3100 to 3800 Engine Swap

[Ray_McAvoy]

Hi Andy,

It'll probably be a few more months before I start on this swap. I've got a few other projects to finish up first and the old 3100 is still running okay enough for the car to be driveable.

I'm still not entirely sure if the van harness will be anywhere close to a plug-n-play solution in the A-body or not. If it's not too much trouble, could you take some pics of the harness and/or help me out with some of these questions I have about the van wiring:

(1) Does the majority of the engine harness pass through a square plastic "grommet" on the passenger side of the firewall?
(2) Shortly after it passes through that "grommet", does it have 3 plugs going to the PCM as well as a rectangular plug where it hooks to the under-dash harness?
(3) Does the van have a bulkhead connector on the driver side (near the strut tower) with both the engine and front light harnesses plugged into it?
(4) Is the cruise control wiring part of the front light harness? It is on the A-body so I'll probably have to tie into some wires there no matter what engine harness I use.
(5) Similarly, is the wiring for the transaxle range switch and 4T60E connector part of the engine or front light harness? The A-body has them both on the engine harness ... hopefully the van is the same. I believe the LeSabre engine donor has those connectors as part of the front light harness.
(6) Does the van have a bank of about 5 relays on a bracket off to the passenger side of the radiator like the A-body? Or are the relays for the fuel pump, fans, etc mounted elsewhere?

Thanks,
Ray

[86euro]

Hi Andy,

It'll probably be a few more months before I start on this swap. I've got a few other projects to finish up first and the old 3100 is still running okay enough for the car to be driveable.

I'm still not entirely sure if the van harness will be anywhere close to a plug-n-play solution in the A-body or not. If it's not too much trouble, could you take some pics of the harness and/or help me out with some of these questions I have about the van wiring:

(1) Does the majority of the engine harness pass through a square plastic "grommet" on the passenger side of the firewall?
(2) Shortly after it passes through that "grommet", does it have 3 plugs going to the PCM as well as a rectangular plug where it hooks to the under-dash harness?
(3) Does the van have a bulkhead connector on the driver side (near the strut tower) with both the engine and front light harnesses plugged into it?
(4) Is the cruise control wiring part of the front light harness? It is on the A-body so I'll probably have to tie into some wires there no matter what engine harness I use.
(5) Similarly, is the wiring for the transaxle range switch and 4T60E connector part of the engine or front light harness? The A-body has them both on the engine harness ... hopefully the van is the same. I believe the LeSabre engine donor has those connectors as part of the front light harness.
(6) Does the van have a bank of about 5 relays on a bracket off to the passenger side of the radiator like the A-body? Or are the relays for the fuel pump, fans, etc mounted elsewhere?

Thanks,
Ray

I'll see what I can do then, it looks like I may have everything apart before you are ready to get started.

1&2... yes, and I believe so.

3&4... I believe so, and I'm not sure.

5... yeah, I think they are part of the engine harness.

6... I think there are some relays there, and also a couple others that are elsewhere.

If it stays dry long enough this weekend, I'll take a better look at things and get some pictures too. You may want to send SCREECH a message, he is very familiar with the U-van harness and I think he said at one point that the harness can be easily used in the A-body.

[Ray_McAvoy]

Thanks Andy,

Your answers to those questions I posted sound encouraging ... seems like the U-van harness is pretty similar to the A-body.

I sent a message to SCREECH to see if he can confirm that the harness will fit.

Ray

[Carlton]

(3) I know the 93 & older A-bodies use the vacuum style cruise servo like the 3800 engine donor LeSabre, but is it controlled by the PCM or a separate cruise module?

Thanks for the suggestion though.

I have the book for a 91 Ciera and on that the cruise control is controlled by a seperate module on the 3300. It does send a "cruise on" signal to the ECM.

Module should be just above the accelerator pedal. On the 2.5 it's ECM controlled btw.

[Ray_McAvoy]

Thanks for the info Carlton, I had a feeling it was probably like that ... my 88 Cutlass Ciera w/3.8 is setup the same way with a cruise module.

It looks like the cruise control is one area that'll need some re-wiring no matter what engine harness I end up using. The existing setup for the 94 3100 has a cruise module & servo all built into one assembly under the hood with wires leading back through the headlight harness to the switch on the column. What I'll have to do is tap into thsoe wires coming from the switch and re-route them to the 3800 PCM. Then run some wires from the 3800 PCM to the cruise servo. And add a brake light switch (probably from one of my older A-body parts cars) that has the vacuum release valve.

Andy, did you get a chance to take a closer look at the van harness yet? No hurry, just wondering.

Ray

[86euro]

Yes I did, but I forgot to take a look at the cruise control setup. Everything else seems to be as I thought before.

[Ray_McAvoy]

Hi Andy,

Sounds like it will probably fit. I haven't heard back from SCREECH, but I'm not sure if he received my message or not since my "PM - sent" box is empty.

How much are you asking for the engine harness, PCM, and engine mounts from the van? -- send me a PM if you'd like.

On the engine mounts, I mostly just need the upper one that attaches the "dogbone" to the engine. I could probably use the lower bracket from my 3300 parts car but will consider buying that one too just in case it's different. I'm pretty sure I can re-use the existing A-body transaxle mounts since they're both 4T60E's.

Oh, one other thing, do you happen to know the tire size & final drive ratio of the van? I'm wondering if it'll end up being close enough to work okay or if the PCM will need to be re-programmed for that.

Thanks,
Ray

[deathamatend]

I was trying to follow your thread. If you have both cars together and complete, I would proceed as a transplant operation. You will never know for certain if what is being changed/repinned etc., is ever correct. How can you be sure? By removing entire wiring/engine/ECM harnesses completely from plug to plug. All of the wiring harnesses are installed at the factory without cutting/splicing/repinning. All body openings accommodate the wiring to pass though during assemby, with all the connectors attached. Also, all of the harness plugs only plug into the correct connectors/sensors. I would remove all the wiring harnesses you need completely. I would lay out the '92 Century harness, cleaning and checking every wire and if all looks well, get a roll of electrical tape and retape all the sections that look tattered. I can't say there might be sections that are oil soaked, so clean those wires with a touch of brake cleaner and a soft cloth letting it dry before taping it up. You could use harness loom cover from the old harness to recover the '92 replacement harness for sections that are cracked, missing or brittle. Everything should mount as the old parts/original positions. Trying to re-engineer one part to do the job of the old part will end up being very frustrating and discouraging when you are unable to trace (and re-trace) what is going on/what went wrong, when there is no harness diagram that will match your hybred harness. And most importantly, the only way you will ever be able to use a scan tool to trouble shoot a problem/check engine light is if the harness is original. You just select a 1992 Buick Century 3800 on the scanner menu if all was transplanted successfuly. Mixing and matching components will not IMO make a reliable daily driver.

[Ray_McAvoy]

Hi deathamatend,

I understand what you're saying about the harnesses being factory installed without any splicing/repinning. However, I'm doing an engine swap between two different body styles. The 3800 engine donor car is a 95 Buick LeSabre (C-body) and the physical layout of it's underhood wiring and sizes/locations/pinouts of it's passthrough connectors are significantly different than the 94 Cutlass Cruiser (A-body) that the engine will be going into.

I'm hoping that the U-body van harness that Andy and I have been discussing will allow me to do basically what you're saying ... a "plug-n-play" swap using a factory-made harness.

All this talk of splicing & re-pinning is only my plan B. I have factory service manuals for both the 95 LeSabre and 94 Cruiser that contain wiring diagrams and connector pin-outs so I know what needs to be done in order to make the wiring & pin-outs correct. Basically, I would be using the PCM and all it's associated sensors and such from the 95 LeSabre and only changing the physical layout of the wiring to make it fit the A-body. So any scan tool troubleshooting could be done by selecting a "95 LeSabre" in the menu.

Oh, and the 92 Century only got brought into this discussion when occupant asked if using a 92/93 3300 harness would be easier. Unfortunately, that harness won't work because of the batch vs. sequential injection, lack of EGR, and other differences between the 3300 & 3800.

[86euro]

Hi Andy,

Sounds like it will probably fit. I haven't heard back from SCREECH, but I'm not sure if he received my message or not since my "PM - sent" box is empty.

How much are you asking for the engine harness, PCM, and engine mounts from the van? -- send me a PM if you'd like.

On the engine mounts, I mostly just need the upper one that attaches the "dogbone" to the engine. I could probably use the lower bracket from my 3300 parts car but will consider buying that one too just in case it's different. I'm pretty sure I can re-use the existing A-body transaxle mounts since they're both 4T60E's.

Oh, one other thing, do you happen to know the tire size & final drive ratio of the van? I'm wondering if it'll end up being close enough to work okay or if the PCM will need to be re-programmed for that.

Thanks,
Ray

I believe it is a 2.97 final drive, that number seems to stick in my memory. I'll assume the stock tire size was 205/70/15, that's what was on it when we bought the van. When it was time for tires, we got 215/65/15's and the speedo still read correctly as far as we could tell.

For pricing, I really don't know. I'd like to get it all apart and make sure everything is still in good shape. It will be cheap though, so that with shipping, it will still be worthwhile to you.

[Ray_McAvoy]

Hi Andy,

That will probably work out pretty good on the drive ratio. The LeSabre transaxle I'll be using is 2.84 but the Cutlass Cruiser it's going into has 195/75r14 tires. I did a few quick calculations and it looks as though the smaller diameter tires will more or less cancel out the taller gears.

Just let me know once you get everything all apart. Even if the harness does end up needing some repairs, it should still save me a lot of work compared to modifying what I have now.

Thanks,
Ray

[Ray_McAvoy]

Hi Andy, Just checking back to see if you have gotten around to pulling the wiring harness, mounts, and such out of the van yet.

We had some really nice weather here this past weekend so Dad and I started tearing the donor Buick apart to get the engine ready to pull. I'll probably start a build thread on this project once it gets a little more involved, but here's a few pics for now:

The wrecked LeSabre that's donating it's engine:


The engine with almost everything unhooked & ready to pull:

Once it's out, we're going to give it a good cleaning and replace some gaskets, seals, belt, plug wires, and anything else that looks bad (like that rusty modulator on the trans).

And finally, here's a pic of the 94 wagon that this engine will be going into (along with my 88 parked beside it)

[Jr's3800]

When you go to clean the motor and replace some gaskets.... Make sure you replace the lower intake gaskets as well... It will need it... also will give you an excuse to do this...


If you look at the pics above you will see I use a new gasket to trace on the lower intake... I did not gasket match, I used the marks as a guide... You will notice that the casting of the lower intake is a bit rough and jagged.. It would be a good time to clean up the ports and get rid of the jagged edges and open them up a bit to get a little more flow also increasing the volumetric efficiency...


Once I was finished with the lower intake this is what it looked like..


I also cleaned up the ports on the heads... Had the lifter valley covered quite well, also had the ports stuffed with shop rags... and that handy dandy shop vac always comes in handy.... The intake ports on the heads have some rough casting as well, so I did some smoothing and opening there as well..




Every little bit counts... I look forward to seeing this come to life... Should make for a great A Body Wagon Cruiser...

[Ray_McAvoy]

Hi Jr,

Thanks for the tip on the lower intake gaskets ... I'll be sure to add those to the list of gaskets to replace.

I've done the rough casting / port clean-up on a number of other engines that I've rebuilt in the past, so yeah, that'll be a good excuse to do this engine too while it's apart

[Ray_McAvoy]

Just a little update here .... we pulled the engine/trans out of the Buick this past Saturday.



Now comes the not so fun part of cleaning it up