Misfire #4 cylinder

[Elmer Fudd]

I have a 1996 4.0L V6 pushrod X VIN series 142,000 miles. In response to worse mileage I seem to be getting I replaced the spark plugs and wires maybe 6 months ago. It did not seem to help. I seem to have a small coolant leak. I replaced the radiator and it has continued, so I assume it is in the engine somewhere. I noticed the engine running rough and then got a OBD code for a #4 misfire. It also made a sporadic, faint tinny, kind of a knocking sound, like something on a sheet metal cover. I checked the plugs, wires, and coil. The #4 plug looked fine, although it seemed to have a lot of gunk on the threads (thickened oil?). When I looked at the coil, there was a lot of corrosion in the #4 receptacle and on the spark plug wire connector. The coil tested high for resistance, so I bought a replacement, and new wires. I used the old plugs, they only had 4300 miles on them. Can I replace a single plug?

Still getting the code for #4 misfire. I will replace the plug next and do a compression test. Any thoughts on what it might be?

 

[Dan Whitaker]

It could be a head gasket starting to go. This would explain the coolant loss & misfire.

 

[Elmer Fudd]

just finished the compression test. Per Haynes, cranked each cylinder 4 times and read the pressure. Did a second round putting 3 squirts of oil in each cylinder, which obviously raised the psi..

3 - 155psi/170psi 6-155psi/175psi
2 - 155psi/180psi 5-120psi/140psi
1 - 170psi/180psi 4-155psi/170psi

All the plugs looked normal per the chart, except for #4, which had oil around the threads only, the tip looked good.

Looking at the pressure, #5 looks out of spec, as the instructions that came with the compression test gauge said the cylinders should be within 10% of each other. Anyone have any ideas? This is the first compression check I have ever done.

I guess I will put new plugs in and see if that helps.

 

[Elmer Fudd]

I priced rebuilt engines today - best I found was $2000 at Advanced Auto Parts. I bought one from them a few years ago for a Chevy 1500 and it has performed very well on low mileage since.

I swapped the misfire cylinder spark plug onto another cylinder to see what would happen. The misfire code moved, but to a third cylinder and ran even rougher than before.

I then put new plugs on and used dielectric grease on the plug boots and where they plug into the coil. I test drove it afterward and it ran fine. Hmmm ....

I'm hoping that the problem was me doing a sloppy job when I originally replaced the plugs and wires, and did not get the boot attached properly on #4, then botched it again a few days ago. With the tight fit around the engine it was real hard to tell if the plug boot was all the way seated, and they were very tight. Plus, I did not use dielectric grease. I also bought a spark plug boot wire pliers, which helped a lot tonight, both in getting them off and pushing them back on.

I also noticed how hard it was to get the wire plugs to seat in the coil and latch on. This might have been part of the problem, since I found corrosion in the coil receptacle for the misfiring cylinder. The grease seemed to help them fit.

 

[nolimitssjca]

I replaced the fuel injectors in mine. When I removed them it was clear they were clogged. My knock went away and mile mileage improved about 20%.

If you think about it, your o2 sensors are working on the data they receive which is all 3 in the bank. It averages them and adjust the flow respectively.

The injectors that work get more fuel and the clogged injectors don't respond. The second half of the equation would require replacing the coil pack. Good Luck!

 

[ChriszTruck]

When I went to NJ state inspection last year one of the reasons the truck failed was a cylinder misfire (#6 i think). I figured it was time for plugs and wires, so at the auto parts store I was told the plugs I bought for my old '96 4.0 were factory gapped. According to my Chilton's manual the factory gap on the plugs was WAY off. I gapped according to chilton's, and the engine ran like a top. I'm assuming you checked the gap, but I'm just relaying what happened to me.

 

[Elmer Fudd]

When I went to NJ state inspection last year one of the reasons the truck failed was a cylinder misfire (#6 i think). I figured it was time for plugs and wires, so at the auto parts store I was told the plugs I bought for my old '96 4.0 were factory gapped. According to my Chilton's manual the factory gap on the plugs was WAY off. I gapped according to chilton's, and the engine ran like a top. I'm assuming you checked the gap, but I'm just relaying what happened to me.

Thanks, yeah, the plugs I bought were factory gapped at approximately what the Haynes manual said was correct, .054in. I had to tweak them open a little more with the gauge. I would think plugs are factory gapped for the most common application, but that some cars differ quite a bit from others.

The Explorer is still running smoothly, so I guess my previous post still holds. Now if I could just eliminate the Check Engine OBD code of 141 I keep getting (and posted about) ...