Intermittent CEL!

[tpham32]

I haven't have too much time to dive in and diagnose this problem on the 80, but for the past week I have been noticing some intermittent rough idling and intermittent check engine light. I was going to see if you guys have had this problem before.

So what's happening?

On some days without the check engine light, I will notice a rough idle. The needle will probably fluctuate about 200 rpms and I have never seen my exhaust down pipe shake so much. I have not noticed a difference while driving it. No power loss whatsoever.

Then there are times when my CEL comes on. When I read the codes with my Torque app, I am getting 2 codes for the O2 sensor for bank 1, and 7 other codes for cylinder misfire (1 random misfire, and 1 misfire for each cylinder). Again, no noticeable power loss.

When I get some more time, I will try verifying the codes with a better scanner and check my dizzy cap, plugs, and wires.

Anything else I should look for?

 

[mtweller]

When's the last time you replaced the dizzy cap, rotor, and wires? You play in the mud a lot - could be some corrosion on the rotor/cap causing an intermittent misfire. That's where I'd start!

 

[tpham32]

It was probably around 90k when I did a tune-up. I am at 140k now. Lol, I haven't messed with mud in a long time. Like today on lunch break, no CEL, and no rough idle. I figured if I was in need of a tune-up, the problems would be more consistent but I could definitely be wrong.

 

[JohnVee]

I forget the code I get but I have the same symptoms on my 94. Rich, I think.


...via IH8MUD app

 

[GLTHFJ60]

Both John and Thomas' trucks are stock (aside from armor + lifts) right?

I'm with Ramon on attributing random misfires to an ignition problem. You can easily take the cap off of the dizzy and inspect the cap contacts as well as the rotor for abnormal wear / shorts.

Did you replace the spark plug wires at 90k or just plugs/cap/rotor? It may also be prudent to test the spark plug wires if there is a procedure in the FSM.

 

[S.CarolinaFZJ80]

Pham - I had the same codes for the O2 sensor(s) last week. I just replaced them like 5,000 miles ago ie 4 years ago trying to cure a rich mixture that wasn't throwing codes. I Haven't thrown the codes again since I reset them though, probably haven't driven it enough.

I replaced the Idle Sensor years ago due tryin to trouble shoot a rough idle. I also cleaned and eventually replaced the MAF sensor but what finally worked was cleaning out the throttle body and upper intake plenum from all the EGR exhaust gas crude mixed in with oil that formed an asphalt like residue all throughout the TB and intake.

It was blocking just about every vacuum port and orafice. After cleaning it out, no more rough idle. I used a lot of throttle body cleaner, old coat hangar & pipe cleaners to get the crud out. Jam some towels attached to a string far into the intake to block any of that crud from getting down into the engine. Then just pull it out when finished cleaning.

Hope that helps. Good luck.

Oh & times 2 on checking the distributor, plugs, wires and engine wire harness by the EGR.

 

[tpham32]

Pham - I had the same codes for the O2 sensor(s) last week. I just replaced them like 5,000 miles ago ie 4 years ago trying to cure a rich mixture that wasn't throwing codes. I Haven't thrown the codes again since I reset them though, probably haven't driven it enough.

I replaced the Idle Sensor years ago due tryin to trouble shoot a rough idle. I also cleaned and eventually replaced the MAF sensor but what finally worked was cleaning out the throttle body and upper intake plenum from all the EGR exhaust gas crude mixed in with oil that formed an asphalt like residue all throughout the TB and intake.

It was blocking just about every vacuum port and orafice. After cleaning it out, no more rough idle. I used a lot of throttle body cleaner, old coat hangar & pipe cleaners to get the crud out. Jam some towels attached to a string far into the intake to block any of that crud from getting down into the engine. Then just pull it out when finished cleaning.

Hope that helps. Good luck.

Oh & times 2 on checking the distributor, plugs, wires and engine wire harness by the EGR.

Thanks! Did you say that you used to live in Highland Park?

Both John and Thomas' trucks are stock (aside from armor + lifts) right?

I'm with Ramon on attributing random misfires to an ignition problem. You can easily take the cap off of the dizzy and inspect the cap contacts as well as the rotor for abnormal wear / shorts.

Did you replace the spark plug wires at 90k or just plugs/cap/rotor? It may also be prudent to test the spark plug wires if there is a procedure in the FSM.

Yes, the motor is stock. I replaced the wires, plugs and cleaned the dizzy cap and rotor.

 

[mtweller]

And the problem is still there?

 

[tpham32]

And the problem is still there?

Oh sorry Michael, I was answering Johnny's question. I haven't done anything to it yet. The O2 sensor is always a pending CEL code on my reader regardless of the CEL being on or off so I am going to replace it first and see what happens.

 

[tpham32]

Case closed. I was missing two screws for my dizzy cap which allowed gunk to get inside. Swapped new rotor, cap, and o-ring and shes back to purring. I still haven't got the CEL for the O2 sensors yet, but I have them on hand just in case. Both Denso sensors for less than $100 off of Amazon.