Andxrs

Hi all, I'm looking for some advice for my 1998 Impreza Turbo. The engine is the standard EJ20G and a few weeks ago it started misfiring so I changed the spark plugs, and when I did I noticed number 4 was very black, but the others were fine. This didn't fix the issue so I replaced the ignition leads as well, which still didn't fix the issue. The car already has a fairly new coil pack as I put this on myself about 4 or 5 months ago, and has a brand new knock sensor installed about a month ago. There is no check engine light and the car will run fairly smoothly for about 30 seconds and then pop as it misfires, but then run okay again for a bit and cycle like that constantly. If I hold the revs at, say, 2k rpm while stationary it will run fine but then suddenly drop a few hundred rpms every now and then, and when I let go of the throttle it falls well under idle, almost dies and then runs at normal idle again. I'm really unsure what could be the problem as basically all the ignition system is new, yet it seems intermittent enough that it's an electrical issue. Any help would be appreciated. Thank you and I apologise for the lengthy post.

nicam49

It is if course entirely possible that your new coil pack has developed a problem.... If you still have the original one you could try fitting it to see if the symptoms change.

NOSSY_89

Just off the top of my head, injectors could be at fault. Have you done a compression test?

Andxrs

I don't have the original coil any more but I could look to see if I can get a proven working one to test it, thank you

Andxrs

I have now done this and cylinders 1, 2 and 3 are all around 130psi, however cylinder 4 showed 0 compression. This is the one with the misfire but I'm still confused because if it really didn't have any compression at all then I would have thought it wouldn't run smoothly at any point, yet it is still quite an intermittent misfire. The compression tester was definitely fixed in properly too so I can't see it as being a loose fit or anything.

stockcar

most likely you have a failed piston / ringland failure.......... you 'may' see something with a borescope but often it can't be seen by viewing the piston crown only
sounds like its coming to bits regardless!!

Andxrs

Ouch, was hoping it wouldn't have to come to that yet lol, but I suppose it's the best option. Would it be worth having the engine rebuilt or just getting it out and putting another in? If so what sort of wiring differences would be needed to install an EJ205 for example? If I have the current engine rebuilt would it be worth going for forged internals?

stockcar

you mention EJ20G so presumably a MY98 car (coilpack centrally mounted) rather than an MY99 car (coilpack offset mounted on NS)

that being the case in general terms then any Turbo engine prior to MY98 will be a direct fit and you simply reuse your manifold, ancills, etc......
IMO its not worth he grief trying to adapt / use a later engine as they use a totally different inlet spacing, etc BUT you could use a later short engine and build your heads onto it
is it worth going forged then that all depends on what your future ideas / power targets are??

nicam49

Ouch! Sorry to hear that... Good call tho'!.
Could it just be a burnt out valve? Take off the head - plenty of youtube vids how to change chg in situ without removing engine.
At least weather is ideal for oudoor work, and light evenings too!
Before throwing serious money at expensive new engine bits, give the body shell rear end around the turrets and rear arches a really good inspection.... serious corrosion in that area can render the car unrepairable or at least prohibitably expensive to save.
Just an added thought.... could it be a seal gone on the injector in cyl#4 causing loss of compression..(does that sort of thing happen?) .
Let us know how you get on!

Andxrs

Thank you for the input, I'll be having a good look around at my options then. As for using a later block, do my heads just bolt straight on or is anything else different needed to make them fit? With regards to power goals I'd quite like to see between 350-400hp eventually so I'm thinking standard internals won't hold up well at that sort of power level. Out of curiousity generally how reliable would you say a freshly rebuilt stock engine would be at a little over 300hp as I've been looking at a place called TDR that seems to do engine builds (Both standard and forged options) so I'm thinking the standard rebuild would be good at 300hp and then put the difference into suspension, brakes and good tyres for example. Thank you

Andxrs

Well it's the joys of cars haha, when I can get it in a garage I'll be taking the head off to check that (Hopefully it turns out to be just a valve) and go from there I think. Regarding the corrosion I know of a small patch on the inner skin of the arch but the outer has been sorted by a previous owner. Fortunately I have qualifications in MIG welding so that's already on the plan for getting sorted (Knowing how to weld is always a benefit when you have a Japanese car lol). Just a waiting game now until I can get started with it again, I have missed that boxer sound. Thank you

stockcar

yes the heads basically swap over to a newer short block with the correct h/gaskets, etc........