So I managed to kill the ECM on the 4.9. Let all the magic smoke out.

My question is this. When that happens whats the likelihood of the whole board being fried vs just the prom? If the board is fried is it likely it would hurt a new prom? Also can you make your own VATs bypass?

I am pretty sure what happened was one of the wires either from the C203 or from the ECM itself had an exposed lead and it touched the box and that fried it. Not actually sure as I was trying to turn around in a parking lot and the car just died I looked over and all the smoke was escaping from the ECM, any other ideas what may have caused a failure like this? Other than it just being me

Anyone else have anything on this? I read the other post about the duke and the hot lead from the c500 going kaput and causing a fire. This is different I still have full power on everything and can crank it. I even took the prom out and put it in another ECM box I had and tried that. Interestingly it cranks like mad but no go. When it first died I could get it to crank and fire but it ran like a$$ and would quickly die again.

Might have more info later.

I'm not sure anyone can answer your questions. The possibilities are endless regarding what could have been affected by the short circuit... and even then, it sounds like you're not sure that's what caused it. Your best bet is going to be replacing the PROM and the ECM and trying to get it to run. Before plugging the new one in though, I'd get a circuit diagram for the wires leading to the ECM and test each wire individually for continuity end to end, test for 12V on the power wires, and test for proper resistance (ie zero ohms) on the pins that are supposed to be grounds. At least then you'll be reasonably confident that whatever caused your first ECM to burn out will be caught if it was an external problem, and you can rectify anything abnormal you find before you plug in the new one. Once the new ECM is plugged in, hopefully you'll be able to troubleshoot any other problems using a diagnostic tool or downloading any codes. Wish I could help you more.

That was helpful. I don't always approach things so logically. Thank you.

I doubt the prom killed the ECM or the ECM killed the prom. The prom is a low power item. The only time I have seen a prom fail is when it was installed backwards. If your prom was properly installed it should be good even if the ECM is bad.

Note the word SHOULD. No guarentees other than the positive guarentee that I'm not totally sure I know for sure what really really happened maybe. I think.

[This message has been edited by phonedawgz (edited 08-26-2010).]

Is it possible that you removed the prom and reinserted a modified prom?I know ocasionally the pins can bend on the prom when being reinserted.

quote Originally posted by James Bond 007: Is it possible that you removed the prom and reinserted a modified prom?I know ocasionally the pins can bend on the prom when being reinserted.

Not on the 4.9 - it uses a memcal pak - it plugs into the ECM using a row connector (the eprom is actually soldered into the memcal along with a 'limp mode pack'. You have to go out of your way to bend the pins in the memcal connector.

Dizzixx >> as mentioned verify your wiring, also make sure your ECM is isolated - that is to say that the case is NOT grounded or touching the metal in the car. It has to be mounted to the plastic frame. You should be able to start the car with a stock eprom, but it will shut down due to the VATS (and throw some engine codes) - you can build your own VATS (see my wiring thread for circuit diagram). I have driven my car on a stock chip (I have a VATS bypass) - but got a whole mess of error codes.

[This message has been edited by Mickey_Moose (edited 08-26-2010).]

quote Originally posted by Dizzixx: So I managed to kill the ECM on the 4.9. Let all the magic smoke out. My question is this. When that happens whats the likelihood of the whole board being fried vs just the prom? If the board is fried is it likely it would hurt a new prom? Also can you make your own VATs bypass? I am pretty sure what happened was one of the wires either from the C203 or from the ECM itself had an exposed lead and it touched the box and that fried it. Not actually sure as I was trying to turn around in a parking lot and the car just died I looked over and all the smoke was escaping from the ECM, any other ideas what may have caused a failure like this? Other than it just being me

everytime i have diagnosed a bad ecm because of an electrical short, the chip was fried too... best bet is to replace the ecm and memcal(chip)

I had no idea that the ECM case was not supposed to touch anything. I mean I knew that it was originally mounted on plastic but I thought that had more to do with the mount being easy to make and conform to work in a variety of automobiles; not isolate from grounding. I honestly would have thought that the case was meant to be a ground or at the very least not anything at all. Can anyone else confirm/explain this? It's possible that was the problem. My ECM just kinda rests on the gas tank tunnel next to me (where the plastic skeleton would be) because I have yet to install the interior completely. Granted it was like that previous and has been like that but I could see how it might have rubbed the paint off to bare metal or something and then shorting out. I guess I will have to find that 84 4cyl ecm tray I bought and install it.

When you build your own VATs what kind of codes do you get? I am definately going to be buying a new prom from Aaron (stickpony) but while I am waiting for it to get here it could be nice to still have a car.

I am going to bust out the wiring diagrams again tomorrow and go through the harness pin for pin..... fun, yah!

I originally had my ECM grounded and didn't have any problems for the first year or so, then all of a sudden I started getting all kinds of wierd random crap. Someone suggested removing the ground (since GM isolates them at the factory) and all was good. Could it have let out the magic smoke, I don't really think so, but one never knows. It could be that your ECM was on the way out as well.

VATS >> no codes with the circuit. Maybe I confused you in my post the codes came up when I was running a stock chip - codes that related to missinig BCM and such that are normally programmed out as well during the reprogramming process.

On my car, if the VATS condition is not met, the module does not send a the signal to the ECM so I get the typical car fires and then stalls condition. Hoping any would be thief would just called in a pile of junk and leave it after a few tries.

quote Originally posted by Dizzixx: I had no idea that the ECM case was not supposed to touch anything. I mean I knew that it was originally mounted on plastic but I thought that had more to do with the mount being easy to make and conform to work in a variety of automobiles; not isolate from grounding. I honestly would have thought that the case was meant to be a ground or at the very least not anything at all. Can anyone else confirm/explain this? It's possible that was the problem. My ECM just kinda rests on the gas tank tunnel next to me (where the plastic skeleton would be) because I have yet to install the interior completely. Granted it was like that previous and has been like that but I could see how it might have rubbed the paint off to bare metal or something and then shorting out. I guess I will have to find that 84 4cyl ecm tray I bought and install it. When you build your own VATs what kind of codes do you get? I am definately going to be buying a new prom from Aaron (stickpony) but while I am waiting for it to get here it could be nice to still have a car. I am going to bust out the wiring diagrams again tomorrow and go through the harness pin for pin..... fun, yah!

don't delay bro, send out that chip as soon as you can. if i get it by monday or tuesday, chances are i can have it back out to you later that day, wednesday at the latest.

Will do. I have to go to the junkyard to get two more proms and a good ECM. Thats tomorrow and I will send them then. Thanks.

Aaron you have an email. I sent the chips. Write me back.

Finished going through the wiring. Everything matched up. So I took care of wrapping the loom and taking care of some other little things. I also noticed I blew a fuse as well. The one for the fuel pump. Put it all back together and fired it up with the fieroaddiction chip in a new box. It works again. I am still getting the new chips from Aaron (Stickpony) so we will see how things go. I also think I know why my belts are having problems. The Alt Bracket is cracked.

Good to hear you've made some progress. Since your wiring checked out OK, the initial problem probably occured within the ECM itself. It's a pain in the butt to test the wires but at least it gives you some peace of mind when you plug that new ECM into the system.