Engine Miss After Tune-up

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Mar 16, 2001 | 10:20 AM

lanero

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From: South Sioux City, NE USA

Engine Miss After Tune-up

[font size="1" color="#FF0000"]LAST EDITED ON 16-Mar-01 AT 11:20 AM (EST)[/font][p]I originally posted this to the 302 forum, but thought I would try here, also.

OK, first, this is what I'm working on: 1989 F250, 5.0L, M5OD.
Next, this is what I replaced: Plugs, wires, cap, rotor, and fuel filter.
Now, here is my problem, I seem to have developed a miss after the above items were replaced. The miss is most noticable at part throttle, low RPM usage (IE: crusing at 35MPH in 4th).
This is what I have tried to diagnose this problem, I have seperated the 7 an 8 plug wires, I've triple checked all plug wires (firing order and routing), and I have made sure the cap and rotor were installed right.
My, question is, what in the world do I check next? I've been pulling my hair out for almost 2 weeks trying to find the problem. If anyone has anymore suggestions for me, I'm all ears.
TIA

Roger Lane
Test Analyst
Sr. Automated Test Engineer
IBP, Inc.

Mar 16, 2001 | 11:01 AM

Chuck P.

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From: SE PA

Engine Miss After Tune-up

After you've run for a while with the miss present, pull the plug on the cylinder that you think is missing, it would be dirty compared to the good firing ones. It's not out of the question to get a weak new plug, if you hung on to the old ones, you might try switching one bank at a time and see if this cures it(depending on how hard they are to get to). Same rule applies to the new wires also(you can check resistance while moving/flexing the wire off the truck to make sure vibration isn't "opening" one of the wires when running). I'm leaning towards the plug from the way you have discibed the miss. Hope it's something this simple.

Mar 17, 2001 | 05:57 PM

jakegypsum

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From: Linwood, N.J. USA!

Engine Miss After Tune-up

What type of plugs did you use for replacements? I have seen platinum plugs cause a slight mis-fire at idle/low RPM. Does your truck have many miles on it? Certain brand spark plugs seem to make an engine not run properly. If it is a dead miss at any RPM, then I would follow the above post. Your problem does sound like it could be a plug not firing. Good luck. Jake.

Jakegypsum // Ford fleet, soup to nuts.

Mar 19, 2001 | 08:26 AM

lanero

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From: South Sioux City, NE USA

Engine Miss After Tune-up

I think the type of plug may be my biggest problem. I used Autolite's, I've used them in the past and have never had a problem. I will check them sometime this week (the temp is suppose to get upto the 50's)
And the truck has about 130,000 miles on it. The reason I say about is that the speedometer quit working about a year ago.
Thanks for all the help.

Roger Lane
Test Analyst
Sr. Automated Test Engineer
IBP, Inc.

Mar 19, 2001 | 05:46 PM

jakegypsum

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From: Linwood, N.J. USA!

Engine Miss After Tune-up

Roger, I know that Autolite is a good brand name but I have never had much luck with them. It could be me but I have always had the best luck with Motocraft plugs. I used a set just last week and I developed a miss within 4 days. I replaced them with Motocraft and everything has been good since then. Good luck. Jake.

Jakegypsum // Ford fleet, soup to nuts.