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Discussion Starter · #1 ·
Dave here. Wife's vehicle is a 99 sport, 2WD, 4.0 pushrod at 190K
Developed an issue, cannot find it.

Was missing (maybe), plugs been in there a while, changed them, better for a couple of weeks if not fine, then started again. Belden wires showing halos, swapped them under warranty (9 years old). Now it hammers. Sometimes. Occasionally. I thought the engine was going to rip the mounts out. Not consistent, does not appear to be a misfire, and if it is, it's the strangest I've seen.
Been a mechanic for a long time, retired.

Thought trans, my buddy at the trans shop went out with me, he says no, when it does it (real light evidence for him on this drive) the tach never wavered..
I cleaned the MAF with proper stuff, no change. Fuel filter done earlier this year.

So new plugs, wires, coil pack, fuel filter, last year did plenum and fuel rail gaskets (lean bank 1 and 2), that's fine.

NO check engine, NO codes, did the requisite "wiggle test", no change.

I've never seen this set of symptoms before.

In and out of OD, same. Shift into second, no change. Ride the brake, looking for anti-lock issues (a stretch, I know), no change. No discernible vacuum leaks anywhere.

No valve clatter, no rod knocks, fuel pressure right at 60 PSI.

Added gas dryer to tank, making sure no water up to the pickup sock, no change.

Thinking about dropping the trans pan, looking for debris, changing fluid, but anybody ever seen this before?

If there is a 99 Sport forum here, tell me where, I'll put it there!

Thanks

(my Flatheads never do this!)
 

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Discussion Starter · #2 ·
Here's what we found My new scan tool showed no codes at all. I test drove, real-time data, everything looked just fine. SFTF, O2's, loading, all of it.

Had a shop go through my list and have a look, and it was mice.

#4 injector harness wire eaten through, red wire making intermittent contact.
 
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