So, backstory. I inherited an 84 Cutlass from my dad when he passed. We’d always talked about LS swapping it. Due to finances, best I could do was a LM7 out of a 2004 Silverado with DBW.

Fast forward, engine and trans is mounted and able to start. Seemed it was only running on cylinders 1-4. The back four wouldn’t change when the coil were unplugged.

Further diagnoses, I confirmed with noid light that all 8 injector plugs were working, and 6 coils were working. Coils 6 and 8 did not light up the spark light. I switched coils 4 and 8. The dead spot stayed at 8.

So, I guess my question is, how do I go about testing for signal to the coils? I don’t have access to an O-Scope. I do have a couple of multimeters, test lights and basic diag tools.

Chinese harness from eBay, I verified the injectors were in the right pins, but I don’t think I did the coils. Also running the computer from the truck with VATS deleted.

Thanks for any help y’all might be able to give me. I appreciate it..

 

You just said you didn't check the Coil wiring, check it in the Harness. You have the tools so get at it and make sure that's right.

 

That’s my next check. That and the crank sensor.

 

That and the crank sensor.
If the engine runs, it's not the crank sensor.

 

Crank sensor won't give you a steady 1 cylinder dead. view this even cyl ign schematic
PCM pinouts Thanks to lt1swap.com

 

Thanks for the schematics. I’ll report back as soon as I can.

 

So. Finally got some time to dig into it. Turns out, the number 8 coil was pinned to the MAF sensor, and MAF was pinned to number 8. Coils 3 and 6 were also pinned backwards. I got those straightened out, and now the ECU won’t command the fuel pump to come on. I double checked the continuity from the pin to the relay, it’s fine. It’s only putting out 0.8v to the relay. I’m at a loss on it. About to tear the new harness apart, and use the fuse/relay block from it onto the original harness.

I double checked every other sensor on the harness according to the pinout sheets from lt1swap and everything seems right.

grounds are good.

is the PCM fried?

 

Good job so far. PCM C2(green side) pin 9 should be the fuel pump relay power. Is that where you checked it?

 

Yes. Pin 9. I’m going to double and triple check my work in the coming days. Just to make sure I’ve not jacked something else up.

 

Check all your grounds to the PCM, there are 4 of them. Check the Constant 12v power wires and then the Ignition (Key on) 12v wires to the PCM as well.

 

Thank you. I will do this as soon as I get a chance too.

 

HEY, I've seen this one before...


STOP BUYING SHITTY CHINESE WIRING HARNESSES. TELL ALL OF YOUR FRIENDS.

I'd trust a harness pulled off a truck in the junk yard before I'd trust some Ebay special. I've had guys ask me to diagnose problems on their swaps, and they used shitty Chinese harnesses, and my answer is always that I will throw out that harness and rewire it with a factory harness.
They never want to do that; they want to stick with their shitty $199 harness, because they don't want to "lose money." **** those guys.

Trust me, bro, even after you fix all of the incorrectly pinned wires, you've probably got some bad crimps hidden in there, waiting to show up at an inopportune time.
And what quality is that wire? Is it flame retardant? Is it copper, or aluminum?

 

The next swap I do, will be at a minimum, the factory harness.

 

I've fixed a bunch of $199 eBay harnesses over the years, just how it goes. Cheap wiring is not good wiring.

 

I’ve learned that the hard way. Like most everything else in life😂😂

 

What you have can be made to work as long as the wire quality is right, again though you shouldn't be doing the work to fix it. Should have been right to begin with.

Chicom kids building it don't know schematics..

 

Well, I got to work on it today, and now I have fuel pump, just no spark😂😂. About to swap out to another PCM and see if this one is fried or what.

 

I can confirm it is in fact in the harness. Gonna bite the bullet, and buy a better one. Who do yall recommend? BP Automotive? Or who. Call this a lesson learned.