Connecting... Need help on lt1-ls1 electric
05-05-2012, 09:23 PM
#1
Connecting... Need help on lt1-ls1 electric I'm getting ready to say I need to try another PCM
Here's what I have done:
1) all pinks + orange have power and traced back to pcm connectors 1x1 to make sure power is getting to the PCM = OK
2) continuity check from pcm to OBD2 port = OK
3) continuity check on fuel pump to relay is = OK, getting 12 volts on green/white wire at relay
4) all grounds tested for continuity at pcm and on body =OK
5) all connections nice and tight on battery and distribution block =OK
I can crank just fine no issue. I cannot connect to the PCM, just getting a 'connecting...' on my scanner, so I can't tell what is wrong.
Also- fuel pump will not prime by itself via PCM, VATS is disabled in the tune, but I'm thinking it's a relay for now, because when I give power to the grey wire, I can hear the fuel pump working. at the fuel pump relay, key on, I have a good ground, and have power at the pink and PCM wires.
I don't know how I would have bricked my PCM, but thought I would try here and see if I'm missing anything obvious in my configuration or something I may have overlooked.
Thoughts?
Here's what I have done:
1) all pinks + orange have power and traced back to pcm connectors 1x1 to make sure power is getting to the PCM = OK
2) continuity check from pcm to OBD2 port = OK
3) continuity check on fuel pump to relay is = OK, getting 12 volts on green/white wire at relay
4) all grounds tested for continuity at pcm and on body =OK
5) all connections nice and tight on battery and distribution block =OK
I can crank just fine no issue. I cannot connect to the PCM, just getting a 'connecting...' on my scanner, so I can't tell what is wrong.
Also- fuel pump will not prime by itself via PCM, VATS is disabled in the tune, but I'm thinking it's a relay for now, because when I give power to the grey wire, I can hear the fuel pump working. at the fuel pump relay, key on, I have a good ground, and have power at the pink and PCM wires.
I don't know how I would have bricked my PCM, but thought I would try here and see if I'm missing anything obvious in my configuration or something I may have overlooked.
Thoughts?
05-06-2012, 01:33 PM
#3
Fuel pump relay wiring is factory on these cars, I just need to bring the relay green/white to provide PCM power which I did. Obd2 is wired correctly with the two grounds and PCM
Feed traced for continuity.
I think I have to try another PCM at this point, not sure what's left
Feed traced for continuity.
I think I have to try another PCM at this point, not sure what's left
05-06-2012, 05:12 PM
#4
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Make sure you have the correct wire for the obd2 because the PCM actually has 2 and one won't work with the scanner. What year PCM? Make sure the fuse is good inside the car
05-06-2012, 09:42 PM
#7
Yup, i did at with the engine out of the car when i plugged the harness in first. I bolted all of them to he back of the head on the drivers side. Also my ground strap is going from drivers side cyl head to frame.
Tried the pcm in another ls1 car, fired right up, and died a few seconds later, assuming thats because of my much bigger injectors in the tune vs stock ls1 injectors. I was able to scan and read the tune off my pcm in the other car.
Also, made a new obd2 connector directly off the pcm and still cannot connect. Hate these gremlins!
Checked voltage at coils and fuel injectors and good there.
Tried the pcm in another ls1 car, fired right up, and died a few seconds later, assuming thats because of my much bigger injectors in the tune vs stock ls1 injectors. I was able to scan and read the tune off my pcm in the other car.
Also, made a new obd2 connector directly off the pcm and still cannot connect. Hate these gremlins!
Checked voltage at coils and fuel injectors and good there.
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05-07-2012, 07:19 AM
#11
I tested all the wires right at the PCM connector. so I have grounds on 1 and 40 on red and blue connectors, i have good continuity on them back to the chassis ground bolt by the battery. my resistance on the ground cables for the battery grounds and block grounds are all less than 1 ohm so don't think it's the cables.
For power, confirmed my constant power is there at blue 20 and 57, then with key on, I have power at blue 19.
I have the basic for it to fire wired, which is frustrating. I also ran a new wire from the pcm directly to the fuel pump relay just to make sure I don't have any short in the harness.
so with all the grounds good, and the pcm power good, i should at least be able to connect and read it with my obd2 connector directly coming off the pcm now with my rewire.
ugg when i did my 24x conversion, this fired up right away with this pcm and I repinned my entire lt1 harness from scratch.
now actually using a ls1 harness I can't get it to fire
For power, confirmed my constant power is there at blue 20 and 57, then with key on, I have power at blue 19.
I have the basic for it to fire wired, which is frustrating. I also ran a new wire from the pcm directly to the fuel pump relay just to make sure I don't have any short in the harness.
so with all the grounds good, and the pcm power good, i should at least be able to connect and read it with my obd2 connector directly coming off the pcm now with my rewire.
ugg when i did my 24x conversion, this fired up right away with this pcm and I repinned my entire lt1 harness from scratch.
now actually using a ls1 harness I can't get it to fire
05-07-2012, 12:37 PM
#13
i just ran a new wire to pin 58 that's about 18" long, I have the obd2 now by the pcm to eliminate anything in the wiring harness.
I had a lt1 engine in here running 24x with this pcm. so the only new variable here is the ls1 harness and the ls1 engine. everything else is the same as it was in the car previously.
I had a lt1 engine in here running 24x with this pcm. so the only new variable here is the ls1 harness and the ls1 engine. everything else is the same as it was in the car previously.
05-07-2012, 06:10 PM
#14
and it RUNS! Thanks to G-Body for stopping by to help me out!!! Turned out to be my constant power was failing under load and pcm wasn't getting enough power to turn on. I used what I thought was a good constant, but once we checked it under load, we realized it was not ( it was the air pump relay constant for those searching and don't tap that for constant power for the PCM) Once we reran the constant power it fired right up.
05-08-2012, 12:39 PM
#16
Completely agree and I thought I had it through the factory harness. I was trying to use as much factory wiring as possible myself, and just got greedy too quickly with this circuit. Now I have a 10amp fuse going directly to the battery power distribution box
Now I can finish off the rest of the wiring and get my alternator signal and all the other gauges working. Your thread on that is helping big Merv, thanks!
Now I can finish off the rest of the wiring and get my alternator signal and all the other gauges working. Your thread on that is helping big Merv, thanks!
05-08-2012, 03:36 PM
#19
when it goes well, it's the easiest thing, when it doesn't it just takes longer, but don't let it scare you. It is really simple and easy, one line at a time and don't overlook any of the details (e.g. like my obvious overlooking of just assuming my constant power was good enough that I had in the harness. Trace it back and test it to make sure you really have good constant power that doesn't drop voltage under load like mine did).
