Flat spots

[junior]

Hi Guys

Just wanted to rack your brains on a few issues.

I've got a 2007 St Patrol Wagon with the 3lt common rail Turbo Diesel manual. Done 75,000km
My fuel economy has started to blow right out. i am currently getting around 14.5 ta 15 lts/100km and i don't drive it hard, ya know changing gears at 2500 rpm and sit on 100 to 105 km/hr on the high way using cruise control, and the vehicle is unloaded and not pulling anything. 99% of my driving is highway work as i work some 650 km form home working week on week off.
It is also developing flat spots once the turbo spools up from around the 1600 rpm mark to around 2600 rpm cutting in and out, more noticeable in 4th and 5th gear. I was driving up this hill on the highway (10% grade) last week in a 100km zone and was doing 100 at the base got half way up and had to change back to 4th, so i change early at around 2000 rpm and once i was engaged in 4th at around 2000rpm it would not pull out it just stayed flat at that 2000rpm, it should have marched over the top of that hill no probs.
I have had Nissan put a new MAF sensor in 4 weeks ago under warranty, replaced the air and diesel filters.
Am not running any tires bigger than standard, 265/70/17 Mickey Thompson ATZ 4 RIB.
Has a genuine Nissan snorkel fitted and a bull bar, no roof rack or anything else to cause extra wind drag.

This one has really Got Nissan stumped.
Please any ideas???
Junior

[NissanGQ4.2]

hi junior, when you get a chance tell as a little about yourself and your rig under the introduction thread, also a location would be good for the members map.

[junior]

Thanks toddrhind, i have uploaded a few show pony pictures in my profile and introduced my self in the intro thread now.

[junior]

The guys at Nissan have decided that it needs a new turbo boost solenoid, they believe that its not functioning properly and only opening 40% so basically at times it is running naturally aspirated. well i will see how it goes tomorrow once its fitted.

[Woof]

Does it do this when you have got the cruise control engaged, as my 2007 GU sort of "hunted" when it was engaged, had to get a new program sent from Japan.

[junior]

Hey Dogman
Nah its when your driving it through the gears. It picks up then dies flat then picks up again, it feels like its hunting or starving itself, sometimes Mine feels like it hunts when on cruise but it is just the cruise cutting in and out when there is no load on the engine and when it goes down hills to maintain the set speed.
Its made my fuel economy go through the roof to average 15lts/100 which really hurts the hip pocket.

[junior]

well guys, the "mechanics" at nissan have fitted the turbo boost solenoid to my nissan and it has made no difference to the flat spots. They have no idea where to look next. they have tested the injectors and searched through all the computer settings and have found nothing, no faults no codes nothing. NO idea where to go from here

[junior]

still having problems, have had some more advice and now we seem to think it could be the boost actuator that's malfunctioning, pretty much the turbo could be over boosting and so the actuator lets all the boost pressure out the waste gate causing the engine to run naturally aspirated. still not 100% certain yet we'll give it a go and see. makes some sense but considering there are no fault codes coming up so this means its more of a mechanical issue than an electrical fault with a sensor or something like that. If this is the cause than it explains it self

[leadfoot]

have you sorted the problem,
I have a 2008 st doing exactly the same thing, started doing it at 75,500km, Nissan have been concentrating on the MAF sensor but it is obviously not the problem.

[junior]

Hey Leadfoot, nah mate haven't got it sorted yet, still trying to work it out, my patrol has now done 82,000 km. Yep we have replaced the MAF and throttle position sensor, its got them stumped. I am sick of it, don't know which way to turn now.

[CornwallTreeTom]

Don't know if you guys have managed to sort this out.... I have a 2001 zd30 with 46,000miles (similar to your 75-80,00km). Had the ECU re-mapped for "economy" the other week. Since then it has been really lumpy or lurchy under heavy acceleration between 2000 & 3500 rpm, seems to smooth out a bit higher up. The tuning company advised me to check turbo & egr function before returning to them. They boosted the pressure in the turbo by 0.15bar so its interesting what junior is saying about potentially a turbo overboosting..... It feels like it could be something like that as in mine it pulls for about half a second then goes flat for half a second before pulling again all the way through that rev range but only seems noticeable when i am really tanking it.
Had a good look this afternoon at turbo & egr, no hissing indicating turbo leaks, no black exhaust or staining or difficult ignition to indicate egr probs. Have a appointment for a retune next week, I may suggest they take the boost valve back to standard and see if that works?
Power increase in the tune seemed good they guessed its up to 195bhp but not been on the rolling road, but I really wanted more economy and I don't think its made any significant difference - maybe 1-2mpg sorry I don't know what that is in foriegn. Tuning company offers a money back garrantee so i will get them to remove the tune completely if its not smoothed out. Cheers. Tom

[junior]

All we could put it down to was the turbo over boosting to around 20psi and the ecu cutting it back to a safer level of 16psi, Nissan had a boost gauge on it and showed me the print out. In the end I end up trading the old girl in on a brand new 1 and it leaves the old girl for dead. I know that doesn't solve the problem but the new 1 doesn't have that problem and the new one had a variable vein turbo where it boosts from the word go and not just kicking in at 1800rp

[Farook]

Hi Tom. May i ask if you ever got the problem sorted out? i have something similar in my car and it is 2005 zd30 (auto) from UK. It has 45,000 miles on the clock.

[CornwallTreeTom]

Hey Farook
I bought an after market MAF sensor which sorted out the lurchy acceleration, cost me £30 I think, but now I think I need to tinker with the Throttle Position Sensor - I saw something about it in a thread on here somewhere. I get a flat spot which it won't pull out of like Junior describes, if i can clean that sensor i hope it will be fixed - fuel consumption has gone bad, if someone else sees this and knows the thread i am refering to could you point me in the right direction. It talked about drilling the TPS sensor flushing it with a spirit and resealing it - I think there were photos...
Cheeers

[Farook]

Hi Tom. Thanks for the advice. I actually have bought a new MAF and it made no difference. The problem is still the same!!!
The drives really well on a flat road, but on any sort of incline you loose power and the turbo just doesn't kick in correctly. I was really betting on the turbo booster solenoid as being the problem, but i see it made no difference to JUNIORS car.
Has anyone out there ever solved this problem??? Is this a factory defect on the Patrol?
Somone HELP!!!

[Robo]

Don't these suffer from waste gate problems.
it's electrical isn't it.
can't handle heat , bad design or both ! .
something along these lines !.

[Farook]

Hi ROBO. Sounds interesting since my car is an import from the UK to Kenya. Do you know of anyway to check or fix the waste gate problem???
I spoke to a Nissan engineer and he has told me to get the catalytic converter cleaned. We have a poor quality of diesel in Kenya and this could clog the whole thing up. I will check this as well as the turbo boost solenoid again and post the results.
Thanks for the input.

[Farook]

I talked to a guy at Nissan and he told me to bypass the turbo boost solenoid by taking off the two air hoses and putting them together. This is a simple way to see if the boost sensor & solenoid are working correctly. Well i did this in the morning and the car was like NEW!!! This car can fly.
Talk about some serious power. No more flatting out while accelerating in 2nd/3rd gear (i have an auto).

However, been advised not to leave car like this since it is on FULL BOOST, you can blow the turbo.

So now we know there is a problem with either the solenoid or boost sensor. Will try a solenoid from a friends car this weekend and see what happens.

Hope this helps some of the other guys.

[Robo]

so how did it go, fixed?

[jimamott]

I seem to be having the same issue.

Just recently, I did a 800km trip coming back from Port Lincoln, SA, when there was no acceleration at about 110km/h. Took my foot of the pedal and then the thing started to accelerate again.

[Chaz]

I talked to a guy at Nissan and he told me to bypass the turbo boost solenoid by taking off the two air hoses and putting them together. This is a simple way to see if the boost sensor & solenoid are working correctly. Well i did this in the morning and the car was like NEW!!! This car can fly.
Talk about some serious power. No more flatting out while accelerating in 2nd/3rd gear (i have an auto).

However, been advised not to leave car like this since it is on FULL BOOST, you can blow the turbo.

So now we know there is a problem with either the solenoid or boost sensor. Will try a solenoid from a friends car this weekend and see what happens.

Hope this helps some of the other guys.

This is why we fit manual boost controllers. The ECU pulls back boost when the EGR valve opens, so bypassing the control solenoid solves many problems. In most cases the flat spot is caused when the EGR valve opens under load, which doesn't happen with most cars, but does on a VNT equiped Patrol. Blocking the EGR and fitting a manual boost controller usually eliminates this common issue.