Rpm dropout and ECC-IV code 57

[rtg]

Last week the engine started misbehaving - it intermittently dips in RPM. It runs really smooth and then rpm drops to near zero. I can then hear the injector piezo's buzzing, big inrush of air through the AFM's and then engine recovers with a bit of overshoot. Has anyone come across this type of fault?

My initial thoughts are electrical, so I've plugged in the Gunsons code reader and it's giving 11(OK) for test 1 & 2 apart from on test 3, where it reports 50(european ecu) and then displays 57(Intermittent in Neutral/Drive Switch (NDS) circuit). To the best of my knowledge I don't have one of those. Any ideas what 57 actual is?

The plan is to perform a vacuum test (when I've figured out how to..) compression test and then use a scope to check all sensors for noise & faults which the reader cannot detect. Also, any chance this could be from the distributor module losing timing?

Any ideas welcome!

[GreenV8S]

When you say the rpm drops etc, do you mean the engine actually slows down, or are you referring to the rev counter?

[rtg]

Yes, engine speed slows (nearly stalls) - rpm indicator then tracks the change.

[GreenV8S]

I guess this is when the engine is idling. Does it happen when the engine has been idling for a while, or just when the revs are dropping down to idle?

This type of symptom could come from an idle speed control valve sticking, which can happen if it is gummed up. They need cleaning every year or so. Usually this would cause the engine to idle too fast when it is dropping down to idle, and then hunt. An obstructed air bypass could cause similar symptoms by pushing the idle control valve outside the normal range of operation. I suppose an electrical / wiring fault could cause similar symptoms.

Any intermittent problem causing the engine to run out of tune could cause similar symptoms, such as fluctuations in the fuel pressure, air flow sensor fault, ignition advance fault, weak spark. If you aren't familiar with working on engines you might consider consulting a specialist since it would be easy to introduce faults if you don't know what you're doing. These should be relatively quick things to test and check and not likely to be very expensive to get fixed professionally as long as you get somebody familiar with these engines, rather than a fitter who expects the laptop to tell him what to do.

Edited by GreenV8S on Tuesday 23 August 16:53

[rtg]

Thanks for the info - I've recently cleaned out the ISCV as it was sticking, so should be ok. The problem's like a cylinder (or burst of cylinders) intermittently failing to fire. It always happens at idle speed, but more frequently when hot. Under hard acceleration & normal cruising speeds it's fine.
I'll see where i get to this weekend but would rather solve this myself - that way I've learnt something new!

[Barkychoc]

If it helps with your troubleshooting the injectors are batch fired in 2 groups - so there are actually only 2 injector circuits which I think on the 2.9 relates to each side of the engine.So that means when No 1 injector fires 3 and 5 also get triggered and fuel is delivered if that makes sense.

If you have a dodgy injector, or cable - that could be taking down 3 injectors - although to be honest if you were losing 3 injectors I would expect it to stall or have the power of a lawn mower - does that sound credible?

[rtg]

A possibility - it does lose all power for a fraction of a second and then recovers. The wiring on the s could well do with replacing, but it's a job for the winter. I've got a 4 channel scope so will be working around the electrics this weekend.