Ecu/pcm Logic For 2003-2007 Classic

Chevydriver · February 4, 2010

I salvaged the low mileage engine out of my 2003 Silverado and put it on a stand to play with. It is a 4.8 vortec, but the electronics I understand is universal between the 4.8 5.3 and 6.0.

Using GM wiring schematics, I have it wired almost identically to the factory setup(took me a couple months of spare time). Everything pertaining to all modules is complete except i did not attach the BCM or any transmission circutry. I have a seethrough plastic tub containing the fuel system and see that it is working properly. I have an off/run toggle switch and a push to start button that supplies 12v to the "crank volt" wire if depressed.

When I start the engine, I have to run the hot directly to the solenoid wire and the engine will run for 1-2 seconds and shut off. If I try run the start signal through the ECU(by sending 12v to the crank volt wire), it does not crank. I also tried grounding the 4 ECU wires that go to the transmission park/neutral sensor. If I depress the accelerator while starting, it doesn't even sputter- but not touching the accelerator allows the engine to run for 1-2 seconds.

When I hook up the OBDII, I only have a code for evap (I never hooked that crap up), I reset the code and still only get the engine to run for 2 seconds.

Any idea what is inhibiting the ECU from running the engine for longer than 2 seconds? Thanks.

truckofwinandawesome · February 4, 2010

I salvaged the low mileage engine out of my 2003 Silverado and put it on a stand to play with. It is a 4.8 vortec, but the electronics I understand is universal between the 4.8 5.3 and 6.0.

Using GM wiring schematics, I have it wired almost identically to the factory setup(took me a couple months of spare time). Everything pertaining to all modules is complete except i did not attach the BCM or any transmission circutry. I have a seethrough plastic tub containing the fuel system and see that it is working properly. I have an off/run toggle switch and a push to start button that supplies 12v to the "crank volt" wire if depressed.

When I start the engine, I have to run the hot directly to the solenoid wire and the engine will run for 1-2 seconds and shut off. If I try run the start signal through the ECU(by sending 12v to the crank volt wire), it does not crank. I also tried grounding the 4 ECU wires that go to the transmission park/neutral sensor. If I depress the accelerator while starting, it doesn't even sputter- but not touching the accelerator allows the engine to run for 1-2 seconds.

When I hook up the OBDII, I only have a code for evap (I never hooked that crap up), I reset the code and still only get the engine to run for 2 seconds.

Any idea what is inhibiting the ECU from running the engine for longer than 2 seconds? Thanks.

I might be wrong, but I think it might be the PassKey system (or in this case, Lack Thereof) the PCM is not seeing the 'go' signal from the Anti-Theft part of the BCM, so the PCM 'thinks' its being stolen, so its pulling the plug on the injectors.

thearborbarber · February 4, 2010

The above was the first thing that came to mind as well.

Chevydriver · February 4, 2010

quote]

I might be wrong, but I think it might be the PassKey system (or in this case, Lack Thereof) the PCM is not seeing the 'go' signal from the Anti-Theft part of the BCM, so the PCM 'thinks' its being stolen, so its pulling the plug on the injectors.

Thanks for the insight... I suspected it might be that; however, I am surprised that the engine will run for 2 seconds and not be completely inhibited.

I still have the original BCM and lock and keys- just have to find a BCM wiring harness as mine got tossed. I would like to avoid this PassKey thing unless it is absolutely necessary. Any other possible causes for this situation?

Is there some resource available that shows all the conditions that must be met in the ECU for the start? Looking at EFI Live, I see that one can only change "clutch depress to start" for starting requirements but not a whole lot more to removing the barriers to a successful start.

cgalford · February 5, 2010

I love your setup, looks like fun. I agree with the other, its a immobilizer thing. Run for 2 seconds then die and not restart is what would happen when we would install remote starts and not have the immobilizer programed right.

Found this online: http://motorage.search-autoparts.com/motor...809/article.pdf

It says the BCM is what decides the start condition and sends PWM to the ECU so unless you have a pretty high end function generator it would be easiest to incorporate the BCM into your set up.

thearborbarber · February 5, 2010

HP Tuners will let you turn it off.

VATS is Vehicle Anti Thenft System

Rat4go · February 5, 2010

While it might be passkey, I'd bet that it's something else. I learned the hard way that the Trans needs to send a signal to ECM (or BCM per above comments) saying you're in Park or Neutral so that the PCM will enable starter relay (just ask one of us Allison owners who had to replace the Neutral Start switch at the trans!!).

truckofwinandawesome · February 5, 2010

I love your setup, looks like fun. I agree with the other, its a immobilizer thing. Run for 2 seconds then die and not restart is what would happen when we would install remote starts and not have the immobilizer programed right.

Found this online: http://motorage.search-autoparts.com/motor...809/article.pdf

It says the BCM is what decides the start condition and sends PWM to the ECU so unless you have a pretty high end function generator it would be easiest to incorporate the BCM into your set up.

that's a good idea, but there's one problem, he threw away his BCM Harness.

Chevydriver · February 7, 2010

Thanks for all of the good ideas, guys... I will report back with it if/when I get it running.

Thanks for the screenshot, arborbarber, it is good to know that HP Tuners has that feature. I was thinking about picking up EFI Live, but perhaps I will go that route. How do you like HPTuners?

I am out of town for a few days with work, but will give the Passlock+BCM wiring a try in the next week or so.

minibike132 · February 7, 2010

I might be wrong, but I think it might be the PassKey system (or in this case, Lack Thereof) the PCM is not seeing the 'go' signal from the Anti-Theft part of the BCM, so the PCM 'thinks' its being stolen, so its pulling the plug on the injectors.

Thanks for the insight... I suspected it might be that; however, I am surprised that the engine will run for 2 seconds and not be completely inhibited.

I still have the original BCM and lock and keys- just have to find a BCM wiring harness as mine got tossed. I would like to avoid this PassKey thing unless it is absolutely necessary. Any other possible causes for this situation?

Is there some resource available that shows all the conditions that must be met in the ECU for the start? Looking at EFI Live, I see that one can only change "clutch depress to start" for starting requirements but not a whole lot more to removing the barriers to a successful start.

Crap you really have aot of time on your hands. You should donate that setup to a local automotive program. It looks pretty close to what you might see in a GM training facility.

Chevydriver · February 16, 2010

Thanks for all the info, guys, especially 09LowesSilverado and arborbarber.

Turns out it was the PassKey system. I bought a BCM wiring harness out of an '04 Silverado from a local wrecker and wired the BCM to my ECU and key cylinder(BCM+key+ECU were all the originals from the same truck)

I rotated the key at the same time as pressing my toggle switches and "voila!", the engine started! After trying this a few times, I cut the wires between the ECU and BCM while the engine was running to set the VATS into the "fail enable" mode. I left it overnight with the battery power off and tried it again this morning and it started right up with only the toggle switches and the key and BCM removed from the system.