Missing under load?

[David in NC]

My 97 XLT has developed a miss under load on the left bank (driver side) of cylinders of my 4.0 pushrod engine. The Autolite Professional wires and Double Platinum plugs were new a couple of months ago and the coil pack was swapped with my 99, so I don't think any of those are at fault. Any suggestions where to look next? Thanks, David

 

[marragtop]

Make sure that one of the wires isn't laying on the exhaust manifold, which could of damaged the wire. If not, you need to isolate the problem to which cylinder/wire/plug is the problem. Also, pull the codes as they may reveal something.

 

[jamester_a]

Bad plug, bad wire, or bad connection are the common culprits. For starters pull the plug wires one by one looking for arc spots, corrosion (it can ocur faster than you think depending on climate) or poor fit at both the plug end and the coil end, clean the plug boots, then re-seat. If that is not it, pull the plugs one by one and inspect. If that's not it, do a basic resistance test on the wires with an ohm meter - (should be about 5-8K resistance per foot with Motorcraft wires anyway, perhaps less with your Autolites) - regardless all wires should be close with proportianlly greater resistance for the longer wires.

How does it idle?

- James

My 97 XLT has developed a miss under load on the left bank (driver side) of cylinders of my 4.0 pushrod engine. The Autolite Professional wires and Double Platinum plugs were new a couple of months ago and the coil pack was swapped with my 99, so I don't think any of those are at fault. Any suggestions where to look next? Thanks, David

 

[David in NC]

There are no codes. It seems to idle well, but my mechanic hears a slight miss.
The middle wire on the driver's side hopped off while my son was driving last week. I pushed it back on. Maybe that fouled it. I'll check. Anything else I should look for? Thanks

 

[marragtop]

If the wire was off, make sure it get burnt laying on the manifold.