View Full Version : Engine Misfire
cjspindler
30-08-2011, 12:57
Hi,
I have a problem with my Williams with it misfiring under part load conditions. I've just had the following changed, so can only think that it could be fuel related now.
Spark Plugs
HT Leads
Dizzy cap
Rotor arm
Ignition Coil
Crank sensor
The car drives fine on full throttle, but is a pretty bad misfire on light acceleration and now some constant speed.
Does anyone else have any similar experiences of this and could point me in the right direction?
The car has a adjustable fuel pressure regulator, which i have adjusted and it has improved it slightly, but still not fixed.
Cheers
Chris.
Can you identify which piston has the misfire?
Is there a constant fuel pressure at the fuel rail? No leaks?
Possible dirty injector, intermittent ECU fault, fuel leak or loom issue maybe.
Why do you use an adjustable FPR out of interest?
Check your injector plugs aren't loose
Also, when did the problem start? Could be cam timing as well, but probably something much simpler.
Spec of car?
could well be a lean spot in the fuelling at that point causing a misfire, maybe due to the map not being right for the mechanicals, or maybe due to a sensor fault putting you on the wrong point on the map.
PS
Have you monitored the AFR when it is happening?
ratboyvalver
30-08-2011, 20:12
check your earths buddy,
cjspindler
31-08-2011, 07:51
All,
Thanks for the replies.
That gives me something to work with over the weekend.
But to answer some of the questions:
No, I havent identified which piston the misfire is coming from. Is this an easy job?
I will try and put a fuel pressure tester on, and see what happens when it misfires
The car had a FPR already fitted when i bought the car.
The problem has started after i filled the car up with fuel - it had a very slight similar problem previously, but this happened once in about 50miles. Now it's everytime I try and maintain speed and apply light throttle.
The spec of the car - well...the car was used as a hill climb car, and now I use it as a track day car. The engine has had gas flowed head, Kent cams, ECU re-map, full Devil exhaust, and lots of other bits and pieces, but last time it was dyno'd it was running 170bhp
The car has been checked with diagnostics, and the only fault found was the crank sensor, which i've had changed and doesnt seem to have made any improvements.
Does anyone think it could be fuel pump?
Two things I would do as simple tests are a compression test and swap the ECU over with a spare if you have one.
Check the wiring loom along where it comes out of the relay box on the passenger front inner guard in engine bay. I had a similar problem where the loom rubbed through against the body and had corroded some injector earths.hope this helps I know it's nasty when your trying your best to fix something and no matter what you do it doesn't work.
Check the wiring loom along where it comes out of the relay box on the passenger front inner guard in engine bay. I had a similar problem where the loom rubbed through against the body and had corroded some injector earths.hope this helps I know it's nasty when your trying your best to fix something and no matter what you do it doesn't work.
Check the wiring loom along where it comes out of the relay box on the passenger front inner guard in engine bay. I had a similar problem where the loom rubbed through against the body and had corroded some injector earths.hope this helps I know it's nasty when your trying your best to fix something and no matter what you do it doesn't work.
Is that under the inner splash guard, or where the fuses are next to the washer bottle?
It's the big black box behind the passenger headlight.the loom runs to and from that.
zmaster2k
01-09-2011, 07:15
Check the wiring loom along where it comes out of the relay box on the passenger front inner guard in engine bay. I had a similar problem where the loom rubbed through against the body and had corroded some injector earths.hope this helps I know it's nasty when your trying your best to fix something and no matter what you do it doesn't work.
This! Also check the earth strap to top of gearbox....that was my issue.
sideways danny
01-09-2011, 11:17
The car had a FPR already fitted when i bought the car.
put a standard one back on. If it's an FSE boost valve, this is most likely the source of your problem
The car had a FPR already fitted when i bought the car.
put a standard one back on. If it's an FSE boost valve, this is most likely the source of your problem
If it has been remapped with the current FPR and then he changes it back to standard then things could easily get a LOT worse as a result.
NEVER make a change to the FPR without wideband equipment to check the changes havent leaned your fuelling out or you could end up with a melted engine as a result.
cjspindler
03-09-2011, 22:18
I've checked the compression of each cylinder today and have the following:
Cyl 1 = 192 psi
Cyl 2 = 190 psi
Cyl 3 = 200 psi
Cyl 4 = 198 psi
This looks very good to me, so i think there is no problem with the head gasket.
I've checked to see if there is any earth issues and cant find anything there either, although i must say the wiring on my car is a bit all over the place.
One thing i noticed when i started the car after completing the compression test was the car smelt like it was running very rich.
I adjusted the FPR a little to see if this changed, and when turning it down 1/4 turn it almost stalled on me, and when turning it up 1/4 turn it started to smell even more rich.
Does anyone have any more suggestions i could try for tomorrow?
Cheers.
zmaster2k
04-09-2011, 08:21
Has the car been mapped or chipped or anything with that fpr?
The compression is good.
If my cars misfiring I locate the problem piston by either pulling the spark plug lead off one by one and starting the car each time, being bloody careful not to get electrocuted, or the injector power. When you disconnect the misfiring one the engine note will not change, the other three will make it run even worse.
I would fit an OEM ECU and go back to a standard regulator/rail., or at least borrow a set to trial fit and test.
The richness will be because you had a bunch of unburned fuel doing the comp test.
cjspindler
04-09-2011, 17:13
I've just changed the fuel filter, and been out for a test drive.
It seems to have improved it somewhat, but I still get the occasional misfire.
I've also heard that there could be a problem with a leaky rocker cover and oil leaking into the chamber. Is this something that anyone has experienced?
Starting to struggle for other items to try myself now, but i'm prepared to try any other suggestions before it goes in to the garage!
Cheers.
sideways danny
06-09-2011, 00:41
honest to god, if it's an FSE power boost valve, remove it and refit a standard one
I've just changed the fuel filter, and been out for a test drive.
It seems to have improved it somewhat, but I still get the occasional misfire.
I've also heard that there could be a problem with a leaky rocker cover and oil leaking into the chamber. Is this something that anyone has experienced?
Starting to struggle for other items to try myself now, but i'm prepared to try any other suggestions before it goes in to the garage!
Cheers.
Just to eliminate a possible easy solution, remove spark plug cover, disconnect king lead from dizzy (just in case hehe), pull the HT leads off the spark plugs, get a torch, shine down each plug well and if you see any wells full of oil, you need to clean it up.
Clean it out by taking the 10mm securing bolts off the plastic plug cover, remove oil filler cap, yank the plastic cover up and put to one side, clean out plug well (I often just pop the plugs out to clean them of oil as well and let the oil drain into the chamber hehe).
I have a leaking camcover gasket (rubber megane one) and it can cause misfires.
cjspindler
14-09-2011, 09:30
Right - the plot thickens!
I've taken the car to a Renault Specialist, and he has diagnosed the problem as a short on the throttle cable.
I havent seen where exactly he is on about, but apparently there is signs of wear on the cable and it has gone green.
I've looked on RPD and can get the cable for about £20. Is this an easy job to change? Or do you think it's worth just getting the "specialist" to fit?
volymmannen
15-09-2011, 07:46
Right - the plot thickens!
I've taken the car to a Renault Specialist, and he has diagnosed the problem as a short on the throttle cable.
I havent seen where exactly he is on about, but apparently there is signs of wear on the cable and it has gone green.
I've looked on RPD and can get the cable for about £20. Is this an easy job to change? Or do you think it's worth just getting the "specialist" to fit?
So the real problem is lack of earth cable between engine and car..
cjspindler
15-09-2011, 07:51
I got home last night and had a look at where the guy was on about with the throttle.
It turns out, that he meant the throttle position potentiometer. The cable connection on this do look very dodgy to say the least, so i think it best to change this.
Does anyone know where i can just get the part from, without having to buy a whole throttle body? Also, how much would we be talking for this part?
I've read that there is a special set up required for this, so is this something i could do myself, or does it need a plug in device to re-set the max/min positions?
Cheers
robi1000
15-09-2011, 14:56
You don't want to change just the TPS. It's just not worth the hassle. Just buy the whole working TB and fit that.
You don't want to change just the TPS. It's just not worth the hassle. Just buy the whole working TB and fit that.
Totally agree :thumbsup:
cjspindler
26-09-2011, 12:35
I've now changed the complete throttle body with a different TPS. I've also done a voltage check to make sure the TPS is working correctly.
I took the car out, and it still has the misfire problem.
I thought i was going to crack it with this, but now i'm back to the drawing board.
Any more suggestions?
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