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Misfiring four cylinders

Tiny
AUSTINTXCROWNVIC
  • MEMBER
  • 2004 FORD CROWN VICTORIA
  • 4.6L
  • V8
  • RWD
  • AUTOMATIC
  • 220,000 MILES
Car is running on four cylinders and is misfiring cylinder one, two, five and six. I checked power to coils and injectors. I then replaced spark plugs then coils and next injectors. Only five and six plugs were burnt. The car runs like a puttering snail until fifty mph then runs smooths to wherever after just fine. I unplugged battery to reset. But I have yet to do more wrenching down deeper. I have researched as much as possible. Only thing I can think of is PCM or cylinder header temperature sensor. I need some advice. Thanks.
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Tuesday, May 23rd, 2017 AT 10:30 PM

7 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check fuel pressure with a gauge first It may be low causing this and check for a vacuum leak. Auto parts rent gauge. See link.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Wednesday, May 24th, 2017 AT 12:50 PM
Tiny
AUSTINTXCROWNVIC
  • MEMBER
  • 4 POSTS
Normal pressure. Had just replaced fuel pump and filter right when I started having troubles. All four cylinders still out.
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Wednesday, May 24th, 2017 AT 1:15 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
What are the codes? If you do not know have it scanned at auto parts I need all the codes if other than misfires. Have you checked for a vacuum leak?
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Wednesday, May 24th, 2017 AT 1:17 PM
Tiny
AUSTINTXCROWNVIC
  • MEMBER
  • 4 POSTS
P1000, P0174, P0316, P0300, P0305, P0306. The o2 codes are from no catalytic converters.
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Wednesday, May 24th, 2017 AT 1:51 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
P1000 could be the cause of all of your codes maybe not. Since you took the converters off you may not be able to get rid of this code and your misfires. This may never be able to be corrected because of missing catalytic converters and the p1000 code which means it is thinking it has never been driven. Also, with the cylinders that misfiring I still believe it is low fuel pressure or injector or a large vacuum leak. Should be 20-60 key on only and 25-40 engine running. Also run a compression check on all cylinders.
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Wednesday, May 24th, 2017 AT 3:41 PM
Tiny
AUSTINTXCROWNVIC
  • MEMBER
  • 4 POSTS
Okay just checked fuses and #19 was showing no power which is a PCM. Swapped fuses could hear the other two relays kick on. Ran out of time tonight on this project and I'm renting the compression tester in the morning. I have a feeling it might be a leak in the intake manifold. Just have to go all the way through it I guess.
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Wednesday, May 24th, 2017 AT 10:26 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,256 POSTS
Hello,

It sounds like you have a valve train problem like a valve spring is broken or you have a blown head gasket between two cylinders. Can we start with a compression test, please follow this guide.

https://www.2carpros.com/articles/how-to-test-engine-compression

Please run this test and get back to us so we can continue helping you.

Cheers, Ken

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Saturday, May 27th, 2017 AT 1:01 PM

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