Have a 87 w/ 302, and I'm getting a misfire sometimes. It's not consistent, meaning some days on the same hill at the same temp, it will hiccup, and other days it won't. It seems to happen more once the engine is warmed up, but I'm not sure. It's pretty bad, the tach will drop and the truck will buck when it happens. Sometimes I will also notice a loss in power without the felt "misfire", but not always. Happens mostly while going uphill.

Anyway, genius PO zip tied EVERYTHING. This includes the spark plug wires. I cut the zip ties but the wires are still in pretty close proximity. He has 3 wrapped around the dipstick that I have not cut yet, I need to get some kind of wire holder before I do that one. I read that it's common for certain wires to crossfire with others, but I don't know which one is 1, 2, 3, etc. Any help?

Anyway, no codes on the scanner, nothing changed with seafoam treatment, and not sure what to do next. I'm getting frustrated sinking money into this thing. I know it's PO neglect, but it's getting expensive. Any ideas? He claims he did a recent tuneup, but I'm sure he found some way to fubar that all up too. Does this sound like a possible issue a tune up would fix? Thanks, just looking for options.

 

Back in your era, there was a service letter not a bulletin about the incorrect routing of bank 2, thats cyl 5-8. It would prematurely foul out plugs. Wish I could be of more help.

 

Your cylinder numbers are as follows, standing in front of the truck facing the cab and passenger compartment. Left side is 1234 front to back. Right side is 5678 front to back. what Bill stated above is correct. The 2 and 4 wires can crossfire causing a miss, as well as the 7 and 8 wires. Make sure they are spread a good distance apart. Once you're done, pop the hood one night, start the truck and spray a mist of water onto the cap and wires. If you have a light show, get new wires.

 

Thanks guys, that's what I needed to know. I'll post up in a couple days and let you know what happens.

Does it sound to you like this could be a possibility?

 

Absolutely, it's an extremely common issue and can drive you nuts trying to figure out a misfire.

 

i have the 300 6cyl and it just started hicupping today. it isnt bad but i replaced plugs 4000 miles ago. are the plug wires bad or would it be crossing over also?

 

Best way to check is to mist the wires with water at night, with the truck running and look for a light show.

 

Wanted to follow up. I did a full tune up including cap and wires. Problem actually seemed to get worse. I misted with water tonight, and the light show began. I've already put in separators, but tomorrow I'll go crazy and space off each wire. All the action was close to the cap. Wires were arcing with each other, the intake, and the pick up diode. I'll let you know how it goes.

 

 

Thanks for the diagram. Where are the pickup diodes supposed to go? One is just thrown on top of the wires at the cap, and the other is thrown on top of the alernator. Thanks.