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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 03-01-2007, 06:42 PM   #1
BlazeGT
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Default Black exhaust, unsteady idle, hesitation...

Lately my car has been acting up a lot with the following symptoms:
-Black smoke from the exhaust
-smells like gas when i drive...waaay more than it should
-when i push the gas pedal i have to pump it once quickly or it dies
-when im stopped the idle goes crazy, from somewhere around 250 to 1500 just revving up and down

The car runs fine once it gets going, but i was wondering if any of you could diagnose the problem. Any guesses would be appreciated
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Old 03-01-2007, 06:46 PM   #2
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Default RE: Black exhaust, unsteady idle, hesitation...

sounds like you are having a fuel/spark problem when was the last time you did a tune up?
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Old 03-01-2007, 06:49 PM   #3
BlazeGT
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Default RE: Black exhaust, unsteady idle, hesitation...

My last tune up was actually pretty recent...id say probably 3000 miles back and this car sees about 250-300 miles a week
so around two or three months if my math is correct
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Old 03-01-2007, 07:03 PM   #4
91ford302
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Default RE: Black exhaust, unsteady idle, hesitation...

what year and engine/trans combo. need more info
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Old 03-01-2007, 07:17 PM   #5
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Default RE: Black exhaust, unsteady idle, hesitation...

It's a fuel delivery related problem. You're running horribly rich. Clean your MAF wires first. If the MAF cleaning doesn't solve the problem, run codes and see if anything pops up. I'd lean towards a dirty MAF or ECT sensor, possibly bad oxygen sensor(s).
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Old 03-01-2007, 07:25 PM   #6
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Default RE: Black exhaust, unsteady idle, hesitation...

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ORIGINAL: 92hatchLX

It's a fuel delivery related problem. You're running horribly rich. Clean your MAF wires first. If the MAF cleaning doesn't solve the problem, run codes and see if anything pops up. I'd lean towards a dirty MAF or ECT sensor, possibly bad oxygen sensor(s).
^ + a billion. You be runnin rich man. Absolutely no doubt about it. Fuel pressure should be 30psi at idle and 40psi with the vacuum line off the regulator. Drive it without the MAF and evaluate. Typically they create lean conditions over rich, but anything is possible. If your PCM power (VPWR) is too low, it will run extremely fat. You oxygen sensor voltages may be stuck at zero, but you will go into open loop and never notice smoke. You could have bad gas, so keep that in mind if you can't find any rich contributors. IAT or ECT reading way too low shouldn't make it pour black smoke, but you need to validate their accuracy.
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Old 03-01-2007, 07:45 PM   #7
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Default RE: Black exhaust, unsteady idle, hesitation...

OH woops sorry i forgot, this is a 1994 gt so there ya go for whoever asked. Thanks for all of the help so far, ill definately check it out.
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Old 03-03-2007, 12:19 AM   #8
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Default RE: Black exhaust, unsteady idle, hesitation...

i have the same idle problem but my car is speed density...any ideas??!5.0 i 89lx conversion
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Old 03-03-2007, 12:19 AM
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