Need help diagnostics: crank no start no power to ODB port
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Teching In
Joined: Mar 2017
Posts: 14
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From: Nashville, TN
Need help diagnostics: crank no start no power to ODB port Hi guys,
PLease forgive me if this is the wrong forum. I've got an issue with a Restomod powered by a LS1.
This just started. I've got crank no start, no power to ODB port, and no fuel pump engagement. I can bypass the fuel pump relay and engage the fuel pump so I know its working.
What should I look for? Where do I start?
What sends power from the ignition switch to the coils, fuel pump, PCM, and starter? I am almost certain its a wiring issue but I don't know the chain; if its multiple relays or just one? The only thing I got is starter and some accessories.
Consistent failure. No start 100% of the time as of this week.
Thank you in advance.
PLease forgive me if this is the wrong forum. I've got an issue with a Restomod powered by a LS1.
This just started. I've got crank no start, no power to ODB port, and no fuel pump engagement. I can bypass the fuel pump relay and engage the fuel pump so I know its working.
What should I look for? Where do I start?
What sends power from the ignition switch to the coils, fuel pump, PCM, and starter? I am almost certain its a wiring issue but I don't know the chain; if its multiple relays or just one? The only thing I got is starter and some accessories.
Consistent failure. No start 100% of the time as of this week.
Thank you in advance.
Moderator
Joined: Aug 2010
Posts: 7,320
Likes: 527
From: Ann Arbor, MI
First, you are in the right place to ask for help.
No power to OBD indicates that either you have no power to the PCM, the PCM wiring is bad or you have a bad PCM. I would start by verifying power to the PCM which should go through a fuse.
The PCM controls the relay which powers the fuel pump; you already figured that out.
Technically "power" goes to the coils through fuses; the PCM then grounds the coils to fire them at the correct time. Same with the injectors; they also get power through a fuse.
In short, your "no power to ODB port" makes it most likely your PCM is not getting power, likely due to a wiring issue.
Are you using an aftermarket LS1 wiring harness or an OEM/JY one? It is non-trivial to modify an OEM one as it is designed to plug into an OEM fuse block and you need to figure out which wires to the PCM, Coils and Injectors need to get power through aftermarket fuses when your ignition is on.
I recently bought an aftermarket LS1 wiring harness for a swap into a 1977 Jeep; the harness had high quality connectors and only cost about $180. Best it included a fuse block and relays built in so that it only required about 6 wires going to the rest of the car. (Battery power, Battery ground, Ignition/Starter on, Tachometer, Speedometer, Brake switch and maybe something optional I forgot). This beats taking an JY harness, removing unused crap, cleaning it and figuring out how to add a fuse block to it.
No power to OBD indicates that either you have no power to the PCM, the PCM wiring is bad or you have a bad PCM. I would start by verifying power to the PCM which should go through a fuse.
The PCM controls the relay which powers the fuel pump; you already figured that out.
Technically "power" goes to the coils through fuses; the PCM then grounds the coils to fire them at the correct time. Same with the injectors; they also get power through a fuse.
In short, your "no power to ODB port" makes it most likely your PCM is not getting power, likely due to a wiring issue.
Are you using an aftermarket LS1 wiring harness or an OEM/JY one? It is non-trivial to modify an OEM one as it is designed to plug into an OEM fuse block and you need to figure out which wires to the PCM, Coils and Injectors need to get power through aftermarket fuses when your ignition is on.
I recently bought an aftermarket LS1 wiring harness for a swap into a 1977 Jeep; the harness had high quality connectors and only cost about $180. Best it included a fuse block and relays built in so that it only required about 6 wires going to the rest of the car. (Battery power, Battery ground, Ignition/Starter on, Tachometer, Speedometer, Brake switch and maybe something optional I forgot). This beats taking an JY harness, removing unused crap, cleaning it and figuring out how to add a fuse block to it.