Wire to draw PCM power

[Gordonr1973]

http://67-72chevytrucks.com/vboard/s...d.php?t=461018

Hi,

quick question for you all if you have a minute...

I understand that not all wires have power to them when the key is cranking the motor.

I need to find a wire to draw power off during cranking as well as when the key is in the 'on position' for my PCM so my engine will fire and continue to run.

I don't have power in the wire I chose before when the key is in on position.

Which wire did you use to power my PCM?

I got my PCM & wiring harness from PSI Conversions and their instructions & diagrams are pretty weak.

I think that they expect me to supply the source wire (maybe one that is always on) to the relay in their supplied fuse block and the relay will switch it into two power sources....one always on and one one with ignition??) I'm not 100% positive but I will do some investigating today.

Thanks!



(this below is a msg that Ben sent me to help out and my response if it gives a bit more info to narrow down stuff)



Thanks Ben;

I'll look again for a distributor wire I can use....I rewired my truck with a Painless harness and it's been a battle to get things right; next time I will rewire myself using the existing stock harnesses for the truck & the LS motor.

Do you know which PCM pins these two sources of power are going to the PCM?

I got my PCM & wiring harness from PSI Conversions and their instructions & diagrams are pretty weak.

I think that they expect me to supply the source wire (maybe one that is always on) to the relay in their supplied fuse block and the relay will switch it into two power sources....one always on and one one with ignition??) I'm not 100% positive but I will do some investigaing today.

I can get the motor to crank no problem and there is fuel pressure to the rails but I just can't get it to fire and I'm pretty sure this PCM power issue I'm having is the issue to fix.

Gordon



Gordon

Gordon, The large purple wire should only have power during cranking and is only used to activate the starter. On my swap, I did add a relay to the starter circuit and used the truck's purple wire for + and the neutral safety switch for - to activate the relay. The relay I added is unnecessary for for normal operation, I just did it to take the load off of the ignition switch because I've seen a few melt and to make use of the LS neutral safety switch.
You probably know this, but the PCM needs two sources of power, constant which should always have power as long as the battery is hooked up and Key on power. For "key on power" for I was able to use the wire that originally went to the distributor. The distributor wire triggers a relay which the supplies the PCM and everything else on the engine with power.

Hope this helps, Ben

[Gordonr1973]

Here's what is happening now....

I did use a coil power wire that had power both with on ignition and during cranking.

Still did not fire.

http://youtu.be/KBNVtI3HHKQ

[gringoloco]

Sounds like you have that part wired correctly. Do you have spark? Fuel pressure?

[Gordonr1973]

Definitely have fuel pressure and I made sure the fuel rails were full of fresh gas before cranking it.

Also double checked my fuel pumps to make sure they were operating and the switch valve between tanks is good.

I'm going to start with the multimeter right now and start checking circuits but I'm pretty sure all the wires are hooked up correctly and that all the grounds are good. I might change the PCM ground to another site that I am running for grounds for the gauges & radio that I know is proven a good ground point.

[usmcchevy]

I replied to your pm with the pins. You can use a jumper wire straight to the battery for the key on power just to test, but if it starts the only way to kill it is to remove the jumper.
Posted via Mobile Device

[gringoloco]

If you have fuel pressure, I'd say the PCM is working. Does the PCM prime your fuel pump at key on? Maybe clogged injectors? Are you getting spark from the coils?

[Gordonr1973]

Hi Ben: yes I saw the PM, thanks!

I brought a wire directly from the battery to the "key-on" power-in switch on my ignition relay just for testing and I put a fuse on it too.

Gringoloco, you are correct: I did some searching with the multimeter and found that there wasn't a constant power supply (which the relay would connect through it when the relay would be triggered) for the ignition system coming to the ignition relay.

So I mapped it backwards and found that it was connected as a ground wire (it really looked like a ground wire).

I connected it up to the starter on the same terminal that the power in from the battery connects to.

I did start, but ran rough! and cut out after a few seconds. PSI Conversions was supposed to delete the VATs so I don't think that is causing it.

I'm going to check a bunch of lines and wires while the garage airs out, then I'll try it again and take a video.

If anyone has any suggestions on why its running rough, feel free to say.

One other thing, there aren't any muffers on it yet so maybe that lack of backpressure might have something to do with it.

[Gordonr1973]

http://youtu.be/oSYJa33Zncs

Maybe it is the VATs??

[gringoloco]

Could be a number of things: VATS, tune if you have modifications, crank re-learn, dirty injectors... Do some searching on those things on LS1tech- lots of good info and this kind of thing happens quite frequently on start up.

Congrats on getting it going! You'll get it figured out

[ls1nova71]

Originally Posted by gringoloco

Maybe clogged injectors?

This would be my guess as to why it runs rough. If VATS isn't tuned out it will run fine for a second or so, not rough. If the engine has been sitting for an extended period of time, the crap they put in gas these days tends to varnish/stick them.

EDIT: I just watched your video, that does indeed sound like VATS is killing it, unless what you have your power hooked to is losing power after a second or so. Is it dieing when you let off the key? You have power in the crank position, are you sure you have power in the run position?

[Lower]

It could be the vats but it also sounds like its trying to still run but running out of fuel

[Gordonr1973]

Originally Posted by ls1nova71

This would be my guess as to why it runs rough. If VATS isn't tuned out it will run fine for a second or so, not rough. If the engine has been sitting for an extended period of time, the crap they put in gas these days tends to varnish/stick them.

EDIT: I just watched your video, that does indeed sound like VATS is killing it, unless what you have your power hooked to is losing power after a second or so. Is it dieing when you let off the key? You have power in the crank position, are you sure you have power in the run position?

Yes it has power in the run position because I ran the ignition relay power directly off of the battery...but I will check it again.

The engine was totally torn down, cleaned, then rebuilt with a new Compcam Camshaft, springs and rods.

I did soak the injectors in cleaner overnite before reinstalling them in the fuel rails so they shoud be fairly clean.

PSI was supposed to reprogram the PCM too with these new parameters, but I can't guarantee what they actually did.

[Gordonr1973]

Originally Posted by Lower

It could be the vats but it also sounds like its trying to still run but running out of fuel

The fuel pumps might be it....I can hear them pressurize the fuel system when I first click the key on but the way I wired them was stock to 1987 --- spliced them into the wire off of the tank selector switch and had the tank selector switch provide power to them.

I'm not sure if I should be powering the fuel pumps off of the fuel pump relay that was included with the PCM fuse block as I have two fuel pumps / one in each tank.

[Tri5Nerd]

I think you need to to a relearn, I had to do that to my setup and I ran it directly from the battery after it relearned, try doing a relearn using the direct battery connection and see if the rough idle goes away.

Tri5

[tk-mpl]

By the sounds in the video it seems to be the VATS killing it. I had a mess of problems with getting mine started, but turned out to be tuning. I wasn't getting a flare up at all. It would just crank and not start. If you have a noid light plug it into the #1 injector connector, a 194 bulb with the terminals bent down will work to. see if you are getting injector pulse after it dies, keep it cranking. If you are using a mass air flow sensor try unplugging it. That will put it into default mode. I have seen it a couple of times where the MAF sensor is no good and the engine will start and die like VATS..
Any codes setting???
Sorry, I did not read your build thread... Post some details like what year the engine and PCM are..

Trevor

[Gordonr1973]

The engine is a 2004 LQ9 6.0 litre.

PCM and wiring harness were bought separately from PSI conversions. PCM was supposed to be reprogramed by PSI as well.

Engine was torn down, cleaned & rebuilt to the short block by Prostock Performance here in Edmonton. I did the rest.

As for the fuel pumps, that might be it....I can hear them pressurize the fuel system when I first click the key on but the way I wired them was stock to 1987 --- spliced them into the wire off of the tank selector switch and had the tank selector switch provide power to them.

I went out there tonight and was trying to see if I had power to the fuel pumps while the key was just in "on" position --- there doesn't look like there is any power there.

When I checked the pumps earlier, I think I made a mistake. I know for sure the pump grounds are a-okay because I reground the connections on the frame and reconnected them very carefully and checked them with the multimeter.

Any ideas on how to wire the dual tanks verses the fuel tank selector switch verses the fuel relay on the PCM fuse block?

[Gordonr1973]

Originally Posted by Tri5Nerd

I think you need to to a relearn, I had to do that to my setup and I ran it directly from the battery after it relearned, try doing a relearn using the direct battery connection and see if the rough idle goes away.

Tri5

Sorry, how do I go about the steps to do a relearn?

I found this thread but it says I should take it to a dealer?

http://ls1tech.com/forums/pcm-diagno...m-changes.html

Can I command the PCM to do one via an OBD scanner/reader?

[gringoloco]

Crank relearn sounds like a possibility given the rebuild. Maybe try temporarily sucking one of the pumps directly to the harness relay. That will let you at least know if that's you're problem...
Posted via Mobile Device

[Tri5Nerd]

Originally Posted by Gordonr1973

Sorry, how do I go about the steps to do a relearn?

I found this thread but it says I should take it to a dealer?

http://ls1tech.com/forums/pcm-diagno...m-changes.html

Can I command the PCM to do one via an OBD scanner/reader?

Make sure your grounding is correct, ground from engine to chassis and to body.

Try this:

Automatic transmission:
1 Turn off the ignition

2 Restore the PCM battery feed

3 Turn Off the AC controls

4 Set the parking brake and block the drive wheels

5 Start the engine

6 Allow the engine coolant temperature to reach 176 degrees F

7 Shift the transmission selector into the drive range

8 Allow the engine to idle for 5 minutes

9 Turn on the AC controls (Omit for 2000-02 model)

10 Allow the engine to idle for 5 minutes (Omit for 2000-02 model)

11 Shift the transmission selector into Park

12 Allow the engine to idle for 5 minutes (Omit for 2000-02 model)

13 Turn off the AC controls (Omit for 2000-02 model)

14 Allow the engine to idle for 5 minutes

15 Turn off the engine for 15 seconds


Manual Transmission:

1 Turn Off the ignition

2 Restore the PCM battery feed

3 Turn Off the AC controls

4 Set the parking brake and block the drive wheels

5 Transmission in neutral

6 Start the engine

7 Allow the engine coolant temperature to reach 176 degrees F

8 Turn on the AC controls (Omit for 2000-02 model)

9 Allow the engine to idle for 5 minutes (Omit for 2000-02 model)

10 Turn off the AC controls (Omit for 2000-02 model)

11 Allow the engine to idle for 5 minutes

12 Turn off the engine for 15 seconds

[Gordonr1973]

Thanks for that, I will definitely try that after I get the motor to run better.

Am trying to figure out how to match up the duel 1987 in-tank fuel pumps and wiring the fuel system into the LS / PSI fuel relay.

Here's what I was sent from PSI...

Now on my Painless harness, neither power wire that can be used for the fuel switch have power to them during cranking.

However, I cvhecked te PSI fuel relay and it seems to have power when cranking, but not just when I first click on the key to go through the cranking sequence.

That leads me to believe that the PSI relay is only powered when the truck is running.

Does anyone have any thoughts on whether:

1. I should bring power into the supply side of this relay from the battery and then have it go through to the fuel tank selector switch?

2. If I did that would it be pushing too many amps through the fuel tank selector switch and possibly melt the wires?

3.Is there a way to bring less power through the PSI fuel relay, send it to the fuel tank selector switch when the engine is running, then put a relay on each of the wires powering each of the in-tank fuel pumps so power is delivered directly from the battery to the pumps when their respective relay is engaged by the tank selector switch?

I read somewhere that the tank selector switch has a strange set-up inside where it grounds one pump out when the other is engaged or something...

Any thoughts??

[Gordonr1973]

Some PSI instructions if it was a single fuel pump.

[mooseknuckles]

I hope you get this figured out man....

[gringoloco]

Sounds like you're getting fuel when cranking, but losing it when running. What wire did you use from your truck to actuate the fuel relay? You should be using your truck's ignition wire that is hot in START and RUN. The PSI harness appears to be in order, as long as it follows what they have in their instructions...

Your #3 solution sounds doable, but I have no clue on the selector switch operation.

[Gordonr1973]

Thanks everybody for the advice!

Gringo, Tri5, Lower, Ben, Hick & everybody was on the right track b/c when I tore the cab down last year I saw that the previous owner had a couple new fuel selector switches under the seat.

When I took out the wiring harness I also noticed that his harness behind the switch was melted a bit.

So like a robot I just went out and found a new harness connection at the scrap yard thinking that was all it needed....well I was wrong.

What it actually needed was the 1987 TBI fuel selector switch that stays engaged and allows power to flow through it at all times with the key hot.

What the prevous owner had done was just shove the wrong switch into the wrong harness connection that he must have replaced as well at some point.

Anyways, long story short, it runs!

[Gordonr1973]

http://www.youtube.com/watch?v=xmzyt...ature=youtu.be