Occasional mis-fire - not the usual suspects.
 

Right - looking into a "misfire" that occurs under some rather unusual situations. Start the car from cold, keeping it under 3000 revs for 10 minutes. Come to a brief stop (roundabout, lights etc) pull away and it will begin to misfire - although misfire is probably putting it lightly, as it feels like all 4 cylinders fail to fire briefly. It occurs when reacing 2500 revs, and it will simply fail to reach 3000 revs as the misfire kicks in and out. Stop the car for 5 minutes, restart it and it won't happen again all day.

So far, the garage and I have changed :-

• 4 new coil packs
• 2 sets of new spark plugs
• New lambda sensor
• New MAF sensor
• New coolant temperature sensor
• Walbro fuel pump
• New exhaust manifold
• Cam and cranckshaft sensors
• Earthing points cleaned and checked.

Next to be tried is the OE knock sensor. No CEL's thrown. I've got logging software (equivalent to subaru Select Monitor) for logging data but nothing obvious is showing up. Current theory is the OE knock sensor is failing, causing massive retardation of the ignition and hence why all cylinders fail to fire, especially as the turbo will be kicking in by then.

Theories ?

Bet Pete is really loving you these days Paul. Fancy a gallon of four star and a match :D:D

Seriously though if you can hang on a week I'm pulling mine apart to do some work and you can borrow my KL sensor if you want?

Jim

Well, Peter's been trying to fix this for nearly a year now : I think everytime he see's me at his place he runs away and hides ! :) Thanks for the offer, I'm considering replacing the OE sensor with the KL one, assuming I can of course : also going to try logging the OE sensor during the misfire to see if it is indeed going berzerk. PM me when your working on yours and I'll let you know if I need the sensor.

Ta ! :) Anyone else got any theories as to what is happening ?

This is going to sound daft, you have checked that you've got decent fuel pressure? I know you've changed the pump but is the reg ok? What about a crappy fuel filter?

It could be the regulator, or the fuel filter. Fuel filter is due to be changed over next week sometime, difficulty is identifying the fuel pressure as the problem with out plumbing in a guage to measure it - I've replaced too many expensive sensors and parts to carry on doing it and hoping to get it right eventually ! :) I might be tempted to install a SX regulator, if the knock sensor theory doesn't hold water.

Mine has been into a specialist for the same symptoms.

They tried all the connections and it went away, then it came back. So they refitted a Standard STI4 ECU (It has a Link fitted) and it went. Their end diagnosis (after checking everything) was that it was the LINK.

Since getting the car back (with the LINK refitted), I have not had any problems. 400 Miles. So Id nt think it was the LINK after all.

I do wonder if maybe the ECU connections were loose and removing and refitting it, may have just sorted the problem.
I hope your problems dissappear in the same way.

What is Selmon showing for ignition retard Paul when the missfire happens? If the Knock sensor is the fault this will be showing big numbers......

Tony.

Tony - Managed another run today, triggered the misfire, but the damn laptop battery dies before I could save the log :( Before it died however, I noticed the retard values had moved from 0, can't remember what the min/max values were but it had definetly retarded. Knock values had also moved from 0 value, so it does look like the knock sensor for whatever reason thinks the engine is detting - which it shouldn't of been, given I was doing roughly 30-40MPH/2500 revs.

Might try another logging run tomorrow, this time with my 240/12v invertor ;)

OK, looks like my thoery doesnt' work : had the car out today, logging all relevant values, and the ignition retard and knock values don't seem to be excessive. Peak values didn't seem to relate to when the misfire occurred, but at least my KL was also quiet during the missfire.

Looks like Theory No. 9 is out the window : time for a new theory... :(

Did you ever manage to check the ecu.... can't remember. If you want to try mine for a week let me know. It's just sat on the shelf doing nothing. It will obviously have a wrx map but maybe worth a go????

Tony.

Thanks Tony, but it's not the ECU - swapped it for a UK ECU + chip running my standard STI map (at least when I fix this problem I can actually start mapping the damn thing !), with the same symptoms. Beginning to wonder if the ignitor module is failing, it's definitely failing to fire all 4 cylinders.

Or possibly the OE fuel reg... running with a Walbro pump atm.

Paul.... got 3 OEM regs too if you want to try one of those ;)

I'm going for a SARD reg soonish (which the evo boys seem to like).... only £60. Not bad compared to Aero/SX

Tony.