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Old 03-10-2011, 11:50 AM   #1
Momosaurus WRX
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Default Diagnosing the issue with my car...

Ok, so I have a 1993 Impreza L wagon. I have been fixing a "stutter" problem for quite some time, and I had it fixed for a little while.

Between 2-4k rpms, if I go WOT the car stutters and "falls on its face". Its a random misfire, and because my car is obd1, it's a little difficult to find what the problem is.

I replaced the spark plugs, which fixed the problem. The old ones were burnt, too large of gapped, and were even tweaked to the side. It ran and drove great for a couple days, then I added a neon coil pack (for those with ej18s and ej22s, you know what this is). It is the equivalent of adding a "high performance coil pack". It ran even better, for two weeks. Then the other day, it started stuttering again.

-I pulled the plugs, they're all gapped correctly, and not burnt.
-I pulled my o2 sensor just out of curiousity, and it looks "ok" (but of course you can't tell just by looking at it).
-It seems like it's running lean.
-I swapped mafs with a friend's car, that I know is running good and strong, and it didn't change anything.
-I checked the vacuum to the fuel pressure regulator, it's good. I pulled it while the engine was running, and the rpms jump up like they're supposed to

But for the life of me I can't find a service spec for what fuel pressure should be. I don't know what else would be the problem.

Anybody have any suggestions? i think, and so do a few others that I have talked to, that it is a fuel starvation issue.
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Old 03-10-2011, 12:04 PM   #2
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You did all the stuff i was going to have you check for: maf, vacuum leak. I'm guessing the intake is tighten and no air is getting in which would cause it to stutter? You sure all your vacuums are hooked up? (I had a problem exactly like this and found out it was a damn vacuum that wasn't hooked up (little tiny bitch in the back)
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Old 03-10-2011, 12:10 PM   #3
Momosaurus WRX
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I'll be honest, I don't know that much about engines. Pretty much everything I've done is because somebody told me to check it lol.

The thing that gets me is that it ran great for 2 weeks after replacing hte plugs, now it's running like I still have bad plugs.
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Old 03-10-2011, 12:17 PM   #4
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Grounding issues?
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Old 03-10-2011, 12:18 PM   #5
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Quote:
Originally Posted by Touge86 View Post
Grounding issues?

+1, smart.
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Old 03-10-2011, 12:22 PM   #6
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grounding issues are worth checking. get some wire and follow a faq on it. you can probably test it will smaller wire and then build a ground kit if it helps.
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Old 03-10-2011, 12:23 PM   #7
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grounding issues? explain. I understand electrical stuff. I already think I have a few bad grounds, as my parking brake light has turned into an actual load that makes my headlights dim lol.

edit: I'll go pick up some wire and make a grounding kit a bit later. But why would that cause a random misfire?
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Old 03-10-2011, 12:31 PM   #8
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Bad ground means a voltage drop. Voltage drop causes systems to malfunction.
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Old 03-10-2011, 12:36 PM   #9
Momosaurus WRX
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So what would it be that's not getting enough voltage? injectors? coil pack? plugs?

I could see it causing electrical problems like the radio and headlights, but a misfire? Forgive me for being skeptical and testing your knowledge lol. I just want to understand completely here. I like to learn.
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Old 03-10-2011, 12:48 PM   #10
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Sounds like you either have a bad ground or a very very large vacuum leak. Id double check your vacuum lines then add some grounding wires.

It's not a matter of voltage, is a matter of cleaning up the electrical signals around/on the engine. Adding grounds just helps the sensors avoid confusion.
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Old 03-10-2011, 12:49 PM   #11
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will do. Hopefully this resolves my issue.
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Old 03-10-2011, 12:51 PM   #12
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I still think its a vacuum that is loose or completely off.
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Old 03-10-2011, 12:51 PM   #13
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You are more than welcome to test my knowledge as I don't know a lot

The issue is that your car draws more current under larger loads. Your car uses less voltage at lower RPM's. As you "Get on it," the entire system will need more power, if the power isn't there, it will fail. Bad grounds = Bad sensor readings.

When your battery or alternator goes out, is the only thing that doesnt work the lights or radio? Can you just jump start it and run the car with the battery unplugged?
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Old 03-10-2011, 01:03 PM   #14
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Dirty fuel tank? have you checked the fuel filters?
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Old 03-10-2011, 01:15 PM   #15
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+1 for ground, never a bad idea regardless.

And I have also seen somewhat similar issues with bad plug wires, except it was across the entire RPM range. As others have said I would check all the basics like the air filter, fuel filter, fuel pump, vacuum leaks etc.. But it does sound electrical to me.

Thanks,
Rick
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Old 03-10-2011, 01:45 PM   #16
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^^^ No, thank you Rick.

Have you checked the timing?
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Old 03-10-2011, 02:01 PM   #17
Momosaurus WRX
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Timing is fine. I replaced the water pump 4k ago.

I'll check vacuum lines, clean my grounds, I'm going to go pick up a new fuel filter right now. The filter is newer (not stock) but I don't know how new, or what brand or any of that crap. After that I'll go pick up some wire and make a grounding kit. But considering I fly to Phoenix for 10 days today, I don't know how much of this I'll get done lol.
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