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Runs rough and shakes when car is warm

Tiny
PERTPAT
  • MEMBER
  • 1990 MERCURY MARQUIS
  • 130,000 MILES
1990 mercury grand marquis. Runs rough and shakes when car is warm especially going up hills. Put on new distributor car was worse. Only 6000 miles on spark plugs and wires.
when car is cold car runs much better
Monday, September 9th, 2013 AT 5:22 AM

22 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
The age of the wires doesn't guarantee anything. The wire could be damaged or burnt and the plug could have been cracked during installation. The first thing that needs to be done is to isolate which cylinder is causing the problem.
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Monday, September 9th, 2013 AT 5:59 AM
Tiny
PERTPAT
  • MEMBER
  • 9 POSTS
How do you isolate which cylinder is causing the problem?
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Monday, September 9th, 2013 AT 6:07 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
That will require equipment and experience which I suspect you don't have either of. You're probably going to need a shop to help you with that.
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Monday, September 9th, 2013 AT 6:53 AM
Tiny
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  • MEMBER
  • 9 POSTS
Is it bad to use Bosch Platinum +4 in a 1990 mercury grand marquis?
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Monday, September 9th, 2013 AT 7:31 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
Yes, very bad. Use Motorcraft only
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Monday, September 9th, 2013 AT 7:48 AM
Tiny
PERTPAT
  • MEMBER
  • 9 POSTS
Could you tell me why they are bad
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Monday, September 9th, 2013 AT 8:16 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
They are nothing but gimmick that the car was not designed for and they do not work in a Ford engine. NEVER put ANY Bosch plugs in a Ford.
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Tuesday, September 10th, 2013 AT 7:08 AM
Tiny
PERTPAT
  • MEMBER
  • 9 POSTS
Ok, replaced plugs with autolites, wires, distributor, map sensor, coil.
Idle is rough almost missing. Car bucks wildly when plugging in spout connector for electronic timing advance
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Friday, September 13th, 2013 AT 5:43 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
So, it only runs bad when the spout connector is in place?
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Friday, September 13th, 2013 AT 5:47 AM
Tiny
PERTPAT
  • MEMBER
  • 9 POSTS
Yes the problem only occurs with the spout connector in place.
New distributor timing advances about 20 degrees, old distributor timing advanced 4 degrees when plugging in spout connector.
New distributor much worse than old due to incease in advance timing I assume. What computer sensors could be feeding the wrong signal to the computer.
Throttle position sensor?
Coolant temp sensor?
Problem amplified when engine is hot after driving at least 7 miles
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Friday, September 13th, 2013 AT 6:02 AM
Tiny
WRENCHTECH
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Did the new distributor include an ignition module?
Was the problem the same before and after the distributor?
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Friday, September 13th, 2013 AT 6:12 AM
Tiny
PERTPAT
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  • 9 POSTS
Yes, worse after the new, not remanufactured distributor
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Friday, September 13th, 2013 AT 6:43 AM
Tiny
WRENCHTECH
  • MECHANIC
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It seems obvious that there is some kind of issue with the new distributor. If you still have the old one, try swapping the ignition modules.
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Friday, September 13th, 2013 AT 6:52 AM
Tiny
PERTPAT
  • MEMBER
  • 9 POSTS
We already tried that
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Friday, September 13th, 2013 AT 7:01 AM
Tiny
PERTPAT
  • MEMBER
  • 9 POSTS
Its doing the same with the old one too
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Friday, September 13th, 2013 AT 7:02 AM
Tiny
WRENCHTECH
  • MECHANIC
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Then I suggest you let a professional look at it. There is only so much that can be done without seeing the car.
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Friday, September 13th, 2013 AT 7:16 AM
Tiny
JERRY LAITINEN
  • MEMBER
  • 5 POSTS
My question for PERTPAT is did you ever resolve this issue? I have 140,000 miles on my 1990 Mercury Grand Marquis with similar issues that I cannot diagnose myself. I am down to inspecting the wiring harness by individual wires. Nothing else has worked.
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Sunday, November 17th, 2019 AT 6:04 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,256 POSTS
Hello,

I have seen the engine coolant temperature sensor cause this issue. here is a guide to help walk you through the steps:

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Please run this test and get back to us.
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Wednesday, November 20th, 2019 AT 7:29 PM
Tiny
JERRY LAITINEN
  • MEMBER
  • 5 POSTS
Thank you, even though the coolant temperature sensor fell apart in my hands and I replaced it. The problem was still not resolved. I have an update though. There seems to be some issues with the aftermarket distributors for these engines. After two attempts with 2 car quest distributors I’m trying a Cardone distributor when it arrives tomorrow.
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Wednesday, November 20th, 2019 AT 7:41 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Okay, sounds good. That can cause the issue, please let us know what happens with the new distributor.
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Thursday, November 21st, 2019 AT 12:39 PM

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