Hey all,
I am a C6 guy but my uncle has an 88 that shuts off intermittently. It loses all power no lights, no engine, no nothing. If he waits 15 minutes it starts right up and everything works fine. He has been told that it is the ECM, I have checked for ECMs on Ebay and they all say that they are for 85-89 is that correct or do I need one for an 88, or does anyone think this is even the issue???? Thanks and God Bless!!!

 

The ECM used is GM # 1227165 , commonly called a '165 ECM
A later or service version of it may have #88999194 or #16198259
Used in a multitude of different GM cars 86 - 89 TPI F-Bodies etc
All identical ECM's to yours; Pay no more than $50 used

All you need is the memcal ( chip ) inside the ECM that holds the tune details unique to your particular car / engine swapped into any new ECM
( and don't lose or break the memcal because now almost impossible to find , long discontinued from GM )

 

This sounds like a Battery,Cable, or Connection problem. ECM isn't going to control the head lights.

 

Sounds like a ground problem.

 

 

How someone got to the ECM is beyond me.

Start by following the POS battery cable from the battery to the starter. Make sure its not grounding on the block where it lays around behind the engine to reach the far side. Lots of places for it to rub and short out. There was a guy here a few mts ago that had his short on the dipstick tube, somehow, and welded the dipstick to the tube.

Next, go thru the battery grounds AND the hot wire that jumps from the battery over to the battery jumper pole near the driver door hinge,. along the firewall. Those are ALL hot wires for the most critical systems on the car and under the hood. They are also ALL on fusible link behind or under the battery. Check every connection, every wire for breaks/rot.

Look carefully at the wires to the dist. These get loose and end the ignition but they do not stop power to lights etc,....

Your problem is power supply. The BIG clue is that everything stops. Lites, engine, all. The ECM has absolutely nothing to do with power failure at the lights or radio. JUST the engine mngt system...nothing else.

THEN, find the ground bundle near the oil filter. These need to be cleaned anyway..That will be 5 black wires from the firewall harness that drops these 5 important grounds down to the block where they are bolted down. Either on the block, trans bellhousing or something similar, nearby. Close to the oil filter.

Worst case scenario, use the FSM detailed electrical drawings to trace power to the point of failure...follow it back with a test light to the point where it ends. Start with a lite for example and follow its power wire to the point of origin. Same with headlites, ECM power etc. The FSM elect book is so detailed that it almost tells you how many inches from 1 pt to the next....almost. Its priceless in an easy diagnostic like this.

Your problem is in there. The wire.

 

following

 

Here is the clue that your uncle needs to know.
If we were to erase the codes in the ECM, we would tell you to remove the negative battery cable for a minute, and reconnect it.

The only indication you will get in the driver's seat is the average fuel mileage goes to zero.

Tell your uncle to flip over to average fuel mileage on the dash, and leave it there. When he turns the key back on after the 15 minutes, the average fuel mileage should read zero if it is a battery, ground, etc.
I think it is a ground because if the ground is good, and the battery positive cable was bad, the car would run on the alternator. I have seen cars running, and the battery was removed and replaced while the engine is idling. So it's not the ECM. Or the battery, or the alternator, or the battery cables.
I think it may be where the fusible links are connected or the engine ground at the back of the left engine cylinder head, or a broken starter relay cable. I'd look at the starter wiring first.
If he starts it up and all is well for a while, something is using a large amount of current possibly and fusing the wiring together untill it vibrates loose and the car shuts off.