misfire under load

[waltru]

Hi there,

My '95 mtx has a random misfire that occurs only under load in higher gears at mid to full throttle. The misfire is not present if I keep to 1/4 throttle or less. No oil in plug wells, only code found is 542 in non volatile memory during KOEO test. Any ideas?

 

[kmetros]

There is a stud that goes into the rear passenger side of the head - it has two purposes - one is to hold the bottom of the intake support bracket in place, the second is to ground the engine. There should be a ground strap coming off of that stud. The end of the stud can wear into the wiring harness that runs along the firewall. If the stud has worn through the covering on the wiring harness it'll runs fine at speed, but when you get on it and the engine torques, the stud pushes into the wiring loom, causing a short and some stumbling. Don't ask me how I know this. Let's just say that on all of the SHO's I've owned I put a vacuum plug over the end of that stud to keep it from chafing the wiring harness. If you're not getting any other codes, that's something quick and easy to check....well, maybe not that easy, but if that's your problem you will see a hole in the covering of the wiring harness created by the stud. At least it's a cheap fix!

 

[sdpatt]

A misfire without any directed codes is usually attributable to plugs and/or wires.

 

[1993MTXSHO]

A misfire without any directed codes is usually attributable to plugs and/or wires.

second that

 

[waltru]

Problem solved, thanks guys. Plug wires were the prob.

Wally