Need help misfires when hot?

FoxRod87

Active Member

Feb 1, 2006

243

1

27

Carolina

Aug 5, 2010

#1

• Aug 5, 2010

• #1

I can crank the car up and head down the road and it will run fine for a minute or two then it will develop a misfire and sometimes it will backfire. I can stop somewhere and let it sit for 10 min or so and take off again and it will run fine and then start to misfire again. what could this be? crank or cam sensors? wiring or what? Thanks!

 

K

Kilgore Trout

Fried or Broiled ?

10 Year Member

Mar 30, 2005

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Aug 5, 2010

#2

• Aug 5, 2010

• #2

clogged cats or clogged air filter could be the cause

 

FoxRod87

Active Member

Feb 1, 2006

243

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Carolina

Aug 5, 2010

#3

• Aug 5, 2010

• #3

New air filter and no cats

 

trinity_gt

10 Year Member

Jan 31, 2003

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Aug 5, 2010

#4

• Aug 5, 2010

• #4

Probably a coil pack or (hopefully not) a coil driver in the PCM.

Can you scan the PCM to find out which cylinder(s) are misfiring now, then swap the coils left to right and see if the problem follows the coil?

 

FoxRod87

Active Member

Feb 1, 2006

243

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27

Carolina

Aug 5, 2010

#5

• Aug 5, 2010

• #5

Already put different coils on both sides and still same problem

 

K

Kilgore Trout

Fried or Broiled ?

10 Year Member

Mar 30, 2005

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Aug 5, 2010

#6

• Aug 5, 2010

• #6

is it a mustang? enough of these guessing games!

 

FoxRod87

Active Member

Feb 1, 2006

243

1

27

Carolina

Aug 5, 2010

#7

• Aug 5, 2010

• #7

Yes the one in my sig

 

FoxRod87

Active Member

Feb 1, 2006

243

1

27

Carolina

Aug 5, 2010

#8

• Aug 5, 2010

• #8

Yes the one in my sig

 

FoxRod87

Active Member

Feb 1, 2006

243

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27

Carolina

Aug 5, 2010

#9

• Aug 5, 2010

• #9

96 gt

 

trinity_gt

10 Year Member

Jan 31, 2003

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Aug 5, 2010

#10

• Aug 5, 2010

• #10

More possibilities:

• crank position sensor
• PCM/coil driver
• PCM/injector driver

Have you scanned the codes? Is it one cylinder consistently or are you getting random misfires?

 

trombonedemon

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Jun 25, 2009

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Aug 5, 2010

#11

• Aug 5, 2010

• #11

Poor or unregulated engine timing is often a cause of intake backfires, but can also be responsible for exhaust backfires

Improper wiring in the ignition can also lead to timing issues and backfires

Low fuel pressure, clogged fuel filters, and weak fuel pumps could cause a severe lean air-to-fuel ratio during fuel injection

Missing or damaged catalytic converter can result in backfires out the tailpipe

These are some of the causes I've researched. I would check for intake leakes and maybe your cats have gone bad like the forementioned. Clean your MAF also. Might be some unmetered air.
Don't drive your car anymore until you figure this one out, b/c, early detonation will destroy pistons.
What octane of gas are you using?

 

FoxRod87

Active Member

Feb 1, 2006

243

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27

Carolina

Aug 5, 2010

#12

• Aug 5, 2010

• #12

93 octane just rebuilt engine so all gaskets are new was doin same thing before rebuild but not the reason it was rebuilt

 

FoxRod87

Active Member

Feb 1, 2006

243

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27

Carolina

Aug 5, 2010

#13

• Aug 5, 2010

• #13

#1cyl ring broke and was smoking really bad is the reason for overhaul

 

FoxRod87

Active Member

Feb 1, 2006

243

1

27

Carolina

Aug 5, 2010

#14

• Aug 5, 2010

• #14

ChAnger fuel filter still same problem

 

FoxRod87

Active Member

Feb 1, 2006

243

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27

Carolina

Aug 5, 2010

#15

• Aug 5, 2010

• #15

It has no codes. Does this mean it isn't an electrical issue?

 

FoxRod87

Active Member

Feb 1, 2006

243

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27

Carolina

Aug 5, 2010

#16

• Aug 5, 2010

• #16

What is fuel pressure supposed to be? Idle I got 30-31 and with vaccum off reg it was 40psi is that good?

 

wmburns

SN Certified Technician

Aug 14, 2009

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Houston Texas

Aug 5, 2010

#17

• Aug 5, 2010

• #17

40 PSI delta is perfect.

What is the condition of the spark plug wires? How old? What about routing? Try running the car in a totally dark location. Can you spot any spark leakage (blue)? Also do a visual inspection. Look for white spots esp where the wires touch anything.

Consider having your fuel injectors cleaned and flow tested. Try injectorrx.com. They have done well by me.

 

FoxRod87

Active Member

Feb 1, 2006

243

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27

Carolina

Aug 5, 2010

#18

• Aug 5, 2010

• #18

Sparkplug wire was bad found it by cutting off all the light and found it glowing so thanks wmburns it worked

 

trombonedemon

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Jun 25, 2009

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Aug 6, 2010

#19

• Aug 6, 2010

• #19

wmburns said:

40 PSI delta is perfect.

What is the condition of the spark plug wires? How old? What about routing? Try running the car in a totally dark location. Can you spot any spark leakage? Also do a visual inspection. Look for white spots esp where the wires touch anything.

Consider having your fuel injectors cleaned and flow tested. Try injectorrx.com. They have done well by me.

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Once again,!