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ECM Relay Control - 3900 by UND_Sioux
Started on: 09-21-2011 11:32 PM
Replies: 9
Last post by: Joseph Upson on 09-22-2011 04:02 PM
UND_Sioux
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Report this Post09-21-2011 11:32 PM Click Here to See the Profile for UND_SiouxSend a Private Message to UND_SiouxDirect Link to This Post
I'm finally starting the daunting task of wiring my 3900. I took all the wiring from the donor car including and hooked it all up on the garage floor. I wanted to see if I could at least get the engine to turn over. The fuse box has an Main Ignition relay that goes to a Crank Relay. The diagram shows that the relay is powered in "start" and "run" at the fuse box and the other side goes to the ECM "start relay control". When the key is in "run", I'm getting 12 volts between the start relay control wire coming from the ECM and the fuse box. It seems to me that the ECM is providing the ground to close the circuit.

Does anybody know how these newer ECMs work for relay control? I'm wondering if the ECM will shut off the ground allowing the relay to close, and thus send power to the starter solenoid.

I'm stumped at this point. Having relays that are controlled by computers seems like a bad idea. It makes it very difficult to troubleshoot.
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Report this Post09-22-2011 12:06 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzDirect Link to This Post
If power is sent to one side of the relay coil, then the ECM will need to ground the other side to energize the coil and pull up the relay.

There are a number of reasons GM used relays to activate the ignition power to the engine, and to control sending power to the starter solenoid.

On the 3800 swaps the common way to handle it is to NOT use a relay to control power to the ICM and to NOT use a relay to send power to the starter solenoid. The Fireo already has wiring sized large enough to handle both of these circuits that runs directly from the ignition key switch.

Worst case you might need to provide some phantom resistors that are connected to a power source to 'fool' the PCM into thinking the circuits still exist. That is if the PCM monitors those circuits, and if so that it gives a trouble code if they are not as expected and also if they can't be 'programmed out' of the PCM.

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The standard for a fuel pump relay seems to be that the PCM supplies +12v to the relay.

The standard for the other control relays (Fan) seem to be that the relay is supplied power on one side of it's coil and the PCM grounds the other side. Consult your engines specific wiring diagram.

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They used relays controlled by the PCM because they wanted the PCM to be able to control those things. For example if the PCM is in VATs alarm, it might not allow you to crank the engine, even if the key is turned to start. High power items (Starter solenoid, fuel pump, radiator fan) when controlled by the PCM need to be ran through a relay. They use way too much power to run the circuit through the PCM.

[This message has been edited by phonedawgz (edited 09-22-2011).]

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UND_Sioux
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Report this Post09-22-2011 12:15 AM Click Here to See the Profile for UND_SiouxSend a Private Message to UND_SiouxDirect Link to This Post
Here is the diagram. No power is getting to the purple wire at the crank relay. The relay checks out ok.

http://dl.dropbox.com/u/416...plander%20wiring.pdf

When I turn the key, the voltage doesn't change which leads me to believe that somewhere the ECM is not removing the ground. I have all of the matching passkey stuff with the correct key, BCM, ECM, and TCM. It clearly isn't happy about something.
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phonedawgz
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Report this Post09-22-2011 12:45 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzDirect Link to This Post
The PCM will APPLY a ground to the yellow/black wire of the crank relay to crank the engine.

Because there is +12v applied to the other side of the relay, and the PCM isn't grounding the relay, you will read +12v (referenced to ground) on both sides of the coil, that is until the PCM applies ground to the yellow black wire.

You do realize also that this PCM connects to the automatic transmission selector switch (either internal or external) to determine if the engine is in park/neutral? If the transmission is not, the PCM won't energize the relay thus not allowing the starter to crank.

Have you hooked up something to the 'theft' light to see what it is doing?

To me it's simpler to rebuild the harness into what you are wanting, rather than to try to adapt and figure out all the issues and work arounds of the existing harness.

There is no 'crank relay' in a rebuilt harness.

[This message has been edited by phonedawgz (edited 09-22-2011).]

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1fatcat
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Report this Post09-22-2011 12:48 AM Click Here to See the Profile for 1fatcatSend a Private Message to 1fatcatDirect Link to This Post
It looks like you might need the ICM too in order to make it happy. I would do as Phonedawgz said and try to simplify the starter wiring. Eliminate some of the modules if possible.
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Darth Fiero
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Report this Post09-22-2011 01:24 AM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
What vehicle (year/make/model) did you get the PCM from?

Has the PCM been reprogrammed to disable the VATS? If not, it is likely it will NEVER command the crank relay on (to crank the engine) without the BCM and VATS modules connected to it.

Case in point: 3800 Series 3 PCM and wiring. When using a 3800 Series 3 PCM, since the VATS cannot be disabled in the programming of these boxes (yet), you MUST install the BCM and VATS modules from the donor car in your swap so the engine will crank and run using the Series 3 PCM. The BCM connects to all ignition switch circuits, and it is the BCM that sends the engine crank (desired) signal to the PCM. Once the PCM receives the engine crank signal and determines the VATS fuel is enabled, it will activate the crank relay which will send power to the starter solenoid. If the VATS system does not provide a valid fuel-enable password, the engine may not crank at all; and even if it does, fuel injector pulse will be cut.

If you don't have a BCM present in your wiring, then nothing is going to work right - unless you've had the PCM reprogrammed to disable VATS. In which case you will probably need to bypass the crank relay (activate starter directly from ignition switch).

-ryan

------------------
OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

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UND_Sioux
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Report this Post09-22-2011 07:26 AM Click Here to See the Profile for UND_SiouxSend a Private Message to UND_SiouxDirect Link to This Post
That is good advice. That was/is my original plan. I was just curious if it would turn over since I have a BCM, TCM, ECM, and the Passkey module all from the same car. I plan on simplifing the harness because the 2 enormous fuse boxes have a ton off stuff that is not needed.

 
quote
Originally posted by phonedawgz:

The PCM will APPLY a ground to the yellow/black wire of the crank relay to crank the engine.

Because there is +12v applied to the other side of the relay, and the PCM isn't grounding the relay, you will read +12v (referenced to ground) on both sides of the coil, that is until the PCM applies ground to the yellow black wire.

You do realize also that this PCM connects to the automatic transmission selector switch (either internal or external) to determine if the engine is in park/neutral? If the transmission is not, the PCM won't energize the relay thus not allowing the starter to crank.

Have you hooked up something to the 'theft' light to see what it is doing?

To me it's simpler to rebuild the harness into what you are wanting, rather than to try to adapt and figure out all the issues and work arounds of the existing harness.

There is no 'crank relay' in a rebuilt harness.



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UND_Sioux
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Report this Post09-22-2011 07:32 AM Click Here to See the Profile for UND_SiouxSend a Private Message to UND_SiouxDirect Link to This Post
 
quote
Originally posted by Darth Fiero:

What vehicle (year/make/model) did you get the PCM from?

Has the PCM been reprogrammed to disable the VATS? If not, it is likely it will NEVER command the crank relay on (to crank the engine) without the BCM and VATS modules connected to it.

Case in point: 3800 Series 3 PCM and wiring. When using a 3800 Series 3 PCM, since the VATS cannot be disabled in the programming of these boxes (yet), you MUST install the BCM and VATS modules from the donor car in your swap so the engine will crank and run using the Series 3 PCM. The BCM connects to all ignition switch circuits, and it is the BCM that sends the engine crank (desired) signal to the PCM. Once the PCM receives the engine crank signal and determines the VATS fuel is enabled, it will activate the crank relay which will send power to the starter solenoid. If the VATS system does not provide a valid fuel-enable password, the engine may not crank at all; and even if it does, fuel injector pulse will be cut.

If you don't have a BCM present in your wiring, then nothing is going to work right - unless you've had the PCM reprogrammed to disable VATS. In which case you will probably need to bypass the crank relay (activate starter directly from ignition switch).

-ryan



The ECM, TCM, BCM, and Passkey are from a 2006 Uplander. I bought the engine last year and have an ECM and TCM that came with the engine, but I was able to pick up another ECM, and TCM when I found an Uplander recently. I was able to take just about everything. Right now, everything is plugged in including the BCM and I have the Uplander steering column sitting on the floor with everything connected. I'm actually trying to crank it from the Uplander column in the conventional way through the factory harness at the BCM.
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Darth Fiero
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Report this Post09-22-2011 02:23 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
 
quote
Originally posted by UND_Sioux:


The ECM, TCM, BCM, and Passkey are from a 2006 Uplander. I bought the engine last year and have an ECM and TCM that came with the engine, but I was able to pick up another ECM, and TCM when I found an Uplander recently. I was able to take just about everything. Right now, everything is plugged in including the BCM and I have the Uplander steering column sitting on the floor with everything connected. I'm actually trying to crank it from the Uplander column in the conventional way through the factory harness at the BCM.


I built a custom mail order harness for a guy with a street rod earlier this year. He had a 2005 3800 Series 3 SC engine and was keeping the drive-by-wire which meant he was using the 2005 Series 3 PCM. He sent me the BCM and VATS modules from the same donor car but the PCM came from a different vehicle. After I finished building the harness, I discovered the BCM/PCM would not command the engine to crank. I attempted to do a PassKey3 relearn and while the learning procedure was successful, the BCM disabled cranking because the VIN in the PCM didn't match what was on the BCM. I had to reflash the PCM with a VIN that matched the BCM so cranking would be enabled. The BCM was locked (factory issue) so it could not be reprogrammed, not even by my Tech 2 while connected to GM SPS. After I did all that and re-learned the VATS again, the crank relay was activated when the key was turned to crank.

I boxed everything up and sent it to the customer. After he got it installed, the engine would not crank. He had to do the VATS relearn again - then it worked. I can only assume there must have been some change in the signal the VATS module saw when it was installed in the vehicle vs. what it saw sitting on my table in the shop.

So those are two things right there you will need to look for - that the VIN numbers on the BCM and ECM (and if applicable, TCM) all match; and that you do the proper VATS relearn for your system; which is explained below:

 
quote

30-Minute Relearn Procedure
Use this procedure after replacing the following components:

• The PASS-Key III (PK3) keys

• The BCM

• The PCM

Important: This procedure is not available on vehicles equipped with option code (Z49).

If replacing a BCM with an GM SPO replacement part, perform the procedure to setup a new BCM prior to the 30-Minute Relearn Procedure.


•With a master PASS-Key III key, rotate the ignition to the CRANK position.
•Observe the SECURITY telltale. After approximately 10 minutes, the telltale will turn OFF.
•Turn OFF the ignition, and wait 5 seconds.
•Repeat steps 1-3 two more times for a total of 3 cycles or 30 minutes.
Important: The vehicle learns the key transponder information and/or passwords on the ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.

•With a master PASS-Key III key, start the vehicle. The vehicle has now learned the key transponder information and the PCM has now learned the fuel continue password.
•With a scan tool, clear any DTCs.


Good luck and let me know how it turns out.

-ryan
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Joseph Upson
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Report this Post09-22-2011 04:02 PM Click Here to See the Profile for Joseph UpsonClick Here to Email Joseph UpsonSend a Private Message to Joseph UpsonDirect Link to This Post
Sounds like you may need to invest in the HELMS shop manual/CD for your swap. It should have all of the technical info necessary to make getting past the trouble spots easier.

You may want to consider looking for a cooler thermostat to substitute in place of the OE, you will not find an exact replacement but you should be able to find something with the appropriate diameter. The reason being the relocation of the thermostat to the water pump housing and the overall design has a tendency to keep the engine running on the warm side and there may also be some efficiency differences between the Fiero water pump and the fwd water pump that maybe more pronounced as a result of the design change.

The coolant configuration has a loop design where in you always have some hot coolant coming from the heads being recirculated right back to the water pump instead of directly to the radiator.
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