Random Cyl Misfires

[ghettoracer]

Have a 97 EB, took it to get diagnosed for a "tug" at 35mph, 55mph and 65mph. Ran a cylinder misfire check, came back as cyl 1 50 misfires, cyl 2 30 misfires, cyl 3 30 misfires, cyl 4 30 misfires, cyl 5 20 misfires, cyl 6 40 misfires, cyl 7 30 misfires, cyl 8 40 misfires. What can be causing this and what can be done to remedy this problem? Thanks

[ELVATO]

I can't remember, were you the one who replaced all COPs/spark plugs, or only 1?

So many people having these cylinder misfires, it's hard to keep track

[ghettoracer]

Yeah, Im fearing it may be a cat converter that might be clogged but the misfires are on all cylinders.

[ELVATO]

Have you noticed a decrease in engine response? Lower fuel mileage? Does the cat get hotter than normal (I've heard you can sometimes see clogged cats faintly glow from the heat).

[ghettoracer]

yes I have noticed a decrease in engine response but it has this tug kinda like a pulsating at 35mph, 55mph and 65mph. The spark plugs were changed and the the #6 COP was dead and replaced, and the EVAP solenoid vacuum line was replaced cause it was leaking. They changed the fuel filter also but I also noticed that the injectors were ticking really loud. He put in a really strong injector cleaner and ran the misfire test. And thats the result of the misfire test.

[ELVATO]

Misfire test? What is that, hooking up a scanner, and driving around? Did he does this right after the cleaner?

[ghettoracer]

He has one of those expensive Snap-On scanners that does like everything. He drove it around with the scanner but he did add the injector cleaner before he drove around. He said he had it on for about a couple of hours while driving then let it sit for another 2 hours.

[ELVATO]

I see. Just wondering. Well, he's the mechanic, what did he have to say?

[ghettoracer]

Well he thinks its a short in the wiring harness but instead of having him track it down I can give him some suggestions on what it can be.

[ELVATO]

The number of misfires you listed above, was that the total number in the 5+ hours he had the truck on?

[ghettoracer]

The misfires I listed were per hour with the truck running. He drove it for about 2 hours and let it sit at idle for 2 hours after he got back. Its a very random misfire he says. He is going to track it down tomorrow and let me know what it could be. But till then Im stumped.

[ghettoracer]

Ok my truck has been in the shop for 6 days already. His findings:

Cat converters are clear, O2 sensors are good, could be a possible bad head gasket.

Now he threw in new NGK spark plugs, and replaced the #6 COP, fuel filter, ran a strong injector cleaner.

Could it be that the ECM can be bad? There is no coolant in the oil, no hydrocarbons in the expansion tank.

Im leaning towards bad spark plugs. He's going to run a full compression and leak down test but I wont know the results until the end of the day.

This is stumping him as well as me. Thanks.

[ELVATO]

To eliminate spark plugs as the factor, I would have put Motorcrafts in.

[walnuts4x4]

+1 for motorcraft... but I have had good luck with Autolite double Plats...

[ghettoracer]

Ok, after the leakdown and compression test, they determined that there is no head gasket leak, 150PSI on 7 cyl, 100psi on cyl #4. They put in motorcraft spark plugs and it doesnt misfire anymore. Im kinda worried about the #4 cyl tho. Maybe a sticking valve?

[ghettoracer]

UPDATE: The truck is now fixed. Put in Motorcraft spark plugs, found out the #4 cyl COP was bad also. The ground wire from the ECM to the tranny and engine was split because it deteriorated over time. Total cost of all testing, fixing wire, replace #4 COP, fuel filter, fuel injector cleaner, spark plugs: $215. Not bad.

[ELVATO]

Not bad at all.

I forget, did you order new ebay COPs last time, or was this a stock COP that was bad?

If OEM, I would order a couple of the ebay COPs to have as back up since it seems your OEM COPs may be starting to go.

[ghettoracer]

Nah a couple of my COPs went bad. But my mechanic has has spare ones for $30. I guess the wire that went from the engine to the ECU got sliced and caused a short making the truck to run sluggish and hesitate as well as the misfires. Could have killed those COPs so Im lucky it wasnt more than that.