check that the VNT control solenoid is open between ports A & C with the ignition off and that ports A & B are open when you put 12v across the solenoid terminals.
Also check that your intercooler hoses are tight and not leaking under pressure.
The 0905 code comes up when there either isn’t enough boost pressure or too much for a given time outside of the map parameters. If you fit a gauge and find that there is too much boost, it would be wise to wind down the actuator arm limiting screw a touch and chances are it may cure your problem. These things are mechanical, so there will always be wear and if the screw has moved, it may move up which will increase boost. It usually has a dab of yellow or white paint on it to show its original position, but with vibration and wear, the setting may change.
 
#12 · (Edited)
Firstly I would check the vacuum line with a vacuum gauge and make sure that you have at least 28 to 30”Hg. If that’s ok, check that the VNT control solenoid is open between ports A & C with the ignition off and that ports A & B are open when you put 12v across the solenoid terminals.
Thanks for that. I'll check it tomorrow

It usually has a dab of yellow or white paint on it to show its original position, but with vibration and wear, the setting may change.
It does have a dab of yellow paint. So far as I could tell, it hasn't moved from new - but I'll check again in the morning.

Andrew
 
#13 ·
Firstly I would check the vacuum line with a vacuum gauge and make sure that you have at least 28 to 30”Hg. If that’s ok, check that the VNT control solenoid is open between ports A & C with the ignition off and that ports A & B are open when you put 12v across the solenoid terminals.
I don't have a vacuum gauge. The VNT lever is at the bottom with the ignition off. It's pretty much at the top of its travel on tickover. Doesn't that suggest that the vacuum is probably OK?

These things are mechanical, so there will always be wear and if the screw has moved, it may move up which will increase boost. It usually has a dab of yellow or white paint on it to show its original position, but with vibration and wear, the setting may change.
It does have a dab of yellow paint that suggests it hasn't moved. The locknut is tight.

Andrew
 
#19 ·
Andrewk,

If you look under the fuel filter near the motor you can see the EGR, in LHD GU is not to hard to reach, but since yours must be right hand drive I don´t know if there's much space on that side of the motor.

I remember reading a post here about someone that had strange behavior with the MAF sensor and after switching several times he ended up using new wires to connect the MAF to the ECU. I work with electronics and sometimes you can have wires broken inside but since the two copper sides are held by the isolation they only give small glitchs. This is not easy to discover so is best to try all the other options and if you don´t find the fault then go for the harness.

Here you can see the EGR valve (sorry for the french:D)



 
#20 ·
A bit of a move forward on this. I have now installed a boost gauge (stepper motor, electronic type) in the cab and connected it to power and have run the signal cable into the engine bay. I have yet to connect the gauge sensor into the intake airstream - a job for tomorrow.

As the gauge is a dual purpose vacuum/boost gauge, it occured to me that it might be interesting to see what the ECU & VNT control solenoid are asking the turbo to do by temporarily teeing into the hose between the solenoid and the VNT actuator and using the gauge to measure the control vacuum in the hose - and then have a drive around and see what's happening.

1) At tickover, the VNT lever is at the top of its travel (or near - I haven't checked with a feeler gauge yet) with the vacuum gauge reading 18-19" Hg. I *think* this is pretty much what it is supposed to do.

2) Over a gentle run of about 5 miles on mostly small throttle openings, the vacuum readings stayed at or near 18" Hg. It only fell below that reading if I leaned on the throttle. Even leaning hard on the throttle (at any engine speed & gear) rarely took the vacuum reading below 10" Hg (maybe to 7 or 8" Hg) and then only momentarily if I suddenly floored the throttle pedal. I suspect (but don't know) that this is normal behaviour).

3) I headed towards a junction onto the M62 heading east (motorway/highway heading up the Pennine Hills). Before going onto the M62, I stopped and cleared an 0905 ECU fault code. I tried to keep a fairly steady speed around 65mph (2600-2700 rpm in top) up the hill on maybe half throttle or so. Though I didn't notice any reduction in performance (though maybe I was daydreaming), on a couple of occasions without any change in throttle opening, the vacuum wandered back & forth between 14-15" Hg and 10"Hg. Lifting off the throttle and then reapplying sent the vac straight back up to 10"Hg. When I got back home, I discovered that the ECU had stored another 0905 code.

I can't help wondering why the vacuum never goes (much) below 10"Hg - and why when the 0905 overboost occurs it doesn't go back up to 18-19"Hg. Does anyone have any insights on this?

Andrew
 
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#22 · (Edited)
I've now replaced the vacuum hose between the VNT control solenoid and the VNT actuator "just in case". I've also finished the installation of the boost gauge and had a drive around to see what is happening. I need, though, to be a bit more scientific and plan it properly. I've certainly learned a few things though ..........

In normal footling around at low speeds & small throttle openings, I'm seeing boost pressures of only a couple of psi. Boost seems to start at about 1200rpm ish. Leaning on the throttle a bit, again at low speeds sees boost pressure rise to somewhere in the region of 10-15psi. Once the engine was good and hot, it occasionally flickered up towards 20psi but only for a fraction of a second before again settling somewhere between 10-15psi whilst accelerating and then dropping back below 5psi at a constant 50mph in 5th on the flat.

After a few miles of wandering about, I was feeling quite optimistic as I hadn't yet seen much amiss (I think) - so, I decided to take it for a blast on the M62 motorway (Highway, I think, in Oz speak). There is an uphill section about 5 or 6 miles long which I would normally drive at anything up to 70mph (110kPH) in 5th. I gradually increased speed to about 2500rpm in 4th. Boost pressure stayed somewhere between 10 and 15psi. I then floored the throttle and held it there. Boost pressure increased to 25-30psi :shock: & after 5 or 6 seconds at round about 2800-3000rpm, I got the sudden power loss that I associate with an overboost error. The boost pressure immediately & quickly dropped to a low level, just a few psi. Lifting off and reapplying throttle restored normal behaviour. Definitely an overboost error, I think. Just to be sure, I repeated the exercise a couple of times and got the overboost error each time.

Just to clear up a point or two about sensors.

* I did swap the MAF sensor about 12 months ago (for a cheapie off Ebay) with no evidence that the olriginal was faulty - just an attempt at a quick fix.

* The quick fix didn't work, so I swapped the MAP sensor (boost sensor) for a genuine new Nissan Part, as the next most likely culprit. For 8 or 9 months and about 9000 miles (including maybe 2000 miles towing a 1500kg caravan) I didn't see a single instance of an overboost - until Xmas 2010 when it happened again. Nissan kindly replaced the boost sensor under the part warranty. Replacing it again didn't fix the problem.

* After my drive around this afternoon, I decided that I'd check the voltages on the two boost sensors. The latest one produces a signal of about 2.7 volts at atmospheric - a tad high, but still within spec. The original boost sensor (i.e. fitted from new and replaced as faulty 12 months ago) produces 5.6 volts at atmospheric - so, totally goosed!!! The goosed sensor was, I think, almost certainly responsible for the original overboost symptom.

Ponder ............. is it possible that I replaced the original MAF with a doubtful one that was just about OK when I installed it - but which has subsequently failed? I still have the original OEM MAF sensor (40,000 miles from new when I replaced it) - so I'll test the voltages on both in the morning and slot the old MAF sensor back in (now cleaned properly) and have another drive around tomorrow. I don't really feel very confident - but who knows .......


Andrew
 
#23 ·
Ponder ............. is it possible that I replaced the original MAF with a doubtful one that was just about OK when I installed it - but which has subsequently failed?
I need to do some more testing, but I think I might know the answer to that one!!! It's a definite maybe. :p

I've swapped the MAF and reinstalled the original Nissan OEM MAF (that one that was in the motor from new and has done about 40,000 miles) and have been for another drive. Boost pressure seems to be a lot more predictable.

At constant speeds, on the flat or uphill, in any gear, boost pressure doesn't seem to go above 15 psi.

At medium engine speeds in 2nd, 3rd or 4th, flooring the throttle sends the boost pressure up to about 15 psi instantaneously. It then falls quickly back to 10 psi and gradually rises again as the engine revs rise, if you keep your foot to the floor. Even being brutal and keeping my foot to the metal up to 4500rpm only saw 18 psi.

I'd say it was fixed, apart from one incident on the motorway. I was going a steepish hill at maybe 2500 rpm in 4th. I leaned on the throttle a bit and just as boost pressure increased to 15 psi, floored it. It went well over 20 psi, which is not good news. It dropped back very quickly, but I'm not sure whether the ECU did that or whether I lifted off to avoid smashing into the back of a truck that was only doing 40 mph (not a great idea!!).

I think I need to do some more testing - and maybe give it an "Italian" tune up. Just maybe I'll buy a brand new (genuine) Nissan MAF sensor too. I can't be certain yet, but I think I'm quietly confident. :D

Andrew
 
#25 ·
From all that i have read on here this is a very common problem, probably one of the most common thing that ZD30 owners come across, especially after fitting a larger exhaust.

Why it does it after many years of motoring? My guess is the EGR getting blocked up and held open.

Easy way to prevent it doing it (and your engine blowing up) - Block the EGR and fit the Dawes / needle valve combo with the boost and EGR gauges. If you get really keen get the inlet manifold cleaned out. Also get the VNT screw turned in half a turn to slow down the spool up rate, or, open the needle valve a bit to do the same thing (What whitie was referring to)..
 
#26 ·
fitting a larger exhaust.
Mmm .... but I haven't.


Why it does it after many years of motoring?
It started at just over 40,000 miles when 4 years old. Not exactly "many years".


Easy way to prevent it doing it (and your engine blowing up) - Block the EGR
Isn't that illegal in your part of the world? It is here.


Also get the VNT screw turned in half a turn to slow down the spool up rate
I assume you mean lengthen the VNT actuator rod.

So, how easy is it to remove the EGR valve and "unstick" it ??

Andrew
 
#27 ·
Hi, Andrewk,

As I said earlier maybe your EGR is not fully closing so you have an extra boost plus the usual turbo boost leading to limp mode.
Now to clean the EGR is not to much dificult it depends how confortable you are dealing with tools, it's better to block it and fit a dawes + needle valve and forget the EGR.
In Portugal as in most countries it's illegal to block the EGR but they won't pay you a new motor and you can bet the EGR is killing your zd30 slowly.

Try to clean your MAF (the original) with some MAF spray and give it a run.

Edu
 
#28 · (Edited)
Try to clean your MAF (the original) with some MAF spray and give it a run.
I did that before I reinstalled the original (genuine) MAF - so the boost pressures shown above already reflects that. I'm going to check the MAFs calibration tomorrow and buy a new one if its not perfect. After that, some more road testing.

maybe your EGR is not fully closing so you have an extra boost plus the usual turbo boost leading to limp mode
That does make a lot of sense. The EGR valve is supposed to be closed at full throttle and at high engine revs - and that is exactly when the overboost occurs. If the fault does persist, I think I've no option but to look at the EGR valve. I'll test it and clean/unstick it if I can. If I'm not happy with the EGR valve after that, then either I buy a new one or block it. Decisions, decisions ............

Andrew
 
#29 ·
Do you have an oil catch can fitted to catch the excesive oil blow by?

If you do not have one, this would possibly explain the reason for your MAF & Boost sensor to give false readings due to being contaminated with oil residue.

As already stated above, your boost appears to be eratic due to the ECU attempting to correct boost levels when getting too high thus going into limp mode.

Also, by installing the Dawes & needle valve and taking away the ECU control of the boost will dramatically improve the drivability of the ZD. "THIS" is the best solution to the overboost issue that the ZD suffers from over time and is cheaper than replacing the MAF sensor. And buy genuine MAF as already stated above, much, much more reliable than the unknown brands.

However, if you desire, re adjust the VNT "GRUB" screw as per the reference document AND NOT THE ACTUATOR ROD as you suggested.

Yes, blocking the EGR is illegal in AUS, but many if not all on this forum will have blocked it for piece of mind. By doing this, the oil is a lot cleaner due to no EGR soot entering the oil, which must be beneficial to the motors life.

Its your decision in doing so if you desire, but highly recommended!

I also disagree with oilrig6, the air cleaner goes in with the rubber seal facing DOWN not up.

Keep us posted with your progress mate.
 
#30 · (Edited)
Do you have an oil catch can fitted to catch the excesive oil blow by?
No, but I'm not convinced there is any excessive blow by. The MAF I removed yesterday looked clean. The original MAF (done 40,000 miles) that I cleaned & refitted wan't especially mucky either.

However, if you desire, re adjust the VNT "GRUB" screw as per the reference document AND NOT THE ACTUATOR ROD as you suggested
Logic suggests that adjusting the stop screw (if that is what you mean) can have no effect on the operation of the turbo unless the VNT lever is in contact with it.

Andrew
 
#31 ·
Have you taken the Intercooler pipes or Intercooler off to see if there is any oil residue in the intercooler? This is the easiest way in identifying excessive oil blow by, or it may be evident around the intercooler where its crimped together.

Adjusting the grub screw is the prefered way to adjust it and is what many people do to reduce or stop the overboosting that you have described. I cant recall if it restricts the vanes from opening or closing though............

Adjusting the Grub screw is similar to adjusting the VNT arm length longer i'd assume? but adjusting the grub screw is the prefered way by forum members. Its also stated this way in the Reference bible by Aksniss as already stated mate. It will also alter your spool rate which is one reason for overboosting ( with mine anyway and many, many others). Give it a try first, its the cheapest modification to do on your Patrol, its free!

Refer to the ref doc for instructions. And while your at it clean the EGR/throttle body as per the ref document, you will be suprised.
 
#32 ·
Have you taken the Intercooler pipes or Intercooler off to see if there is any oil residue in the intercooler? This is the easiest way in identifying excessive oil blow by, or it may be evident around the intercooler where its crimped together.
No - but I do intend to.

Adjusting the Grub screw is similar to adjusting the VNT arm length longer i'd assume? but adjusting the grub screw is the prefered way by forum members.
I really cannot get my head around this. My present understanding is .........

When 18 " Hg or more of vacuum is applied to the VNT actuator, the VNT lever is at the top of its travel and is in contact with the stop screw. The turbo vanes are closed (i.e. the turbo is pretending to be a small one). The vacuum readings I took (see about a dozen posts back) suggest that in running around on small throttle openings, the VNT lever will probably stay against the stop. At anything other than very small throttle openings, the ECU wants the turbo to become a large one, so wants the turbo vanes to open. It achieves that by changing the pulse width applied to the VNT control solenoid (on the ZD30, it is a PWM device) which reduces the average vacuum applied to the VNT actuator, which moves the rod - and the VNT lever then leaves contact with the stop screw. Once the lever has left contact with the stop screw, the setting of the stop screw is irrelevant, it wouldn't matter if it didn't exist.

If that understanding is correct, adjusting the stop screw *might* affect the point at which the turbo vanes start to open, but once that has happened, it cannot have any effect at all on the perrformance of the turbo. Interestingly, the VW TDi folks (also has a VNT turbo) reduce spool up rate by lengthening the VNT rod. Doing that will, they say, affect boost across the rev range. I can see that adjusting the rod will affect the relationship between the vacuum level applied to the VNT actuator and the position of the turbo vanes - but whether that change might constitute an improvement is moot.

Personally, I'm more than a bit reluctant to fiddle with the VNT calibration if I don't need to - far too dangerous in my view. I'd much prefer to identify the fault and fix it. My next step is to check the MAF calibration (and buy a new one if I have to - but I hope not to). If the MAF is OK, then I'm going to have to take a very sharp look at the EGR valve. If it isn't fully closed at large throttle openings and high engine revs then I think that would explain the occasional high boost pressures that I'm seeing on the gauge. I'll have a go at cleaning it, but I may have to replace the EGR valve if that doesn't work.


Cheers
Andrew
 
#34 ·
I've been re-reading the "Reference" document & decided it would be a good idea to go out for a test drive and try out the overboost test suggested. Before setting off, I cleared an 0905 ECU boost error. I drove along the M60 motorway at about 65 mph (2600-2700 rpm) on the (nearly) flat for as long as I could - maybe three or four miles. Boost pressure was maybe 12 psi or so - and didn't exceed 15 psi. I felt no power loss that is symptomatic of the overboost condition - so no problem there, I think.

After leaving the motorway, I drove the 3 or 4 miles home in town traffic. On a couple of occasions at lowish revs and relatively limited throttle opening, boost pressure spiked to nearly 20 psi (for a fraction of a second). When I got home, I checked again for ECU error codes and guess what - I have another 0905 error code. :confused: I'm sure this motor is being vindictive!!!! I think I'm getting more confused not less.

Time to test the MAF and have a look at the EGR valve, I think ...........


Andrew
 
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#38 · (Edited)
If you are to clean the EGR you can take off the intercooler, inlet hoses, throttle valve and inlet manifold and give it a clean. After seeing the intake guts you will understand why we block the EGR valve :D!
I do understand why you block the EGR valve. I want to be sure, though, before I block it that it is NOT something else that is causing the overboost/limp that I now have at high throttle openings and engine revs.

I thought I understood how it worked and had concluded that it had to be the EGR stuck open that is causing the overboost at 3000 revs & full throttle. It cannot be the cause of the overboost if it is stuck closed, because it is supposed to be closed.

Andrew
 
#39 ·
And rew, i think we need to get back to basics. The overboost you dwscribe is typically caused by the maf sending a reading of over 4 volts to the ecu when it should not.
The voltage is a combination of rpm and boost. At idle with a working egr, the voltage should be between 1.6 and 1.8v, if it sits closer to 2.1 volts, it means either your maf is failing or the egr has blocked itself.
 
#44 ·
And rew, i think we need to get back to basics.
Agreed

the egr has blocked itself.
I think we might be failing to communicate here. Do you mean blocked, i.e. the valve is closed & not passing any exhaust?

The page from the workshop manual that I was quoting from is ......


It clearly says that the EGR valve should be closed at high engine speeds and at large throttle openings.

ANdrew
 
#40 ·
i am on the mobile which limmits me to size of post....
Can you post the maf voltages that you meaured before, i assume in neutral and at idle, then in 500rpm steps from 1000 rpm.
also, what air filter are you using and how is it installed?
 
#42 ·
i am on the mobile which limmits me to size of post....
Can you post the maf voltages that you meaured before, i assume in neutral and at idle, then in 500rpm steps from 1000 rpm. also, what air filter are you using and how is it installed?
The air filter is the stock genuine Nissan filter, installed by Nissan at the Patrol's last service just before Christmas. It is installed with the thick foam rubber ring downwards and the flexible rubber seal upwards. Isn't that correct?

I didn't write down the voltages, just checked that they were somewhere near right. IIRC, it was about 1.55 volts at idle and rose to something over 3 volts by 3000 revs. The next time it stops raining here (we get a lot), I'll check again and make a note of the readings.

Andrew
 
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#45 ·
1.55V is to low at tick over it should be 1.83V as Mr White say's
The workshop manual says 1.5-1.9 at idle.


If you use the OB Nissan Software you have to make sure the engine oil is changed and fuel filters or it will give you a false reading. It does say this in the software book from Nissan.
I am measuring it directly at the MAF terminals using a DMM.


Consult III or Consult II. I had the same issue with comms are they using the wireless interface or direct cable. If they use wireless ask them to log in under Consult II dont ask me why I dont know.
I have no idea what hardware Westway Nissan used. The "mechanic" said that he thought the diagnostics socket on my Patrol was faulty (it isn't AFAIK). I later learned that was because he was using Consult III and didn't know to use Consult II.

Cheers
Andrew
 
#46 ·
Andrew, here is the Nissan software that I have with a blocked EGR. The voltage is 1.93 and thats showing no fault codes. I runing at 18 PSI max boost. You know even if your Vaines are moving it could still be case that the Turbo EX side is full of Carbon. At the momment its like pissing in the wind untill you get some pictures posted for us to help you out.
 

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#47 ·
Thanks for your help folks. I appreciate it.

My best guess at the moment is that the EGR valve is stuck open and that uncontrolled exhaust gasses passed through it are raising the pressure in the inlet manifold alarmingly at high revs/throttle. This is, I think, what is causing the 0905 boost pressure error. The boost pressure measured cruising at 2600/2700 rpm is exactly what it should be - so the sensors, ECU, VNT control solenoid and turbo are doing pretty much what they should be doing.

I think I'm persuaded that blocking the EGR valve would give me an immediate solution to the boost pressure error I'm seeing - so I can't really see a downside to doing that. I understand that I may have to wind the VNT stop screw (in - clockwise) by half a turn or so to correct the boost pressures at cruise. It's entirely possible that I might relent on that at some time and buy a new EGR valve. If I do then I'll have to restore the VNT screw to its previous setting - shouldn't be a problem - the VNT arm should just touch the stop at 18" Hg vacuum.

I would have already sorted this if I had another motor. The Patrol is used as a family daily driver and I need to keep it on the road.

Best wishes
Andrew
 
#49 ·
hi Andrew, flip the air filter over and see if that fixes the problem.
Other members have reported similar overboost issues with the air filter installed that way.
 
#50 ·
also, if the egr valve was stuck open allowing copious amounts of EG into the intake manifold, the EG would displace a lot of oxygen and you would probably see plumes of black smoke from the exhaust.
When the EGR valve opens and nothing else has changed, say at cruise, it decreases boost in tne manifold and the EGTs go up accordigly,, anyone with EGT and boost gauges on a CRD will confirm that :)
 
#51 ·
also, if the egr valve was stuck open allowing copious amounts of EG into the intake manifold, the EG would displace a lot of oxygen and you would probably see plumes of black smoke from the exhaust.
I can see that - but if it was stuck closed then blocking it with a plate would have no effect.

When the EGR valve opens and nothing else has changed, say at cruise, it decreases boost in tne manifold and the EGTs go up accordigly,, anyone with EGT and boost gauges on a CRD will confirm that :)
Yes, but the overboost isn't occuring at cruise.

flip the air filter over and see if that fixes the problem. Other members have reported similar overboost issues with the air filter installed that way.
Isn't it supposed to be that way? Should it have the flexible rubber seal at the bottom & foam rubber at the top? Why would it make a difference anyway?

Andrew
 
#53 ·
To further add to whitie's comments on the filter.
With my rig, having the foam seal to the bottom of the air box allowed dust to pass the filter when clogged and dust the engine. Perfomance is better this way but is obviously not good for the engine in this situation.

When I turned the blocked filter upside down (rubber seal now facing down), no dust was passing the filter there after for another 300km. However the performance of the motor had dropped off and slight diesel smoke was evident out the rear.

My conclusion was that when the Air filter is new, it does not really matter too much which way the filter goes in, but once its slightly clogged, it filters better with the rubber seal to the bottom. Basically, the rubber seal to the bottom works better due to the Foam seal being at the top is not able to compress as easy as the rubber seal, it also enables the rubber seal to be able to fold in at the bottom ensuring a perfect seal when the air filter is sucked up against the lid of the air box, even though the filter appears to be tight when the retaining clips are clamped down.

With the rubber seal facing the top, the rubber seal can be compressed against the top of the air box.

This is why I install the filter "when new" with the rubber seal facing the bottom. Each to their own really.

Having said that, the new or latest Nissan filters aparently have a larger rubber lip to stop the above mentioned issues.
 
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