Hey folks, Not too sure, but I think I may have cracked the porcelain on the passenger side middle or rear plug while doing a tune up. This is the 4.0 SOHC and, as you probably already know, those two particular plugs are quite difficult to get to. I also changed out the wires and coil pack. Before I did them, I replaced all four catalytic converters & 3 new Bosch oxy sensors. I ran the truck after the cat change and it had a ton more power! I think I was running lean on the right bank beforehand, which I believe led to the demise of the stock cat's, so I did the tune-up just in case there was a ignition problem. I now have high quality stainless cat's and as mentioned, all new oxy sensors, new plugs, wires and coil pack, also cleaned the MAF sensor with CFC. After installing the last item (plugs) I started it up only to hear (and feel) what appears to be a missfire, also smell fresh gas (running rich) so I'm thinking I may have inadvertently crossed a couple wire's or possibly cracked the porcelain on one or more of the pass. side plugs. After I finished, I didn't let it run long enough to trigger a light but it most likely would have. I do not look forward to having to pull the inner fender plastics again and redo the right side plugs over. I know that it's no big deal for most folks, but my problem is that I have a 1 year old son and I can only work on the truck between his naps, which are usually short lived! I also used an older spark plug socket with no protective rubber insert which could possibly have led to a cracked plug. I don't have a scanner so I can't narrow it down to a specific cylinder. I'd also like to see a wiring diagram for the coil pack/plug wires so I can be sure I got them in the right spot's but I can't seem to find a definitive diagram online for the 4.0 SOHC. Any thoughts would be greatly appreciated. The truck is basically stock, except for a Super chip, K&N air intake coupled with a Granatelli MAF and a stainless Bassani Aft cat exhaust.

 

Sorry! I noticed that there was a 4.0 Tech column AFTER I posted this here.

 

Yep, sounds like you have mixed up the wire sequence when putting them back on the plugs. (Either that or your gap is way off on the spark plug).

 

Na, neither, it actually turned out to be broken porcelain on the right side center spark plug. I used an old socket without the rubber protector inside it. The wiring was actually correct.