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Jerking misfire?

Tiny
J.STIEG
  • MEMBER
  • 1999 FORD CROWN VICTORIA
  • V8
  • 2WD
  • AUTOMATIC
  • 190,000 MILES
I have some minor problems with my car. There is some misfire/jerking that can be felt when I am cruising, mostly when it is in overdrive at less throttle. It consistently smooths out every time when I accelerate at any speed range. It starts right up every time and idles perfectly, cold or hot. I am trying to figure out if its fuel related or spark related. Do you have any ideas on what to do or try?
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Friday, September 25th, 2009 AT 9:23 AM

7 Replies

Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
This sounds like a classic spark plug misfire which can be fixed by doing the tune up the engine here is a guide that will help you fix the problem.

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

Please run down this guide and report back

Cheers
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Friday, September 25th, 2009 AT 9:31 AM
Tiny
J.STIEG
  • MEMBER
  • 352 POSTS
I have not had any parts installed in the last few months since I owned it, I did put spark plugs in it a couple months ago. Check engine light has not been on at all. Tell me what you think, or lets talk some more, thanks. Jared
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Friday, September 25th, 2009 AT 1:03 PM
Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Ok well I would replace the fuel filter if you haven't just so I know how old it is may not fix the problem. Now I would like to test the tps (throttle possition sensor). You will need to have a digital multi meter. Let me know if you are ready to do a couple of tests.
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Saturday, September 26th, 2009 AT 8:34 AM
Tiny
J.STIEG
  • MEMBER
  • 352 POSTS
I think the fuel filter is fine, I disconected the in-coming line at the fuel rail and get about 1 cup of gas in a pan in two seconds, pint in about 4 or 5, with the pump jumped at the relay. I have a digital multimeter and am ready for tests on the TPS at any time, thanks. Jared
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Saturday, September 26th, 2009 AT 9:36 AM
Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Ok sounds good so far. Now with the TPS you will need to back probe the gray wire with the white strip at the tps connector. You can use a paper clip to back probe at the connector. Now with everything hooked up and plugged in with key on engine off you should read.8 to 1 volt. Now slowly lift the throttle and the voltage should increase slowly and steadily with no drops or glitches as you open the throttle. Now at wide open throttle you should read 4.5 to 5 volts. Let me know what you find here. If this tests good then we will look at the crank sensor next.

Also a ignition coil can cause this issue as well. Remove all coils and look for a burnt arch inside one of them.
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Monday, September 28th, 2009 AT 12:59 PM
Tiny
J.STIEG
  • MEMBER
  • 352 POSTS
The voltage reading I got was 1.1v constantly going up to 4.7v, I think this reading means the sensor is fine, what do you think? Do you think any other sensors can be bad without the check engine light on? Jerking is felt when in overdrive, mostly when engine is under small load, it tends to smooth out when accelerated. Could be anything like bad fuel, dirty injectors, faulty pressure regulator, or spark cutting out, or more, but it idles and accelerates fine and smooth, so I removed each coil I found the bad one, all black inside, replaced it and the engine runs great! I love this site.
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Tuesday, September 29th, 2009 AT 6:45 PM
Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Good to hear, please use 2CarPros anytime we are here to help.

Cheers.
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Wednesday, September 30th, 2009 AT 9:52 AM

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