armysnipe

I have a 1993 LT-1 with DTC codes: module 1 - C41; module 4 - error; module 9 - H72. I have done extensive troubleshooting and need advice to what I should do next.

History: Bought car with around 65,000 miles (Corsa exhaust). Car put in garage, water pump went out. Replaced water pump, but not Opti. Installed; P-1SC Procharger w/ FMU, dougs headers, magnaflow cats, WT sensor, O2 sensors, added wide band sensor befor cat on passenger side, knock sensors, no tune, would cut out at WOT (stock injectors probably at 100% duty cycle), had squeal at idle and would go away when car warmed up. Drove car off and on for a few months and then sat for three months. Battery was replaced, and put on tender when I was gone (may have left battery connected while on tender). Upon my return from Haiti I disassembled the engine compartment again to fix a power steering leak and sueaky pulley (alternator bearing went out). I replaced alternator, installed meziere WP (wired into wiper motor harness for battery on power / installed relay and grounded where I think ECM ground is, at front of car near fan relays), installed ZEX plugs set at .040', MSD 8MM wires, MSD street fire coil, and decided to replace Opti with MSD Pro billet. Then I messed with the timing (advanced) and the car ran strong and idled fine. Then the car shut off on me. So, I reset the timing to 1 1/2 turns out (back to stock / called MSD and verified). Then the car started idling high. So, I thought I may have messed up the IAC when cleaning the throttle body, so I replaced it. Reassembled all, started car, a lot of steam starting coming out of exhaust and a distinct odor (blew head gasket). Performed compression test, coolant in #7 CYL, disassembled, inspected all components (found slight wear in cap of distributor and spark plug terminals were loose so I tightened). Replaced all gaskets, cleaned necessary components, changed oil, installed the following; edelbrock heads, edelbrock intake, 24# Bosch type III injectors (so I wouldn't have to tune yet), fuel filter, B&M shift kit, EGR valve, stock fuel rail pressure regulator, MAP sensor, 1.6 GM performance roller rockers (set valves per instructions), adjusted throttle cables and torqued / installed all per FSM. Started car and it idled at @ 1500 RPM. Found vacuum leaks (forgot to put plug in intake). Also NOTE: ventilation for ignition routed to IAT (after intercooler discharge) and tee'd into intake manifold ASR vacuum. Restarted and would intermittently idle high, service ASR light would come on and service engine soon light would come on.

Currently: Have followed FSM troubleshooting. Fuel pressure is fine. Hooked up accutron scanner and have only been able to read diagnostics twice then codes set. Checked codes, cleared codes, they continue to return, loosing LCD gauges and then return above 190F. I have followed the DTC 41 chart and found nothing. When I unplug and reinstall plugs on the ECM the car starts fine and then stumbles, lights (service ASR / engine soon) come on and the cycle starts all over again. Then I can go for a drive, as long as light is on the timing is retarded and will not allow a heavy foot on the gas pedal, when off all is well. Yesterday I removed the CCM (opened up and inspected, no apparent signs of melting solder or burnt smell) and unplugged it, reconnected, reset codes, started fine. Reinstalled CCM (not fun) and started car, after a minute or two it started all over again. Now, unless I unplug the CCM or the ECM the fans will come on constantly (built in safety) and the codes can't reset. I have also been disconnecting and reconnecting the battery a lot (13.4 volts at start up and rises while driving, so I think the charging circuit is fine). I even charged the battery overnight with the battery tender.

I am leaning towards the ECM, but don't want to keep throwing parts at the car. I also don't want to remove the CCM again unless I absolutely have to. I found a highly recomended company (K&B in Georgia) that I will use for the ECM if needed. I have read numerous posts on this forum and some have not been resolved. I hope I am not the next victim, because I need to drive mine a few hundred miles in the coming months due to relocation. Any help or ideas would be greatly appreciated. Sorry if I posted in wrong location (first post).

armysnipe

Forgot to add, I recently replaced ignition control module. Today I checked codes again and I have a DTC H54 in module 1. This is the second time this has popped up. I plan on clearing codes again and seing if 54 shows up again.

armysnipe

Well today I narrowed my problem down to a faulty ECM or PROM. When I tap on the ECM it kills the engine. So, I am sending it off for repair.

BrianCunningham

If you get stuck again, be sure to post in the FI section