Firstly hi everyone

I have a Impreza Terzo with running issues now



It had a new fuel pump a few months ago (Walbro 255) and its been great


However, a few days ago it suddenly started misfiring and popping on the way home.


I replaced the coil, leads and plugs firstly as they were old and the resistance on the leads was high.
Its running a little smoother but still misfiring.

MAF Sensor seems fine (unplugging it stalls car)



I decided to do a compression test....
Engine had cooled for about 30 minutes (So I could actually get near the plugs )

Oil temp at time of test was 75 degrees celcius.


Listed in order of testing:

Cylinder 1 (drivers front) - 102psi
Cylinder 2 (passenger front) - 125psi
Cylinder 4 (passenger rear) - 122psi
Cylinder 3 (drivers rear) - 110psi

(Oil temp was just under 70*c for final cylinder, cylinder 3)



So any thoughts or ideas? :/


Hoping its not a rebuild or new engine as not exactly flush for cash at the moment!

 

Firstly try resetting the ECU. I had very similar issues when I first got my 97 T2000. Once it was reset, car ran perfectly. There had been worked carried out on my car before I got it but the ECU was never reset.

 

Did you ago the plugs before you fitted them. Plugs don't come pre gaped

 

for compression test u need a good battery, warm engine and all plugs out. wide open throttle when cranking.
ususally 10% between cylinders is ok. looks like you have one side with higher compression than the other. no big deal but id wonder why....
as siad check ther gaps, what plugs grade plugs? 7b if modified a bit...

 

Ecu reset twice now.

Plugs are 7b gapped to 0.7mm

Engine was warm and good battery



Cylinder 1 plug is dirty already compared to rest.
Other 3 have slight tanning on insulator as i would expect....cylinder 1 plug is dark overfuelled look


Im worried why that pair is low compression :/

 

Sticky injector? Seen that a few times on here.

 

Sticky injector wont cause the low compression though will it? :/


Granted it could be a sticky injector causing the misfire, but surely the 102psi compression test result is more concerning?????



Really need some advice as to what is the best course of action!!!

 

Could it be a failing head gasket???

No water in oil and there is no noticeable water loss.

slightly blowby in crankcase but not what I would consider enough to worry about


However, I noticed the coolant smells a little different :/

 

Leaking down test will be better than compression test,
I did mine mine today 4,22,15,and 10 % leak not impressed with number 2 but car still running.
cost me 50 quid, I did research and price is from 67 to 100 plus vat

 

not sure I can get it leakdown tested :/

 

I will coolant sniff to see if that shows anything

Couple more questions.....

Obviously the engine has lowish compression anyway (just over the 120psi mark on 2 cylinders), so do you think I should replace the head gaskets (STI MLS ones rather than the current composite ones), or simply chuck in a known running engine?


I can get a 1999/2000 engine (I know it has different coil, MAF, etc), but if I fitted my maf etc would it be fine? basically are the engines themselves the same?

 

The other explanation of your findings is leaking valves. This would explain low compression and misfire. The way to check this without removing the engine would be to measure valve clearances. They will have closed up if this is the cause. Chances are it will be the exhaust valves on the two with low compression. Head gasket still possible cause as well.

 

OK I will check the valve clearances asap