1984 K10 LS Swap - Lots of Little Problems

[Bextreme04]

Well, the Terminator is in there now, so there's no going back. The harness is a Holley product, so no kludges from the mechanic. Temporarily I fixed the fuel system by removing one leg of the t on the return so I'm basically running from just one tank thru the selector valve. In the future I'll have to determine exactly how the tanks will be set up. I'm leaning towards mimicing the 87 style setup with the 6 port valve.

I don't think I would trust anything the previous mechanic did, nor that holley harness is actually correct. You can find their wiring diagram and instructions for the kit with wiring harness here: https://www.holley.com/products/fue...s_kits/terminator_x_max_ls_kits/parts/550-926

I would ring out the harness to make sure that you do actually have the correct pins going all the way to the injector as it is supposed to. Hopefully the stock LS injectors were kept and the Bosch EV1 harness was ordered to match that.

 

[Bruce Wingate]

@Bextreme04 - I'm not trusting the prior mechanic and will go over everything but I really want to get the truck running well enough to take it to get a proper tune. The big picture is getting it running and then concentrate on troubleshooting and double checking systems one by one later/as needed. Injector are original to the engine. I also have a copy of the wiring diagram blown up to poster size and laminated (cheaper than you would think from Staples)

Progress as of 2-21-2026: Someone suggested flood clearing the engine, which I did and it helped a little. The engine now runs "acceptably rich," or without the yellow warning on the handheld, but regularly dips into too rich. Checked cylinder temps and all were in the 300F range except #2 which was cold. Double checked wiring for that cylinder. The coil wire might have been loose so I reattached that, but the real problem seems to be that the coil (edited to correct) harness is damaged for #2. I wish this was something I could check by swapping cylinders, but I will have to order a new coil harness.

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Also, the truck was running kind of OK until I changed the throttle body from stock to a 92mm TB. I started backing up my work, slowly undoing things. First thing I did was unplug the silver tube on the TB thinking it was somehow blocking the PCV circuit instead of sealing a vacuum. Its not the PCV as that is routed to the manifold behind the TB. Any ideas what the silver tube is for? Can I plug it?

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Next: Compression test while waiting on the harness. Maybe - I might prefer ignorance to knowing about another problem.

 

[Bextreme04]

@Bextreme04 - I'm not trusting the prior mechanic and will go over everything but I really want to get the truck running well enough to take it to get a proper tune. The big picture is getting it running and then concentrate on troubleshooting and double checking systems one by one later/as needed. Injector are original to the engine. I also have a copy of the wiring diagram blown up to poster size and laminated (cheaper than you would think from Staples)

Progress as of 2-21-2026: Someone suggested flood clearing the engine, which I did and it helped a little. The engine now runs "acceptably rich," or without the yellow warning on the handheld, but regularly dips into too rich. Checked cylinder temps and all were in the 300F range except #2 which was cold. Double checked wiring for that cylinder. The coil wire might have been loose so I reattached that, but the real problem seems to be that the coil (edited to correct) harness is damaged for #2. I wish this was something I could check by swapping cylinders, but I will have to order a new coil harness.

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Also, the truck was running kind of OK until I changed the throttle body from stock to a 92mm TB. I started backing up my work, slowly undoing things. First thing I did was unplug the silver tube on the TB thinking it was somehow blocking the PCV circuit instead of sealing a vacuum. Its not the PCV as that is routed to the manifold behind the TB. Any ideas what the silver tube is for? Can I plug it?

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Next: Compression test while waiting on the harness. Maybe - I might prefer ignorance to knowing about another problem.

That sucks about the coil harness. I have a few laying around, but that doesn't help you any.

As others have said, those throttle bodies will almost always cause more problems than they will fix. You don't need a bigger throttle body. The stock throttle body is plenty big enough to support a 6.2 with a cam, it will be fine for your stock LS. I would send it back and run the stock throttle body.

Are you running a MAF sensor? That port being open is a massive vacuum leak, and it's going to have a hard time running right with it just open. Generally, the stock PCV system on an LS takes air from the intake between the throttle body and the MAF into the passenger side valve cover. The intake manifold has a port on it that connects to a fixed orifice in the drivers side valve cover to ventilate the crankcase fumes into the intake manifold. This means all air circulating through the PCV is accounted for by the MAF.

 

[Bruce Wingate]

@Bextreme04 - I'm going to keep the bigger throttle body for now. I have the original in case this one goes bad or causes problems. Honestly - it looks better.

Holley Terminator does not use MAF - it uses MAP, so no MAF sensor is being used (and I don't think that there is a connection for it either. I traced to PCV system and it exits the engine and goes into the intake to a port on the intake just behind the throttle body. I have to set the PCV system up to take filtered air from the intake.

Parts should start coming in today, but there's two feet of snow outside, so it might take a couple of days to resolve this chapter.

 

[Bextreme04]

@Bextreme04 - I'm going to keep the bigger throttle body for now. I have the original in case this one goes bad or causes problems. Honestly - it looks better.

Holley Terminator does not use MAF - it uses MAP, so no MAF sensor is being used (and I don't think that there is a connection for it either. I traced to PCV system and it exits the engine and goes into the intake to a port on the intake just behind the throttle body. I have to set the PCV system up to take filtered air from the intake.

Parts should start coming in today, but there's two feet of snow outside, so it might take a couple of days to resolve this chapter.

The reason I brought it up is because you say it runs bad with the new throttle body on there. This LS is a truck engine, so it wouldn't have that big port on the throttle body in the factory set up. The F-body cars and corvettes had that tube to feed the PCV system filtered air after the MAF. You will need to either cap it or run it to the passenger side valve cover vent hose. If you already have that connected somewhere(looks like maybe it is already connected behind the throttle body) then you need to just cap the tube on the throttle body.

Whoever sold you on wasting $1500 on that terminator system should be shot. You'd be time and money ahead by just using the stock harness and computer that was originally on that engine. They are good for boosted race car applications, but it's very limited for daily driving and drivability. Speed density is a big step back in my opinion. I know you already have it and aren't going to change it now, but it's gonna just keep being a problem. I won't mention it again though.

You probably need to do an IAC reset and adjust the throttle screw for the new throttle body when you swap it over. I'm not sure how the holley handles this, but its a whole thing on stock PCM's and require quite a bit of fine tuning to get it right with larger than stock(and frankly garbage quality) aftermarket throttle bodies. The effective area of the throttle body is different between the throttle bodies and the IAC valves being used, so the settings will be completely different. As you adjust the home throttle blade position, you will need to adjust the TPS sensor as well to keep it at what the PCM sees as 0% throttle.

 

[Bruce Wingate]

Well, it runs bad with the new throttle body because its only running on 7 cylinders . . .

I spent a lot of time researching how to control the LS and I felt the Terminator would be worth it. I did not feel that relying on someone to modify/flash the stock computer and running a modified harness would either look as clean or be as reliable. There was also very little information on how it would control the transmission. There are also things I think will be easier to get working correctly like cruise control and AC. In a past life, I was a computer programmer and feel comfortable with what goes into tuning this thing even though I probably won't do everything myself. In the end I think I'm going to be happier with the Terminator.

Once the injector harness is replaced, I'll start over with an IAC reset and see what happens

 

[Bextreme04]

Well, it runs bad with the new throttle body because its only running on 7 cylinders . . .

I spent a lot of time researching how to control the LS and I felt the Terminator would be worth it. I did not feel that relying on someone to modify/flash the stock computer and running a modified harness would either look as clean or be as reliable. There was also very little information on how it would control the transmission. There are also things I think will be easier to get working correctly like cruise control and AC. In a past life, I was a computer programmer and feel comfortable with what goes into tuning this thing even though I probably won't do everything myself. In the end I think I'm going to be happier with the Terminator.

Once the injector harness is replaced, I'll start over with an IAC reset and see what happens

This is the way. One little problem solved at a time.

Does the terminator have the inputs for AC active and different cruise control tables? I know the stock one will allow you to adjust additional torque output when AC clutch is engaged to keep the idle from dropping. Same for cruise control, you only send the computer a signal when cruise is active and it gives you an entire separate table for shifting schedules.

Does your truck already have a cruise system, so you have the controls on the turn signal stalk? Mine had a factory cruise system, but it was only the single button on the turn stalk, I think they went to the full four control stalks by the time yours was made. The GMT-400's and early DBC LS's used a separate cruise control module that had a single electrical connector and a single cable connected to the throttle body. You give it the cruise control button inputs from the stock cruise stalk, VSS from the PCM, brake inputs from the stock brake switch, and that's it. I think your engine should have been DBW originally though, right? So with a DBW setup, they do all cruise function in the stock PCM, you just put the brake switch input and cruise inputs from the stock stalk right into the PCM. With the conversion to the Terminator, I think it would work similar to a stock DBC setup and you can use a GMT-400 cruise control module mounted to the firewall and the cable attached to the new throttle body. I have some wiring diagrams for that if you are trying to get that to work.

 

[Bextreme04]

Here's the cruise control module and cable that would be stock on a DBC Tahoe. Mounts to the firewall and is completely standalone, just feed it control signals and VSS. They are pretty widely available in junkyards and on ebay.

https://www.ebay.com/itm/2571785573...1jNOlScEgf1Nlolvs_zVimYUTq6bGvUhoCBk0QAvD_BwE

Post #5 on this thread has all of the pinouts and wiring diagrams for the module and how it ties in and needs to work.
https://67-72chevytrucks.com/vboard/showthread.php?t=455725

 

[Bruce Wingate]

This is the way. One little problem solved at a time.

Does the terminator have the inputs for AC active and different cruise control tables? <<snip snip snip>>

Does your truck already have a cruise system, so you have the controls on the turn signal stalk? <<snip snip snip>>

The terminator has some accomodations for AC, but I'm not sure if it goes much beyond increased idle and fan control. AC might not be conquored this year.

The '84 came with cruise control and a 4 way switch on the stalk. It was originally controlled by by some sort of vacuum arrangement. When I get ready for cruise control, I will have to convert the drive by cable to drive by wire.

 

[Bruce Wingate]

Coil wiring harness came yesterday and I installed it today with no change. #2 cylinder was still running cold. I forget the order I checked everything, but I pulled the plugs and the #2 plug was clean as a whistle - like it was unused. So I swapped #2 and #4 coils and there was no change again.

Next was compression checking. My battery was running low so I only checked 3 cylinders: #2, #4 and #1. All came in at around 180 psi I did not do a leak down test. One thing I notices was that there was a gas smell from #4 and #1 but not from #2. I'm thinking I have a bad injector.

It looks like I will be getting an injector tester and testing all 8 injectors.

 

[Bextreme04]

Coil wiring harness came yesterday and I installed it today with no change. #2 cylinder was still running cold. I forget the order I checked everything, but I pulled the plugs and the #2 plug was clean as a whistle - like it was unused. So I swapped #2 and #4 coils and there was no change again.

Next was compression checking. My battery was running low so I only checked 3 cylinders: #2, #4 and #1. All came in at around 180 psi I did not do a leak down test. One thing I notices was that there was a gas smell from #4 and #1 but not from #2. I'm thinking I have a bad injector.

It looks like I will be getting an injector tester and testing all 8 injectors.

Bummer. Did you ring out the Holley harness for the injectors too? Make sure you are moving the harness around while checking the circuit, because you could have a broken wire at the connector that is intermittently making contact.

180psi should be close enough that you know it isn't a bad cylinder mechanically. It's unlikely that the injector would be totally dead, but it is possible. One of the few things I do on a rebuild is send the injectors out for inspection and repair to a local place. They charge about $20/ea to inspect, clean, repair the injectors and return with a flow report and all new filters/seals.

I have a set of LT1 swap 35lb/h Bosch D3 injectors in my Gen VI 454 that I got from South Bay Injectors. I have always had top notch service from them, and I see they are local to you and charge around the same price for that service.
https://www.southbayfuelinjectors.com/order-services

 

[Bextreme04]

You can also see if the injector has failed internally by disconnecting the connector and check resistance between the two terminals. It should have 12-18 Ohms of resistance. If it is less than 12 or open, then the injector is failed internally and likely won't work at all. I would also swap the injector itself to a different cylinder and see if #2 suddenly comes alive or if it is still dead. If you swap injectors and it stays at #2, then you have a wiring or internal PCM fault. If it follows the injector, it is a bad injector.

It could burn out the driver in the Holley of it is internally shorted and you try to run it for any amount of time. The OEM PCM's have protection on those circuits but I've seen the holleys actually burn the driver out.

 

[Ricko1966]

Put a noid light in number 2 injector connector. You can make one with 2 led lights twist the connectors together long tail to short tail and vice versa. That way you have an led that will light no matter what polarity when you stick it in the connector socket.

 

[Bruce Wingate]

I gave the wiring a quick check and the power and ground are going to the battery like required. I do not fully understand it, but the Terminator computer likes clean power and the battery is basically a big buffer/filter that provides the cleanest power. The connections from the Terminator to the sensors etc. is all with preterminated connectors so they should be in the right place. I checked the temp and pressure sensors that I could see and they were correct.

I have been trying to figure out what the effect of a dead cylinder would be on an overall rich condition and I'm really stuck. IMHO, a cylinder not getting any fuel should not have any effect and might make the engine seem lean because there is one cylinder of air being pumped through. [Hmmm --> maybe the Terminator is making everything richer to compensate?] 3 out of 8 cylinders have compression test results of about 180 psi. I'll do the remaining 5 cylinders soon. It might bite me in the @ss, but I will assume good enough compression overall for now. One thing I noticed was that the temperature of the exhaust pipes on the right side were about 100F cooler than the left side. The right exhaust smokes significantly more than the left side as well.

This leads me to believe that I might have leaky injectors. This engine sat for about two years while I gathered parts and tried to find time to start the swap. Maybe the injectors are gummed up. Since the swap, there is probably less than two hours of run time on the engine.

My next step is to pull, inspect and clean the injectors. I have some tools on the way to help with this. Depending on the results I will either repair or replace suspect injectors. BTW, South Bay Injectors is just a town or two away, so if the injectors are repairable that might be the way to go. I thought about swapping injector #2 with another one, but with all the work to remove the fuel rail, it is just as easy to clean them all first. I'll keep track of #2 and put it in a different cylinder upon reassembly unless it is replaced.

 

[Bruce Wingate]

Here are two of the plugs I remeoved. #2 looks brand new, even if you can't see the electrode in this picture.

All the rest looked like #4, a little sooty, but OK enough.

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