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  #1  
Old 05-02-2005, 07:38 PM
bcpianoman bcpianoman is offline
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Engine has a miss and I can't find out why

My ‘92 SVX has had an intermittent miss for the past several weeks. I’ve had it to three shops (one of them a Subaru dealer) but the problem persists. The problem doesn’t occur until the engine warms up to operating temperature. It seems to be less prevalent (or non-existent) in cooler weather (below 55 degrees). It is most noticeable when in 1st gear and pulling away from a stop (until I hit about 2500 RPM). When this happens the engine runs very rough. But it also happens in 4th gear when I attempt a slow acceleration at about 2000 RPM. Shifting down to 3rd (and increasing RPM accordingly) restores smooth operation. When it misses in 4th gear it’s almost like the transmission is slipping for a very brief instant, then re-engaging. The miss in 4th gear isn’t nearly as rapid as the miss in 1st gear described above. When the engine is at operating temperature it idles rough in neutral as well in warm weather (but not as bad as when in 1st gear).

So far the first mechanic checked all the spark plugs, pronounced them in good condition and gave up. The second mechanic (at the local Subaru dealership) plugged it in and the O2 sensor came up. That mechanic said that that is a common occurrence and he didn’t think that the O2 sensors were causing the problem. He found one ignition coil to be weak and replaced it. He also found a number of vacuum leaks and repaired them (although he thought there might be more). The third mechanic found that the fuel pressure regulator wasn’t allowing sufficient fuel pressure (only 28 lbs. instead of 34 to 36 as required). He replaced the fuel pressure regulator but that didn't help either.

Any ideas?
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  #2  
Old 05-03-2005, 02:52 AM
KCROGUEDOG
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when i get an o2 ce light my car will run like crap. i clear the light wala all good. see i got a 97 obd2 car and third o2 is not picking up catylist. also i did have a bad coil pack. pain in the ass. but all your spark plugs are good. i would do it yourself and double check i had to. i got the coil pack replaced and everything was good to the shop. a week later i had to replace all plugs they were badly burned. also a fuel pump change i changed made a big response differnce. try that. also timing chain may have slipped pull cover and check marks.
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  #3  
Old 05-03-2005, 02:55 AM
KCROGUEDOG
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beside the point on the fuel pressure regulator u can use a legacy one that allows more pressure chike i think did this. but u got it all ready replaced
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  #4  
Old 05-03-2005, 04:58 AM
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KC, the third O2 (downstream sensor) has absolutely no effect on how any car runs - period. It's sole purpose is to monitor catalyst efficiency.

BC, I don't know how the first mechanic determined the spark plugs to be good. Just pulling them out and looking at them doesn't mean much. However, they would probably be bad at all temperatures. When the engine is cold it operates on fixed parameters, warmed up the ECU takes over and adjusts timing, fuel mixture, etc. A lot of that is dependent on the O2 sensors. Vacuum leaks will cause a rough idle but nothing noticeable above idle.

It sounds to me as though you need to find someone that knows what they are doing and will do a COP (coil-on-plug) analysis with suitable equipment and actually hook up a GMM to the O2 sensors.
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Old 05-03-2005, 09:53 AM
blacknite blacknite is offline
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check your coils. again, mine use to run fine when cold until it reaches normal tempeture after a while. then the misfiring started.. I tough or maybe i wanted to believe it was the injector because of price. i end up getting the coil and problem solve. to teste what piston was doing it. while car was running i unplug each injector at the time until finding the one that didn't make any difference when umpluging. and that is the one that is bad. good luck
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Old 05-03-2005, 02:56 PM
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Ya, when cold mixture is rich and easier to ignite.
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  #7  
Old 05-04-2005, 12:04 AM
bcpianoman bcpianoman is offline
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Thanks Guys. I'll let you know how I make out.
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  #8  
Old 06-01-2005, 07:09 PM
bcpianoman bcpianoman is offline
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Blacknite - step up to the front of the class

It was the ignition coils - two of 'em. Problem solved. Thanks.
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  #9  
Old 06-01-2005, 08:21 PM
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all the procedures to find that was it. pain in the azz huh? exspensive to. glad everythings good now and your back on the road.
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  #10  
Old 06-05-2005, 03:43 AM
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Just a thought. I had a weird miss that did not cause a check engine light last year. Mine only happened under hard acceleration, but its a thought. Mine was the MAF (mass air flow). I was not convinced that it was the unit cause the select monitor did not have a listed code for it (ie, it was not causing a trouble code). I got a cheap used one off a wrecked SVX at a junkyard, put it on and all problems went away. That was a year ago, still running on junk yard part today.
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  #11  
Old 06-05-2005, 05:14 AM
KCROGUEDOG
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speaking of the maf i asked about a replacement on another thread. ours on the svx maxes out at 5600 rpms i want to replace but could another vechiles maf be a plug and play type thing. like a wrx or z or any fast well built sports cars maf.
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