New build & OBD1 LT1 PCM won't turn on??
03-21-2010, 05:38 PM
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New build & OBD1 LT1 PCM won't turn on?? Just finished assembling a 95 LT1 setup using a modified Roadmaster wiring harness. All the emissions crap was stripped, wiring harness was split out and rerouted and tucked. Everything should be fine (TPS, IAC, Opti, Injectors, water temp sensor, Ignition, etc). Turn key, fuel pump does not fire & cannot connect via laptop.
Checked battery and grounds at PCM, all good. Fuel pump fires when you send it the ground, injectors all wired good and fire when you send them a ground. Using a known good PCM that worked when removed last fall.
No clue where to start looking, need some direction. First question, what sensors are required for the PCM to initialize the fuel pump? Is there something that is needed before the PCM will send a ground to the fuel pump? Or perhaps teh proper question is are there sensors required before the PCM will even talk via the ALDL port?
Could the addition of a MSD 6AL cause the PCM to not turn on?? That's the only oddball thing but it should be wired correctly (I'll double check that next)
Help!
Wallyman
Checked battery and grounds at PCM, all good. Fuel pump fires when you send it the ground, injectors all wired good and fire when you send them a ground. Using a known good PCM that worked when removed last fall.
No clue where to start looking, need some direction. First question, what sensors are required for the PCM to initialize the fuel pump? Is there something that is needed before the PCM will send a ground to the fuel pump? Or perhaps teh proper question is are there sensors required before the PCM will even talk via the ALDL port?
Could the addition of a MSD 6AL cause the PCM to not turn on?? That's the only oddball thing but it should be wired correctly (I'll double check that next)
Help!
Wallyman
03-21-2010, 05:51 PM
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Some progress but not enough..
Have comms now, sensors all appear to be reading. IAT, MAP, TPS, both O2's, coolant temp.. still won't turn fuel pump on, though. Crank, no start and don't hear the injectors firing.
Wallyman
Have comms now, sensors all appear to be reading. IAT, MAP, TPS, both O2's, coolant temp.. still won't turn fuel pump on, though. Crank, no start and don't hear the injectors firing.
Wallyman
03-21-2010, 05:59 PM
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FWIW, last year before we disabled VATS it would start and run for 3 seconds.. the injectors and fuel pump are just not firing this time.
03-21-2010, 06:10 PM
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Might have a bad opti.. just plugged in a spare and spun it and the injectors fire, but fuel pump is still not turning on for prime.
Can't tell if the injectors are firing when cranking that well due to open headers, but can't feel them or hear any clicking over the open exhaust so assuming no fire on them.
Regardless, the fuel pump not priming is the primary issue (and probably *the* issue).. but I don't know why the PCM wouldn't prime???
What is required to be present to get a valid prime output? Even with VATS enabled, it primed but it wouldn't keep running after it started.
Can't tell if the injectors are firing when cranking that well due to open headers, but can't feel them or hear any clicking over the open exhaust so assuming no fire on them.
Regardless, the fuel pump not priming is the primary issue (and probably *the* issue).. but I don't know why the PCM wouldn't prime???
What is required to be present to get a valid prime output? Even with VATS enabled, it primed but it wouldn't keep running after it started.
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03-22-2010, 06:16 PM
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Checked every wire continuity and I found nothing out of place, everything goes where it is supposed to go. Double checked MSD, also wired per directions.
No prime, no injectors firing, pretty sure it's not firing either.
Need help guys, I'm stuck here.
No prime, no injectors firing, pretty sure it's not firing either.
Need help guys, I'm stuck here.
03-22-2010, 07:35 PM
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I just took a spare harness, no sensors, nothing.. just hooked power and ground and hooked up the PCM. Checked the FP lead, and it triggers properly.. WTF.
Not a single thing on this harness except PCM, and it WORKS?!?!?! Soooooo.... the proper question is what is fucked in my harness that is preventing it from working properly???
03-26-2010, 07:49 AM
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Ahhhh..... feel better now... a little, anyhow. Was feeling quite frustrated after 3 months of daily work and stuck with a simple problem. I'm better now. 
Thanks to those that have offered insights, but the problem persists. The relay wasn't triggering. I broke out the ohm meter, and the PCM sends a ~600ohm to ground signal to the fuel pump wire, not enough to trigger a light or a relay though. Ended up bypassing and just grounding the relay to get the car running.
Other issues, perhaps related, perhaps not:
1 - Cooling fan turns on with key on, which indicates trouble code of some sort, right? I don't have a CEL/SES light hooked up yet so can't tell if it is on.
2 - Can't communicate with PCM via laptop at all now. Can't pull the program, can't datalog. I need to have Autozone/Advance pull the codes if they can, maybe that will shed some light.
The build is this:
94 Impala SS block, 0.030 bore, 10.9:1 CR
Keith Black -7cc Hypereurtectic pistons
Comp 467 cam
Manley double valve springs
BBK 58mm TB
ported and match intake to the TB and heads
2.00 and 1.55 valves in stock alum. heads, ported, polished
Crane gold 1.6 RRs
30lb Accell injectors
dual 2.25" exhaust, no cats, Magnaflow 6" cans (in a 91 RX7, not much room under there)
Stock PCM tune right now (-AIR/AC/EGR/VATS/speed limiter, etc) because I can't load MadZ tune I bought.
Car starts and idles fine (a little high idle most times), and runs strong. Seems to be relatively fine (never had a cammed car so new territory for me, but it feels right so far).
Going to try and get the codes pulled, then report back.. any further thougths, anyone?
Thanks to those that have offered insights, but the problem persists. The relay wasn't triggering. I broke out the ohm meter, and the PCM sends a ~600ohm to ground signal to the fuel pump wire, not enough to trigger a light or a relay though. Ended up bypassing and just grounding the relay to get the car running.
Other issues, perhaps related, perhaps not:
1 - Cooling fan turns on with key on, which indicates trouble code of some sort, right? I don't have a CEL/SES light hooked up yet so can't tell if it is on.
2 - Can't communicate with PCM via laptop at all now. Can't pull the program, can't datalog. I need to have Autozone/Advance pull the codes if they can, maybe that will shed some light.
The build is this:
94 Impala SS block, 0.030 bore, 10.9:1 CR
Keith Black -7cc Hypereurtectic pistons
Comp 467 cam
Manley double valve springs
BBK 58mm TB
ported and match intake to the TB and heads
2.00 and 1.55 valves in stock alum. heads, ported, polished
Crane gold 1.6 RRs
30lb Accell injectors
dual 2.25" exhaust, no cats, Magnaflow 6" cans (in a 91 RX7, not much room under there)
Stock PCM tune right now (-AIR/AC/EGR/VATS/speed limiter, etc) because I can't load MadZ tune I bought.
Car starts and idles fine (a little high idle most times), and runs strong. Seems to be relatively fine (never had a cammed car so new territory for me, but it feels right so far).
Going to try and get the codes pulled, then report back.. any further thougths, anyone?
