S-10 Forum banner

S10 Ls swap.

1569 Views 31 Replies 10 Participants Last post by  oldeerslayer
I have made it to the end of my journey just to be stepped on by who knows what. I put in a new harness made by a company for a 97 5.7L motor from a Silverado. They also re did the programing of the ECM from the very same vehicle to match up with the 96 S10 Blazer. I have power to all my accessories like lights and other features radio and heater for example. I replaced the instrument cluster in the blazer from another S10 that had a tach already in whereas my original did not. Now to the problem there is no power to the Coil module, coil and from what I can tell the fuel tank. Now I know that there are different types of Anti thief systems and I believe I have the Pass Lock system, I only use or have a regular key. I also know that the BCM is specific to the blazer when it was installed with the 4.3 engine.
1. Does the BCM require to be reprogramed? I understand that it controls the accessories and that could be why they appear to be working, except fuel system.​
2. Could my lock cylinder be bad since the anti-thief system is based or housed in the lock cylinder.​
3. Can that Pass lock system be reprogramed, or do I need to get a whole new ignition lock system?​
All in all after all this time I have no juice to start the vehicle. It does crank over but not spark or fuel.
Can anyone help me get over this last hurdle please.
1 - 7 of 32 Posts
A 97 5.7 into a 96 Blazer doesn't need any harness. Just add 2 wires from PCM to the injectors and 2 pink wires and repin 5 of the 6 in the connector to the computer and you should be good to go.
Who made the custom harness? AFAIK you can't make a 97 ECM work correctly a 96. Has something to do with changes in A/C wiring and ABS systems. Folks have tried it. 95, 96, and 97 were all one year only wiring harnesses. That's why GM totally redid the trucks complete electrical in 98.
  • Like
Reactions: 1
I thought I remembered you had tried a 97 Ecm in a 96 and it was a no go.
Sounds to me like whoever built his harness and ECM has a bit more to learn about S10's.
It's no wonder the OP is having issues.
If your truck is at a performance shop they should be able to figure it out. That's what you are paying them for.
On TV I never see the Martin brothers or Dave Kindig calling up their customers asking for help to figure something out.
Maybe at Cousin Ricky's auto body, engine swap, and Tacoria they do it that way. :rolleyes:
Post #6 he corrects it. It's an L31 Vortec 5.7L.
There is a redundant oil pressure circuit to the fuel pump relay. If the ECM is receiving a pulse from the distributor it turns on the fuel pump by activating the relay. Or if you have oil pressure, that will activate the pump directly. Not all swappers use this type oil pressure switch. Later year 4.3 Vortec's didn't have that circuit either, but a 96-97 would have had it. It's not necessarily needed. If you aren't getting an ignition pulse no need for fuel. Prior to computers GM used it as a safety feature. If you didn't have oil pressure, you didn't need fuel. Like if the truck is upside down.
It sounds to me like something from the ignition switch to the ECM is wired incorrectly. Sounds like you have 12V in run, but not in start. Check fuse #10 ECM/IGN to be sure it has power in both run and start. I've run across custom harnesses that failed to provide power in both positions. Usually when someone is building a harness they check for continuity in run, but don't always check it in start. Basically all pink wires are hot in run, but not all are hot in start. This is done to prevent surges from damaging sensitive electrical components.
Or it could be a problem with the ignition switch.
See less See more
Putting a 97 Vortec style 4.3 into a 95 would be a giant nightmare even if the truck was originally a 4.3. 96 up engines, wiring, and computers are completely different from 95 and earlier. There are also exhaust, cooling system, and other differences. I've been working on S10's since they came out, both on my own and professionally and I wouldn't attempt it.
You'd spend the next 2 years chasing parts.
1 - 7 of 32 Posts