Help me diagnose this weird misfire please
#1
Help me diagnose this weird misfire please
I have a 94 Impreza with what we think is an early sti engine fitted with 440cc injectors, front mount intercooler, power fc, avcr etc whilst mapping it the other week it highlighted a problem that has stumped me. Over 1.4 bar of boost it coughs and splutters occasionally and at idle you can feel and hear that it's not running on all 4 cylinders, on boost it does tend to cough and go though and I can get it to fly without an issue
We have disconnected the coil packs at idle and noticed that the offside bank don't really notice too much i you disconnect a coil, the nearside makes a huge difference
far we have swapped the following but got nowhere:
Spark plugs
coil packs
ignition amplifier
cam sensor
crank sensor
ecu
It's always the same.
We then checked the compression & cambelt timing and both were good
Last night I tried to demonstrate to a mate how bad it is at idle but when the engine is cold it makes a huge difference disconnecting the coil packs but once it's warm it hardly notices if you disconnect coil number 3
What on earth could be causing it? I'm at my wits end now and I just want to break the bloody thing because it's pissing me off and I can't be bothered anymore
We have disconnected the coil packs at idle and noticed that the offside bank don't really notice too much i you disconnect a coil, the nearside makes a huge difference
far we have swapped the following but got nowhere:
Spark plugs
coil packs
ignition amplifier
cam sensor
crank sensor
ecu
It's always the same.
We then checked the compression & cambelt timing and both were good
Last night I tried to demonstrate to a mate how bad it is at idle but when the engine is cold it makes a huge difference disconnecting the coil packs but once it's warm it hardly notices if you disconnect coil number 3
What on earth could be causing it? I'm at my wits end now and I just want to break the bloody thing because it's pissing me off and I can't be bothered anymore
#3
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Isn't #3 the one that tends to run lean because it's furthest from the fuel pump? Maybe that's on its way out, or the fuel filter is blocked, and you're not getting enough fuel to that cylinder?
#6
Andy
It's got a walboro pump on there and I also wouldn't expect fuel pressure to be an issue at idle once warm
Blu
I've tried a different ecu and because it's an early car it has individual coils and I've changed them. I haven't checked the engine earth but it's a good thought
V4
It's got a Z32 on there at the moment, could that cause a misfire?
Any other ideas for me to try please?
Thanks
It's got a walboro pump on there and I also wouldn't expect fuel pressure to be an issue at idle once warm
Blu
I've tried a different ecu and because it's an early car it has individual coils and I've changed them. I haven't checked the engine earth but it's a good thought
V4
It's got a Z32 on there at the moment, could that cause a misfire?
Any other ideas for me to try please?
Thanks
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#10
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Is it possible for, say, a scored bore or damaged valve to pass a compression test but still leak significantly under combustion loads?
Was the plug you took from that cylinder any different to the others? Might be a clue?
Was the plug you took from that cylinder any different to the others? Might be a clue?
#18
The cause of the misfire has been found but not until I'd broken the car for parts One of the cam pulleys was loose and it must have been wobbling around and throwing the timing out. It was that loose it had actually damaged the cam and taken a chunk out of the locating lug
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The cause of the misfire has been found but not until I'd broken the car for parts One of the cam pulleys was loose and it must have been wobbling around and throwing the timing out. It was that loose it had actually damaged the cam and taken a chunk out of the locating lug
Steve
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03 November 2021 11:07 AM