Hi,
I have a 1992 Olds 88 that has been giving me Code 26- QDM #1 forever. I have to date, checked all vacuum lines, replaced fittings etc. I have replaced the Vacuum modulator on trans as well as the purge valve solenoid on the evap cannister. I recently changed the fuel injectors, fuel pressure regulator, fuel filter, and fuel pump and sending unit. All new here!
The O2 sensor has been replaced as well as coils, ignition module, plugs, wires, and computer. The MAF, IAC, and TPS have also been replaced. Trans has been flushed and new filter.
Okay, so now that you know what I have replaced, I have an issue in which the car will not start at certain times. I can crank for as long as I want but nothing. If I cycle the ignition key several times, it will eventually start. In situations where I am taking off from an intersection or giving the gas hard acceleration to merge on a highway, the car is prone to stall and die! (Rather scary with 65mph cars coming at you and no f*ing pwr steering to get out of the darn way!)
The car currently is giving me these 3 codes:
DTC 26 Quad Driver Module #1
DTC 42 (EST) circuit - open or shorted
DTC 58 trans temp high or Anti Theft System fault.

Please help me figure this out. I am at a total loss and need my car to drive without being scared to drive it somewhere.....
Thank you in advance.....

just for the heck of it, I unbolted the ICM and coils and took everything apart. I cleaned the ground connection under the ICM and made sure that the ground was good there. I cleaned the aluminum pad with brake cleaner/electrical cleaner and put a bunch of dielectric grease on the copper squares to ensure a good ground between the ICM and that mount. I cleaned the connector on the harness, (no visible wear or loose wires) and put everything back together. I then disconnected the ground to reset all the codes that were present. So far, it seems to start and drive okay and doesn't stall under full acceleration as before. But, I imagine it is too soon to tell as the cel hasn't racked up enough data yet or something. I'll update in a day or so but if anyone can think of anything else, would you please advise me on where to go next? The neighbor thought that if there was a bad ground, then there might be an issue somewhere?

DTC 26 Came right back.....Quad driver module 1
Not too sure where to go from here guys and gals....

The only thing that comes to mind is possibly the crank sensor.

I've kind of heard that those are tough to change. Do you know?

I changed my crank sensor twice. Dan has a good write up on how:

https://www.gmforum.com/mechanical-134/change-crankshaft-position-sensor-279066/

That'* the procedure Randy, the only difference is your sensor will be a two piece that needs to be adjusted. It'* not a big deal and the instructions will come with it.

The QDM1 apparantly has the purge valve solenoid, the gauge light for temp, low fan relay, brake switch, and tcc solenoid on this circuit, according to a friend who had the schematics. I have changed the purge solenoid and the temp sensors and also checked the low fan relay and all seem to be good. I have tried the tcc switch test in order to get the rpms to go up , say around 45-50 mph, and can't remember hearing a change in RPM. I want to switch out the brake switch, as it is less than $10 to do so, in order to see if that is the amperage issue on this circuit. Otherwise, I think the car will have to visit a trans shop to get the TCC solenoid changed as I don't have time for that one considering it is a pan on the side of the trans and a bunch of headache without proper tools etc....
Any thoughts out there? Like my friend said, you have to focus on the original issue, code 26 and narrow down what is on that circuit that keeps popping it like a breaker....