Ok guys im seriously scratching my head. My pick up coil went out on my 4.3 tbi. I replaced it and in the process through the timing off. Long story short I just got tired of never having time to work on it so I took it to a mechanic. Put a whole new distributor in and now it runs like a top...until it gets warm,then it cuts itself off. The mechanic told me it was the computer so I went and got it and put new ECU in and it cranks but seems like the timing is off. So my question is after all that could I be accurate with blaming the timing or is there a sensor malfunction or something else to blame.

 

Extremely rare for the ECM to fail on these things. They usually tell you that when they don't have a clue what the problem is, and try to scare you out the door. That's about the only time they get replaced, or, on a misdiagnosis


Some of the older ECM's had a chip that you had to swap from the original ECM to the new ECM. Can't remember if 89 had the chip or not. Pull the coil wire out of the distributor and check for injectors squirting fuel, and for spark while cranking. Needs to jump a half inch gap to ground with a blue, not orange, spark. The EST wire must be disconnected to set base timing on your vehicle. Behind the top of the carpet, above the passengers feet. Single wire, unplug the connector and check/adjust ignition timing, and reconnect the EST wire. Post your results.

 

Ill agree that its rare for it to go out but something is shutting it down after it gets to opperating temperature. While idling it has three or four different speeds if that makes sense. Basically it'll idle high for a minute then seem to even out then go low for a minute and come back even again and so on. At this point I'm stumped and dont have a lot of spare time,which is why I took it to the mechanic to start with. It really isnt making any sense to me right now

 

It does have the prom chip and im going to assume the wire you speak of is an orange wire? While I was replacing the ecu today I noticed a white box bolted to it with two pig tails,one with just one orange wire. Its important to note that I just had similiar problems with the ecu in my 87 2.8 s10 and had to replace it,but it didnt have the white box I just mentioned. But I got a steal on it at 35 bucks on ebay! Which is why I went with the suggestion to start with because for that price I couldn't pass it up,and will probably need it later on any way. But my main question is if the timing was set with that wire before mentioned still connected would it cause the problem im having now? If so how can I correct it?

 

If the timing is set with the EST wire connected, ignition timing will be ~20 degrees late, and that's a huge problem. IIRC the wire is tan with a black trace. Should be a white "VECI" decal under the hood that instructs to disconnect it, and what timing should be adjusted to.

 

Yea I don't have that decal under my hood. And the only connector I remember seeing under my carpet is the one I described yesterday that was running into a white box screwed down to the metal harness that houses the ecm under dash. Im just going to assume theyre thr same wire and my color description of it was jut off due to not paying attention. And if everything we are discussing is spot on then I'm going to assume,and pray,that if I disconnect the wire and reset the timing that it should solve the problem. But one more question if you dont mind, if the timing is off 20° like we discussed would it cause the issue im having now of erratic idling until operation temp is reached and then shut off? Thanks so much for your help brother,you're a life safer.

 

Yank the carpet back, sometimes the wire falls down a ways. Pretty sure it's tan with a black trace, and only that wire is in the harness... maybe 18 gauge wire, quite small.


Incorrect timing will cause problems, no doubt. When the engine is first started, the ECM operates in open loop and the oxygen sensor data is ignored. It applies a "given" set of adjustments to injectors, timing etc. When the ECM switches to closed loop, oxygen sensor data is used for fuel mixture and ignition timing will change as necessary. Several different things determine when the ECM switches to closed loop, and when it does, you can notice changes in how the engine runs immediately.

 

Ok then,any idea what that wire/harness is called? Only reason I ask because I just recently restored this vehicle and I litteraly I had everything ripped out of it because I replaced the carpet and ran all new wires to the speakers. The only harness I recall was around the seat.

 

No clue what harness it is, but you can run a new wire. Goes from the ECM to the ignition module. With it unplugged the ignition module applies base timing. When it's plugged in, the ECM sends a modified pulse that includes ignition timing advance. It overrides the ignition module base time pulse as soon as it's connected. Let me know the year and the 8th character in the VIN, and I'll figure out what pins you'll need.

 

So can I just unplug the ignition coil and get the same affect? The year is a 1989 and I'll get you the vin tomorrow. Thanks