TD5 missing at low revs

[Gt]

I have an ongoing intermittent miss on my TD5 Disco that is currently baffling my mechanic. Problem stated about 3 months ago when starting the car from cold in the afternoon leaving work. It will idle ok, but develop a miss when trying to drive off or if the revs are increased above about 900rpm. Once it starts missing,it also blows a lot of white/grey smoke. Engine will continue to miss up to about 1200 rpm, and occasionally it loses revs and returns to idle. Once the engine has been running for a few minutes, the smoke disappears. Engine will miss/smoke when ever started from cold and ambient temp around 17/18 deg. Once engine is at operating temp, miss is just noticeable when revs slowly raised, but no smoke.
Problem was originally diagnosed as a blown head gasket so this was replaced, but didn't fix the problem. Work since then has included.
Set of serviced injectors
New fuel pump.
New MAF, wastegate modulator, inlet manifold pressure/temp sensor. Wiring harness checked for chafing etc, no oil in ECU plugs, silicone intercooler hoses and turbo checked.
No faults logged and nanocom fuelling inputs and throttle pots look ok.

Has anybody in AULRO land come across same problem before or have any suggestions?

2003 D2a done 160k.

[Pippin]

I would replace the injector harness to rule that out.

Nick

[schuy1]

The symptoms do point towards a faulty harness. The oil does not have to appear at the ECU plug to cause problems it seems. A cracked head into a gallery can not be totally ruled out either. Cold its open, heats up, alloy expands and seals the crack. That is a probably a unique scenario though. Has the engine to your knowledge ever over heated?
Another possibility is low compression on a cylinder. Or it could just be a faulty connection in the loom :) There we go, I think I have scared you enough for now :D
Cheers Scott

[BIG O]

May still be the throttle potentiometer /position sensor . Maybe dodgy fuel filter or the injectors are not so good .Is it an intercooler full of oil. Do you still have an EGR fitted ??

[Psimpson7]

I would look into the harness, but I don't think it will be the cause I am afraid. I have had one with a faulty crimp on the terminal for injector 5 that caused a miss, but that didn't cause any smoke, and it wasn't temp dependent.

I have had exactly this issue on a car.

Cold start, revs to around 1000, noticeable miss coupled with lots of white smoke. It also smoked on a closed trailing throttle when cold. i.e idling down a sloped drive to the road. When warm the miss was still just there, if you were trying to find it, but no smoke

In the end it was caused by one or more of lash adjusters either not priming properly / pumping up.

This took a lot of time to find due to other issues we found when the engine was apart which masked the actual cause.

Another head ache here, is if that is the reason you have to remove the head to change them. If you have the head off check the piston protrusion as well.

[PhilipA]

Ok , I will probably show my ignorance here BUT.

Has a compression test been done on the engine?

If fuel is introduced to a diesel and there is compression, then nearly always a Bang occurs.

White smoke indicates that a bang is not happening.
I know with mine in iuts short history that it either goes or it doesn't if there is something wrong with the MAF or fuel supply, but a miss implies there is something different about one or more cylinders.
Another place to check I guess would be the continuity of the individual wires to the ECU from the injectors as each injector has its own input wire.
Regard sPhilip A

[djam1]

Pete could you hear any noise when it was in this state?


I would look into the harness, but I don't think it will be the cause I am afraid. I have had one with a faulty crimp on the terminal for injector 5 that caused a miss, but that didn't cause any smoke, and it wasn't temp dependent.

I have had exactly this issue on a car.

Cold start, revs to around 1000, noticeable miss coupled with lots of white smoke. It also smoked on a closed trailing throttle when cold. i.e idling down a sloped drive to the road. When warm the miss was still just there, if you were trying to find it, but no smoke

In the end it was caused by one or more of lash adjusters either not priming properly / pumping up.

This took a lot of time to find due to other issues we found when the engine was apart which masked the actual cause.

Another head ache here, is if that is the reason you have to remove the head to change them. If you have the head off check the piston protrusion as well.

[Gt]

Thanks guys for the suggestions. A few more details below that may help.
The car has never been overheated and when the head gasket was replaced, the head had a complete overhaul at the same time. It didnt have any other issues ie oil or water use. No leaks have been found in the internal fuel galleries and or injector washers. Oil testing has also confirmed no fuel in oil. Intercooler was also cleaned when the head work was completed along with the 160k service fiiters etc. EGR is also blanked.
Injector harness was replaced about 20k ago, but is still on the suspect list. The rover specialist who does all the work is looking to change out the injectors again for another set and I will also ask for the harness to be done at the same time. Today it has also had a slight miss when cruising at 90-100 that comes and goes.

[SiddersC]

Check the complete engine harness for chaffing, there are various rub points

[Pippin]

I had similar drivability problems and ended up replacing the main engine harness as well as the injector harness, both were causing problems. Cleaning the ECU connection of oil only gave partial improvement, however the change of the engine harness cured all problems and left a much smoother engine performance.

Nick

[Gt]

New injector harness was fitted 2 weeks ago and main engine harness checked again for any chafes etc with nothing found. Engine harness was then removed from car last week and every wire checked for resistance/continuity. Fuse box removed and checked, throttle pot and alternator also checked out ok. Rocker cover removed and timing checked over again. No fault found anywhere and when I started it yesterday about 10 am, it started missing and smoke again at approx 1000rpm as I tried to drive off. Shift back to neutral and let the engine idle and its ok. Bring the revs up again to around the 1000rpm and it will start to hunt by 100-200 revs and the smoke starts.

[OffTrack]

Can you post up a recording of the fuelling inputs with the engine running and post it up. Someone might be able to pick something up.

cheers
Paul