Clogged Injector or Limp Mode

Have had a lumpy idle at startup / smoke on my mk1 TD4 since I got it. It quickly levels out after a minute or so.

Recently changed the fuel filter and filled the new one with Kerosene to try to clean the system. After that ran through I put some diesel treatment in a Qtr tank of fuel and gave her a hard, high revving drive. On the way home from that journey, i lost power completely and it developed a misfire. No MIL. Starting it up after that was difficult with a lot of ringing required. It was starting on 3 cylinders.

While it was lumpily idling, I removed the injector electrical connections one by one. 3 of them caused the engine to die and one only caused the slightest change in engine note. I noticed that the nut on the fuel line to this injector wasnt actually very tight, so I tightened it and restarted. The engine started normally. Took it for a drive and it was fine, no power loss or misfire.

After an hour of uneventful driving today, it again developed a misfire......
I'm in two minds about whether my diesel treatments have caused something to dislodge and clog the injector or if this was limp mode brought on by something not liking my 4000prm spin the other day........ Im not getting an engine warning though.
Any thoughts?

Sounds like you have a blocked injector. It's been known to happen after using a fuel system cleaner. As you said, something has probably dislodged, causing the issue.

Yeah seems so. No problems again today on a half hour drive, pulling well at all times. Think I'll just keep the diesel treatment in it for the next while and see if it unclogs it fully.

Update on this. Lost power again today and there seems to be a pattern emerging which is odd if it was a blocked injector. Goes fine from the start up until it reaches normal operating temperature and then run lumpily with absolutely no pull. When I got to where I was going, I was over 2 hours away from the car and the engine had had time to get cool. When i returned, again, it was fine until it reached halfway on the temp gauge and then went into a sort of limp mode again.

It's very similar to Higgins' problem in this thread. Considering this only started since I gave it a high revving drive the other day, it might be possible theres a split hose somewhere? Not sure if this would cause misfiring though, maybe in that case it should run normally but underpowered?

You could try pulling an injector wire off 1 by 1. This would be the easiest way to determine which injector it is. Once you can trace the faulty one, I'd be tempted to fit a second hand replacement. It could be a faulty internal connection that only appears when hot?
Oh but remember that disconnecting injectors does carry a small risk of damage to the injector drive circuit.

I did try unplugging each injector the other day and all but the one nearest the drive belts causes the engine to cut out. I just tried it again while it was idling from cold and this time none of the injectors unplugged caused a stall, only a misfire.....

So I then unplugged the MAF. It started much better, much smoother. Took it for a spin to get it up to temp and up some challenging hills, it pulled like a train and not a single hesitation, nevermind a loss of power.
Would that mean its simply a duff MAF sensor? I'd assume if it was a clogged injector, unplugging the MAF would have no affect. And the fact that this problem only occured when the engine got hot too.........
I have cleaned it with contact cleaner months ago.

Just use it and monitor the way it runs.

Would a MAP sensor completely clogged with black crud be a possible culprit here too? That's what I found after removing the manifold.

Have driven for a couple of days with no MAF and the car is transformed. Seems a bit heavier on the juice alright though. Going to hook it back up tomorrow and see how it goes.

The MAP sensor tends to have more effect on higher speeds, but that's not to say it isn't having some effect.
As it's running ok with the maf unplugged, I think you have already found your culprit.
Mike

Reconnected the MAF this morning and thankfully all was well when she got up to temperature. No hesitation or power loss. Im thinking the clogged MAP may have been the original problem, unplugging the MAF possibly negated it and allowed plenty of fuel in and then cleaning both has resolved it........... touch wood.

Another update on this. May have found the real culprit which turned out to be none of the above....

Found a mechanic who plugged in a code reader and told me two of the injectors were showing faults. He cleared the codes and I went on my way. Still hesitating at best and misfiring at worst. He mentioned to me that the on again off again nature of it would be unlikely to be an injector failure and could quite possibly be wiring related. This made me think, because while I had the manifold off recently, I bent the injector loom up and out of the way and the problem seemed to worsen after that.

I decided to see if I could get a secondhand injector harness and managed to bag one locally for just €20. Before fitting it, the car was misfiring from the first turn of the key. After I fitted the other one, started fine and over the past 3/4 days, I haven't had a hesitation under load or any poor running to speak of.
Fingers crossed that was the issue but it certainly looks like it.

Would you prefer me to sacrifice a chicken or a goat to the appease the God of troublesome td4's
Mike

The injector loom isn't that expensive, if it's causing the trouble. It's something I plan to test mine at some point. I want to see what's causing the 2K misfire, I've a hunch that the injector loom could be the culprit.

It certainly can feel like the equivalent of a rain dance is needed to keep these things on the road sometimes Mike!

Definitely worth trying, especially if you can test a known good second hand one first for cheap. A new one here would work out at €80 or so I think.
As well as the mechanic's tip off, another thing that got me thinking wiring was the wheeler dealers show on tv! I recently saw an episode with a Discovery that had a misfire and it was resolved by a loom replacement, not an injector refurb. Not a very scientific approach to troubleshooting but for once a hit and hope worked..... it seems for now. (Grabs table)

I suspect that the loom is responsible for many so called injector faults. It's definitely worth changing the loom first instead of the costly injectors. Interestingly the TD5 loon is available for half the cost of the TD4 equivalent which makes little sense to me. I'm now wondering if the TD5 loom can be "adjusted" to fit the TD4.
The VW PD engine also suffers injector loom failure, giving random misfiring on that engine too.

Well I got a trouble free 3 months of driving out of it, but Im back to square one with misfiring again.

Travelled about 20 miles somewhere yesterday, no issues as usual. Then when I was heading back I noticed the SRS warning light had popped up on the dash and wasnt going out. On that trip home I noticed a few stumbles and hesitating under acceleration. I checked the yellow plugs under the seats, replugged them and checked the airbag connector in the steering wheel. I know I need a new slipring as the horn and the radio functions dont work so I put the SRS light down to that too and am due to try a good 2ndhand one next week.
Anyway, made another trip today and the car ran like a dog from start to finish. 3 cylinders all the way. Now obviously the SRS light shouldn't be related but it would be some coincidence that it came on and on the very next trip, I have the misfire back. Since a new loom solved it the first time, it's surely an electrical issue, so could the airbag system flagging a fault in someway have affected the fuel delivery.....?

I'd say the SRS is only related by the fact that you have some sort of electrical issue.
I believe the SRS is controlled by the CCU behind the dash. Where as the injectors are done by the ECU in the engine bay.
Have a check of your earth connections and other connections in general.
Any chance you could get it plugged back into a reader.
Mike

Yes, I'll try to get it diagnosed with a reader next week when Im picking up the new slipring. Im hoping that fitting that will restore the horn, radio, kill the SRS light and magically restores the smooth running! I know it sounds far fetched, but after a 20 quid loom solving it before, Im starting to think anything is possible with these cars!

Another update. got a new slipring and my steering wheel functions are all restored. The SRS light is still on but I reckon it will need cancelling with a reader so i have to wait til next week to get that done.

On the misfire, I have gotten another known good loom to try and as expected it has resolved the problem. When I took off the loom I got back in May, there was a coating of black oily moisture everywhere. I popped off each injector plug, cleaned them out with contact cleaner and blew them out with compressed air. I then gave it a test and it started fine and drove perfectly for 3 miles before it developed the miss again. Left it over night and same scenario the following morning, fine for a few miles then when up to temp, started to miss. I swapped out the old loom for the new one and it seems to be cured.

Looking at the old loom, one of the injector plugs is noticeably oily on the inside and I suspect this is causing the issue. Where could that be coming from though......

Possibly the washer/seals holding the injector in is won out, can't think where else it would come from.
Mike