Misfiring and Troubleshooting?

[hefftone]

1990 TBI

A week ago my truck started running really bad, rough, and low on power. Eventually it cleared up, i thought maybe it had something to do with how cold it was that morning.
Then it started to run progressively worse over the next few days. I discovered the Passenger side TBI injector was leaking. I took it apart and replaced the upper o-ring.
No more leak, it is running better but there is still a significant roughness and power loss....with some popping and stuttering especially under load. Feels like it is running on 6 or 7 cylinders under load.

I feel confident in the fuel system, as I've replaced the entire fuel tank, pump, sender, and filter and rebuilt the TBI in the recent past.

I can hear what sounds like a missfire in my exhaust, even at idle. But I'm not sure how to find it. I pulled spark plugs #2 and #4 and they looked nice...no carbon build up. No CEL at the moment.

Not sure how to diagnose this one, please help.

 

[96Z71ECSB]

If your satisfied with the fuel system, start looking at the ignition system.
Look at the cap, rotor, spark plug wires, and spark plugs.
Make sure the spark plug wires are not touching anything. including themselves. They should be mounted in looms and separated.
If the wires are touching anything, check the contact point for wear or a white residue. That's usually a sign of arcing. Sometimes you can actually hear them arc (snapping sound) while the engine is running.
When in doubt, replace.

 

[John Deere 4240]

If your satisfied with the fuel system, start looking at the ignition system.
Look at the cap, rotor, spark plug wires, and spark plugs.
Make sure the spark plug wires are not touching anything. including themselves. They should be mounted in looms and separated.
If the wires are touching anything, check the contact point for wear or a white residue. That's usually a sign of arcing. Sometimes you can actually hear them arc (snapping sound) while the engine is running.
When in doubt, replace.

I agree, mine did that bout a month ago. The rotor screws were rusted, the blade was warped from arching and the points on the cap were chalky white. There were no leaks but have come to the conclusion that spiders build nests it the breather holes and they get clogged which leads to trapping moisture.

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[dowsewashere]

Ignition and or timing. Plus make sure your plugs are in the right firing order.

 

[John Deere 4240]

Ignition and or timing. Plus make sure your plugs are in the right firing order.

It was running right and only pulled off 2 wires so I'd maybe lean to the timing

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[hefftone]

Popped of the distributor cap...the terminals inside feel dimpled in and has some crusty corrosion which I scraped off with my finger nail. The output terminal on the coil is chalky white with corrosion.

I'll clean all that crap off and see if it runs any different....will probably order new cap/rotor anyway. Going to ohm test the plug wires too (new looking Delco 8mm)

Wondering which distributor cap to get....saw a Delphi for about $14 the AC Delco is $21.....they both have aluminum terminals... There is a Standard and a Airtex/Wells with brass terminals they are only a few bucks more. Any advice?

 

[John Deere 4240]

I went with heavy duty cap and rotor, then put in acdelco 10mm Spiro-wound plug wires

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[hefftone]

Figured it out.

After Ohm testing all the plug wires, only the #5 wire was bad. That terminal on the cap was also a little more corroded.

The diz cap terminals on the bottom were in terrible shape. New BWD brass cap, rotor, and spark plug wires solved it.

I am having an issue with that same injector pod started to leak again. I need some kind of sealant that is gasoline resistant!!!!

 

[michael hurd]

Did you use new gaskets? Seal-all is gasoline resistant.

 

[TerryKing]

Old Trick: Look at the plug wires with engine idling in TOTAL Darkness with your eyes adjusted. Often you can see any arcing...