Prepping for my GM 3.8 Swap - JeepForum.com
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post #1 of 34 Old 04-23-2021, 10:15 AM Thread Starter
eodjeep
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Prepping for my GM 3.8 Swap

So I'm collecting parts for my 1990 2.5 to 3.8 (GM/Buick 3800 Series 2) swap. FYI the 3800 is a 90-degree V6 that uses the 60-degree bellhousing bolt pattern that is the same as the AX5. Mine came from a 1998 Camaro so it was a RWD. The engine is uber common, known to be reliable, and weighs very close to the stock 2.5 4 cylinder but with a bit more power. The L36's 200hp is kinda peaky while the torque curve (225ftlbs) is pretty flat across the RPMs.

I'm neither a rock crawler nor a mall crawler. I use my jeep as a daily driver as well as to work on a tree farm with steep dirt "roads". If the 2.5 had 15-20 more HP I would just keep it. I would like to be able to maintain reasonable freeway speeds on inclines while running up to a 31" tire. I don't want a V8 and was leaning towards a 4.3 until I really took a look at the 3800. Light and efficient are the goals...

The Jeep is one I brought up from Arizona and is completely rust-free. I don't want to sell or trade it for a different one. I also already have the complete 3.8 for the swap.

1. Initially, I'll be dropping the 3.8 in and using the AX5 that's already in my YJ. In order to mate the two, I seem to just need a 1"/14 Spline clutch disc. The best I've found is to either use the stock YJ disc or one from an old Camaro that has just a touch bigger diameter...like 9.125" vs 9.188" but otherwise look identical. I don't plan on making any other transmission-related alterations until the AX5 either blows up or I just decide to slide in an AX15 or other transmission later.

2. Motor mounts. I've yet to find any that are for this engine. Novak mentions some that are "in development" but they don't seem to sell any for this particular engine. I'll likely drop in the motor to just see where things are in relation to the stock mounts. I'd like mounts that mimic factory-style antivibration mounts to the max extent possible if anyone has any suggestions? When positioning the motor I'd prefer to leave the trans/t-case/drivelines as stock but I'll have to see where/how the engine fits. It's a pretty compact unit and my electric fan conversion has already made the engine bay seem ridiculously big.

3. Fuel pump/lines. At this point, I'm thinking of an inline pump. I'm really tired of having to drop the fuel tank on this jeep for pump-related stupidness. I think that I should be able to utilize the factory lines except for the part between the pump and injector rail as that is the high-pressure portion but could use advice on this. Also, I'll need a compatible fuel level sender.

4. Wiring. I have the factory engine harness(es) and computer. It was all taken from a manual '98 Camaro. Has anyone seen a DIY tutorial on how to work this over? I could buy a stand-alone harness if I had to, but I'd rather DIY it as the harnesses are usually over $500. In particular, I'm concerned about the GM "anti-theft" ignition harness which I do not have.

5. Gauges. I'm thinking of just using a tablet via the OBD2 port. I've already converted to a CJ dash so It'd just be a flat tablet on a flat dash in the stock gauge location. Tesla meets caveman.

I've found a few references to this swap but nothing like a complete swap post/guide on how someone else has done it. If you know of any helpful posts that would be appreciated.

What am I forgetting?


Last edited by eodjeep; 04-23-2021 at 10:29 AM. Reason: added model year
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post #2 of 34 Old 04-23-2021, 11:00 AM
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Sorry I got nothing to add - just looking around, hoping I could learn something....

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 34 Old 04-23-2021, 11:20 AM
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Didn’t the 3.8 have a supercharger option on some cars? Please keep up with the thread because most of these different engine swap threads tend to stop without resolution. I think it’s interesting thinking outside the box and would like to follow along.
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post #4 of 34 Old 04-23-2021, 12:06 PM
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Quote:
Originally Posted by eodjeep View Post
So I'm collecting parts for my 1990 2.5 to 3.8 (GM/Buick 3800 Series 2) swap. FYI the 3800 is a 90-degree V6 that uses the 60-degree bellhousing bolt pattern that is the same as the AX5. Mine came from a 1998 Camaro so it was a RWD. The engine is uber common, known to be reliable, and weighs very close to the stock 2.5 4 cylinder but with a bit more power. The L36's 200hp is kinda peaky while the torque curve (225ftlbs) is pretty flat across the RPMs.

I'm neither a rock crawler nor a mall crawler. I use my jeep as a daily driver as well as to work on a tree farm with steep dirt "roads". If the 2.5 had 15-20 more HP I would just keep it. I would like to be able to maintain reasonable freeway speeds on inclines while running up to a 31" tire. I don't want a V8 and was leaning towards a 4.3 until I really took a look at the 3800. Light and efficient are the goals...

The Jeep is one I brought up from Arizona and is completely rust-free. I don't want to sell or trade it for a different one. I also already have the complete 3.8 for the swap.

1. Initially, I'll be dropping the 3.8 in and using the AX5 that's already in my YJ. In order to mate the two, I seem to just need a 1"/14 Spline clutch disc. The best I've found is to either use the stock YJ disc or one from an old Camaro that has just a touch bigger diameter...like 9.125" vs 9.188" but otherwise look identical. I don't plan on making any other transmission-related alterations until the AX5 either blows up or I just decide to slide in an AX15 or other transmission later.

2. Motor mounts. I've yet to find any that are for this engine. Novak mentions some that are "in development" but they don't seem to sell any for this particular engine. I'll likely drop in the motor to just see where things are in relation to the stock mounts. I'd like mounts that mimic factory-style antivibration mounts to the max extent possible if anyone has any suggestions? When positioning the motor I'd prefer to leave the trans/t-case/drivelines as stock but I'll have to see where/how the engine fits. It's a pretty compact unit and my electric fan conversion has already made the engine bay seem ridiculously big.

3. Fuel pump/lines. At this point, I'm thinking of an inline pump. I'm really tired of having to drop the fuel tank on this jeep for pump-related stupidness. I think that I should be able to utilize the factory lines except for the part between the pump and injector rail as that is the high-pressure portion but could use advice on this. Also, I'll need a compatible fuel level sender.

4. Wiring. I have the factory engine harness(es) and computer. It was all taken from a manual '98 Camaro. Has anyone seen a DIY tutorial on how to work this over? I could buy a stand-alone harness if I had to, but I'd rather DIY it as the harnesses are usually over $500. In particular, I'm concerned about the GM "anti-theft" ignition harness which I do not have.

5. Gauges. I'm thinking of just using a tablet via the OBD2 port. I've already converted to a CJ dash so It'd just be a flat tablet on a flat dash in the stock gauge location. Tesla meets caveman.

I've found a few references to this swap but nothing like a complete swap post/guide on how someone else has done it. If you know of any helpful posts that would be appreciated.

What am I forgetting?
1. Would highly discourage using the AX5 but that's your call. It's barely strong enough for the 2.5. I suspect it'll blow up sooner rather than later and they you can't even sell your AX5 to help fund the new transmission. Also, dropping a transmission SUCKS! Probably a lot easier if you have a lift but I don't. Even on 33's the transmission jack isn't tall enough and the frame rails are too low to slide the transmission out from underneath so it's the worst of both worlds. Didn't the camaro's come with the 4L60E transmission? If so, I would think that'd be the simple solution and you'd just have to buy the transmission to transfer case adapter for around $500.

2. I left things where they originally were when I did my V8 swap and bought some generic mounts. It's certainly doable but I've never seen a custom engine mount solution from anyone that accomplishes this for you even on the super popular chevy V8's. IMO, if that's what you want you need a generic engine mount and you need to position things yourself. I'm a huge advocate of doing that anyway and I've never figured out why people don't do it but so far I've never seen anyone else want that. I still don't understand why it's more popular to buy a Jeep specific engine mount for 4-5x the price and still requires you to resize both driveshafts. Either way, I think the generic mount is the easier method by far.

3. You will need a new fuel pump because the TBI fuel pumps likely can't produce the fuel pressure required for your more modern engine. I don't know what that engine needs but I suspect it's more than 30-35psi. I've been running a stock fuel pump for a 95 Jeep in the stock tank with stock fuel lines and it's enough for my 5.3 LS although just barely. I think the stock pumps for a 95 2.5 engine are around 26gph at 12v which should support 260hp. However, even those tiny pumps aren't running at 12v, they're running at 13.5v which raises their output. I'll probably upgrade my pump soon but I'm also never pushing the engine to it's max and it works fine.

4. You'll need to get the ECU flashed to remove the anti theft system. If the camaro had an automatic transmission, you'll probably need to turn that part of the ECU off as well. This is common practice on almost every engine swap these days. As for a wiring harness, keep digging for a wiring schematic. I'm sure you can do it if you're motivated enough. I figured out how to rewire my LS harness but most people say it takes around 10-15 hours to accomplish the first one you do. Between time, money spent on fuse blocks and new wiring loom, tape, OBDII port, etc, I figured it was less than $50 to send my harness off to someone and have them do the work for me.

5. Running gauges when you aren't trying to maintain a "factory dash look" is actually really easy since you can pull the signal off the ECU or off the sensor itself. However, running a tablet is actually cheaper than buying even budget friendly gauges. That said, you're still going to need a gauge for fuel as most ECU's don't track that. I ran a set of Jegs gauges and really liked them but one day my speedo started freaking out. I now run an old phone running the torquepro app in place of the old speedo. I still run the remaining gauges since they still work.

edit: You're forgetting exhaust and chassis wiring. Maybe an exhaust shop will run you a custom exhaust for a reasonable price. I built my own because I had a specific things I needed. There is a lot of wires in your Jeep that you won't be using anymore but plenty that you will. You are going to have to pour through the wiring schematics of both vehicles to figure out how to marry the two harnesses together.


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post #5 of 34 Old 04-23-2021, 12:26 PM
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I know nothing about that engine or it's management system.

Agree with Waternut on the fuel pump and transmission issues.

If it were me, and it's not but if it were.....I'd pull all the wiring from the Jeep, buy a generic hot rod wiring kit to run the chassis electrical (lights etc) and power the harness for the 3800 and then modify that stock harness as needed for engine management. We bought a CJ5 tub and frame sitting in a field and used a generic 12 circuit harness (about $120), ran a 350 so little engine wiring needed, but I had the whole jeep wired in about 2-3 hours once we got to that point.

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post #6 of 34 Old 04-23-2021, 12:27 PM
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Quote:
Originally Posted by shaggyjim View Post
Didnít the 3.8 have a supercharger option on some cars? Please keep up with the thread because most of these different engine swap threads tend to stop without resolution. I think itís interesting thinking outside the box and would like to follow along.
The Buick Grand National. It was a beast for that time frame and I almost bought it. Then realized at 18, I could afford the payments since I worked 3 jobs, but not the insurance and gas lol. Was a terribly defeating realization that showed me early that just because you can, doesn't make it a smart decision. Still almost did it anyways lol

It was a very sharp looking car for the time also.

https://www.caranddriver.com/feature...l-gnx-history/
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post #7 of 34 Old 04-23-2021, 02:35 PM
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Well if you can do a factory supercharger you MUST do a supercharger... it’s da law.
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post #8 of 34 Old 04-23-2021, 02:42 PM
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While I really have nothing to add as far as the mechanical aspect is concerned (it sounds like a cool concept though!!), from an electrical aspect I might have a little. The 3800's (along with all the rest of the 60 degree V6's) use a P04 ECM, which looks like a 0411/P01 ECM on a typical V8 Vortec, but is wired differently internally and has a different OS. It is supported by HPTuners (I just downloaded a stock file to check). If I were you however I would do what I did with my Vortec swap.....have someone at a GM dealer reflash the PCM with a manual trans calibration, THEN delete VATS and continue on. I didn't have to bother with deleting out all the transmission codes, and dealing with the idle idiosyncrasies that pop up by doing so. Integrating the GM harness into the Jeep won't be too much different than doing an LS swap.
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post #9 of 34 Old 04-23-2021, 05:36 PM
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Sounds like a well-considered swap and am interested in following along.

I have a question about the transmission. In my experience, the automatic that they put behind the 2.5 YJs was pretty stout. It has a lockup converter and I imagine it would bolt right up. Am I correct in my assumptions?
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post #10 of 34 Old 04-23-2021, 06:59 PM
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The 3800 series II is one of my favorite production engines for some reason. They were very smooth, fuel efficient in larger cars, and pretty much bullet proof. I like the looks of them, just everything. I have thought of a 3800 swap into a jeep.

The Series II supercharged models were all FWD IIRC. The blocks motor mount bosses were different IIRC and some other things compared to a RWD block. The supercharged block and heads are not the same as the naturally aspirated version. You cannot just bolt the factory supercharger onto your application.

The Grand Nationals were a different era and version of the 3.8 some commonality there does not exist.

The fuel pump is much higher pressure than your 2.5L. I don't know why you have issues with it being in the tank. That is really the best place for it.

Wiring, fabrication, and solving problems that nobody else ever has needs to be your forte if you plan on pulling this off. You will have to mesh electrical systems together to some degree. Nobody makes a kit or harness that will have instructions that will really help you.

You will have to make mounts.

The 700r4 does come in a version that will bolt up. The AX-5 is very poor choice.

Somebody said a Dealer can program out your VATS and change to a manual trans program.... Not true. Reprogramming in a dealer requires stuff to be done vin specific and it will match the RPO codes of the vehicle. You may possibly lie to it by inputting a VIN that has the RPO codes you want such as manual, etc. but good luck finding such VIN # to match. A dealer will not disable VATs. (So I will learn that somewhere some shady f'r in a dealer will do it but it is not with factory equipment). There are different VATS or Passkey systems. The first one is as simple as taping one of 17 resistance values into two wires and badaboom baddabing it works. A lot of the programming that is spoken of is aftermarket, can be quite pricey, and can be limited to one vehicle.

I love the idea. Just be realistic with yourself. Your post sounds like you have pretty good insight already but you are not going to find off the shelf products or even people who can help you based on experience with the swap.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #11 of 34 Old 04-24-2021, 11:05 AM
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Quote:
Originally Posted by Boojo35 View Post
Somebody said a Dealer can program out your VATS and change to a manual trans program.... Not true. Reprogramming in a dealer requires stuff to be done vin specific and it will match the RPO codes of the vehicle. You may possibly lie to it by inputting a VIN that has the RPO codes you want such as manual, etc. but good luck finding such VIN # to match. A dealer will not disable VATs.
That was me! And you misunderstood me. You are correct, dealer cannot tune out VATS. I reflashed the PCM in my Jeep with my own 2 hands, as I have an MDI and access to GM SPS. My engine came from a 2001 Silverado with an auto. Went on to CarGurus, did a search for a *2002* Silverado 4.8 with a manual, grabbed the VIN from that.....and loaded the calibration from SPS with said VIN. Reason being was two-fold.....the obvious deletion of the automatic trans, and a little known extra bonus.....EGR deletion (as well as improved e-fan control.....earlier OS' can be touchy about e-fans). GM no longer deemed EGR necessary on 2002 vehicles (my LS1 Camaro is one of them), so I ditched it all

VATS of course had to be disabled with HPTuners.
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post #12 of 34 Old 04-24-2021, 02:14 PM Thread Starter
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I'll try to keep up with the thread...

Quote:
Originally Posted by shaggyjim View Post
Didnít the 3.8 have a supercharger option on some cars? Please keep up with the thread because most of these different engine swap threads tend to stop without resolution. I think itís interesting thinking outside the box and would like to follow along.
Mine is a NA RWD motor out of a Camaro. My understanding is that the internals are different and that my engine runs at a higher compression than the SC cars. With that said...if I get bored someday...

I'm not really looking for high horsepower in my YJ. Fuel efficiency and reasonable power are my goals
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post #13 of 34 Old 04-24-2021, 02:29 PM Thread Starter
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Waternut,

1. You are probably right on the trans but I think I'm going to give it a shot. At the very least we'll get to see if it's an easy bolt-up kind of a situation.

2. I've actually been looking at the generic and factory-style mounts. I'd like to see the ones actually in the Camaro to see how GM mounted the engine.

3. My fuel pump is even worse than yours. I have a 1990 with the Renix system. My fuel runs at abut 15 psi. It's definitely going to need replaced. I'm more concerned amount the lines and plumbing but it shouldn't be too bad.

4. Yes, the anti-theft system is a problem. I'll have to either deal with it or find someone that does it. The car was a manual so that's good.

5. I'm not super concerned about gauges or YJ wiring. When I acquired my YJ, it was the victim of an engine fire so I had to replace all of the wires, hoses, tubing, plastic...etc. in the engine compartment and firewall which left me pretty familiar with what my YJ has. Someone else actually had a really good idea about using a generic hot rod wiring harness to re-wire te YJ and as mine are crusty, cracking, and 30 years old I may just do that. If I can make the tablet idea reliable I think it's a winner. If not, I'll just get some decent gauges that look good to me. That's the thing about the CJ-7 dash. It's SUPER easy to change and replace. The hardest part of that swap is the heater controls.
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post #14 of 34 Old 04-24-2021, 02:31 PM Thread Starter
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Dude...that's a good idea...


Quote:
Originally Posted by timatoe View Post
I know nothing about that engine or it's management system.

Agree with Waternut on the fuel pump and transmission issues.

If it were me, and it's not but if it were.....I'd pull all the wiring from the Jeep, buy a generic hot rod wiring kit to run the chassis electrical (lights etc) and power the harness for the 3800 and then modify that stock harness as needed for engine management. We bought a CJ5 tub and frame sitting in a field and used a generic 12 circuit harness (about $120), ran a 350 so little engine wiring needed, but I had the whole jeep wired in about 2-3 hours once we got to that point.
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post #15 of 34 Old 04-24-2021, 02:37 PM Thread Starter
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Yes, I believe that it would bolt right on. The 2.5 and 3.8 inherited the same bolt pattern for transmission hookup. There might be some light mods for the starter and crank trigger depending upon your jeep but nothing that is overly complicated. Indeed, as most 3800's had an auto it may make it even a touch easier...? Someone would have to research the flex-plate to TC mating but I don't see why it couldn't be done.

Quote:
Originally Posted by 11-11-11 View Post
Sounds like a well-considered swap and am interested in following along.

I have a question about the transmission. In my experience, the automatic that they put behind the 2.5 YJs was pretty stout. It has a lockup converter and I imagine it would bolt right up. Am I correct in my assumptions?
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