Engine Misfiring sometimes


New Member
Aug 23, 2020
Seattle, Wa
My 5.0 runs perfectly when its completely cold, and also when it is up to temp, but about halfway through the warm-up period, it will misfire for maybe a minute or so and then go back to running great. I can tell because the car shakes at idle and it feels down on power during acceleration. Sometimes it does not miss at all, I would say about 80% of warm-up cycles it misfires. No check engine light. This has been happening for a while and I haven't really concerned myself with it too much because the car runs perfect 99% of the time. The motor is all stock except for EGR delete, long-tube headers and h-pipe, and an air intake. Does the car need to be tuned for those modifications? What could be causing this?
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
polk county florida
No tune needed. Likely a bad connection someplace like the 'salt an pepper' connections.
Check for codes, it may have a stored code that will hint at what has a connection problem.


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SN Certified Technician
Mar 10, 2000
Dublin GA
Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/
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