Stumped with a misfire problem

[Darkn3ss]

Ok I have searched these forums for months along with NASIOC and others as well, Tested a few theories and had no results so I am sorry if this answer is somewhere else but I have taken a good hard look.

Car Details
2002 wrx sedan
currently 102k miles
SPT intake w/ heatshield
TGV's deleted (rods left in place sensors functioning)
Up pipe cat deleted (CEL fix in place)
Paralleled fuel rails
Lightly ported throttle body and intercooler inlets
cheap ebay CBE (hey it came with the car)
Oil changes - royal purple 5w30 and Purolator Pure One filter changed religiously at 3000 miles (have gone to 3200 but never further than that)
Tranny fluid - red line super light shockproof changed at factory specified interval
Rear diff fluid - red line 75w90 gear fluid changed at factory specified interval
Spark plugs - NGK iridium changed at factory specified interval
Coolant – subaru green only changed at factory interval
MAF cleaned regularly (every month or two)
91 octane always
Driving habits – daily driven, no redlining at stop lights

Brief history
Let me start by saying in no way has this car been a problem, I have thankfully (knock on wood) had no major issues with it whatsoever since I purchased it with 77k miles on it.
The problem I have did not start after a major mod. When I bought the car it had a cheap-o ebay intake, I changed it out within a week to the SPT with heatshield – I also got a factory intake scoop and chopped it short to bring cooler air in when moving. It was about 5k miles until the first misfire codes.

Issue Details
1st occurrence – cyl 1 and cyl 3 while cruising on the freeway: no engine stutter, hesitation or difference in feel/noise

Changed plugs, Reset the ECU – car ran the same; perfectly fine.
Approximately 700-800 miles later another misfire this time on the other 2 cylinders.

2nd occurrence – cyl 2 and cyl 4 while cruising at about 55 on a small downhill: no engine stutter, hesitation or difference in feel/noise

Swapped coil packs #1 and #2 with #3 and #4 – reset ecu
Went away for about 4000-5000 miles later another solid CEL.

3rd occurrence – cyl 1 and cyl 4 after accelerating away from a stop sign: no change in engine behavior, no stutter/hesitation.

I didn’t clear codes at this point – don’t really have a reason was just thinking more about the problem then what I should have been doing but that ended up playing a role in the next odd occurrence.

4th occurrence – Solid CEL is lit while cruising on the freeway at night and suddenly I notice – its gone.

Checked with a scanner misfires were still there (presumably a corrected problem since the light had turned off) did not clear codes.
Another 1000 miles later it came back.

5th occurrence – cyl 2 and cyl 3 misfires (1&4 still remain but are from previous occurrence)

Cleared the codes 2 more times in the next few months – car gets in a wreck spends 6 weeks in the shop. After approximately 3000 miles after I get it back (yesterday) another CEL.

8th occurrence – cyl 1,2,3 & 4 misfires while cruising about 40 on a flat road: again no change in engine behavior, no stutter/hesitation.

I have talked to the shop I use for all of the installs I didn’t feel like doing and a couple things I just couldn’t (alignment, suspension components, rear diff plug stuck) which is run by a reputable tuner another guy who owns a rally shop (and a nice subie rally car himself) and they were pretty stumped by it.

At this point I am relatively sure no major damage is being done so It’s not going to stop me from driving my car (for now) but it does raise concerns. Anyone have any ideas? Anything you can throw out there I would appreciate. Again I am sorry this is lengthy but I wanted all the facts to be there.

[mycologist]

That is a tough one.

I guess one possibility is that you are periodically getting bad gas.

[Darkn3ss]

could gas really have that much of an impact? That would be something I never considered, is there any way to combat such a problem with additives? I live in southern calif. and anything above 91 is rare, I know of one gas station (30 miles away) that has 100 octane but it runs about $7+ per gallon (and during the price spike last year it was 11) Not like the east coast where 93 is common.

[Darkn3ss]

CEL stayed off until this morning, this time it came on during a shift

Clutch in
3rd->4th
Cluth out = CEL

again no stutter or anythng strange.

[evoeater1985]

Ok a couple things come in to mind. what controls spark? well of course the ecm does and so does the COP (coil on plug) well lets think more basic. how about the wires that go to the plugs any wear. Now when you got those miss fires 24 13 those are companion cylinders so that tells me ECM! but hold up was it rain at any of these misfires and do you know what kind of misfires they are,,A or b and you know it could be Injectors fuel filter.. fuel presser crank position sensor all those things you have to check those tell me what the codes are and i can find out more for you

[Donkey]

Things that generally cause misfires on bugeye subarus:

1. Wrong, worn or incorrect gapped spark plugs. You should run only NGK stock range plugs gapped to 028.

2. Clogged injectors. Have the injectors cleaned or at least run several bottles of a good injector cleaner through the engine.Also change fuel filter if needed.Check fuel pressure as well.Pump could be going bad.

3. Carbon build up on motor. Real common on EJ205's. Get some BG Chemtool, GM top end cleaner,Seafoam,BG44K or other type of carbon remover. GM top end cleaner seems to work really well.

4. Oil or dirt build up on MAF sensor. This causes an incorrect load reading which make for AFR corrections out of line. Misfires can result. Remove the sensor, place in plastic bag. Spray out with NON clorinated brake cleaner or use CRC MAF specific cleaner. Let it sit on table for 30 minutes and install.

5. Vacuum leak. Check the turbo inlet pipe where it connects to the turbo. The stock oem pipe is famous for ripping and causing a huge preturbo leak.

6. Clean the ground cables that run to the intake manifold. These are sensor grounds and must be kept clean.

7. Lightened flywheel or pulley

8. Cylinder losing compression.Get a compression/leakdown test down

[Darkn3ss]

Thanks for the responses

- No it wasn't ever raining when the misfires occured
- I forgot to include 2 things
fuel filter was changed about 10k miles ago
one mod I did not include was my samco turbo inlet
- I just cleaned MAF couple of nights ago
- I ran almost 1/3 of a bottle of seafoam through it about 2 months ago

Things I will investigate
- Replace fuel filter
- Run some injector cleaner (I use either redline or seafoam)
- Check and clean ground wires
- How do I test the crank sensor?
- Do a compression test
- Check plug gapping
- Check for vacuum leaks

[evoeater1985]

you would need to get some that knows how to use a DSO so you can look at wave forms then you would have to find spec from the factory lol.. or you can find a known good sensor replace it then see if it could work

[Darkn3ss]

was under my hood for the better part of the day
- replaced fuel filter
- cleaned and tightened ground wires and contact points
- cleaned the MAF just because its so simple and easy
- added a whole bottle of seafoam to the gas tank
- checked for vacuum leaks (none found)
- checked the gap on the spark plugs

Compression test results
(Compression in PSI / PSI after allowed to sit for 30 seconds)

Cyl.#1 - 148-146
Cyl.#2 - 149-147
Cyl.#3 - 150-148
Cyl.#4 - 149-147

I don't know much about compression but those numbers dont seem too bad, let me know what you think and I will be tracking my miles closely so if/when it comes back this time I will have an even more accurate number on how many miles it took.

[Donkey]

The compression #'s look good.The 02-03's were plagued with misfire problems.Some of this was fixed with an ECU update from the dealer.What EM are you using?With Opensource you can upgrade the ECU to the newest ROM from Subaru and if needed there is a misfire fix you can select.

[Thecabindweller]

im going through the same thing. my 2003 wrx keeps misfiring. mostly when i idle ive noticed. but a couple times when im just cruising around 35-40. i took it to the shop after replacing the plugs and inspecting coils and wiring. and was told to visit a dealer and have an update to the computer. and if that doesnt do it. to replace the coils, to start. so its been about 3 weeks since i went to the shop and the check engine light comes on and off from time to time. but i plan on taking it over saturday to see if theres an update or anything a dealer can do for me.

[Darkn3ss]

521.4 Miles - CEL came on during acceleration out of a right hand turn

Now theres no guarantee that its a misfire but seeing as how there were no symptoms whatsoever - when I get the code scanned I can reasonable say - its probably at least one misfire.

will update when I get to an OBDII scanner.

[Sarra]

Wow, that's odd. I'd suggest cleaning injectors, but... I don't think it would help.

The ECU detects misfires by 'watching' the acceleration of the crank each time a cylinder fires, if it expects to see an acceleration and one doesn't happen, it counts a misfire. So, either your ECU is screwed up, or whichever sensor the ECU uses to monitor for misfires is going bad (could be crank position sensor, cam sensor, etc, I don't really know on our cars ).

[Darkn3ss]

Ok the last CEL was indeed a Misfire on cylinder #1.

Being that no symptoms have shown I just brushed it off for a few days driving around with the CEL on.

I reset the ECU after adding a bottle of seafoam to the tank and filling it up. Car ran fine as always 157.2 miles after the reset the CEL came on after shifting 3rd->4th@4500 rpm - as usual no signs or symptoms.

Current theories-

- Some slight connection fault in the ECU
- Cam/Crank sensor malfunction
- fairly clogged injector
- Any of the above + horribly oxygenated california 91 octane

And I am so sick paying people to do a half @ss job figuring out problems and reading codes that I'm saving up for an AP - better late then never lol.

[erakem]

This sounds like a headache I'm really sorry and I know how big of a pain in the @$$ these things are. I'd start with Ignition coil, spark plugs, wires, injectors, there was just another thread on this the other day, could even be timing like one stated...These are usually the times when I just take it to a mechanic that wont rape me too have it looked at...Again some of the theories Darkn3ss stated is were I would start as well, cheap gas...its iffy but I doubt fueling is your problem here...