Possible Misfiring?

1986 FORD F-250

165,000 MILES • 7.5L • V8 • 4WD • MANUAL

CAJUNATOR

MEMBER
3 POSTS

I just acquired this vehicle, and I can't tell exactly, but it seems like my engine is misfiring. It has a very apparent shake while idling, mainly shown by the dipstick flopping back and forth. I pulled the spark plugs and all looked fine, but cylinder 8's plug smelled like gas and looked a little bent at the contact. I installed new plugs, and it didn't seem to make a difference. I checked the ignition, and the plugs are getting spark, and the firing order is correct. There is light to medium white smoke coming from the tailpipe and the throttle seems a little slow, but I've only had it in this condition, so I don't know if it has a loss of power. I will be pulling the valve covers at a later time to replace the gasket and look at the rockers and pushrods while I'm in there. I would greatly appreciate help in diagnosing this.

Video (Click to enlarge)

Oct 13, 2023 at 1:16 PM

JACOBANDNICKOLAS

✓Experienced Mechanic
110,240 POSTS

Hi,

How long does the white smoke from the exhaust last? Could it be simple condensation? Also, if the white smoke is excessive and long-lasting, it could indicate that coolant is getting into the combustion chamber and burning. Take a look through this link.

https://www.2carpros.com/articles/recognizing-the-symptoms-understanding-a-blown-head-gasket-in-your-vehicle

Now, I listened to the video a couple of times. (very helpful). I do see the engine shaking, but it doesn't sound like a misfire. Have you checked to see if there are any engine vacuum leaks? If not, start with that.

Here is a link that explains how to do it:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

One other thing, here is a link that explains how to retrieve diagnostic trouble codes on this vehicle. This has an OBD1 system and doesn't require a scanner to retrieve codes.

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

If there are codes, it should help point us in the right direction.

Let me know what you find or if you have other questions.

Take care,

Joe

PS: Could you take a pic of the cylinder 8 spark plug that appeared bent and upload it for me to see?

Oct 13, 2023 at 2:52 PM

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