Howdy,
Recently I've had some weird misfire problems on MY 95 WRX. I have owned the car for over 2 years, and only just started having these problems. I'm looking for any advice. Here is the story;

In a two week period, I had two occurrences of severe misfire whilst using small/medium throttle position (and no boost). The car would idle OK, and rev when standing OK (though sounding a bit rough) - but when attempting to drive off, it would fire on 3 cyl at best. Power was very low, and it was a struggle to get going. However, when large throttle openings were used, it did misfire, but as it came on boost (it was a pain to get it there).. the problem almost went away - it revved freely to the redline. In each case - over a two day period the problem gradually went away. However I could only drive the car on full boost, or coasting.. which sucked big time.

I could not get in for a service whilst the problem was happening. When it did go in, all was pronounced OK. Since the service it has happened twice again ! I have replaced the O2 sensor, the spark plugs, and the coil packs.

Whilst the car was behaving badly, I tried doing an ECU reset, leaving it idle for 10 min (to warm up), not driving it for 2 days….. nothing helped….. just time being driven made it gradually get better.

I have detected a theme - in all four cases I gave it a fairly big boot only 1-3 seconds after the car had started (I know this is bad.. sorry). Since then I have been vigilant in warming up the car, and I have had no problems. But it does not explain what was going wrong.

I suspect that when the car is cold, the large dose of right foot is causing oil to go to some sensor it shouldn't , and clogging it up - sending screwy signals to the ECU (this is my guess anyway).

But I would like an idea on what sensor, if my hypothesis is correct, and why has it just started doing this ?

Any Help Appreciated

dave

 

Hi,

Oil pickup usually affects the boost solenoid, causing the infamous overboost cutout.

Some dealers recommend only filling the oil half way as a workaround.

What type of plug are you running?. This engine seems a bit fussy with plugs, with bosch, champion and others having had problems reported. NGK platinum plugs seem to be be best - sorry don't have the part no.

Good luck,

Alex

 

check the throttle pot for intermitent values and the water temp sensor.

 

Alex,
This is definitely not the over-boost thing…. As the problem is 10 times better when the boost gets above 6psi… and is almost not noticeable at 12 psi. I suspect it is over-fueling badly.. but it's weird the way it comes for a day or two, then goes away.
I am running Subaru standard plugs, which are NGK PRF6G (from memory I think).. and have tried changing them.

Tks
df

 

Dave
Try the obvious first before going to deep.
Have the HT leads checked if they have been in for any length of time. I had the same fault on a year old car. It was only in the morning the problem came about but after the car had run up to temp it started without any problems. This was diagnosed after ECU fault checks were done and no faults found.Sometimes we jump in way to deep.
Cheers
Jack C

 

John,
The throttle sensor was checked by Suby (while the car was behaving though).. and was OK - I also checked it whilst the problem was occurring - and the voltage was OK. (4.7 at idle I think.. dropping with opening)
I did not think about the water temp sensor though !.. that is a good idea.. I know the ECU uses it to help determine air/fuel ratio....
Jack,
The problem is not quite that consistent... it does not go away when the car is war, even after several hours...basically something 'snaps' and the car runs badly for 1-2 days.. then comes good. It only seems to 'snap' when given a boot when cold.... I don't have any HT leads.. as the 95 in Aus has one coil pack per plug

thanx for the advice

df

 

I have heard of a few people with occasional or persistant problems with earlier WRXs which was eventually rectified by a replacement ECU.

You shouldn't "boot" the car at all until it has warmed up properly!