1995 mustang gt misfire at idle - Mustang Evolution

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Old 05-13-2013, 12:23 PM   #1
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1995 mustang gt misfire at idle

hello mustang evolution peers, my name is matt and i bought a 1995 mustang gt 5.0 a few months ago and am battling a miss at idle now its pretty bad like a very mild cam even though its not, also when i put the car into park its bad like blup blup than goes away slowly, now i replaced plugs, wires, cap, rotor, distributor had no play. anyway i also replaced 80 percent of vacuum lines with minimal improvement. what threw me for a loop was last night i took the purge valve off the car and put a straight fitting their and it ran excellent still slightly under powered but its stock, but the miss was 99 percent gone a little hit here and their. i have sprayed carb spray over every vacuum line with no change in idle and the egr is new.
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Old 05-13-2013, 05:05 PM   #2
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Your timing could be slightly off or if you have cats it could be plugged
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Old 05-13-2013, 05:56 PM   #3
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i dont have a timing light, but i loosened the distributor hold down and slowly moved it with the car running (i marked original location) and had no difference the car actually runs worse, and feels like a possibly vacuum leak or fuel issue which makes sense, when i bypassed the purge valve which sucks fuel vapors from the fuel tank to the intake it ran awesome no more miss? as soon as i put it back it started missing again. and the vacuum on a guage says 20 on start up and goes down to 15-16 once it starts missing. any thoughts?
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Old 05-13-2013, 06:02 PM   #4
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Did you remove the PIP when you adjusted the timing?
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Old 05-13-2013, 06:07 PM   #5
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PIP??
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Old 05-13-2013, 08:32 PM   #6
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okay this is weird, I borrowed a timing light and when I take the pip out and start the car the timing is right at 10, the weird thing is that when I put the pip back in and start the car and check the timing it's at about 20? Is that normal? And I marked the timin marks
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Old 05-13-2013, 08:41 PM   #7
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okay this is weird, I borrowed a timing light and when I take the pip out and start the car the timing is right at 10, the weird thing is that when I put the pip back in and start the car and check the timing it's at about 20? Is that normal? And I marked the timin marks
That is normal
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Old 05-13-2013, 08:43 PM   #8
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now that timing is not it what could it be? runs great if bypassing the purge valve
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Old 05-13-2013, 08:48 PM   #9
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Replace the purge valve it might be stuck or hook it up and tap on it and see if it unsticks
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Old 05-13-2013, 08:53 PM   #10
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right now if I suck on the one side of the purge it always let's you pull air and the other side wint do anything even when supplying power to the purge valve it opens up but won't let me suck through
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Old 05-13-2013, 09:02 PM   #11
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Sounds like the purge valve isn't doing its job by purging the canister to release the fuel vapors into the engine at the correct time either way it sounds like your close if you can bypass it and it runs fine
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Old 05-13-2013, 09:10 PM   #12
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That's what's confusing if I delete the valve and put a plastic line in its place their for sucking fuel vapors at all times, once I do that it runs great
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Old 05-13-2013, 09:14 PM   #13
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If your purge valve and canister are fine and it only runs good when its constant fuel vapors your having a fuel issue have you put a gauge on the fuel rail to check the pressure
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Old 05-13-2013, 09:31 PM   #14
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no not yet I'll do that tomorrow at work and post my findings, I checked vacuum with a gauge and had 20 at idle
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Old 05-13-2013, 09:37 PM   #15
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If its getting more fuel than it should by bypassing the purge valve and its running fine then it's not getting enough when it's correctly hooked up
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Old 05-13-2013, 10:00 PM   #16
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i agree I'm guess I'm not gettjng enough fuel so either pressure regulator or pump. I lost almost all of misfire by doing that
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Old 05-14-2013, 10:09 AM   #17
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Another thing is you may have a clogged or bad injector so try and check those to
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Old 05-14-2013, 10:13 AM   #18
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Another thing is you may have a clogged or bad injector so try and check those to
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Old 05-14-2013, 10:15 AM   #19
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If vacum leeks and ingnition arnt the problem I agree that a dirty or fouling fuel injector would be where Id look next.
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Old 05-14-2013, 10:41 AM   #20
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how do I test the injectors? Ohm when cold and hot?
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Old 05-14-2013, 10:44 AM   #21
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You can run some injector cleaner
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Old 05-14-2013, 10:46 AM   #22
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There's a light you can buy specifically for testing injectors if there getting a signal the light will flash every time it sprays so its real fast flash you can try a test light but they don't always work for injectors
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Old 05-14-2013, 10:50 AM   #23
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I believe your talking about noid light? and how will that show if it's clogged? that just shows it gettin power doesn't it?
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Old 05-14-2013, 11:02 AM   #24
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It won't show a clog but it only shows if its getting a signal there's a injector tester that plugs into your injector that you think might be clogged and then it hooks to your battery then you prime the fuel system to put pressure in the rail say its 50 psi and the injector bleeds down to 20 psi then the next injector bleeds down to 10 psi that means that injector isn't flowing as we'll as the others or take them out and have them cleaned and pressure tested
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Old 05-14-2013, 11:05 AM   #25
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hmmm good point I'm gonna try to check fuel pressure today I'll post what I find!
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Old 05-14-2013, 03:00 PM   #26
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hey just a tid bit of information the car also has almost no power off the line it will spin the tires for maybe a second and stop and grab just thought id add the underpowered part. ive had people tell me it felt like a 6 cylinder, could this further your thoughts on clogged injectors?
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Old 05-14-2013, 03:53 PM   #27
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alright guys just tested fuel pressure and i have 34 at idle, and it doesnt drain back down while running any thoughts? is that normal?
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Old 05-14-2013, 04:00 PM   #28
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Did you have the purge vale bypassed or hooked up
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Old 05-15-2013, 12:54 AM   #29
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hooked up, fuel pressure was perfect
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Old 05-15-2013, 01:04 AM   #30
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It's supposed to be 39.5 with the hose unattached and blocked off (thumb on it)
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Old 05-15-2013, 01:06 AM   #31
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Which hose? Purge?
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Old 05-15-2013, 12:03 PM   #32
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Old 05-15-2013, 12:49 PM   #33
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Ahhhh that hose lol and I just ran a power balance test with my scanner and got the flowing cel blinks 5, 3, 8
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Old 05-16-2013, 09:52 AM   #34
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I would have just cheated and visually inspected each injector squirting having taken the injectors out just enough to see them spray with a flashlight with someone periodicly cranking the engine but not starting it and imidiately turning it off if it did start. Sometimes you dont even have to do that though because alot of the time if you just pull the injectors you can tell when one is clogged just by looking at it. However watching the injectors actaully spray tells you if they are getting power. If you try this wear some goggles as you dont want fuel in your eyes, it sucks.

Is your engine not throwing a engine code with a check engine light? The only symptom is the loss of power and misfire at idle? Usually when your engine has a misfire the computer detects it and puts the engine in limp mode, which would explain the serious loss in power, and when this happens the check engine light should come on and tell you which cylinder your having an issue with.
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Old 05-16-2013, 02:08 PM   #35
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no engine light at all related to misfires, weird lol but it is obd1 I did run a power balance test and got cylinders 3, 5, 8 misfiring as when I unplug injector #1 the idle barely changes it does change if I raise the throttle I can feel the misfire than and that sounds easier than done I have my intake Sitting over my injectors?
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