05 C2 1.1 poor idle missfire ecu test

[numnut20003000]

hi everyone i have a c2 1.1 with a poor idle/ misfire
i've had i 53 reg saxo beside the car with the same set up and swapped each sensor ,coil, plug etc etc
it left us think the only thing left to change is the ecu which we all know its not cheap if we are wrong
i've seen on a ford a way to test the plug connecting to the coil pack for an ecu fault
we tried this today and we only have is a live going from the red wire (which we think is an earth) to the battery and got nothing else form the other wires when turning the engine over
what we ask is dose anyone know if we should expect anything from any of the other wires? or is this confirming what we think is a faulty ecu
is there a way to test the firing from this plug to the coil pack?
thanks for your time

[Mandrake]

I don't want to sound cheeky but it sounds like you've being doing what I'd call shotgun diagnosis.... eg just replacing stuff on hunches in the hope that you'll stumble on the answer.

I would never condemn an ECU without a proper diagnostic technique, the truth is its quite unlikely to be the ECU.

Is it a single cylinder misfire or a random (multiple cylinder) misfire ? Does it get worse under load, or better ?

Have you checked the basics ? Good and equal compressions on all cylinders ? Have you checked how strong the spark is from each coil ? (How far will it jump to an earthed test probe/light)

Is the fuel rail pressure ok ? Have you done an injector balance test ? Are there any air leaks on the inlet manifold runners ?

Have fault codes and live sensor data been read with a Lexia or OBD-II interface ?

I wouldn't even dream of replacing an ECU on a hunch without doing the above tests and more. Certainly you need to narrow it down to fuel, spark or compressions before you go any further.

There's a fantastic resource on youtube that you should check out which is "ScannerDanner"s diagnostic videos, here:

http://www.youtube.com/user/ScannerDanner" onclick="window.open(this.href);return false;

He's done a lot of videos that specifically cover troubleshooting misfires, which can sometimes be really difficult and elusive to pin down. Its a good evenings worth of watching to look at all the misfire related ones but you'll come away with a far better idea of what to look for and how to troubleshoot it properly.

[numnut20003000]

yes we got a code for multiple misfire and swapped coilpacks and plugs with the saxo
we have done a compression test all 4 are around the 200 mark
checked the timing
i will look it the fuel pressure but i was going off the code which i forgot to say before the car seams to drive ok its just on idle

[numnut20003000]

thanks very much Mandrake
I've sort of found the problem of the misfire looking at a emissions test the hc was 68 which is very low i took out the injector rail an noticed one was fitted incorrect (sitting fever back for the other 3 )
that got rid of the misfire but its still running very ruff i've looked at the ltfrt an its -21 % and stfrt is 48.9 not good i took the o2 sensor out cleaned it up
it ran perfect for 5 secs and when back to ruff so i think its a new o2 sensor tomorrow i'll let you know

[Mandrake]

Glad you've made some progress on it.

68 is not unusually low for the HC emissions reading though, my 3 litre V6 Xantia scored 15 ppm for the HC at its last test. If the cat is working well the HC figure can be very low.

If the long term and short term fuel trim are opposite in sign it means that whatever you did has changed the fuelling balance a lot and it hasn't yet learnt the change. Eg before it was trying to lean the mixture by 21%, (still remembered in the long term figure) now its trying to richen the mixture by 48.9 - 21 eg +27.9%.

I would either take the battery off for 20 minutes to reset the ECU or take it for a 10 minute drive to give the ECU a chance to adapt the long term fuel trim and see what figures you have then.

Is it possible that while you had the injector rail off and found that one wasn't fitting properly that you've actually introduced a vacuum leak somewhere ? As it is trying to increase fuelling where previously it was trying to reduce it.

Another thing you can check is see whether the fuel trim is only high at low rpm and a closed throttle or whether its also high at higher rpm with a wider throttle for example when driving.

A vacuum leak will only affect the fuel trim at small throttle openings, if fuel trim is really positive at wide throttle it could either be actually running lean due to fuel pressure or injectors or your oxygen sensor could faulty and reading lean all the time.

The oxygen sensor you can do a rough test on by watching the voltage through your scanner - it should swing from about 0.1 to 0.9v and back again about twice per second at a steady 2000 rpm. If it doesn't switch at all or its very slow it's faulty.

Again scannerdanner has some excellent videos on diagnosing both fuel trim issues and oxygen sensor testing. Well worth checking out if you run into a wall.

[numnut20003000]

ok i've done a little test my 1st o2 sensor is working ok the 2ed i think is the problem i connected the computer and looked a sensor 2 voltage and short fuel trim
the voltage was 0.925 and trim was 99.2 i earthed my sensor and it shot down to 0.000 and the trim stayed the same
what i did should of took the trim down!
i cleaned all earths around the engine

[Mandrake]

When you say 1st and 2nd oxygen sensors, do you mean upstream and downstream oxygen sensors before and after the catalytic converter ?

I should have been more clear with my oxygen sensor diagnosis method - that is only for the upstream oxygen sensor.

The upstream oxygen sensor is the only one that controls the mixture, and it should switch high and low constantly when in closed loop mode which is when the car has been running for at least 2 minutes and the car is idling or driving with a steady throttle opening less than about 1/4 throttle roughly.

The downstream oxygen sensor has nothing to do with controlling the mixture rich/lean, its only there to monitor the performance (efficiency) of the cat. Normally it will not switch rapidly like the upstream one, if it does that's a sign that the cat is not working.

A fuel trim of 99% is crazy, most cars won't allow for a trim of more than 30-40% so there is something really obvious wrong there...are you sure there isn't a vacuum hose off somewhere ?

Are you sure the upstream oxygen sensor is switching high and low correctly ? If the fuel trim is really high something is making it think its very lean...bear in mind a misfire can make the ECU think the mixture is lean because you get a whole cylinder worth of unburnt oxygen going through into the exhaust and detected by the oxygen sensor which causes the ECU to try to richen the mixture but you just end up with the misfiring cylinder still misfiring and all the rest running really really rich! This will cause rough running and stumbling...

[numnut20003000]

ok i replaced the o2 sensor before the cat and got a good response its moving up and down as you would expect but not lower than 0.5 the sft is now at 0% and not moving up or down and the car running worse i got a closed loop fault took out the thermostat and got it moving again that fault is now gone car sounds like its running on 1 pot and have a open loop fault

[numnut20003000]

was the valve clearance thanks for your time

[Mandrake]

Really ? I would have never guessed that from the symptoms you described...

Was there too much clearance or was there none ? If it was none it might have shown up as poor compressions when hot, I'm assuming a compression test wasn't done earlier. Glad you've sorted it anyway.

[addo]

Excess clearance will give good compression but climb more slowly on the gauge. Rocker tips can wear on the 1.4 and 1.1 motors; makes a good difference when they're dialled in - my 1.4 runs beautifully.

[Mandrake]

I was thinking more along the lines that there was no clearance when cold so the valves weren't closing properly when hot causing a low compression misfire...

[addo]

Wear to the seat or valve margin on a 1.1 or 1.4 is unlikely. That's the condition required for lash to reduce; this behaviour is more common on older motors but the TU is fairly wearproof (save the rocker tips).

[numnut20003000]

the were to close with no gap i brought the car from a car sales i knew they had put new valves in it when i got it the engine bay was covered in oil asif they had been running it with no rocket cover on i was thinking about that and i thought were they looking for a sticky valve ?
so i had a look turning it with a ratchet and noticed the was no or very little clearance i was confused because this should have showed up in my compression test
but thank i learnt abit from those videos