Need Urgent Help! Engine dies below 900rpm

[bcruz4]

Hi guys this is my first post ever on a forum so i wouldn't know if im in the right place. My d40 st-x has problems when starting as i need to give it a bit of gas when trying to start it and when it does want to start it runs fine (Will sometimes go into some type of safe mode and not want to accelarate as fast as it should) anything above 1000rpm, but when you want to put it to idle it will die straight away. The DPF light is also constantly on


These are the things i have tried thinking that it could be resolved:

Cleaned MAF sensor
Changed Fuel Filter
Cleaned Throttle body and EGR valve
Changed Throttle Body
Checked for vacuum leaks (Didn't find any)


One thing that i thought was strange was that the previous owner blocked the EGR from the exhaust manifold. I know this is a common mod but always thought it was done at the EGR valve.


If anybody could help me for what this problem could be i would appreciate very very much.

Thank you for reading this post

Have a great day/night

 

[Old.Tony]

Welcome to the forum.

Obviously one of the DPF sensors is reading differently to the other, there are two reasons this could happen: faulty sensor, or blocked DPF. The only way to clear that is to allow a regen to happen - either "naturally" or forced. Forced regens have to be done by a dealer/mechanic and are accompanied by an oil+filter change afterwards.

The lack of idle is likely to be the SCV. Now whether it's dirty or damaged is hard to tell in text since you need to remove it to inspect it, but you can try a good cleaner that may resolve the whole issue. You'll need to spend about $25 at SCA and have a couple of hours on hand.

Ideally you want less than half a tank of fuel on board - this increases the concentration of the cleaner above what it should be but that does make it more effective. Pour the contents of a can of Liqui Moly Fuel System Treatment into the tank and get ready.

Get the car started and get it on a highway. Just point it at the next major city and drive if you can. If you can't, you can achieve similar results by using a lower gear - what you're trying to do though is keep the engine RPM somewhere between 1600 and 2000 constantly for about 30 minutes. You don't want it to fall below. There's no need for it to go over. You might want to do an ECU reset at the start of this drive - radio pin handy, turn off the car, pop bonnet, undo battery negative lead, press brake pedal, reconnect lead, drop bonnet, off you go (must be performed by a single person not two).

This exercise will do two things: clean the SCV, and allow the DPF to regenerate.

If it doesn't work, the SCV might be faulty or simply too dirty, and the DPF might need either a forced regen or replacement. Most people opt for a DPF delete pipe (about $1K versus the $4K DPF cost) but if you go the delete pipe route, send a pm to 'auggie' on this forum and grab the replacement sensors offered which will prevent future problems.

If you want to retain the DPF then getting one from a wrecker is a viable option. Niss4x4 should be able to help you there.

A replacement SCV is about $240 from a Nissan dealer but you could get it cheaper from eBay (many have, with success). A second hand SCV from a wrecker isn't necessarily a good idea because its condition is questionable, particularly if left to sit with diesel on it for extended periods. In cold weather, normal diesel (as opposed to winterised diesel) forms crystals and blocks up the works - so an SCV from a wrecker might cause more problems than it's worth.

Hope that helps.

 

[shedman1300]

I have just got mine back today for the same problem. The car would run fine over 1000rpm but stall under that. 3 mechanics wanted to replace the cam chain because that is what the computer was saying ( it was replaced 8 weeks ago). It ended up being the crank angle sensor was faulty.

 

[bcruz4]

Thanks boys, This is alot of good information you have told me. Will let you know how it goes