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nissan patrol
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Discussion Starter #1
Hi,
I have been trying to diagnose an idle and power problem with my 2002 gu2 tb48
it has 192,500km on the clock and in the last 2000km it has had:
- head rebuild with hardened seats blah blah for gas (mixer not injected)
- new spark plugs
- coolant and all oils replaced
- Jays PVA and cruise mods
- new maf sensor
- new o2 sensors
- transmission service and flush

each of these things has had no effect on how the car runs on gas but on petrol it keeps getting worse and worse :headwall:

on petrol:
- at startup it idles rough, jumping up and slowly coming back down until it almost stalls, then jumping back up. it gets better when it is warm but its still very noticeable.
- NO power under 2000 rpm; its like there is a hamster in there that used to be in a 3.0 grenade!
- even when i floor it, it takes ages to slowly climb to 2000 rpm and then it takes off like the rocket ship it should be.

on gas:
it drives normally

My thoughts are leading me to replacing the fuel pump in the sub tank (factory 35ltr), but before I start playing with things that can go boom I wanted to get some opinions.
I have read through the 4.8 bible and found a few other threads of interest but none cover this one perfectly, so any thoughts?
 

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nissan
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My thoughts are leading me to replacing the fuel pump in the sub tank (factory 35ltr)
I wouldn't even consider looking at anything to do with the sub-tank. It only ever feeds fuel to the main tank - never the engine.

I know a guy here had a similar problem. Nissan wanted a fortune to rebuild the engine. Turns out it was a small hole in the intake pipework - engine side of the MAF. Completely screwed up the fuel/air mixtures. I'll try to get hold of him and get some more details of the symptoms.
 

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nissan patrol
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Discussion Starter #3
I wouldn't even consider looking at anything to do with the sub-tank. It only ever feeds fuel to the main tank - never the engine.

I know a guy here had a similar problem. Nissan wanted a fortune to rebuild the engine. Turns out it was a small hole in the intake pipework - engine side of the MAF. Completely screwed up the fuel/air mixtures. I'll try to get hold of him and get some more details of the symptoms.
There is no main tank, its on gas which works well and has none of the issues when running on petrol

I will look into the intake pipework. I think its a long shot but easy to inspect and find.
thanks Bulbous
 

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just a good guy.
2009 gu ute
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try adjusting the timing 10deg. and start on petrol and see if that improves it. my petrol/gas had that problem. now runs fine on both. also have the injectors been serviced recently or not.
 

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nissan patrol
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Discussion Starter #5
try adjusting the timing 10deg. and start on petrol and see if that improves it. my petrol/gas had that problem. now runs fine on both. also have the injectors been serviced recently or not.
Head rebuild included injectors being recod. I assume they did the timing when it was all put back together, but that was when the power problems started (about a month ago).
I then changed the maf and o2 sensors making the problem worse. im still pissed the mechanic sis not pick up that the maf was missing its little resistor bit on the side of it :confused:

I might have to make a slightly angry phone call and get the thing dyno tuned before I do the fuel pump.
 

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nissan y61
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Power valve cuts in after 2k so that seems to be working. Maybe for bad rpm have throttle relearn done at any good dealer. I had the same issue on my Y61 and y62 and it solved this problem. You may also be getting bad signals from the temp gauge. The lower temp of coolant the higher the RPM will go. When jump 20 to 30 on computer I can make engine stall out just like what your saying. So unplug the two sensors on the engine located on right side if looking at the engine from the grill. If this solves the rpm issue then you need to replace the two sensors. ZD sensors are the same so if you have spare use that before buying a new one for the 4.8.

For transmission. Do have a delay on hills in shift pattern. You should be able to slam it into R/D and nearly wheel spin. When did the flush did drop the main sump and then add 5L and check on the cold side of fluid gauge while in P with engine running. To much or too little j-matic has this effect.
 

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nissan patrol
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Discussion Starter #7
The trans was done by wholesale automatics in melbourne, who are the only people i would recommend to work on these autos, so im confident that its all good.
I decided to go back through everything that has been done and check all the vacuum lines this afternoon.
my first stop was the MAF, thinking the aftermarket part might not be the right one. so i went to the workshop manual and found no info. onto the forum and found this:
http://www.patrol4x4.com/forum/nissan-patrol-gu-gr-10/how-test-all-mafs-home-41774/
excellent. so i decided to swap out the new one and put the old one back in for funs sake, and started testing. everything tested perfectly so i took it for a test drive.
BINGO it works as its meant to :D
The small idle problem is still there but that has always been there and I suspect it is more to do with timing and the gas tuning than anything else.

At your suggestion dbsep I will be checking all the temp sensors because that might help with the idle prob.

Now off to call the person who sold me the new maf to get my money back
 

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I have found a few times now, that some efi vehicles have a small strainer type filter near the fuel pump (additional to the normal fuel filter. Not sure about the TB48's worth checking.

bit like the strainer/gauze filters in the injector pump on TD42s, sometimes they get gummed up.
 

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nissan y61
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They have strainer on the pump that sit in fluid bath on standard tank. The second filter is mid way down the body. Flat side of filter faces the in pipe.

Both of my 4.8's have a very small idle issue for about 10 to 15 seconds until it gets some data from temp sensors. If plug in computer and drop coolant temp to 10 degrees it goes away. I think it's just a gremlin in the ECU program. The pre start RPM should be 250 RPM higher and solves this issue.

I had to buy a complete mad and housing from Nissan. Couldn't get MAF on its own here or Africa.
 

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nissan patrol
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Discussion Starter #10
Thanks for the help guys.
I'm in the middle of a uhf/stereo changeover with heaps of other wiring going on at the same time so I have left playing with the the fuel system for another weekend.
I will be checking the vac lines and fuel filters and testing the pump but I will wait for the blatz cable to arrive before I get too excited about replacing any parts or testing the temp sensors.
I will keep you all posted on what I find over the next few weeks. Hopefully I can get it running smoothly by melb cup weekend, when my new suspension arrives and I can start some real driving :)
My main concern with it now is the 28ltr/100km its drinking, I was hoping for something closer to 18/20
 

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nissan patrol
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Discussion Starter #11
I had a few hours to spare this arvo so decided to undo the PVA mod and finish the stereo.
After putting the PVA back to standard I took it for a quick spin around the block and every time it went over 2250 rmp it would jerk like it was losing all power and then come back, over and over. When I got home I could see the PVA bouncing up and down when I pulled the throttle on :(
So, I pulled the vac lines off the PVA solenoid and checked them, then off for another test drive. It ran as per normal (idle prob still there) without the jerking.
When the engine is cold I will start chasing a vac problem before anything else. I think this is the main underlying issue.
 

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For what it's worth, and without trying to take you too far off track from your findings...

I noticed the same symptoms only on petrol this week. As I had recently replaced cylinder head, o2 sensors, fuel pump, and air mass sensor, I thought it may have just needed a tune. Sent it off to my gas guy (who does all my work) who wouldn't put it on his dyno due to issues with the trans (codes suggested throttle position sensor). This makes sense as for some time, performing tps learning proceedure would slightly improve symptoms. He made a quick call to the auto trans guy they outsource to who confirmed that tb48 Patrols did indeed have issues with tps which directly effect the transmission/shifting/limp mode, etc.

Is this only effecting your Patrol on petrol? Does the tps learning proceedure (ignition ON 2 secs, OFF 10 secs, ON 2 secs, OFF 10 secs <-complete with stopwatch) temporarily improve performance?

I may re-connect pva and test before chasing a tp sensor or worse, replacement throttle body.
 

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nissan patrol
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Discussion Starter #13
Thanks SkinDog,
I have been reading about the TPS and want to investigate. The trans has been given a clean bill of health and I now have a blatz cable which is showing no fault codes at all.
Next week I get it booked in at my gas guy to get it onto the dyno and for him to have a crack at solving this problem.
I just need it to run normally as the +1 put her foot down last week and im not allowed to do the suspension until the engine is running perfectly.
My current list of things to look at includes:
- all vac lines for leaks
- temp sensors
- petrol pump
- TPS
I've finished all my other jobs and working nights this week so I might actually have some time to get stuck into this
 

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tb48 problems

replace the fuel filter - the best 20 dollars you will spend, speaking from experience. if it runs well on lpg you would presume it is a fuel issue. good luck.
 

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nissan patrol
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Discussion Starter #16
Jasonj - The sensors are in the correct spots (everything got labelled when I replaced them)
Blackfox107 - fuel filter was done at the service with the head rebuild.

I have been through all the fuel lines and vac lines and found them all working properly. I spent about a half hour with the computer plugged in and decided that I did not know enough about the read outs to chase this problem and find it, so I decided to take the are in for a dyno and diagnostics at a local bloke that deals mainly with race cars and LS1 upgrades.
After a few hours he called me and ask about the o2 sensors and if I replaced them with genuine ones, how i did it ect.
Apparently there is heaps of interference with the readout and the computer was always getting the wrong voltages, making it run rich all the time (hence 30l/100). he is now pulling the computer out to test it independent of the car and chasing possible earthing problems.
Best move I have made in a long time :) hopefully this does not cost the world and I can still have the new suspension in by xmas
 

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nissan patrol
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Discussion Starter #17
Quick update:
The mechanic is giving me the car back tomorrow so I can get out on the long weekend and have a little fun with it. He has been working on it on and off (to help save me money on labour) for 3 weeks and knows what the problem is, but can't find the solution :(
The output from the o2 sensors and signal through the wiring is fine but the output is not right. This output causes stops the engine going from a rich start-up cycle to a leaner running cycle, hence the idle dropping (lean cycle) and jumping back up (rich cycle) and causing the car to drink about 30l/100km around town. I don't want to know what it drinks in low range!
I'm starting to think about getting rid of it and cutting my losses... or doing an ls1 conversion!
 

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I thought it was all to do on coolant temp.
 

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Don't the tb48 have a diagnostic plug
If it does has anyone put a scanner on it
This would save a lot of time and money
 

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nissan patrol
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Discussion Starter #20
Bobby, I have had the computer hooked up and it told me not too much (im not a mechanic). there are no fault codes being thrown by this one
The guy I have taken it too has had it on the computer and the dyno to find what is going on; that is how he knows its o2 sensor related.
Dbsep, interesting thought and that makes total sense to me. I will mention it to the guy and find out what he says. As i said in a previous post; this is way beyond my level of knowledge so I have handed it over to the professionals.
After 3 weeks of looking at it on and off (by my request to save me money) he said he will have it done by the end of next week and it will only cost me $250.
If it all happens like that then I am happy
 
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