Couple of wiring questions
Thread Starter
TECH Junkie
Joined: Dec 2012
Posts: 3,615
Likes: 1,327
From: Iowa
Couple of wiring questions Hi All,
I'm using LT1swap for thier pinouts of the pcm and relay box. Some fantastic info there as most already know. I have a couple of questions i think can be answered here.
For pin 71 on the blue connector, tow/haul mode switch, does it need to be supplied with a ground, or a 12v+ signal? My idea is to use this function to switch the trans shift points and aggressiveness for street driving vs track driving. I would like to keep the shift points and mainly converter lockup very docile for the street, then up the shift points, bump the pressure a little, and make sure the converter doesn't lock and wipe out the single disc clutch.
Secondly is regarding the VATS. I can't seem to find the answer worded the way that makes sense in my head so I'll just ask again. Since i'm swapping this engine into something else, will it start without disabling VATS using hp tuners? I will be making a custom relay/fuse board to supply all pcm power supply and key'd on voltage as well. Since the pcm will be powered up, what would be keeping it from firing up? Im not sure how the BCM and PCM communicate and how not having the BCM could cause a no-start as long as i'm giving everything the power it needs.
Thanks for your help everyone!
I'm using LT1swap for thier pinouts of the pcm and relay box. Some fantastic info there as most already know. I have a couple of questions i think can be answered here.
For pin 71 on the blue connector, tow/haul mode switch, does it need to be supplied with a ground, or a 12v+ signal? My idea is to use this function to switch the trans shift points and aggressiveness for street driving vs track driving. I would like to keep the shift points and mainly converter lockup very docile for the street, then up the shift points, bump the pressure a little, and make sure the converter doesn't lock and wipe out the single disc clutch.
Secondly is regarding the VATS. I can't seem to find the answer worded the way that makes sense in my head so I'll just ask again. Since i'm swapping this engine into something else, will it start without disabling VATS using hp tuners? I will be making a custom relay/fuse board to supply all pcm power supply and key'd on voltage as well. Since the pcm will be powered up, what would be keeping it from firing up? Im not sure how the BCM and PCM communicate and how not having the BCM could cause a no-start as long as i'm giving everything the power it needs.
Thanks for your help everyone!
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Joined: Mar 2014
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From: Ohio
Yes, VATS will disable it. It MIGHT start, but it will die immediately. They will have to be turned off. There are some workarounds, but they're usually unreliable.
As for the Tow switch, it supplies ground to the PCM.
As for the Tow switch, it supplies ground to the PCM.
Thread Starter
TECH Junkie
Joined: Dec 2012
Posts: 3,615
Likes: 1,327
From: Iowa
Ok, thanks for the quick reply. Can you explain for me how/what the vats system shuts down? I guess I just don't understand how if the PCM is getting key'd ignition voltage, why it wouldn't run. I'm sure there is something i'm missing, i'm just not sure what it is.
I don't see any pinouts on the PCM that communicate with the BCM. I guess I thought that the BCM would just not supply voltage to the PCM when it wanted to shut things down. For example it wouldn't power the injectors, or it wouldn't supply the coils. something along those lines. But, since i'm powering those via a separate fuse block that will come on with key'd voltage, what is there to keep it from running?
Sorry for the long winded reply, I'm just trying to make sure I have good comprehension of how the system works.
I don't see any pinouts on the PCM that communicate with the BCM. I guess I thought that the BCM would just not supply voltage to the PCM when it wanted to shut things down. For example it wouldn't power the injectors, or it wouldn't supply the coils. something along those lines. But, since i'm powering those via a separate fuse block that will come on with key'd voltage, what is there to keep it from running?
Sorry for the long winded reply, I'm just trying to make sure I have good comprehension of how the system works.
Restricted User
Joined: Mar 2014
Posts: 7,192
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From: Ohio
Blue connector, pin 30, dark blue wire is the wire for the VATS fuel enable in most cases. The VATS module supplies a 30 hz signal to the PCM.
Wiring diagrams like LT1swap don't show this because you would never pin the VATS module in when doing a swap, and the wire comes from the BCM, so its usually labeled as "Not Used".
Wiring diagrams like LT1swap don't show this because you would never pin the VATS module in when doing a swap, and the wire comes from the BCM, so its usually labeled as "Not Used".
Thread Starter
TECH Junkie
Joined: Dec 2012
Posts: 3,615
Likes: 1,327
From: Iowa
Ok, so here is the link I'm using. http://lt1swap.com/99-02_vortec_pcm.htm
Just so I'm clear about what i'm using, so i can get the best help, I have a 1999 silverado engine, transmission, harness, and pcm. Just as it came from the truck. This link for pin 30 on the blue shows it being for coolant level switch.
The red connector pin 30 says not used. Could that be it? I would ideally like to be able to start and run this engine without VATS getting in the way. If that means i HAVE to use HPtuners to delete it, then fine. But if I do that, I'd really like to understand the WHY behind it.
I appreciate your help joe!
Just so I'm clear about what i'm using, so i can get the best help, I have a 1999 silverado engine, transmission, harness, and pcm. Just as it came from the truck. This link for pin 30 on the blue shows it being for coolant level switch.
The red connector pin 30 says not used. Could that be it? I would ideally like to be able to start and run this engine without VATS getting in the way. If that means i HAVE to use HPtuners to delete it, then fine. But if I do that, I'd really like to understand the WHY behind it.
I appreciate your help joe!
Restricted User
Joined: Mar 2014
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From: Ohio
You can bypass the vats temporarily with a resistor, but its known to be fairly unreliable. Its also a lot harder to figure out in a swapped vehicle than it is the original engine/vehicle combination still together.
There are cheap VATS bypass kits on ebay.
There are cheap VATS bypass kits on ebay.
Restricted User
Joined: Mar 2014
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From: Ohio
Nevermind, you have a truck PCM. I ignored that part apparently.
The security setup is different on the trucks, and there isn't a lot of documentation on it.
It doesn't use the exact same VATS system as the F-body did. The PCM doesn't receive the same signal as the F-body to turn off the VATS.
I would have to do a bit more research.
The security setup is different on the trucks, and there isn't a lot of documentation on it.
It doesn't use the exact same VATS system as the F-body did. The PCM doesn't receive the same signal as the F-body to turn off the VATS.
I would have to do a bit more research.
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To put it in layman's terms, VATS works like this... If the BCM doesn't see the right key in the ignition, it sends a message to the PCM via the serial data wire and says "don't allow the engine to start". Just because you have power to everything doesn't take away the PCM's ability to control everything, that's it's job. Just have the tune set to no VATS and be done with it, you're going to be changing other things in there anyway for a swap vehicle.
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TECH Junkie
Joined: Dec 2012
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From: Iowa
Thanks for the simple breakdown. Do you know which pin receives the signal from the bcm?
I checked red connector pin 30 last night and it had a rubber plug in it like all the other unused pins from the factory.
Blue 30, as suggested above, was the signal for the engine coolant level switch.
If the signal is just a 50 Hz, 50% duty cycle, signal, I can build one using a cheap little 555 timer circuit, or probably just buy a premade signal generator for cheap. I could use those to give the pcm the signal it is looking for.
The reason I'd like to do it this way is because it is a 100% bone stock 5.3 swap. It shouldn't need hp tuners for anything. I've removed some things like egr, rear 02's, etc but those should do nothing to effect how the engine runs, it should just light up the dash like a Christmas tree which is fine.
Adding hp tuners to the budget is another 500 bucks that i would like to avoid. I know I could send it out for $100 probably, but if I can build my circuit for $20 I'll save cash and have the satisfaction of doing one more thing on my own for this car.
I checked red connector pin 30 last night and it had a rubber plug in it like all the other unused pins from the factory.
Blue 30, as suggested above, was the signal for the engine coolant level switch.
If the signal is just a 50 Hz, 50% duty cycle, signal, I can build one using a cheap little 555 timer circuit, or probably just buy a premade signal generator for cheap. I could use those to give the pcm the signal it is looking for.
The reason I'd like to do it this way is because it is a 100% bone stock 5.3 swap. It shouldn't need hp tuners for anything. I've removed some things like egr, rear 02's, etc but those should do nothing to effect how the engine runs, it should just light up the dash like a Christmas tree which is fine.
Adding hp tuners to the budget is another 500 bucks that i would like to avoid. I know I could send it out for $100 probably, but if I can build my circuit for $20 I'll save cash and have the satisfaction of doing one more thing on my own for this car.
What you're wanting to do is build a VATS bypass module. That can only be done on Corvette and F body PCM's, the truck PCM uses a serial data VATS so it wont work. The only way to get around it is to have it set to no VATS in the tune, or if you want to do some wiring, you could wire in the BCM. If you used the BCM you could hard wire a resistor to match that of the key and you'd be good to go. It would be easier to just have it tuned out. LT1swap will do it for $75 if I remember correctly.
Thread Starter
TECH Junkie
Joined: Dec 2012
Posts: 3,615
Likes: 1,327
From: Iowa
Ok, I will do more research on it. At this point, it's become sortof a personal challenge just to see if I can do it.
I see now that pin 59 on the blue connector is labeled "serial data to bcm"
Does anyone have a wiring diagram for the bcm that I can use to install it properly?
I see now that pin 59 on the blue connector is labeled "serial data to bcm"
Does anyone have a wiring diagram for the bcm that I can use to install it properly?
There isn't a wiring diagram for the BCM, there are several, but this may help. Also, you will be able to use the tow/haul without any additional tuning if you use the BCM rather than hooking it directly to the PCM, but you will only get the factory settings, not the aggressive type you spoke about in the first post.