Engine misfires intermittently?

DAVEYJONES

MEMBER
2003 FORD F-150
V8
2WD
AUTOMATIC
130,000 MILES

This started in May (7 months ago), when you reach crusing speed between 40 & 60 mph, back off the throttle to maintain your speed the truck shimmies and shakes and misfires, it felt like a trans problem, took it to my trans guy, a private shop I've been using for 30 years, they found metal shavings in the trans pan so I had the whole thing rebuilt, thought it was fixed, then realized it was not, it never seemed to happen when we had a technician in the car so we started fixing things, we thought it might be ignition or fuel related diagnostics showed nothing, no trouble lights were lit, idle control motor?

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

An engine will misfire due to not getting proper spark to the plugs. It could happen for faulty plugs or wires or ignition coil or module.
Typically a misfire will trigger the check engine light.
A good step is to get the vehicle scanned so you can pinpoint the misfire.
If the engine light is on it will tell you which cylinder the misfire is happening.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Here is a helpful video on random misfires:

https://youtu.be/UKB-ytgbnzU

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

First you want to check the spark plugs.
You want to visually check the plugs. Make sure they are in good condition.
Verify the gap is correct.

Please let me know of any questions.

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