1993 instant misfire-much white gassy smoke-1993 89661-60220 ECM questions.

[baldilocks]

I just finished installing the upper plenum and throttle body after replacing all vacuum hoses and coolant bypass hoses and cleaning the throttle body. She started right up, ran well and I was very happy to see that the super high cold idle was also no longer present.

About ten minutes later, at 135 degrees coolant temp, what sounded like a single cylinder misfire hit, was very pronounced and consistent with every power stroke. It rev’d fine but I could still feel the misfire. Then I noticed the garage was filling with a gassy smelling fog. The puddle of condensation beneath the tail pipe also smelled strongly of gas. I cut it off and after the smoke cleared I tried to start it and it wouldn’t even try to fire. At this point dinner was ready.

While eating I thought about this while my wife talked about something and it came to me that my 1993 still has the original, supposedly, problematic ECM. After I ate I went out and sure enough no CEL with key on.

I find it very perplexing as to how it was running fine except for a definite and complete misfire on what sounded like one cylinder but after shutting it off there is no CEL with key on.

Has anyone experience with one of these 1993 89661-60220 ecm’s going bad? What happened when yours crapped out? Do they all basically have the same defect that causes them to be more problematic that the later -60221?

 

[Shoredreamer]

Truck was running fine before you pulled the plenum and TB? Thru my search I haven’t found anybody on here that was stranded or had a 60220 ECM fail on them. Only the known 83,84,85 cel codes that wouldn’t go away.

 

[BILT4ME]

Could have shorted and injector wire with harness near EGR after manhandling the harness on that work?

Dumping fuel into the cylinder (or all of them).....

Just a thought possibly....

 

[baldilocks]

The engine was running great prior to this work. I didn’t touch the wire harness at all and even if I had compromised the harness at one Injector that would not account for the lack of a CEL with the key ON after warming it up and shutting it down. All fuses are good.

After putting it all back together it started normally and ran normally for ten or maybe more minutes then suddenly the misfire accompanied by the gas smelling fog happened. I shut it down and a while later it wouldn’t even try to fire on any cylinder and the CEL is not present with key on. This is where I’m at now. I have read about the -60220 being problematic somewhere on here.

This morning I’m going to look into how to check the ECM but won’t spend too much time on it because I have two spare -60221 ecm’s.

Truck was running fine before you pulled the plenum and TB? Thru my search I haven’t found anybody on here that was stranded or had a 60220 ECM fail on them. Only the known 83,84,85 cel codes that wouldn’t go away.

Could have shorted and injector wire with harness near EGR after manhandling the harness on that work?

Dumping fuel into the cylinder (or all of them).....

Just a thought possibly....

 

[inkpot]

check the wiring connector that is mounted on the bottom of the power steering reservoir bracket. It is a 3 pin socket, but only one wire in it. It is the main power supply to the ECM. Mine corroded badly and eventually killed my motor. NO CE light.

 

[baldilocks]

check the wiring connector that is mounted on the bottom of the power steering reservoir bracket. It is a 3 pin socket, but only one wire in it. It is the main power supply to the ECM. Mine corroded badly and eventually killed my motor. NO CE light.

That connector is in good shape. I slaved in one of my spare ecm’s with no change. I’ve verified the ECM is receiving 12v. While I had the plenum off I did put a little wrap on the bend in the engine harness where wires were not wrapped but all the wires I could see looked good.

If the engine was still suffering from just the misfire that hit instantly yesterday I would be suspecting that I upset an old injury in the harness but that’s not the case. It’s the no CEL that has me scratching my head plus the fact it won’t even try



I removed the fusible links and put my meter to them. The red one with barrel connector had no continuity. These are about three years old. I swapped in the old set, which tested all good and still no change. That barrel connector does not feed power to the ECM.

does the engine harness near the egr pipe contain any wires that could, if compromised cause the CEL failure to illuminate with the key ON?

 

[ZackR]

If the engine was still suffering from just the misfire that hit instantly yesterday I would be suspecting that I upset an old injury in the harness but that’s not the case. It’s the no CEL that has me scratching my head plus the fact it won’t even try

does the engine harness near the egr pipe contain any wires that could, if compromised cause the CEL failure to illuminate with the key ON?

A few years back I spent a ton of time chasing a bad misfire on my 94' and it ended up being a short in the wiring harness by the EGR. It never threw any codes or activated the CEL which made troubleshooting a lot harder. I looked at the FSM and there are no codes specific to misfire like you would find on a newer vehicle (for example, misfire on cyl 2).

 

[BILT4ME]

Also, pull your spark plugs to make sure they all look fuel fouled, as I would expect them to be with this issue. They may need to be cleaned and dried out if they are heavily fuel fouled.



Also to make sure they are not wet with coolant.......

 

[baldilocks]

A few years back I spent a ton of time chasing a bad misfire on my 94' and it ended up being a short in the wiring harness by the EGR. It never threw any codes or activated the CEL which made troubleshooting a lot harder. I looked at the FSM and there are no codes specific to misfire like you would find on a newer vehicle (for example, misfire on cyl 2).

I wish a misfire was my only problem here. The big problem right now is, why is my CEL not lighting up when I turn the key to ON. I will deal with the misfire once I get it to start again.

What wire(s) or single connection or component could cause the running problem described above and then after shutting the engine down lead to no CEL with key ON and cranking with zero ignition when it was just running, if a little rough, just minutes earlier. Again, I shut the engine down when my garage filled with raw fuel, it did not die on its own.

 

[BILT4ME]

Loss of an ignition coil would do this if I recall reading other threads correctly. Maybe do the FSM check on the coil?

 

[fjbj40]

So are you saying you have no spark? Sorry, it’s not clear.
I’m sure you checked but do you have fuel pressure?. I doubt it’s the computer if it was just one particular cylinder misfiring.
None of the injector connectors were removed as you only did the upper plenum? I know cylinder 4 harness makes a sharp
bend off the main bundle. But this should not stop it from starting.
I think fuel delivery.

 

[baldilocks]

I’ve smoked two AM2 fusible links, the red one that has the single pin connector since this problem began. I got another set of FL from the dealer but don’t want to put them in until I figure out why AM2 is burning. Both AM2 connectors had that burnt electrical smell. The male on the chassis side cleaned up well and looks ok. There is no short to ground on the big white/red wire the AM2 fusible link plugs into.

I can’t be any more clear fella’s. I started it up yesterday after engine work, it ran well for 10-15 minutes then developed a complete misfire that appeared to be due to an injector that hung open, I shut it off. That’s the simple part.

Half an hour later the CEL is absent with key ON and now (the next day) I discover that it’s burning AM2 fusible links. All fuses are good. The ECM has 12v at the BATT pin.

I haven’t been forced to become good at reading the wire diagram yet and the info provided about the diagarams in the fsm leaves some unanswered questions.

 

[Tireguy87]

A MAF sensor (AFM on OBD1 trucks) fault will cause a no CEL with the key on. From reading through your thread it doesn’t look like you messed with it, but you might want to check and make sure it’s plugged in. You can also check continuity by metering the plug while manually operating the door or flap inside. You’ll have to unbolt it from the air filter housing lid to do that. Just don’t unscrew the plug from the body of the AFM housing. That will break the soldered connections inside and you’ll be looking for a replacement.

 

[baldilocks]

Loss of an ignition coil would do this if I recall reading other threads correctly. Maybe do the FSM check on the coil?

Factory spec max resistance across the pos and neg terminals of the coil is .55 ohms on a cold coil. My cheap meter shows exactly 1.0 ohm on my installed coil and my spare oil. I’ll go with that.

I think I’m going to have to remove the plenum to retrace my tracks and possibly go a bit deeper and just swap in the new engine harness that’s on my spare engine and has only a few months of use. It’s hard to spend a lot of time trouble shooting when I already have a lot of extra parts.

 

[baldilocks]

A MAF sensor (AFM on OBD1 trucks) fault will cause a no CEL with the key on. From reading through your thread it doesn’t look like you messed with it, but you might want to check and make sure it’s plugged in. You can also check continuity by metering the plug while manually operating the door or flap inside. You’ll have to unbolt it from the air filter housing lid to do that. Just don’t unscrew the plug from the body of the AFM housing. That will break the soldered connections inside and you’ll be looking for a replacement.

I wrecked an MAF a few years ago so I’m up to speed on the screws. Yesterday, when I reconnected the MAF connector I cleaned it with electrical contact cleaner, a toothbrush and compressed air. I have been wondering if fluid got inside somehow so I did do the “on the vehicle” resistance checks and they were good. Tomorrow I will remove it and do the other checks with the measuring plate (flapper).

Right now my first problem is why I smoked two AM2 fusible links, this 80 spent over 20 years in the high desert where its dry. The lecteical system is very clean and hasn’t given me any trouble in the four years I’ve owned it.

 

[baldilocks]

Yesterday it was determined that fusible link AM2 blew twice , which would cause a failure of the CEL to illuminate with the key in ON position.

Today I isolated the ECM from the harness and a check with an ohm meter showed 1.5ohms from the AM2 chassis side connector to ground and a jumper wire from the battery + terminal to the same connector produced a hot alligator clip on jumper wire accompanied by the undeniable confirmation of smoke. This happens only with key ON.

This combined with the fuel injector that became instantly and permanently stuck open causing a single cylinder misfire and a gassy smelling fog to fill my garage two days ago has me thinking that I upset the old engine harness when I wrapped a short section near the egr pipe and then secured that wrap with zip ties.

I will begin tearing it down to the head for harness and injector replacement.

 

[Kay9Cop]

Running fine for 10-15 minutes sounds like just long enough for the engine to get hot and melt through some wire covering. I would suspect a short some where.

 

[fjbj40]

If after maintenance something is not working properly I often ask people”what did you do” they tell me and I say “undo what you did or go back to where you were working”.
You are probably going to find your problem when you go back!

I think I remember you asking me what I think made my high idle go away and my engine run so smoothly after all my work. I also forgot to say I had my injectors tested, cleaned and flow checked.

I would do the same with your injectors vs replacing them.

 

[baldilocks]

@fjbj40
My confusion about why the check engine light was also not coming on with key ON was cleared up when I realized the wire from the ignition switch to the ECM is in the same fat loom with the injector wires that runs beside the EGR pipe and was probably just collateral damage.

I was happy to find that my cold start high idle was about 400 rpm lower after the recent work also.

I have a complete spare engine and the six injectors on it were sent to RC engineering in SO. CA exactly 5 years ago to the day. I know this because i called them this morning to ask if they thought those injectors, which have not ran in 3+ years might need cleaning before use. They said to send them in and they would not charge me for a simple cleaning because of history with them.

 

[LC4LIFE]

I had a rig misfire similarly to that after the #6 spark plug tube got some water down in it. It took lots of brain damage and troubleshooting. I was also surprised how such a small amount of water was causing the misfire. No CEL or anything else odd, just a misfire. Did you happen to get it wet back there during your work?