PCM not reading - no start
Thread Starter
Teching In
Joined: Oct 2020
Posts: 5
Likes: 1
PCM not reading - no start Hello - I have an LS Swap into a 90 rx7 that has run fine for years. On a drive home the car shut off about a block away from my house and I was able to coast home and push it up the driveway. It seemed to be related to a bump or something in the the road as it stumbled a little, ran 100% again and then shut off entirely.
The car has the standard PCM flash with the VATs delete etc, I could always plug in my ELM scan tool to the OBD2 and get a reading.
Now I cannot get a reading from the PCM. I have checked voltage and grounds etc to the OBD2 plug and all is dandy. When I switch the power on I can hear the fuel pump relay being triggered so I know the PCM is pumping out power. The car will crank and every 4th try or so I'll get a combustion on it, a stumble at best. Not like pre-VATS where it ran for 2-3 seconds.
With this said I decided to get a whole new flashed PCM as I thought that might be the issue and have the same problem. I pulled the entire wiring harness and inspected and replaced a few butt connectors just to be safe, redid all of my grounds and still the same problem persists.
I am stumped at this point and checking voltage to the PCM and get maybe a 1-2 volt drop on cranking but that is it. Still no read from my scan tool.
Anything else I should be looking into? Thanks in advance for the help!
The car has the standard PCM flash with the VATs delete etc, I could always plug in my ELM scan tool to the OBD2 and get a reading.
Now I cannot get a reading from the PCM. I have checked voltage and grounds etc to the OBD2 plug and all is dandy. When I switch the power on I can hear the fuel pump relay being triggered so I know the PCM is pumping out power. The car will crank and every 4th try or so I'll get a combustion on it, a stumble at best. Not like pre-VATS where it ran for 2-3 seconds.
With this said I decided to get a whole new flashed PCM as I thought that might be the issue and have the same problem. I pulled the entire wiring harness and inspected and replaced a few butt connectors just to be safe, redid all of my grounds and still the same problem persists.
I am stumped at this point and checking voltage to the PCM and get maybe a 1-2 volt drop on cranking but that is it. Still no read from my scan tool.
Anything else I should be looking into? Thanks in advance for the help!
You have power or ground related issue somewhere. No easy task you gotta check the obvious first, failing that do a pin test and see whats what. Check the biggest wires first, bat, starter, alt
Thread Starter
Teching In
Joined: Oct 2020
Posts: 5
Likes: 1
Where should I start? I just redid all of the grounds to chassis from the block and the harness. I thought the battery would be first, and redid the terminal connection there which I though would be an issue for sure but wasn't. What should I be looking for around the alternator? If that was bad wouldn't the car still start? Car cranks over just fine so what should I look for at the starter?
Start with the biggest wires first; main battery leads, alternator, startor, IGN leads, ALL grounds etc etc etc. Make a list and check them off as you go. If all those produce nothing continuity test the PCM leads to their coresponding connector pins and somewhere in the mess you'll find the issue
