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Author
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Topic: 91 Foxbody Misfire
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Rigo5.0
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Member # 5247
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posted
 
 
- Car starts right away when cold, but runs with what seems to be a bad misfire
- Once warm, car will shut off and not start until engine cools down
I've checked/replaced the following:
- Spark plugs
- Coil
- TFI module
- Vacuum hoses
Anything else I should strongly consider checking?
Thanks.
[ 2015-04-28, 10:11 PM: Message edited by: Rigo5.0 ]
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91 5.0 [331|T56]
87 Grand National
02 Z06
08 Challenger SRT8
13 Shelby GT500
00 Lightning
14 Camaro SS
Posts: 1454 | From: Kansas City | Registered: Jan 2005
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LXjames
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Member # 10791
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posted
Next time it does that, pull the spout connector and try to start it. If it starts you may have a bad pip in the dizzy
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On Point Motorsport prez.
King Lx
Posts: 4761 | From: Pittsburg CA | Registered: Mar 2011
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Rigo5.0
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Member # 5247
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posted
quote:
Originally posted by LXjames:
Next time it does that, pull the spout connector and try to start it. If it starts you may have a bad pip in the dizzy
I'll give that a shot. Anything else?
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91 5.0 [331|T56]
87 Grand National
02 Z06
08 Challenger SRT8
13 Shelby GT500
00 Lightning
14 Camaro SS
Posts: 1454 | From: Kansas City | Registered: Jan 2005
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LXjames
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Member # 10791
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posted
quote:
Originally posted by Rigo5.0:
quote:
Originally posted by LXjames:
Next time it does that, pull the spout connector and try to start it. If it starts you may have a bad pip in the dizzy
I'll give that a shot. Anything else?
What's your plug gap at at and what wires you running
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On Point Motorsport prez.
King Lx
Posts: 4761 | From: Pittsburg CA | Registered: Mar 2011
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NK2186
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Member # 12319
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posted
Keep pulling plug wires until you find a cylinder that does not change when you unhook the sparkplug wire for that specific cylinder.
Check the plug in that cylinder and see if it is white or black.
Once you find the cylinder you can try swapping the fuel injector to a different bank and seeing if the problem follows. If it does then you just need to replace the injector.
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90 LX 5.0 - Stolen/stripped
89 LX 5.0 - Stolen and missing as of 7-24-13. LIC# 4HIP151 :(
99 Cobra
00 Exploder
Posts: 400 | From: Haystack | Registered: Aug 2012
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Fostang
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Member # 3752
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posted
Have you checked the fuel pressure with a gauge?
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67' Fastback TT 408
67' Camaro Lsx
64' Corvette Fuelie
57' Chevy Bel Air Lsx
68’ Pony Convertible
66’ Pony Coupe
Posts: 3012 | From: Stockton/Danville | Registered: Nov 2003
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dohcfox
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Member # 12829
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posted
Sounds like plugged cats. Loosen the exhaust system at the headers and see if it goes away.
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97 mustang track car
57 f100 built on 06 Lincoln navigator frame
83 elcamino d.d.
64 ford galaxie
Porsche turbo
Posts: 139 | Registered: Apr 2013
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LXjames
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Member # 10791
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posted
quote:
Originally posted by dohcfox:
Sounds like plugged cats. Loosen the exhaust system at the headers and see if it goes away.
If it was plugged cats it would progressively get worse with time starting with poor driveability then no start. It wouldn't get bad as it warms then go away as it cools. Plugging is permanent a temporary obstruction wouldn't be permanent but then again its theoretically impossible to temporarily obstruct an exhaust from the engine
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On Point Motorsport prez.
King Lx
Posts: 4761 | From: Pittsburg CA | Registered: Mar 2011
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dohcfox
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Member # 12829
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posted
quote:
Originally posted by LXjames:
quote:
Originally posted by dohcfox:
Sounds like plugged cats. Loosen the exhaust system at the headers and see if it goes away.
If it was plugged cats it would progressively get worse with time starting with poor driveability then no start. It wouldn't get bad as it warms then go away as it cools. Plugging is permanent a temporary obstruction wouldn't be permanent but then again its theoretically impossible to temporarily obstruct an exhaust from the engine
Opposite. As things heat up they expand. And the cats plug with carbon and excessive fuel. So when they are cold it allows small pinhole size amounts of exhaust per catalalist by. Then when it warms up they close up more and more. Furthermore the restriction backs back up into the intake manifold and the computer recognizes the hard to keep running condition, misfires read excessive o2 in the exhaust so it drives the fuel mixture richer and richer making the situation even worse. Then when you let the cats cool down the exhaust can make it back by.
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97 mustang track car
57 f100 built on 06 Lincoln navigator frame
83 elcamino d.d.
64 ford galaxie
Porsche turbo
Posts: 139 | Registered: Apr 2013
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LXjames
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Member # 10791
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posted
quote:
Originally posted by dohcfox:
quote:
Originally posted by LXjames:
quote:
Originally posted by dohcfox:
Sounds like plugged cats. Loosen the exhaust system at the headers and see if it goes away.
If it was plugged cats it would progressively get worse with time starting with poor driveability then no start. It wouldn't get bad as it warms then go away as it cools. Plugging is permanent a temporary obstruction wouldn't be permanent but then again its theoretically impossible to temporarily obstruct an exhaust from the engine
Opposite. As things heat up they expand. And the cats plug with carbon and excessive fuel. So when they are cold it allows small pinhole size amounts of exhaust per catalalist by. Then when it warms up they close up more and more. Furthermore the restriction backs back up into the intake manifold and the computer recognizes the hard to keep running condition, misfires read excessive o2 in the exhaust so it drives the fuel mixture richer and richer making the situation even worse. Then when you let the cats cool down the exhaust can make it back by.
That's probably possible but I've never heard someone have that problem. But just because it's rare doesn't mean it can't happen I guess. But in my thinking, if the ecu is sending a rich signal shouldn't there be an abundance of air and not fuel? I don't think the O2 would get an air mixture as it plugs thus causing the computer to go rich? Also if it is getting richer as it warms wouldn't that just eventually plug the cat all together instead of leaving pin holes like you said?
Edit: if I'm reading his signature right I'm guessing his 91 has a 331/t56 set up I would doubt he's wasting time with cats
[ 2015-04-30, 06:47 AM: Message edited by: LXjames ]
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On Point Motorsport prez.
King Lx
Posts: 4761 | From: Pittsburg CA | Registered: Mar 2011
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dohcfox
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Member # 12829
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posted
Didn't read the signature. Just going of what I deal with every day. I am a triple master ford technician that specializes in gas engine performance and electrical. So I see it once a week with 3v f150s
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97 mustang track car
57 f100 built on 06 Lincoln navigator frame
83 elcamino d.d.
64 ford galaxie
Porsche turbo
Posts: 139 | Registered: Apr 2013
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dohcfox
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Member # 12829
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posted
Could be anything really, but the common cause of a misfire and a no start when hot is pluged exhaust. Plus it's free to check for a pluged exhaust. Tfi issues or stator issues start and run normally then quit. Or are a no start, temprature has little bearing on tfi issues. And fuel delivery or pressure issues are more pronounced cold since the engine burns the highest volume of fuel cold.
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97 mustang track car
57 f100 built on 06 Lincoln navigator frame
83 elcamino d.d.
64 ford galaxie
Porsche turbo
Posts: 139 | Registered: Apr 2013
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Rigo5.0
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Member # 5247
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posted
-Car does not have cats
-Plugs gapped at .054 (have been for the last year it's no issues)
-I will check the wires
Thanks guys. Anything else?
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91 5.0 [331|T56]
87 Grand National
02 Z06
08 Challenger SRT8
13 Shelby GT500
00 Lightning
14 Camaro SS
Posts: 1454 | From: Kansas City | Registered: Jan 2005
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Rigo5.0
¯
Member # 5247
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posted
quote:
Originally posted by Fostang:
Have you checked the fuel pressure with a gauge?
Yes. FP is at 39psi
[ 2015-04-30, 08:39 PM: Message edited by: Rigo5.0 ]
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91 5.0 [331|T56]
87 Grand National
02 Z06
08 Challenger SRT8
13 Shelby GT500
00 Lightning
14 Camaro SS
Posts: 1454 | From: Kansas City | Registered: Jan 2005
| :
|
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Rigo5.0
¯
Member # 5247
|
posted
quote:
Originally posted by NK2186:
Keep pulling plug wires until you find a cylinder that does not change when you unhook the sparkplug wire for that specific cylinder.
Check the plug in that cylinder and see if it is white or black.
Once you find the cylinder you can try swapping the fuel injector to a different bank and seeing if the problem follows. If it does then you just need to replace the injector.
I will give it a shot.
--------------------
91 5.0 [331|T56]
87 Grand National
02 Z06
08 Challenger SRT8
13 Shelby GT500
00 Lightning
14 Camaro SS
Posts: 1454 | From: Kansas City | Registered: Jan 2005
| :
|
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dohcfox
¯
Member # 12829
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posted
Use a noid light and see if the injectors are still being fired when there is a no start situation, +1 on the over fuel situation then on one or more cylinders. If it is being over fueled you should be able to hold the throttle at 3/4 open when cranking and get it to clear and fire.
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97 mustang track car
57 f100 built on 06 Lincoln navigator frame
83 elcamino d.d.
64 ford galaxie
Porsche turbo
Posts: 139 | Registered: Apr 2013
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