1984 K10 LS Swap - Lots of Little Problems

Bruce Wingate · Mar 8, 2026

I'm a little stumped at this point. I swapped the injectors between #2 and #4 and the problem stayed with cylinder #2. Then I swapped the plugs between #4 and #2 and again the problem stayed with #2. I am getting spark and compression at cylinder #2 which were fine (I tried using the timing light again today and it worked). I hooked the noid light up again to the injector harness and that flashed.

With injector #2 unplugged, the engine runs pretty good on 7 cylinders. However, pretty quickly after I plug in injector #2, the engine dies. Too quickly for me to do any testing. I could probably start it with #2 plugged in like before, but again, it will die relatively quickly.

The only thing I haven't done it a Key on, engine off test of voltage through the injector to the harness, but from my understanding if the noid light flashes the problem is with the injector, but I switched injectors and the problem stayed with cylinder #2. I also tested the injectors off the engine and they all worked OK.

Any suggestions would be appreciated.
Thanks

Camar068 · Mar 10, 2026

Bruce Wingate said:
I'm a little stumped at this point. I swapped the injectors between #2 and #4 and the problem stayed with cylinder #2. Then I swapped the plugs between #4 and #2 and again the problem stayed with #2. I am getting spark and compression at cylinder #2 which were fine (I tried using the timing light again today and it worked). I hooked the noid light up again to the injector harness and that flashed.

With injector #2 unplugged, the engine runs pretty good on 7 cylinders. However, pretty quickly after I plug in injector #2, the engine dies. Too quickly for me to do any testing. I could probably start it with #2 plugged in like before, but again, it will die relatively quickly.

The only thing I haven't done it a Key on, engine off test of voltage through the injector to the harness, but from my understanding if the noid light flashes the problem is with the injector, but I switched injectors and the problem stayed with cylinder #2. I also tested the injectors off the engine and they all worked OK.

Any suggestions would be appreciated.
Thanks

not reading the whole post and/or remembering, did you ohm the #2 injector and coil wires back the to ECU and then the grounds for each?

Sorry if you have, nothing meant.

Camar068 · Mar 10, 2026

Also just thought about this, on one of my injectors either the T|T on it is broken off OR the connector part that goes over it is broken (can't remember which lol). I've got it zip tied but a hard enough bump will cause it to jump off and run really bad.

Ricko1966 · Mar 10, 2026

Sounds like #2 injector is leaking. Flooding #2.

Bruce Wingate · Mar 11, 2026

Camar068 said:
not reading the whole post and/or remembering, did you ohm the #2 injector and coil wires back the to ECU and then the grounds for each?

Sorry if you have, nothing meant.

I did a continuity check but not an ohm test. Next couple of steps involve checking ohms along the circuit back to the ECU.

I just spoke with Holley, and they suggested downgrading the firmware to v2 because some older versions of the Terminator do not like v3. Then it is shipping the unit back to Holley for testing

Bextreme04 · Mar 17, 2026

Bruce Wingate said:
I did a continuity check but not an ohm test. Next couple of steps involve checking ohms along the circuit back to the ECU.

I just spoke with Holley, and they suggested downgrading the firmware to v2 because some older versions of the Terminator do not like v3. Then it is shipping the unit back to Holley for testing

That was going to be my suggestion. Per my post #42.. if you have verified that the wiring from #2 injector all the way back to the Terminator is good(at the right pin and less than 1 Ohm of resistance), then you MUST have a problem with the Terminator PCM. Either the injector #2 driver is smoked, or there is something else going on internally. It is not uncommon for Holley, and the Terminator specifically, unfortunately.

Ricko1966 · Mar 17, 2026

Bextreme04 said:
That was going to be my suggestion. Per my post #42.. if you have verified that the wiring from #2 injector all the way back to the Terminator is good(at the right pin and less than 1 Ohm of resistance), then you MUST have a problem with the Terminator PCM. Either the injector #2 driver is smoked, or there is something else going on internally. It is not uncommon for Holley, and the Terminator specifically, unfortunately.

Reread # 46 when he swaps connectors the problem stays with number 2,it doesn't move with the harness. IMHO that wouldn't point to harness continuity, driver issue or even firmware. I need to think this some more this is a puzzler. Did you ever run compression? Have tried pressure testing the cooling system? I'm wondering if number 2 is getting water in it.

Ricko1966 · Mar 17, 2026

If he configures it for batch fire,swaps the plug on 2 and 4 if the problem is still on 2 it's not the injection it's something else.

Bextreme04 · Mar 18, 2026

Ricko1966 said:
Reread # 46 when he swaps connectors the problem stays with number 2,it doesn't move with the harness. IMHO that wouldn't point to harness continuity, driver issue or even firmware. I need to think this some more this is a puzzler. Did you ever run compression? Have tried pressure testing the cooling system? I'm wondering if number 2 is getting water in it.

I read that as he swapped the Spark Plug between the two cylinders. The harness shouldn't have enough slack to allow you to swap injector connectors, but maybe it does. If you switch to batch fire and swap injector connectors, how would that help narrow anything down? You would be firing an entire bank at once, so I would expect you would have it running terribly no matter what the issue is. Maybe a better option would be to swap the #2 and #4 injector connectors and then swap #2 and #4 in the firing order in the PCM. Then you would be running the #4 injector with the #2 driver and vice versa, but it should run just like a normal sequential MPFI.

The fact that the whole system is going crazy when #2 is plugged in tells me that the injector driver is almost certainly trashed. It sounds like when it is getting enough load to really make it work(noid light doesn't actually have a large draw on the driver), it is internally shorting and making the rest of the PCM go haywire.

Based on the response from Holley in Post #50, they came to the same conclusion. If the firmware didn't fix the issue, it is probably down to internal issue. The other option is wiring, but there is only so much you can do to verify that without ringing out the whole harness. The other great diagnostic tool for this is an oscilloscope. I have a decent picoscope that I use for stuff like this, you would be able to see how much load is being applied on the circuit and what the actual injector firing signal looked like on the #2 and other injectors that seem to be working fine.

Ricko1966 · Mar 18, 2026

Bextreme04 said:
I read that as he swapped the Spark Plug between the two cylinders. The harness shouldn't have enough slack to allow you to swap injector connectors, but maybe it does. If you switch to batch fire and swap injector connectors, how would that help narrow anything down? You would be firing an entire bank at once, so I would expect you would have it running terribly no matter what the issue is. Maybe a better option would be to swap the #2 and #4 injector connectors and then swap #2 and #4 in the firing order in the PCM. Then you would be running the #4 injector with the #2 driver and vice versa, but it should run just like a normal sequential MPFI.

The fact that the whole system is going crazy when #2 is plugged in tells me that the injector driver is almost certainly trashed. It sounds like when it is getting enough load to really make it work(noid light doesn't actually have a large draw on the driver), it is internally shorting and making the rest of the PCM go haywire.

Based on the response from Holley in Post #50, they came to the same conclusion. If the firmware didn't fix the issue, it is probably down to internal issue. The other option is wiring, but there is only so much you can do to verify that without ringing out the whole harness. The other great diagnostic tool for this is an oscilloscope. I have a decent picoscope that I use for stuff like this, you would be able to see how much load is being applied on the circuit and what the actual injector firing signal looked like on the #2 and other injectors that seem to be working fine.

Okay,you and I read that different. I thought he swapped the plug between the injectors and the problem stayed on 2. I said throw it on batch fire to see if the problem stays on 2 no matter where the injector plug is would IMHO eliminate the injection as the problem. Again this was my thinking when I thought he was swapping injector plugs ,not spark plugs. I didn't know you could change the sequence in pcm. Never even seen a Holley Terminator system. But I work on a lot of things I've never worked on before,it's part of the job,use what you know,and use some common sense and you can fix a lot of things. Its the mentality of a flat rate tech,you fix what they give you. Was just trying to help.

Bruce Wingate · Mar 22, 2026

I've been silent on this for a while - I have to work on the truck outside and it snowed and then was cold and damp for a few days. Cold and damp is the combination I just can't take.

I followed Holley tech support's suggestions and did not elicit any change. I did find that a power wire was connected incorrectly to constant power instead of switched power, so I fixed that. I also removed the input/output subharness that was really just bodged in, so now my fans won't come on, but I also know I'm not getting any problems from that subharness. I added an engine to battery ground and have to double check that there is an engine to chassis ground.

The engine runs really nice on 7 cylinders without the injector for #2 connected and just dies when the injector is connected. Logically, I was getting some conflicting test results: The noid light should not have flashed for #2 for the behaviour I was seeing. I retested the injector pulse for cylinders #2, #4 and #1 and maybe #3. #1 and #3 flash with a distinct off phase. #4 flashes with a much less distinct off phase. #2 would fluctuate in strength but did not have an off phase. This is really looking like a bad driver and I'll be calling Holley on Monday to arrange a test and hopefully a warrantee replacement.

Just to recap, here's what I did: Once I got the car back from the second mechanic (a good shop that I told to just get the car running), I fixed a broken O2 sensor, wired up the last of the sensors and got the fuel system working correctly ("good enough") from one tank. Then I noticed it running ridiculously rich. I changed all the plugs first. In the course of my testing, I changed the coils, spark plugs and injectors between #2 and #4 one at a time, the problem always remained with cylinder #2. I also tested and cleaned the injectors off the engine. All 8 injectors worked and had a decent spray pattern. Compression in all cylinders was around 180 psi. Finally, I checked continuity and resistance on the harness for injector #2 and a couple of other injectors. As I said above, I misinterpreted the noid light for #2 and took the weak fluctation in brightness as flashing.

@Ricko1966 & @Bextreme04: Thanks for all your help. There's going to be more questions in this thread about wiring, AC, DBW and transmission control. Stay tuned.

Ricko1966 · Mar 22, 2026

If I had to make jumpers to swap #2 and #4 injector plugs I would. If the problem moves to #4 you will know it is the wiring on #2 or the driver for #2. You will need to change during sequence or switch to batch fire.

Bruce Wingate · Mar 22, 2026

Different Question: Any idea what these wires are for?

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Ricko1966 · Mar 22, 2026

Looks like oil pressure switch for choke power.

Ricko1966 · Mar 23, 2026

Ricko1966 said:
If I had to make jumpers to swap #2 and #4 injector plugs I would. If the problem moves to #4 you will know it is the wiring on #2 or the driver for #2. You will need to change firing sequence or switch to batch fire.

1984 K10 LS Swap - Lots of Little Problems

Bruce Wingate

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Camar068

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Ricko1966

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Bruce Wingate

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Bextreme04

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Ricko1966

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Ricko1966

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