My 88 c1500 w/ 5.7 misses under load. Plugs and wires are new. what else could cause this?

 

Is it carb'ed?

 

Do a compression test.

Allan

 

Throttle body injection. Truck has 318,000 miles on it. Original coil(could this be the culpret?). I rebuilt engine at 152,000. Don't remember if I replaced distributor cap. Plan on checking it out. Just drove the truck this morning and it ran fine for a while(two legs of about 3 miles) but when backing it in driveway it started missing.....somewhat of a different deal since it wasn't really under load. Guess I will have to do a compression check. Real pain with the headers I have on it! Another piece of puzzle, MAP sensor is only 8000 mi. old. Was told by a mechanic that MAP and trottle position sensor are only 2 sensors that affect the way it runs under load. Can a MAP go bad that quick?

 

What you are describing sounds like fuel schedule, but that usually is a problem from the git go. However, electronics can do goofy things when the heat up. The map sensor, was it new, and not el cheapo?

 

How long has it been since you replaced the fuel filter?? My 97 silverado 5.7 did this and I replaced the filter and it runs great now