Help; problem after EGR mod

I blanked off my EGR at the intake manifold end yesterday (getting to the exhaust manifold end is a bit painful given I want to trial the mod) on my '08 D40 and had a bit of an interesting experience this morning. Warmed up the engine for ~5 minutes (which is normal for me) and headed off on my journey. After a 5 minute drive I pulled onto a highway near my place, gave it a bootful to merge with the traffic. All went well until around 4000ish (i.e. just before a shift) in 2nd (manual), when it suddently lost all power as if it'd developed a massive leak between the compressor and the inlet manifold. From the seat of the pants gauge, it felt akin to loosing ignition in a petrol car; it just stopped responding to the throttle. It was like hitting a boost cut, but instead of temporarily limiting boost, its like it just wedged open the waste gate or something.
Anyway, I pulled off the road to do some diagnosis:

- Checked the dash for signs of alarm (such as an engine light), however no problems were evident
- Popped the bonnet to check for leaks in the event I'd knocked a vacuum hose of somewhere while working on the EGR. Again, no apparent issue (subsequent driving indicates this wasn't the cause)
- With the engine still running, but the truck in neutral, tried to get the revs up with a stab of the throttle. Extremely slow response and seemingly unable to exceed ~2500 rpm.

Working on the basis I may have exceeded the threshold of one of the sensors for some reason, I waited a few moments (to let things cool, not that I'd been hoofing it prior to reaching the highway) and then turned it off. Waited for a count of 30 and then started it back up again; problem gone. The whole thing lasted for probably 1-2 minutes.
I've since driven around (probably 20K's) at normal rpm (between 1500-3000 rpm) and all is well with no apparent issue. I've not been brave enough to wind it up again to see if the problem reoccurs.

My D40 is totally stock for all intents and purposes (no exhaust, no chip, no other engine mods).

Has anyone else experienced any such problems?

Sounds like its overboosted.

What age is it ?

That was my first thought, but I'd have thought it's behaviour would be analogous to a rev limiter; bounce between the cut and a lower threshold (which is how various petrol/turbo cars I've had behaved). Instead it just killed power. My expectations could be totally off versus the actual behaviour of course...

2008 with ~27000 k's.

Yep, it went into limp. Mine did that a couple of times, just turned it off and restarted no problems, I figured it was overboost in my situations.

I wouldn't panic, but give it another rev out and see if it does it again.

Check fuel flow, i had a Truck once that would be fine on the flat but if i hit a hill or loaded it up blead the filters dry, it turned out to be a blockage n the fuel line.

Thanks Leprechaun. I thought it was boost related, as it was a reasonably chilly morning and it certainly felt to have a smidgen more torque after blocking the EGR (just going by how much better it pulled if you were labouring the engine a bit).

Might try drilling a 10mm hole in the plate to see if that relieves the symptoms.

Cheers Simon. It was only in for a service a month back; then again, that's probably irrelevant as I doubt they'd have changed the filter.

I'll suss that out too.

group3j said:

Thanks Leprechaun. I thought it was boost related, as it was a reasonably chilly morning and it certainly felt to have a smidgen more torque after blocking the EGR (just going by how much better it pulled if you were labouring the engine a bit).

Might try drilling a 10mm hole in the plate to see if that relieves the symptoms.

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I dont think the hole will fix it, Ring Chip it.

I wouldn't drill the hole.

The ECU should not have allowed the overboost. At full throttle the EGR valve is closed so whether you have blocked it or not, it's out of the equation - the overboost came as a result of something else, perhaps a MAF sensor that's reading a little on the low side, or has some muck in it causing it to read poorly.

SimonD40 said:

I dont think the hole will fix it, Ring Chip it.

Click to expand...

Thanks Simon. What makes you say a hole won't fix it? I'd have figured (maybe incorrectly) that it'd be a compromise between a fully closed hole and a fully open hole, when the EGR is open; i.e. instead of full pressure one side of the plate and full....lets call it vacuum, though it may not be....on the other side of the plate you end up with an actual pressure differential.

Keen to hear your thoughts.

Old.Tony said:

I wouldn't drill the hole.

The ECU should not have allowed the overboost. At full throttle the EGR valve is closed so whether you have blocked it or not, it's out of the equation - the overboost came as a result of something else, perhaps a MAF sensor that's reading a little on the low side, or has some muck in it causing it to read poorly.

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Thanks for the response Tony.

I'm not familiar on the operation of the valve admittedly however if the valve is closed at WOT and/or high revs, then it makes total sense that the blocking of the valve is irrelevant.

No real reason for the MAF to be dirty, I've probably done all of 50k's off road and even then we were on fire trails. However, I'll have a peer and see if there's anything obvious; the MAF is located in the airbox near the pipe leading to the compressor isn't it?

Interesting problem. I actually decided to remove the plate last night for some back-to-back testing and its subsequently run fine all day. I'll stick the plate back in on the weekend and see if it happens again.

At full throttle, you have mild pressure on the exhaust side of the plate and about 18psi (turbo boost at full) on the other side. The EGR valve will be closed to stop any boost leaking back down the EGR pipe. (as well as allowing the engine to develop the max power).

Old.Tony said:

At full throttle, you have mild pressure on the exhaust side of the plate and about 18psi (turbo boost at full) on the other side. The EGR valve will be closed to stop any boost leaking back down the EGR pipe. (as well as allowing the engine to develop the max power).

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not quite. exhaust pressure will be far more than 18psi. theres more than enough pressure to allow egr to flow but EGR is shut to allow full power.
you almost never get boost higher than exhaust backpressure, more so with the less efficient variable turbo's.

the problem could be the turbo control valve (well known to fail), dirty/failing MAF or turbo vanes sticking (known problem with variable turbo's).

Hi Group,

I have the same problem in my Nav. Engine goes into limp mode on the odd occasion and have found that it is when i accelerate heavily to overtake ect. Took it to Nissan and their response was that it did not log a code when faulted so they cannot diagnose untill it does. But as you would have experienced the "check engine light" does not illuminate on every occasion. I spoke to an independant diesel specialist and his comment was it is a known problem that nissan have not been able to sort out. He mentioned that the high pressure feed pump suction control valve had been bandied about and when i went to Nissan they denied it. I have taken video footage with my phone when it happend not long ago but i have to trim the clip so i can send it on. Nissan requested any footage as proof of it happening. I will be taking it in to them when i get a chance. I will try and post the footage on here for you look at for you.

limp mode with no check engine light

here is the video.

[YT]http://www.youtube.com/watch?v=LTrbFYnzK90[/YT]

It's just GOT to be something to do with the MAF sensor, possibly underreading (ie indicating to the ECU that there's less air flowing than their is) and causing the ECU to decide to increase the boost? That would continue until the boost sensor read too much pressure in the intake manifold and that sends the ECU into limp mode.

Or it's the boost pressure sensor underreading? I can't see it being that, because then what would tell the ECU that the turbo boost is too high - unless it's the HO2 sensor in the exhaust reading way too much oxygen ... I can't see it being that. I suppose there could be an intermittent connection on the boost sensor, which could do this. It would only ever trip the alarm when the turbo was in full song - which seems to be the case. Dirty wires? Been through water?

I think the MAF sensor is the most likely culprit, either that or the turbo actuator is sticking at some point (perhaps at the extent of its travel?).

Could it have anything to do with fuel delivery sending it into limp mode. I noticed you fuel gauge was reading "NOTHING"!!

i remember the early ones had problems when they got low on fuel. there was a modification done to the tank pickup to help fix it.

if you suck a bit of air in it will cause that sort of problem.

Mine (what I assume to be) over boosted once when under load. Just pulled up restarted and all good again.

My fuel light came on just after entering limp mode as on the clip, but still have 15 litres when it first comes on. Has happened with full tank a few times. I am aware of some navara's runnning out of fuel when on slight inclines when getting low on fuel but i have never experienced this but know a bloke who always does.

Old.Tony i love how everyone tries thier damned hardest on this site to try and assist with issues we have experienced with our Navs, just wish Nissan were focused in recitifying this known issue. Surely with technology it should be logging a fault.

Bosshog mine does this probably once every 3-4 months and seems to reset everytime then nothing for atleast another 3-4 months.