So I have a 1227302 ECM in a 1986 camaro V6 2.8. Im having an issue with the EST circuit. The ECM is sending a far advanced timing signal. Does anyone know what the ECM looks at in order to advance the timing. Ive tried 2 ECM's in order to rule out the ECM.

 

Do you have the timing set at 10* before top dead center ? The ECM gets its signal from the ignition module unless you have the EST wire unplugged to time it .

 

Ya my timing is all set. I replaced everything and still have the issue. the car doesn't start with the EST bypass wire plugged in. As soon as I unplug the EST bypass wire it runs fine. Im just trying to figure out why the car doesn't run in EST mode. Something is causing the ECM to run the wrong signal.

 

Check the pickup coil and module . I would say that one or both may be causeing the problem or you have a plug wire to close to the EST wire causeing interference .

 

Ya i went through all that. I have another post under V6. I posted here to see if anyone knows what modifies the signal that is received from the Dizzy. But I will look at the plug wires being to close, that makes some sensor there.

 

If you have tried different ECM's and no change then it has to be the dist. or a plug wire to close to the EST wire affecting the signal .

 

ya new dizzy, ICM, load tested all the wires ok. THat's why im thinking there is got to be a sensor telling the ecm to either retard or advance the signal too far

 

Just for kicks have you tried to start it with the EST plugged in and unplugging the coolant sensor for the ECM ?

 

No change still won't start well kinda starts and stops as it blow smoke out intake

 

What is your TPS set at ? It could be off causing the problem . Check the voltage and see . If you have everything hooked up can you start it by giving it a little gas ?

 

no car doesn't run if you give it a little gas it starts for a sec then blows smoke out intake.

 

Sounds like it is advanced to far or the distributor is 180* out . Did you make shure you were on tdc #1 when you replaced the dist and not #4 because it will run the other way but not good .

 

Ya i got it set right. THe car runs great no issues with the bypass wire unplugged

 

Just to help out. The ECM uses a load variable based on RPM & airflow (MAF) to set the main spark timing. This is further tweaked by the engine coolant temperature (CTS). Usually more timing on a cold engine. Then no change in timing over the main timing when the engine is up to temperature.

It is strange that during cranking there is a difference when the EST/BYPASS connector is open. The ECM leaves that signal open until the engine is running. Then takes over timing. So during cranking it is the same as if the EST/BYPASS was open.

And while that signal is open, the timing is fired at the distributor base setting.

Although, it may be that the engine does fire OK and gets to running RPM. Then the ECM takes over and the engine dies. You did mention that the engine kinda' starts with the EST/BYPASS connector closed.

I have seen two items that cause this problem: The distributor pickup coil polarity is reversed (going to the ign mod), or the ECM has the wrong calibration in it (one from a DIS engine).

When did the problem start to occur?

RBob.

 

I bought the car like this. It does try to start but then stalls out. Ive tried a few ECMs , rebuilt Dizzy with new ICM, new coil, and even replaced the temp sensor because i cracked it when i pulled the plug off, and even load tested the wires from the dizzy to the ecm with no luck. Im not too sure if it's advancing or retarding. I hooked up my timing light and im getting a steady flash so the coil is firing.

EDIT: Would a mass air flow sensor mess it all up and not set a code?

 

The MAF can't really throw the timing off enough to cause the engine to die. In the calibration are limits to the advance and retard. So even if the timing gets pegged in one direction, it is still limited.

You can unplug the MAF and see if the engine then starts and runs. The ECM will create a default airflow based on the TPS and RPM.

What is the 3 or 4 letter code on the PROM in the ECM?

RBob.

 

That's about where I had it narrowed down to in the V6 forum, the PU coil and the ECM calibration.

So far, what is known is that the car started having trouble after the PO jumped a car. 2 ECMs both do this. Rebuilt dizzy doesn't help, and if the PU in the dizzy is connected the way it is in the pic on the parts store's website, it's done right (green wire on the ICM "P" terminal and the yellow one on the "N"). The BCC is AMBF. I was hoping you or someone would know if this was the proper BCC or not for the 86 RWD 2.8. :edit: He never gave me the BCC for the second ECM.

Although, I have run an FWD MEMCAL in the 730 (until I got the VATS parts to run the F-body MEMCAL)... Timing was retarded 60*, not advanced, and the engine DID run, but like absolute crap. Flint's timing is advanced so far the engine won't even try to run.

 

hey maverick. I have to pull it out of the car to see the number on that one. I posted over here to see if anyone know the sensors that ran the timing which all tested ok. So I have to believe it's a bad ground somewhere. Well hoping lol.

 

Just making sure everyone's on the same page and not passing on bad info.

 

AHHH she runs. So I started today thinking I was going to rip apart the entire wiring harness chasing out all the grounds. I opened the hood and started at the battery. Didn't look at the grounds looked at one of the feeds to the ecm, Oh look someone probed the wire. Oh look the wire is pretty much corroded out. Repaired wire thinking that can't be it. Plugged in EST and the car started and ran great No codes. So I decided to check the wiring a little better and found a few more spots that had issues repaired and the car is running great. Installed a new radio rolled down the windows and went for a nice ride enjoying the 55 degree day. Thanks all for the help. I know more about this car then any of my other cars.

 

... Which is why, when faced with a wiring problem, I start with the obvious... Broken or corroded connections followed by problem wires. It gets harder when you can't find any reason for a problem, even with the parts testing good (such as my 3.1 harness).

Case in point: I worked at a local dealer for my internship. Ford Focus came in with an ignition problem similar to yours. The tech was tearing his hair out trying to find the problem, and all the scanner said was "Ignition Coil Fault". He replaced the coil, plugs and wires, and the car still ran like crap. Why? Because the middle wire in the 3-wire plug running to the coil pack was corroded to pieces. I pointed this out, he fixed it, and the car ran great. Similar issue with a GMC Yukon (or similar) with the air ride suspension, but that's another thing.

 

I worked at a dealer it was for transport refrigeration. 90 percent of those issues where wiring. The funny thing was I went over the harness before and didn't see anything. This time it just popped out at me. The good thing is I needed a new dizzy anyway. I have a spare ECM. I got a new radio installed. I can drive the car now. All she needs is a paint job and she will be good.

 

Glad to hear you got it fixed . Now enjoy your new ride .

 

So I have ecm1227302. HNJ 862981 M523742321 with chip of JT8(B)/AI52
are these correct for 1986 w/2.8?
Last in line it seems to get it fixed.
Thanks Joel