Six_Shooter

iTrader: (2)

Ok, so I was going to tune my friends truck.

This is the same ECM that we had already been using, the only differnce between tonight and previously is that he mouted the ECM, instead of just having it floating like it was.

So I hooked up the Ostrich 2.0, and my ALDL cable as usual, I could upload to the Ostrich just fine at first, but the ALDL cable wouldn't datalog for some reason, I've had this problem before, but it went away. Then after a while TP RT would lose connection to the Ostrich, which to me would seem like an Ostrich or TP RT problem, I was leaning towards TP RT due to the problems I was having with the ALDL connection and the fact that the com port that the ALDL cable would be connected to would switch from COM 2 to COM 3, seeminlg almost at random, but usually after connecting the cable to truck, it would not detect it in the same port. I even tried using my USB to serial interface and setting the proper COM port and still would not connect. The USB adaptor worked flawlessly the other day.

After a while, with just the key on, the fuel pump would all of a sudden, just engage, truck was not running. It would prime as if the key was turned off and back on. After a while turning the key off and them back on would not prime the pump, after this I noticed the CEL would just come on solid. It would not give the flash that indicates that the PROM check was fine, light would just come on and stay on solid. The ECM was quite hot at this point. Opened it up but could not see anything wrong.

Swapped in a different ECM and it primed just fine, did not attempt to start the truck as the PROM does not run the truck well, stock PROM.

I started to modify the ECM while I was there, but could not clean out the solder points to insert the new DIP socket. I will be modfying it tomorrow to use in the truck.

Any ideas of what might be wrong here, and why the ECM would all of a sudden get real hot? Would this also cause connection issues to the Ostrich? I would be emulating fine, uploading as changes were made then all of a sudden lose connection, and upload would fail. I can see how a bad ECM would cause ALDL problems.

I can't see this being an issue, but would having the chassis of the ECM grounded to the truck cab, via the mounting bracket cause the ECM to fry? The other ECM was mounted this way for a while and didn't have any issues, and I know it's along shot (I'm not new at all to automotive electrical), but can only think that a ground offset might cause some problem, but that would only occur if there is a large offset, such as the chassis having several volts on it, whihc is not the case.

just looking for ideas here, spit them out if you have any.

RBob

iTrader: (1)

I don't recommend grounding the ECM case to the frame or chassis. It is already grounded to the engine block via the wiring harness. If the ECM case is grounded to the truck cab that provides another ground path between the cab & engine block (like a ground strap). Note that stock installations the ECM is in a plastic holder, not grounded.

As for the ECM getting hot. In normal operation they do run on the hot side, about 120 F on the case above the heat sink (two screws in the top of the case).

They will get very hot if the 5V supply gets shorted to ground. This can happen if the PROM is plugged in backwards. Unfortunately, they don't last long like this. The PNP pass transister melts internally and shorts out. Once the 5 V short is removed the pass transistor sends B+ through the ECM and it's history.

Plug the ECM into the harness with nothing in the PROM socket. Key-on, engine-off and measure the voltage between pins 12 & 24 on the PROM socket. Should be 5 volts (or -5 V depending upon which probe is on which pin).

RBob.

Six_Shooter

iTrader: (2)

Well, I'll make sure that the ECM gets isolated from the chassis, when it gets re-installed.

As far as testing this ECM, that's not a possibility anymore, after the CEL just coming on solid, and not changing if there was a PROM installed or not, I decided it was FUBARed, and have since removed the connectors to make an adaptor harness, to use a 7730 or maybe a 7749, in a pinch, and for some other testing.

I'll have to try that 5V verify test though, or at least remember about it.

BTW, the ECM was not getting hot around the drivers, it was actually the chips under the daughter board, directly below where the PROM gets installed. I had time to open the ECM, and find where it was hot.