My 99 is misfiring need help!

[latigo1]

Haven't been on here in a while because of family issues. I really need some help. This is my problem: Brought the Expy down to get a sticker and was told they couldn't read the computer. Said the reason was probably a blown ciggarette lighter fuse. I had a 20 amp fuse at home and put it in. Punched in the lighter and the fuse blew. I didn't have another 20 so I put in a 30. Didn't try the lighter and went back for the inspection.

They were able to read the computer and I got the sticker. On the way home which is only 2 miles the truck started running rough and the CEL came on. I turned around and went back. They hooked it up and said it was misfiring on the 6 and 8. I would have to bring back in to be checked next week.

I have a friend who is a Mechanic and he said it was probably the coil pack. He took it in and replaced the coil pack and it ran fine for about 5 miles, then it started missing again and the CEL came back on. He also said he checked and changed the plugs. Does anybody have any idea what might have gone wrong? It has been running smooth and fine for the last year. I'mbeginning to think I did something by putting a 30 amp fuse in. I just figured the lighter was shot because I smoke and use the lighter a lot.

Any ideas would be greatly appreciated! By the way it's a 4.6 motor

Thank you.

 

[stamp11127]

Read the codes again. Putting in a larger than rated fuse only allows for a higher draw on the circuit than it was designed for. Worse case scenario then is a fire.

 

[Shadowless127]

I doubt the bigger fuse has anything to do with it. I'm assuming your mechanic checked the condition of your spark plug wires and COPs?

 

[latigo1]

Mechanic checked everything so far. Now it is just the #6 cylinder. It is dumping fuel into that cylinder and is not burning it. Have done a compression test and it has 150 lbs. in that cylinder. Tried a new spark plug and wire. Also changed the coil pack. #6 plug has spark also. #6 injector had a noid light hooked up and it is pulsing. And last they tried a new injector.

Fuel pressure is holding 40 lbs. for a more than a minute.
The Cam sensor and the Crank sensor were also checked.

Any ideas? Could it be the PCM?

 

[paul_smith_347]

I don't know anything about the computer systems, but here are a few other things you can check. First make sure that the area is dry. It doesn't take very much moisture in the spark plug bore for them to short out. Have you ever had to add power steering fluid? the reservoir sits right up there above five and six, and this could be your moisture problem. Other than that, check out the connector where the COP hooks into the wiring harness. Last time I did plugs I managed to somehow break one of the pins off. I replaced the end and problem solved. Sounds like the problem is in the COP system. Maybe try swaping five and six COP and see if the misfire moves to five, or still is number six misfire. This will tell you if the COP is good. Just because its new, doesn't mean it isn't bad.