1999 Ranger XLT, 4L. 4WD. My engine appears to be missing and intermittently jerks. Starts fine. No check engine light, no codes on a scan, however they can see up to 3,000 misses on #4 cylinder in the history. New plugs, new coil pack, newer plug wires. They ran c-foam through the gas tank and in the intake. The truck is now unreliable. I can find no correlation such as fuel, engine temperature, throttle opening, etc. It does appear to happen under a load (on gentle hills) . Driving to town it may or may not jerk. Some days it acts up and sometimes it doesn't. Occasionally it feels like it "clears its throat", pulls strong, and quits jerking, only to start messing up again.

It would be nice to trust a vehicle for a change.

Any thoughts?
Frustrated and going broke- ggrrrrr,
Thanks...

 

Best to do a compression test on cold engine at this point, to either take compression issue off the table or find out it is a compression issue so not spark or fuel

Remove all 6 spark plugs first
Then test compression on each cylinder and write down results
Expected for 4.0l OHV engine is 150psi, but actual number is not what you are after
You are after differences
Say 5 cylinders are at 135-145psi and one is at 115psi
That one cylinder is the issue, the misfire, usually a burnt exhaust valve

You can put a teaspoon of oil in that low cylinder and retest, if compression doesn't come up to 140psi(in this example) then it is a Valve issue not rings

 

thanks !!!