Weird occasional overfuelling/misfiring issue

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Vulgalour
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Car Ownership: Rover 400 Mk1 (R8) Saloon

Weird occasional overfuelling/misfiring issue

#1 Post by Vulgalour » Tue Jan 09, 2018 9:06 pm

In short, I've had a couple of occasions where the Rover has decided to only run on three on start up and stink of over-fuelling, which is what I suspect the issue is, but no idea why.

First time was when we had that horrendous amount of rain in a very short period of time in November/December. Started the car and it was only firing on three, smelled of fuel. No leaks apparent, nothing loose, no issues with coolant, exhaust and oil mixing and everything otherwise in rude health. Went to the car the following day and it started normally with no problems at all, running on four, no fuel smell.

Today the same thing happened. The main differences were that I'd done a 300 mile motorway slog the day before and temperatures were below freezing. Once the car had been idling for about a minute it went back to running normally, didn't smell of fuel and has behaved impeccably all day long.

I can't find any leaks, any loose components nor any obvious points of failure. Everything seems to be in rude health with no loss of coolant or oil, no mixing of fluids, clean plugs, no loss of compression (head gasket and belts were all done last year). No warning lights illuminate when this happens either. It's like the car gets confused and dumps too much fuel in for some reason, but only for about a minute and then it clears up. Since the problem has only appeared twice I haven't enough data to point at a definite cause because on other very wet or very cold days it starts normally without any issues at all. Fuel economy is close to factory figures and motorway runs are returning in the region of 42mpg. No loss of power, no noises to help identify issues either.

My stab in the dark is a failing injector, dodgy spark lead or perhaps an issue with the ECU. Without something to point the finger at definitively, I'm not sure what to look at now so hopefully someone else has experienced the same and knows what the score is.
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1234dist
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Re: Weird occasional overfuelling/misfiring issue

#2 Post by 1234dist » Tue Jan 09, 2018 9:11 pm

I’d say faulty injector or fuel pressure regulator.
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Vulgalour
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Re: Weird occasional overfuelling/misfiring issue

#3 Post by Vulgalour » Tue Jan 09, 2018 11:44 pm

Is this one of those things where I have to wait for it to break properly, do you think? Or is there a way to test it now? 99.9% of the time it's working perfectly fine.
Current Fleet:
1972 Austin 1100
1980 Austin Princess 2 1700 HL
1994 Rover 414 SLi

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1234dist
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Re: Weird occasional overfuelling/misfiring issue

#4 Post by 1234dist » Wed Jan 10, 2018 7:06 am

Without a pressure gauge already being fitted so you can see if it’s constant or not, you might just have to wait.

It could also be failed/ pinched o rings if you have recently done anything with the inlet or fuel rail.

I’ve got pics on disassembling a t-series inlet to give you a guide if you want to pull it apart to check, should take no more than an hour.
220 Coupe turbo K785OAT (issues :glare )
Rover Sport 220GTI m-series K56AEP
218 VVC Cabriolet R170FEU
220 GTI M-series J777RAL
416 K-series Tourer R461NEB
75 2.0 CDT P80CJM
620 SLI P267LOM HONDA
420 GSI Turbo L191CVP

crepello
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Re: Weird occasional overfuelling/misfiring issue

#5 Post by crepello » Wed Jan 10, 2018 9:29 am

If you stopped it mid-problem and then extracted the plugs one by one, would the dead cylinder smell more strongly of petrol?
That would reduce the potential problem points by 75%. Given software and a special serial cable, it is possible to exercise injectors singly, which might reveal a different 'click' sound.

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Julesmat50
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Re: Weird occasional overfuelling/misfiring issue

#6 Post by Julesmat50 » Wed Jan 10, 2018 10:01 pm

crepello wrote:
Wed Jan 10, 2018 9:29 am
If you stopped it mid-problem and then extracted the plugs one by one, would the dead cylinder smell more strongly of petrol?
If it's not firing at all then it certainly would, plus there is a real chance that the plug nose in the affected cylinder would be wet with unburnt fuel.
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Vulgalour
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Re: Weird occasional overfuelling/misfiring issue

#7 Post by Vulgalour » Thu Jan 11, 2018 11:06 pm

Trouble is catching it mid problem. As usual, it's behaving impeccably now no matter how cold or wet the weather so I will probably just wait until it breaks properly, which it might never do, because R8.
Current Fleet:
1972 Austin 1100
1980 Austin Princess 2 1700 HL
1994 Rover 414 SLi

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