98 4.0 SOHC - Running on 5 Cylinders / Random Misfire - Not plugs, wires, coil, compression, etc.

[cornflakes]

Please help.

I recently acquired a 98 Explorer with 4.0 SOHC. It starts right up every time and drives but seems to be running on 5 cylinders. I got it this way, I unfortunately do not know the details that lead up to this behavior.

The first time I checked codes, it reported a misfire on 1 and 6 with accompanying lean/rich codes. The next day, it reported a misfire on 1, 2, 4, 5.

No coolant issues. Oil smells like gas and it was spitting what seemed like raw gas out of the tailpipe.

I have performed the following in the order listed:

Replaced plugs with Motorcraft dual platinums, all looked good except number 6
Replaced coil pack
Replaced plug wires
Checked fuel pressure, it was good
Checked compression, all good and within 2psi of eachother
Checked for vacuum leaks (spray around method), didn't find any
Replaced IACV
Replaced MAF
Replaced intake manifold gaskets, upper and lower
Replaced fuel injectors with OEM injectors

There has been zero change in behavior from any of these except for maybe a chuffing sound coming from what seems to be near the fire wall on the passenger side. It could have been there before, there was about a 3 week period between the first attempt of repairs and the second half due to ordering parts, getting sent the wrong parts and sorting that out. Nothing seems to change the behavior. I even accidentally wired the driver side plugs in the wrong order and whether in the wrong order or the right order, the engine runs the same.

If anyone has any insight on this I will be eternally grateful, it is driving me bonkers.

 

[koda2000]

As you've replaced all the associated fuel and ignition parts and still have the #6 cyl misfire, have you removed the valve cover to see if the cyl 6 valves are both opening? Having compression is important, but if the valves are not opening you wont get an operational cylinder. Also (and you should do this before removing the valve cover) have you but a noid on the #6 fuel injector to make sure it's getting the electrical signal to open and actually checked for spark on #6? If your not getting an electrical signal to the #6 FI or spark on the #6 plug try re-seating the PCM connector and the large electrical connector over the valve cover.

 

[974X4BLACKSPORT]

Please help.

I recently acquired a 98 Explorer with 4.0 SOHC. It starts right up every time and drives but seems to be running on 5 cylinders. I got it this way, I unfortunately do not know the details that lead up to this behavior.

The first time I checked codes, it reported a misfire on 1 and 6 with accompanying lean/rich codes. The next day, it reported a misfire on 1, 2, 4, 5.

No coolant issues. Oil smells like gas and it was spitting what seemed like raw gas out of the tailpipe.

I have performed the following in the order listed:

Replaced plugs with Motorcraft dual platinums, all looked good except number 6
Replaced coil pack
Replaced plug wires
Checked fuel pressure, it was good
Checked compression, all good and within 2psi of eachother
Checked for vacuum leaks (spray around method), didn't find any
Replaced IACV
Replaced MAF
Replaced intake manifold gaskets, upper and lower
Replaced fuel injectors with OEM injectors

There has been zero change in behavior from any of these except for maybe a chuffing sound coming from what seems to be near the fire wall on the passenger side. It could have been there before, there was about a 3 week period between the first attempt of repairs and the second half due to ordering parts, getting sent the wrong parts and sorting that out. Nothing seems to change the behavior. I even accidentally wired the driver side plugs in the wrong order and whether in the wrong order or the right order, the engine runs the same.

If anyone has any insight on this I will be eternally grateful, it is driving me bonkers.

Are you sure the gas you see out the tailpipe is not just water?

 

[RandomNerd2000]

I have to agree with Koda, check your wiring, you can take an extra spark plug and hook it to the wire and rest it on the frame to check for spark, just don't touch it. Check the injector for power and ground too since either will cause a problem.

 

[cornflakes]

Thanks for the responses!

I did not remove the valve cover. I had checked vaccuum which was low (reason for replacing seals) but it didn't pulse like I thought it might if there was a valve problem. I could be totally off base there.

I checked all plug wires at the plug end with a spark tester

I did not check for power at the injectors, I will do that. Originally we thought it was getting too much. After running for a short bit, there is a strong fuel smell under the hood. It has a lean code on one bank, rich code on the other bank.

It does have some water at the tailpipe on cold start but every Ford I have owned does that, it was my belief it was just condensation. There is zero coolant loss and no oil in coolant or coolant in oil. I suspected fuel because it smelled very strongly of raw fuel.

 

[RandomNerd2000]

I do think if your vacuum isn't bouncing, if memory serves that means no bad valves, not sure if one not opening would cause the vacuum to not bounce though. If you've got spark, there's the possibility it's an injector wiring fault. One question though, have you pinpointed the cylinder that's affected?