how to tell if logic module is bad
Car is a 87 Daytona Shelby Z, log intake turbo 1 with a fwd perf computer. The engine just abruptly shut off while slowing to a stop light. Would not restart. Tried to run diagnostics, but check engine light (power loss) just flickers sometimes, other times just blinks like a turn signal, sometimes starts to blink like maybe a code 12 then disappears not to return. Sometimes can hear relays under hood being cycled. I suspect logic module is bad, but am looking for confirmation or advice. Took 3 hours to get a tow on a friday night.
Re: how to tell if logic module is bad
Does it prime the pump when you flip the key forward?
Re: how to tell if logic module is bad
no, I don't hear the fuel pump.
Re: how to tell if logic module is bad
Run a jumper wire from the + battery terminal to the + side of the coil. If the fuel pump comes on, I would suspect the LM first and foremost, although it certainly could be a bad PM too. If you have a spare LM to try, pop it in there and check for fuel pump prime. If it primes, it's almost guaranteed to be the LM.
Re: how to tell if logic module is bad
Also, logic module connectors/wiring are known to be problematic.
Sometimes placing the LM in another position can make a connection.
Kind of like slowly opening a car door slowly when a PW stops working.
Sometimes the door jamb wiring can make contact only at a certain door position.
Many report their LM/wiring have to be at a certain angle to work if you get my drift.
Thanks
Randy
Re: how to tell if logic module is bad
Quote:
Originally Posted by
GLHS60
Also, logic module connectors/wiring are known to be problematic.
Sometimes placing the LM in another position can make a connection.
Kind of like slowly opening a car door slowly when a PW stops working.
Sometimes the door jamb wiring can make contact only at a certain door position.
Many report their LM/wiring have to be at a certain angle to work if you get my drift.
Thanks
Randy
Great point Randy. In addition, water leaking down into the LM from the cowl area can be a problem, especially in cars which have had the plastic bagging removed.
Re: how to tell if logic module is bad
I am going to take a look at the wiring to the logic module in a few, It still has the plastic bag, and I have never seen any evidence of water in the area. I tried getting my hand up in there while waiting for a tow and moving wires some, thinking maybe it came unplugged, but it felt secure. It didn't change the issue at all. I will also try jumping the solenoid and see if the pump runs.
Re: how to tell if logic module is bad
Car magically decide to start after all the effort of pushing it into back yard. Took the logic module apart and found some corrosion on the board near the blue and red plugs. Cleaned it up, and as of now car seems to idle fine, is giving codes normally 12 & 55, and turning fan on and off ok. So hoping that is the culprit.
Re: how to tell if logic module is bad
Quote:
Originally Posted by
tommyturbo
Car magically decide to start after all the effort of pushing it into back yard. Took the logic module apart and found some corrosion on the board near the blue and red plugs. Cleaned it up, and as of now car seems to idle fine, is giving codes normally 12 & 55, and turning fan on and off ok. So hoping that is the culprit.
Fingers crossed for you. I've never been that luck with them, but I don't live in CA either.
Re: how to tell if logic module is bad
I played with and moved wiring around etc while it was running, looked at all the connectors and didn't notice a change in how it ran, again I will have to wait and see if it does anything wonky again. It wouldn't restart for several days, and then after moving it, it decide to start. Thought about temperature, but it was hot when it died, and it was hot today when it was running...so yah may just drive it and see what happens.
