Hello everyone. I have a very unique (To my knowledge) problem with this Blazer that I just had bought. The security light comes on and it will start then die again. Then it got to the point that it wouldn't even start at all. I took it to the shop and they got all the dash apart and everything and they said they couldn't find anything. I got this vehicle from a friend and he had a PCM replacement that didn't fix the problem. It may have been the fact that it was a used PCM. I do not know what to do. Electrical is not my strongest field. I can do everything else but that. He also has a brand new BCM to put on the vehicle once it starts running again. It has the 4.3. Anyone have or heard of this? I'm at a loss. Can someone please help me out and give me a list of things it could be? My best thought was PCM? For a while if you kept it warm it would start right up and I could drive it to lunch and everything then once it sat outside in the cold it wouldn't start. Then it just stopped all together. Please Help.

 

1st place I'd start is https://blazerforum.com/forum/tech-a...agnosis-23038/
If it starts & doesn't continue to run then I'd say a fuel delivery issue, especially when warm. Could be a fuel filter, wiring to or from the fuel unit in the tank, MAF (mass air flow), cold/high idle circuit (delivers different air to fuel ratios based on vehicle readings) etc. But I'm thinking fuel pressure. They should have around 65psi with ignition on (not running) & not drop below 55 or 50 psi after 10 mins. I'm not so sure on the exact figures but testing the fuel pressure is for sure something that you should try. IMO
As for the security light, it wouldn't start if the security function was an issue. It's something else, I think all the dash lights LIGHT up for an instant when you start the vehicle.
Try to search for the issue - like 'starts but won't run' etc... lots of info in here if you grab a bevy (or 5) & look.

 

It doesn't start at all now, security light stays on.

When the PCM is hooked up it won't read but there is power going to it. Can't get data from the data line. Checked fuses, cigarette lighter, etc.

 

I believe the pcm is programed to the vin of the vehicle. It may need to be flashed and reprogamed to your vin. Also since the pcm was replaced a crankcase relearn should be done. But that wouldn't cause it not to start.

 

'cat is correct. The PCM (& BCM) must be programmed to the VIN of the vehicle to work. Your PCM & BCM are fighting each other at this point.

What was the original reason for replacing the PCM in the first place? What were the symptoms? Is the old PCM still available?

 

The old PCM is in the vehicle. The used one was supposedly flashed. I have a new BCM but I haven't put it in yet. The reason we thought it was the PCM is because it would start then stop after 1-2 seconds. Now it won't start at all. The reason we thought it was the PCM is the alarm light would stay on like it had a security issue. Power is going to it and I checked all fuses, etc. When we plugged the PCM in we couldn't get any data from the data line. This all brings me to thinking it is a PCM? Is there any other possible options? You name it, I have probably already messed with it at some point and time. Been sitting for 3 years now. Even took to the shop and they got as far as removing the dash to follow wires and after a $300 bill I told them to stop. I have no clue what I can do. Any and all help is very appreciated. Thanks guys.
Just a little something to joggle your brains.

 

I'm not sure who gave you the info to chase after the PCM, but that wouldn't be even remotely near the top of my list. At the top would be the ignition switch. It can cause all of your symptoms. Check out the link at the bottom of my signature.

 

He said he has already changed the ignition switch.

 

Was the Passlock Relearn Procedure completed properly?

We're here to help, but you have to help us help you. This post should have started out with a rundown of EVERY repair that was attempted on this truck along with the symptoms & how they changed with each repair (if they changed). Bouncing around like this wastes everyone's time.

 

Most of the stuff done to the truck was done by him. I'm relaying what I have done and then when you guys suggest something I tell him. I'm not trying to waste anybodies time. If it feels that way then we can delete the post. Like I said, I'm being as upfront with everyone as I can. If I haven't disclosed something it is because I do not know if it had been done. Sorry for any confusions.

Well, I am back again. I double checked the ignition switch and contacts inside. Put everything back together and did a passlock relearn. I am still getting nothing. I get cranking but no starting. Same thing as before. Security light back on. I have run into a wall on what to do next. Any other suggestions? I am about to take this beauty to the damn scrap yard.