Powering a LS3 ECU from PDM 30

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Powering a LS3 ECU from PDM 30

Postby Ironhead on Sat Feb 06, 2021 8:12 am

Hello,

I am finished a built that is powered by a PDM30. Car has two CAN bus, one from the PDM to an AIM dash, and one from the ECU to the AIM dash.

Everything is pretty much configured and working as intended, except the GM ECU for the LS3 (LS3 376/525 crate engine).

I have the PDM supplying power to the four pins on the ECU that get power from the GM wiring harness that came with the ECU. My problem: When these power sources are switched on, the ECU is not coming on. It stays "dead".

The stock wiring harness powers the ECU in a sequence from three relays. It gets power from the ignition switch to a couple of pins, then sends signals out to the other relays which switch power on the the final two pins on the ECU. I am assuming that is the basis of my problem....that switching power to all four pins on the ECU simultaneously is not what the ECU wants, and that somehow a "sequence" during start-up is necessary for the ECU to properly power on. That's just my theory though....I really don't know. I don't know what else to try, as I have checked my wiring 100 times....

Is there anyone here who has used a PDM to power a GM LS ECU who might have some insight into this?
Ironhead
 
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Re: Powering a LS3 ECU from PDM 30

Postby David Ferguson on Sat Feb 06, 2021 10:10 am

Doesn't the crate motor ECU have some documentation as to the expected power inputs?

A quick google reveals many threads that mention different models of GM ECUs - for example on one ECU, connector C1 has HAAT (hot at all times -- constant power) to pins 20 & 57, then Switched Ignition Power to pin 19 and 75 are only hot when cranking or run.

Here's a website with lots of info:
https://lt1swap.com/wiringharness.htm

I would start with enabling the HAAT first, then turn on the Switched Ignition Power inputs (and coils / injectors) with the ignition switch.
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Re: Powering a LS3 ECU from PDM 30

Postby Ironhead on Sat Feb 06, 2021 11:27 am

Thanks for the help, but I guess I didn't phrase my question very well...

I know which pins are powered under what conditions, based on the supplied wiring harness and relay box. There are no HAAT pins, blue (connector) pins 10 and 19 power on immediately when +12V is switched by on to the ignition power relay. The MAF also gets power from this relay.

ECU blue pin 40 sends a ground signal to turn on the PT main relay. This in turn powers black (connector) pins 13 and 28 on the ECU, and also sends power to the coils, injectors, and O2 sensors.

Blue pin 13 on the ECU sends a +12V signal to the fuel pump relay and turns it on.

Powering on all these things at the same time doesn't work. The ECU doesn't come on. I have tried using the various relay activation signals from the ECU as inputs to the PDM in hopes of duplicating the power on sequence in a manner the ECU would recognize, using .10 second delays to hopefully simulate the relays in the mix. Thus far, this hasn't worked either.

Either I have the timing wrong, or I am completely mis-diagnosing the problem. I just figured if indeed this sequencing is necessary to get the ECU to function, I figured someone on here would have encountered the problem before.
Ironhead
 
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Re: Powering a LS3 ECU from PDM 30

Postby stevieturbo on Sun Feb 07, 2021 1:05 am

Have you actually been able to power up the GM ecu at all ?

And what do the wiring instructions for the crate/ecu package state ?
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Re: Powering a LS3 ECU from PDM 30

Postby Ironhead on Sun Feb 07, 2021 8:13 am

stevieturbo wrote:Have you actually been able to power up the GM ecu at all ?

And what do the wiring instructions for the crate/ecu package state ?


Nope, I've got everything else on the car working through the PDM just fine, but have never even had the ECU power up.

The ECU/crate engine came with a wiring harness and a fuse/relay box, but since I am using the PDM, I made my own harness.
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Re: Powering a LS3 ECU from PDM 30

Postby Ironhead on Wed Feb 10, 2021 7:21 am

Disregard Gents, I got it sorted.
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Re: Powering a LS3 ECU from PDM 30

Postby David Ferguson on Wed Feb 10, 2021 12:11 pm

Any insights to share?
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Re: Powering a LS3 ECU from PDM 30

Postby Ironhead on Wed Feb 10, 2021 12:40 pm

David Ferguson wrote:Any insights to share?


Nothing brilliant...

Basically I thought the E67 LS3 ECM had four power inputs to function. It has five....that was the biggest part of the problem.

I got it working with the .1 sec delay between power outputs as the ECM sends inputs to the PDM, but it might also work switching them on all at once (although I've heard it won't). It works as I have it now, and I'm tired of dicking around with it. Now I'm having trouble getting the ECM CAN to talk to my AIM dash....

In my defense, the LS world is surprisingly complex. So many generations of engine, going back 20 years +, multiple different ECMs and pinouts. Clear application correct advice is hard to dig up.

Thanks all.
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