1987 mercury grandmarqis


Old 03-03-07, 07:21 PM
Thread Starter
Join Date: Mar 2007
Posts: 1
Unhappy 1987 mercury grandmarqis

i have a engine miss that worsens as it warms up or speeds between 25 to35. i changed plugs, wires, rotor cap , fuelfilter ,mapsenser, distributor pickup and ignition module. symtoms go away for a short time if i race the engine. miss seems to be coming from drivers side engine bank any info would be appreciated. it has a 302 feul injected.
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Old 03-04-07, 05:07 AM
Join Date: Apr 2006
Location: Floriduhhhhh Us of A
Posts: 611
First.localize the miss to a particular cyl............and run a compression test
Old 03-04-07, 05:45 AM
Join Date: Aug 2003
Location: Cape Cod
Posts: 4,320
Check the plug wire routing
There is a difference between the 5.0 "HO" engine and the plain 5.0
Make sure you've got the right one

Also, on the "plain jane" 5.0 the wires from the 7 & 8 cylinders are a trouble spot, and the wires can crossfire
Make sure they are well separated (as well as can be)

7 & 8 would be the "back" two on the driver's side
Old 03-04-07, 07:11 PM
Join Date: Oct 2000
Location: Livonia, Michigan
Posts: 923
That model is an EEC-IV and has self-diagnostic capablility that any good DIYer should be able to master. You should get familiar with the following web site:


It shows you how to make a code reader and interpret engine codes. The check engine light doesn't have to be on for the engine to set and store codes under many conditions, and the code reader will pick up these codes. The car even has the capability to run a cylinder balance self-test to pinpoint which cylinders are a problem. Study the site and you should be able to tap into the amazing self-diagnostic capabilities of your car.

On the other hand, your description of the problem matches a vacuum leak condition.

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