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Discussion Starter #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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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...
 

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Discussion Starter #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
 

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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!
 

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Discussion Starter #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
 

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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
 

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Discussion Starter #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
 

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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
 

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Discussion Starter #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
 

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Discussion Starter #10
I did think about trying to clean the exhaust side of the turbo. Have any of you tried chemical cleaning, without removing the turbo from the car - with this stuff or something similar (oven cleaner for example) Innotec Supplies Ltd. - Turbo Clean Set ??

If you have, did it do anything useful??

Andrew
 

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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.
 

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Discussion Starter #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
 

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Discussion Starter #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
 

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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?

It does have a dab of yellow paint that suggests it hasn't moved. The locknut is tight.

Andrew
Andrew,
It most likely is ok, but I have seen cases where a vacuum leak has caused low boost issues even though the actuator arm was moving up at idle. I guess until you have a boost gauge and you know where you are with boost, it could be hard to diagnose.

Even if the limiting screw hasn't been adjusted, you could have some wear on the screw or the top of the arm which will increase boost. It would surprise me if this was the case with your low K's, but something has either changes or worn to the point that it’s making a difference. These are just the things that I would look into first before spending $$ on parts that you may not need.
We know that these are tuned close to the limit from the factory, so it doesn't take much to tip them over.
 

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Discussion Starter #15
but something has either changes or worn to the point that it’s making a difference.
Yes - but the "something" could still be that the boost sensor is faulty (I could be just unlucky). If its telling porkies to the ECU, that would explain the problem I'm having. I'd be quite pleased if that was the problem, as the sensor is still under warranty. :)

The motor is actually running brilliantly well - at least as well as it ever has. I may be wrong, but I suspect that performance would be adversely affected if there was an underboost condition.

I'll be glad when I get this sorted. It's doing my head in ............

Andrew
 

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Yes - but the "something" could still be that the boost sensor is faulty (I could be just unlucky). If its telling porkies to the ECU, that would explain the problem I'm having. I'd be quite pleased if that was the problem, as the sensor is still under warranty. :)

The motor is actually running brilliantly well - at least as well as it ever has. I may be wrong, but I suspect that performance would be adversely affected if there was an underboost condition.

I'll be glad when I get this sorted. It's doing my head in ............

Andrew
I guess you would be very unlucky to have 2 faulty pressure sensors. In most cases they fail when they get oil or other gunk clogging them up, but Nissan has addressed the issue by mounting them up side down, so it's rare to see one fail on a ZD30 Patrol.

I’m sure that the 0905 code can be generated when the ECU doesn’t see enough air flow for a given rpm and throttle position for a certain length of time. Assuming the turbo is ok and you have full vacuum to it, then I would look for any restriction in the air intake, such as a blocked air filter. But if that was the case, I’d suspect you would lose performance or blow some smoke.

If you can’t find any issues or fault with the system, then maybe try replacing the new sensor if you can swap it over for another one. Another option is to check the voltages and wiring to the sensor. The pressure sensor voltage should increase with pressure.
With the ignition on you should have 5v between terminal 1 on the connector and ground.
If you remove the sensor with the plug connected, you can measure the voltage at terminal 2 (centre terminal) and the voltage should rise as you apply air pressure to the sensor. Something like 4v at 30psi.
 

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Andrewk,

You may want to check your EGR valve too. If the valve can´t close to the end (soot) it will allow some air to pass by. When the Turbo is at max level it will make an overboost.

Edu
 

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Discussion Starter #18
I guess you would be very unlucky to have 2 faulty pressure sensors.
Actually, that would be three faulty pressure sensors (the original, replacement in April 2010 and warranty replacement in Jan 2011). The probability of having three faulty sensors must be very close to zero. Having said that, replacing the original boost sensor did seem to cure the problem and banish the overboosting for about 9000 miles and at least 1000 of that was towing a 1500kg caravan. I tried quite hard to provoke the overboost error but wasn't able to do so.

I have read that, if the VNT blades are sooted up, simply waggling the VNT lever about vigorously can free the turbo vanes enough to get rid of the problem. I do remember trying a bit of that at the time the original boost sensor was replaced, so it is possible that it was sticking vanes that caused the problem and not a faulty boost sensor.

The VNT lever does seem to be moving freely now - but I've just discovered that a 14mm open-ended spanner will neatly fit over the lever, so ...........

you have full vacuum to it, then I would look for any restriction in the air intake, such as a blocked air filter. But if that was the case, I’d suspect you would lose performance or blow some smoke.
Had a look at the air filter. A mucky patch at the intake to the filter housing, but the rest is clean, so should be OK. I rotated it and put it back


Another option is to check the voltages and wiring to the sensor.
Yes, that's easy enough to do, I'll check that.

A couple of questions ................

1) Is there any *easy* way of detecting vacuum leaks (stethoscope??) or is it better just to buy a load of hose and replace them all?

2) Where is the EGR valve, how will I recognise it and how can I tell whether it's working OK? Is it easy/hard to remove and clean?

Cheers
Andrew
 

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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)



 

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Discussion Starter #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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