A4 1.9 Diesel 2004 - Stutters when cruising at constant speed

[Geo]

2004 A4 1.9 TDI. This is the 100bhp 5 speed model. Around 100k on it.

This car is booked in for next Wednesday for me to have a proper look but in the meantime I would appreciate any thoughts on the problem as it seems to be a strange one to me.



Over the past while customer reports that the car stutters/misfires occasionally while cruising at a constant speed on the motorway. It only happens sporadically, maybe up to 5 instances at a time. It generally happens during the first 15-20 minutes of a journey and goes away after that. This info is all from the customer I haven't experienced the fault myself.

He called in this evening but was seriously pressed for time so I just did a quick scan of the engine using VCDS - no codes found.

I didn't have time to do a full autoscan but decided to check ABS for codes as maybe a brake light switch could cause power to be cut and may show up in ABS.

Found this code:

18265/P1857/006231 - Load Signal: Error Message from ECU

Which according to the ross tech wiki suggests there are errors stored in the engine ECU, even though it showed up as clear when I scanned the engine. It must have just been there from a previous error which was subsequently cleared in the engine ECU.

So I am now left with a problem and no fault codes to go on.

Does this sound like a possible injector harness issue? Maybe it's not bad enough yet to throw a misfire code?

Any advice or suggestions on how to proceed are welcome. I will take all on board and report back on any new info after I have had a good look at the car.

Thanks

George

[Dean.]

Could well be a harness fault but also check for oil in the fuel filter.
Fairly common fault now. Oil gets into the injectors past the seals or past the seal on the pump.
Give an occasional misfire or loss of power.

[Geo]

Thanks Dean. Fuel filter was changed recently in an attempt to cure the problem so any oil should be easy to spot in the new filter.

[shaws]

geo
don't rule out egr valve control solenoid playing up, vcds flight recorder/ log was invaluable to me

Steve

[Geo]

Thanks for that Steve, I was thinking possible EGR issue alright

[Crasher]

My money is on code “18074 (P1666) No. 1 cyl. Unit injector valve N240 Electrical fault in circuit”

[Geo]

I was thinking of ordering an injector harness beforehand just in case. I think I will go ahead and do that.

[Geo]

Ok I have this car back today for a better look.

2004 AVB engine. 102k on the clocks but 117k according to the mileage checker in VCDS 

Owner says the stutter/misfire/whatever you want to call it will happen shortly after going onto the motorway while the cruise control is on at around 80mph.

I have taken it up and down the motorway twice. Once last night and once this morning and can't replicate the fault. I viewed all sorts of measuring blocks and can't see anything out of place. The engine starts and runs spot on. Power levels are good. No problems with driveshafts. No DMF issue that I can see.

Still no fault codes logged. I have attached an autoscan but it doesn't show a whole lot. The coolant temp sensor was replaced 2 weeks ago after the temp gauge was acting up so the error in instruments can be disregarded.

Fuel filter looks clean from what I can see looking through the hole in the top where the return line clips in.

I have an injector harness here but I am reluctant to fit it when there are no codes. It seems to me that any problem with the injector harness should show a fault code pretty much straight away. I have only fitted a few looms to these and they were all clear cut cases. Has anyone seen a loom cause this kind of issue? It seems unlikely to me that it would.

Has anybody got any suggestions for me? I am unsure how to proceed with this one really.

One thing that just occurred to me is do these suffer from any ECU relay problems like the Mk4 Golf? Do they use the same "109" relay?

[Sparky Charlie]

This obviously guess work but thinking on the info the owner has given you...

The fault only occurs when on cruise on the motorway.

The only thing that jumps out at me is that is probably the only time when the EGR valve opens to it's maximum and remains there for a time.  Hence I would be inspecting the operation of the EGR, vac, vac valves, and the egr valve itself as well as the airflow calculations, Map, AFM, intercooler leaks. 

Charlie

[Geo]

Thanks Charlie. That certainly makes sense. I have had to give up on it for now as the guy needed the car back. He is going to drive it for another while and see if the problem gets worse then come back to me.