406 coupe v6 Cylinder 3 Misfire woes

[endomorph]

So today I got a P0303 Cylinder 3 Misfire fault and "anti-pollution system defective" warning.

So I changed all the plugs for new (was going to do this anyway) and have changed the coil pack.

Reset the fault code. Idled the car for 30 minutes. All OK

Went to drive and within 5 minutes, the warning and limp mode came back.

Possibly, the car is fine when cool and not being driven, but it happens when being driven after a period of time.

Any ideas ?

Injector ?
O2 sensor ?

[mjb]

Not sure about the O2 sensor - that should register a fault against the bank of cylinders as opposed to a single one (presuming you've got the ES9J4S, not ES9J4 as you've given an OBD code instead of a PP2000 fault)

My guess is it could be the injector, or the wiring to either the injector or coil.

[endomorph]

This is my thinking. Does the injector not have a code of its own?

Someone is coming round tonight with a pp2000.
Will this give a clearer indication than an obd scanner?

[mjb]

The only problems an ECU (at least a 406 ECU...) can detect with an injector are electrical - open and short circuits. If it's electrically sound but not opening properly it's got no idea, although you may be able to tell from watching the live data. I'd have no idea how though

[endomorph]

OK things are getting bad to worse.

A fellow owner brought round his PP2000 and we checked over the car. A few latent errors, car was running fine (it was cold).

Took it for a drive and after 5 minutes it came up with the anti pollution fault and went into severe limp mode (4 mph max)

OK so I have -

Perm Fault. Cylinder no 1 misfiring
Perm Fault. Cylinder no 2 misfiring
Perm Fault. Cylinder no 3 misfiring
Perm Fault. Cylinder no 4 misfiring
Perm Fault. Cylinder no 6 misfiring
Int Fault Front pre-cat. Ageing
Int Fault Rear pre-cat. Ageing

Left the car a couple of hours to cool and went out and started it, running sweet as a nut !

Someone has suggested the CTS (Coolant temperature sensor) maybe at fault. The temperature guage on the same seemed to register normal temps over the last few days of driving. Does the CTS drive the temp guage ?

Anyway, as they are cheapish, I am tempted to get one and try it

[madmadmax]

the cts would cause all cylinders to miss fire and 5 is not so what wrong or right with that one

the question is whats right with no5 pull all the plugs and look at the tell us what color that are the look at the coil packs and move them round and mark number 5 so you can track it then look for spark tracking on them and run the car in the dark as dark as you can get it look for arcs of electricity. it could also be the crank sensor

http://www.underhoodservice.com/Article ... gines.aspx

[mjb]

the cts would cause all cylinders to miss fire and 5 is not so what wrong or right with that one

BZZZZT! That's not how to use diagnostic tools.

The correct thing to say is that the ecu hasn't detected a misfire condition on cylinder 5 on that one very short run. That's not to say anything's actually misfiring, or that cylinder 5 isn't. I haven't seen any PSA/Bosch documentation explaining exactly what combination of parameters make up a misfire condition. Have you?

Perm Fault. Cylinder no 1 misfiring
Perm Fault. Cylinder no 2 misfiring
Perm Fault. Cylinder no 3 misfiring
Perm Fault. Cylinder no 4 misfiring
Perm Fault. Cylinder no 6 misfiring
Int Fault Front pre-cat. Ageing
Int Fault Rear pre-cat. Ageing

I know I said your o2 sensors might be knackered, they may be (they (Bosch) recommend replacement every 100,000 miles), but I'm certain they're not causing this. One being bad might cause a bit of an antipollution whinge, but two at the exact same time, and causing such a massive barf? No.

Someone has suggested the CTS (Coolant temperature sensor) maybe at fault. The temperature guage on the same seemed to register normal temps over the last few days of driving. Does the CTS drive the temp guage ?

Anyway, as they are cheapish, I am tempted to get one and try it

Which one - there's at least 3 CTS' - blue, brown and green - and I do know at least one of them severely affects engine performance. In fact I found my ES9J4 wouldn't even start with that one unplugged Sadly I can't remember which.

If you're in the mood for an hour's DIY, I'd suggest replacing all 3 sensors as well as the thermostat (the 'stat housing needs to come off anyway). While you're at it, a new crankshaft sensor might be a good idea while you're working in that area - smoothed out my old V6 a bit... They can all degrade over time and aren't too expensive. IIRC eurocarparts stock everything

If you're not, or if the budget's tight, someone in your passenger seat *might* be able to see crazy water temperature or RPM readings on PP2000 at the instant the fault appears, which may well limit the culprit a bit, but with the PP2000's low resolution (2 second reading interval iirc) chances are you won't see anything without a logging oscilloscope...


If I were to put my money on just one thing, I'd say crankshaft sensor has the biggest chance of causing severe ECU barfage, but one of the CTS' comes a close 2nd

[endomorph]

Well changing thr green CTS sort of cured it. After changing I ran the car up to temperature.

Fault came back. Scanned it, Cylinder 3.

Changed the coil pack and cleared the codes, ran again and fault came back

Scanned it, Cylinder 3 & 1

Cleared codes and re-started car. Has been indling now for nearly 2 hours and fault has not appeared so I am still very cautious.

Took it for a drive, Cylinder 3 misfire again.

It all seems to revolve around cylinder 3 and being hot.

I have got a few things in mind -

a) Dodgy injector which is running bad but not bad enough to give an error code
b) Head gasket gone / loss of compression ? (I hope to hell not)

[madmadmax]

@ mjb; as a mechanic i have been educated that misfires are registered as a variation in the crank speed so if you have a bad crank sensor or large amount of iron filings on the fly wheel this could cause a miss fire to be register and not be there

[endomorph]

But how would heat affect it ? Remember this is only appearing when the engine is at running temp (90 deg)

[markw]

I hope endomorph won't mind me contributing to this thread, but I went down to see him last Sunday and we deduced between us that coil 3 wasn't being earthed down by the ecu properly when asked to fire. It could handle low rpm idling all day but as soon as the engine was held at 2000rpm or thereabouts, cylinder 3 misfire again.
My limited electronics knowledge tells me that a component or two has gone out of tolerance on coil 3 grounding circuit within the ecu, so when it was being asked to trigger quicker and quicker it couldn't pull the voltage down to ground quick enough and threw up a fault.
Endomorph has since obtained a used ecu from Ade and it has cured his problem.