"Random" Engine Misfire

simpreza2 · Post by **simpreza2** » Tue Dec 28, 2004 10:01 pm

My 92 legacy is randomly misfiring in cyl 4. I replaced all the plugs, wires, and the coil pack (with another one of my other subie) and it still is misfiring. I noticed it usually starts to misfire when the car just gets up to temp. Then from that point on it misfires whenever it wants to(underload or not) What else should I check or look out for?
Thanks
Jon

evolutionmovement · Post by **evolutionmovement** » Wed Dec 29, 2004 12:20 am

What did the old plugs look like? Did you try a compression test?

Steve

simpreza2 · Post by **simpreza2** » Wed Dec 29, 2004 1:58 pm

evolutionmovement wrote:What did the old plugs look like? Did you try a compression test?

Steve

I dont remember what they looked like but they werent that bad that anything bothered me. And Ill do a compression test when I get the car back tonight from getting my snows put on.

And would you reccomend I wait to install a new O2 sensor or can I put it on now. I just dont want to mess it up or shorten its life by uisng it when the engine isnt running correctly.

Thanks

vrg3 · Post by **vrg3** » Wed Dec 29, 2004 4:31 pm

For now you should probably run without an oxygen sensor (just unplug the sensor you have now). Your current sensor might be giving bad signals, and a new sensor would get contaminated by the misfires.

simpreza2 · Post by **simpreza2** » Thu Dec 30, 2004 1:00 am

Compression test results...

cyl 1 - 190,190
cyl 2 - 128,150,165
cyl 3 - 190,195
cyl 4 - 210,205

The plugs looked ok. Nothing out of the odinary. Im just wondering what was up with cyl #2? It kept increasing as I did each test.

evolutionmovement · Post by **evolutionmovement** » Thu Dec 30, 2004 1:08 am

I'm thinking a carbon build up problems. Does it burn any oil?

Steve

J-MoNeY · Post by **J-MoNeY** » Sun Jan 30, 2005 9:09 am

My car is having the same thing. At idle, the needle bounces around a bit, but sometimes the engine shakes. I got out of the car to hear the exhaust tone when it happens and it sounds like it skips a beat, which prolly mean's misfire. Now, I'm sure that my plugs are ok, because I just put a new set less then 3000 miles ago. I've checked all the vaccuum lines and they are solid. I've upgraded to a diamond coil pack. Carbon build up in what aspect? Would running some sea foam though it be a plus? Or, should I just go with the typical, new O2, wires, plugs, fuel filter, PCV valve, and oil?

J-MoNeY · Post by **J-MoNeY** » Sun Jan 30, 2005 9:18 am

BTW: 100.00 fucking dollars for an O2 sensor? How the hell do these people sleep at night! My god.

evolutionmovement · Post by **evolutionmovement** » Sun Jan 30, 2005 9:48 am

I paid about $60 at Auto Zone. Get the generic one or you'll pay $20 extra dollars to have them cut the wire for you. When were the wires last changed? Before the Magnecors I went through a set every year or so. The other things would likely cause stumbling, but not a steady misfire.

Steve

jstriker · Post by **jstriker** » Sun Jan 30, 2005 11:10 am

J-MoNeY wrote:My car is having the same thing. At idle, the needle bounces around a bit, but sometimes the engine shakes. I got out of the car to hear the exhaust tone when it happens and it sounds like it skips a beat, which prolly mean's misfire.

same boat as well.... just replaced the plugs, wires, battery and switched out the coil and it didnt fix a thing... i can pull either the #1 or #2 wire and it barely runs but if i pull the #3 or #4 it dies imediatly.. is this normal or part of my problem?

eagerly awaiting a diognosis to this problem

vrg3 · Post by **vrg3** » Sun Jan 30, 2005 4:04 pm

J-MoNeY - Have you checked for vacuum leaks with the starting fluid test? It's possible you have a leaky manifold gasket or something.

I got my 4-wire oxygen sensor off an almost new Korean car in a pick-a-part. These cars are so easily totaled that you can find 2004 models in yards where the newest Subaru is a 1990 Legacy, and each of them has two 4-wire sensors.

evolutionmovement · Post by **evolutionmovement** » Sun Jan 30, 2005 5:23 pm

Good point, Vikash! So little value combined with so little crash resistance. I'm amazed they pass federal crash standards just looking under the hood of those things. I'd rather have my old Legacy in an accident any day ... well maybe someone else's Legacy.

Are all o2 sensors the same as far as thread count and diameter?

Steve

vrg3 · Post by **vrg3** » Sun Jan 30, 2005 5:44 pm

Almost all, yes. There are a few oddball sensors that use flanges or pipe threads, but almost all use M18x1.5 threads and a steel crush washer (which you should replace when reusing a sensor). The thread length may vary somewhat but I don't see how it would matter unless it was way too long or short.

Some cars do use titania sensors that aren't interchangeable with our zirconia sensors, but those are fairly uncommon too. And they generally use smaller threads -- M12 I think.

I would say that if the sensor comes off the car with a 22mm or 7/8" wrench, it's almost certainly compatible with our cars.

Imprezive · Post by **Imprezive** » Wed Sep 06, 2006 3:59 am

Bump to figure out why the heck his car misfires when its at operating temp. A car I am looking at buying does the same thing!

realfinn · Post by **realfinn** » Wed Sep 06, 2006 4:29 pm

Compression isn't what I would consider good and balanced at all (what do you guys think?) But that could be from having a crappy press in gage like I do...I never get what I would consider "good readings".

Since you changed plugs/wires/coil and still had the problem then the next thing I would point a finger at is the A/F ratio.

Make sure you have no vacuum leaks anywhere - seems unlikely to me. Since this occurs only at operating temperature and is intermittant my best guess (notice the word guess) is that there is a bad electrical sensation. Could this be the evil work of a bad MAF?

Imprezive · Post by **Imprezive** » Wed Sep 06, 2006 8:45 pm

I am planning on doing an overall check of the engine bay/sensors in my car today or tomorrow. I will list my findings/non-findings...

Bheinen74 · Post by **Bheinen74** » Thu Sep 07, 2006 4:18 am

sounds like what my 92 SS was going thru. read my thread "former Justru92 car"

It was the timing off. I would check the timing belt marks. Its easy to check. My car wold run smooth on cold starts, for about 2 minutes. then bad bad idle. can you rev the engine even on cold start. Mine wouldnt rev past 3000 no matter what.

Just be careful taking off the covers, plastic is brittle.

n2x4 · Post by **n2x4** » Mon Sep 11, 2006 8:17 pm

+1 for the timing belt. Mine did the exact thing. I replaced the belt to find that the old belt had a tooth half ripped off, and a 5.5K rpm run got the belt to slip and threw my timing off when it was warm.

Imprezive · Post by **Imprezive** » Tue Sep 12, 2006 1:02 am

Well as for my misfire it could be just bad plug wires. I listened a little closer a few days ago and it seems to be a constant misfire, even when its cold. Turns out its just a bit harder to notice at around 1300rpm than at 700rpm.

Anyway, I've also got a weird CEL, its not really a CEL because there are ecu codes, but it just keeps flashing no matter what.

realfinn · Post by **realfinn** » Tue Sep 12, 2006 4:13 pm

It keeps blinking on and off? As if you were doing a code check?

Or do you mean it comes on for a whiel (a few miles) and then goes off.

Imprezive · Post by **Imprezive** » Thu Sep 14, 2006 6:47 pm

its a constant on/off/on/off etc...Not really sure what it is, but my misfire problem went away w/ new plug wires. I smogged the car yesterday and the smog tech said it was as clean as a whistle.

It still has a small idle issue, it will sometimes dip down to ~500rpm from its normal ~700rpm at idle. Not for long, it eventually goes back up to ~700rpm.

Other than that it seems fine

realfinn · Post by **realfinn** » Thu Sep 14, 2006 7:34 pm

The on/off/on/off sounds funny. I can't remember exactly what the light does in D-test mode. Anyone know for sure? It almost sounds as if the ECU is still displaying codes (the on/off/on/off could just be the ECU telling you its in test mode). Might want to ask around. You might have two of the code checking wires together. I don't think it will hurt anything running the car like that...but it would be annoying as hell!

Imprezive · Post by **Imprezive** » Thu Sep 14, 2006 8:20 pm

No, neither the green or black plugs are connected, and I havent fiddled with any other plugs. Maybe it is confused??

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"Random" Engine Misfire

"Random" Engine Misfire