90 YJ / LS1 Swap - Build Notes

[Fred007]

Started with a stock 6 cyl 258 mated with an AX-15 and NP231 transfer case. The engine had 132,000 miles on it and while it ran okay, had numerous issues with old age (vacuum lines and rusted out air filter, etc.). It also had a problem starting sometimes which I attributed to the nasty carburetor. I replaced the carb thinking that might help get me by, but that had little effect. I think the computer control (new to this year) was pretty bad and I had not done the “nutter” on it.

After doing some research on the Internet, I decided to replace the engine with a Chevy 350 of some kind. Based on what I had read, numerous people had done this kind of replacement and several stores offered custom parts that made the swap easier. I have no experience with fuel injected engines and was leaning towards a carbureted replacement, but lack good carburetor tuning skills and so it seems do most modern mechanics. I found a 2000 LS1 for sale on eBay that had been in a Jeep already and after getting more information on this type of engine thought this would be the way to go.

I got the engine shipped from Colorado and it looked to be in pretty good shape when I received it. The previous owner also included some parts I might be able to use from his wrecked Jeep

Novak transfer case shifter assembly http://www.novak-adapt.com/
Electric radiator fan
PCM and custom harness for LS1 http://www.speartech.com/
External slave cylinder from Toyota
Stainless steel lines for clutch cylinder
Electric Fuel pumps
In-tank electric fuel pump

I then ordered some parts from Advance Adapters to mate this to the AX-15.

Bell housing adapter kit for Vortec 350 to AX-15
1987-2005 Jeep to Chevy manual transmission kit
Chevy LS1 universal motor mount kit
Radiator for LS1
Spall puller fan kit

[Fred007]

Remove Old Engine – October 13th 2007

At this point, October 2007, it was time to remove the old engine and transmission. My plan was to get the bulk of the heavy work done before it got too cold in Wisconsin (which could happen at any time). Removing the old engine took a weekend to get everything disconnected and removed.

At this point I had a mess of wires coming from all over to the engine compartment. My goal was to keep the Jeep as original as possible with a different power plant. I removed the engine wiring harness and computer but left the vehicle wiring harness as intact as possible. I ended up with a handful of wires coming from the firewall transfer housing that I needed to connect or just terminate. One of these wires was the main battery feed to the fuse box, the others were generally wires from the fuse box tied to the ignition switch. There is also a wire tied to the rocker switch on the dashboard that I still have no idea what that is for, seems like some kind of timed defrosting circuit or something.

With the motor and transmission removed, and the bulk of the old wiring also gone, it was time to clean up the engine compartment. I just used some Engine Brite and worked over the areas as much as possible. Generally, this Jeep was pretty clean with little or no deep rust. There are areas of rust on the doors and windshield but generally the tub is pretty clean.

Once the engine space was in decent shape, I removed the old engine mounts. Was a little over zealous on one side and nicked the frame a bit with the torch. Figured I could take care of this when the new mounts were welded in place.

[Fred007]

Replacing the front axle vacuum disconnect mechanism

I also took this time to replace the vacuum connect mechanism for the D30 front axle with a manual setup from Quadratec. (www.quadratec.com) The new engine only had one vacuum line and that was destined for the heater actuator. Plus, the mechanism was really old and I had no faith in the lines themselves. This turned out to be a good move as I swapped a different transmission/transfer case which did not have the vacuum hookups for that actuator.

[Fred007]

Engine

I really did not have to do much to the engine itself. The Jeep it came out of was wrecked and the old radiator was badly damaged but the engine itself looked pretty decent. The old exhaust was cutoff just behind where the headers collected together. I planned on using this same setup in my Jeep and just getting a custom exhaust when things were running. One issue was the oil pressure gauge. The stock oil pressure gauge on the LS1 is on the back of the block and electronic, designed to hook into the PCM. It was not possible to mount the Autometer sending unit to this location as the intake manifold was too close to allow some kind of T adapter.

I searched on the web and found that there is an aluminum casting, just above where the oil filter mounts, that had a port for oil pressure on some engines. Of course, the one I had did not have that provision so I went to the local Chevy dealer to order a replacement with the pressure port. The first one I received was a direct replacement but they re-ordered a new casting and that one came with the threaded port. Of course, the threads were not anything standard and I had to find a hydraulic hose specialty store for the right fitting to allow the 3/8 pipe thread on the manual oil pressure sending unit. Once I got this done it was simple to attach the manual oil pressure sending unit and get everything hooked back up.

I also noticed that the harmonic balancer was showing signs of wear. The rubber between the pulley and the inner shaft was coming out on one side. I figured this may be a sign it got slightly whacked in the accident and with the engine out this was a good time to replace that part. The local Chevy dealer ordered the replacement and I got that detail out of the way.

The other thing that I did not have for this engine was some kind of air filter with the Mass Airflow Sensor (MAF). I had a MAF but no real way of getting an air filter on that. Luckily, the great folks at Street & Performance were able to help out. I really can’t say enough about how helpful they were with all my questions about the LS1. When I ordered the air filter setup, they included a great DVD where Mark runs through the whole LS1 system and modifications you can make to the engine. On the DVD he walked through several things that I needed to accomplish, it was like he was reading my mind on what I needed to know about the LS1. I ended up getting a 4” elbow that connected to the MAF and a K&N air filter.

[Fred007]

Transmission/Transfer Case

After reading many posts on the Jeep forum (www.jeepforum.com) I figured it may be worth the extra effort to replace the AX-15 transmission I had been planning on reusing. I started looking around and found a NV3550 from a 2003 Jeep in New Jersey. Got the ball moving on that and started to figure out what I would need to change. The bellhousing from Advance is the same casting for the AX-15 and NV3550 but with some relief for the NV3550 housing. Also, the throw out bearing is different as the input shaft size is different. For a number of reasons, I choose to not return the kit and get the actual NV3550 kit which meant I had to relieve some of the casting to get the NV3550 to mate properly. You also need to remove a short bit of the throw out bearing shaft but this is all explained in great detail in the instructions from Advance Adapters.

I also decided to install a short shaft SYE kit as it would be much easier with the transmission sitting on my bench. I also figured I would have to get some custom drive shafts and this was as good a time as any. Ordered up the kit from Advance and got started. Once I had the SYE kit installed, I also installed the Novak TCase shifter. Then it was time to mate the transmission to the engine. The end result looked pretty decent and all I needed at this point was to position it in the Jeep and weld the motor mounts in place.

Donor transmission


SYE Installed


TCase Shifter Installed


Engine/Tranny ready to go


You can see the external slave cylinder and the Advance Adapters motor mounts

[Fred007]

Mounting the Engine/Transmission – December 14th 2007

I used a local shop where I knew the owner one snowy day in January to mount the engine. They helped me position the engine/transmission in the Jeep. I had always planned on using the standard skid plate and hoped to get the transmission mount bolts to fit back into the skid plate standard holes. However, with the LS1/Bellhousing/Transmission combination I needed to move the whole thing forward a bit. We modified the transmission mounts and ended up using the forward bolt holes in the standard skid plate. Positioning the engine was a mixture of getting the transmission shifter in a decent place, making sure there was enough room to work on the engine, and generally wanting the engine as far back as possible.

We ended up moving the engine 1” towards the passenger side (left) and cut the motor mount bracket on that side to accommodate moving it over. This left a gap on the driver’s side and we considered welding an extension on the motor mount bracket, but decided it might be easier to just weld an extension to the frame on that side. Using 1x1” square steel stock, we created an offset to the frame and welded the mount to the extension. At this point, I just needed to tighten the engine and transmission mount bolts and all the skid plate bolts.

Jeep ready for new engine


Engine installed

[Fred007]

Electronics

As I was replacing a 6 cyl with a V8 I knew the old tachometer would not work without significant changes and the speedometer was going to be electric. I decided, after being taunted by my son, to do all the gauges with new Autometer Cobalt gauges (his choice). Where possible, I was planning on using existing wiring to limit the number of new wires I had to run through the firewall and generally around the Jeep. The oil pressure, water temperature and fuel sensor wires were just reused and connected to the new gauges. The PCM has a tach output wire that I ran to the tachometer which comes from the factory configured for a V8. The voltmeter was easy and I also installed a clock that somewhat matches. I used some plastic gauge consoles ordered from Quadratec. Wired all the gauges up inside the house as it was pretty cold out at this point. I also created my own “Check Engine” light using a blue LED drilled in the console. (you can see this right above the stereo).

Because of the wiring harness I was using, it became apparent that I needed to mount the PCM in the engine compartment itself. My initial attempt was pretty lame and turned out pretty quickly that I needed to do something different. Because I am using an LS1 from a Corvette, it comes with an Electronic Throttle Control (ETC) which is actually pretty interesting. The throttle linkage is all electronic as has a throttle actuator control (TAC) that needs to be pretty close to the PCM. After surveying the engine compartment and the space where the old computer used to be stored (behind the glove box) I decided the best place to mount the PCM/TAC was under/next to the battery holder. I remove the battery holder, polished it off pretty well and painted with Rustoleum flat black. I originally tried to mount the PCM under the battery holder but was unhappy with the way it ended up sitting on the fender. I constructed some aluminum struts coming down from the battery holder that I used to mount the PCM to on the outside. I also mounted the TAC on the inside of this frame and it seems to be fairly secure and out of the way.

The PCM/Engine harness is pretty simple to connect to the jeep but there are a couple of considerations. There is a simple fuse box and the ODB connector that I needed to mount inside the jeep. This was done with the fuse box accessible under the glove box with the ODB connector just in from of the fuses and below the stereo. Electrically, the wires from the PCM I was planning on hooking up were:

Full time battery connector to the fuse box (orange)
Ignition source to the fuse box (pink)
Hot to Fuel pump (grey)
ODB harness with Check Engine light
TAC module and throttle pedal
Tachometer output (white)
Transmission speed sensor (2 wires for AC type input yellow and purple)
Radiator Fan Relay (green and pink with 2 black stripes)

I got the PCM mounted and all the wiring done before mounting the engine which turned out to be good as it’s much easier to work on this without the engine installed.

New gauges


PCM Behind battery holder


Mounting of throttle pedal

[Fred007]

Speedometer

I knew the old mechanical speedometer was going away, but had not actually figured out how I was going to get the new electronic one hooked up. One major problem off the bat was that the 2003 Jeep speed sensor (in the NP231 transfer case) uses three wires one of which needs a 5v input. Well, I was unaware of where I was going to get a 5v source in the jeep and rather than crack the PCM harness to see if I could get something off the PCM, I opted for a 5v supply I mounted under the dash. I created a wiring harness that had the 5v going to the sensor and the two wires (white and yellow) coming from the sensor. Then the interesting question of how to convert a 16,000 pulse per mile (ppm) dc signal from the tcase to a 228,000 ppm ac signal the PCM was expecting came up. A couple of things really saved me here, one was the unit from Dakota Digital that can convert (and double/quadruple) a DC signal to an AC signal.

I also knew that I could hookup the speedometer directly to the sensor without getting the PCM involved. In fact, the PCM would work okay without the speed sensor hooked up but it does affect how the engine idles when at speed and pushing in the clutch. When I was first running the engine without the speed sensor hooked up, I occasionally got a check engine light if I let off the gas quickly or pushed the clutch in a speed.

When I got the speed sensor wiring all ironed out with the proper voltage input, and got the speed convertor configured correctly, the PCM started getting good speed input which resolved this issue. The Autometer speedometer can be calibrated very easily by just driving two measured miles with the gauge in calibration mode. This worked really well and I now had a working speedometer. The next thing was to verify what kind of speed input the PCM was getting and I did this using some software from Autotap which includes and ODB USB connector for a laptop PC. As it turns out, I was worried about having to program the PCM with the proper ppm setting (16,000) instead of the factory GM settings, but since this engine/PCM setup had actually come out of Jeep, which had already been done. At this point the PCM and speedometer were within 5mph of each other and I did not have the issue of the idle problem mentioned above.

[leftlanetruckin]

so am i right in thinking you are running the dana 35 behind that motor then?
lemme guess you dont hit the gas pedal too much?
excellent work, and a good end result, but i would seriously consider at least a ford 8.8 rear end mate.
i do envy your motor........
again, excellent work!

martin

[smoke_20]

Excellent write up, thanks

[Fred007]

I had purchased a new aluminum radiator and electronic fan from Advance Adaptors and had already wired the fan relay to the PCM. With the engine mounted in the Jeep, I could now mount the radiator and get it hooked up. I built a couple of aluminum frames that matched the original radiator holes in the jeep and used these to mount the new radiator to. First attempt was a little too high and I ended up having to adjust the radiator on the frame I had built several times. I wanted to make sure it cleared the steering box and was not too low to get snagged on anything. With the air filter I was using, I needed to move the overflow connector so I could get a little more clearance on the air filter. I had a local welder who does a lot of aluminum welding secure an aluminum tube in the place I need and plugged the original overflow value.

When I started running the engine I thought it was running a bit hot and the fan would come on fairly quickly, before the whole radiator had heated up. After some research on this, it turns out that the standard thermostat for a LS1 is set to 195. My PCM was programmed to kick off the fan at 205 which, based on the temp sensor in the engine was before the radiator had heated up. I got some advice to install a thermostat for the fan directly on the radiator and ignore the PCM. However, that did not feel right as the engine itself seemed to be running over the desired 195 or so. I read a number of threads that the LS series engines actually make more horsepower at higher temps, but also got some direction that the higher temps are generally for emissions control.

There are both 180 and 160 aftermarket thermostats available for the LS1 but for reasons beyond my understanding (I think it’s because the engine is from a Corvette) these simple thermostats are $50 or more. In trying to figure out what to do, program the PCM with a higher temp or purchase one of these lower temp thermostats, I ran across a replacement thermostat from my local CarQuest shop at 186 degrees. I have replaced the original thermostat with this new one and so far are getting good results. Am waiting to see what happens when it gets really hot, but right now (spring in Wisconsin – 2 days) it is running at about 190 degrees and the fan only comes on when it gets hot (210+).

Finding the right hoses was another interesting pursuit. I started with hoses that were the right size and had bends that I thought would work. I then cut these apart and used residential drain plumbing pipe to hook the end sections together. I ran these for a bit and they seemed to be working fine, but I was worried about them leaking and/or blowing out when it gets really hot.
I ended up taking the custom hoses off and walking through the local CarQuest store and just looking for hoses (actually sections of hoses) that might work. I ended up with two that fit the bill fairly well. The numbers for these are listed in the appendix. That is where I am at today and think the cooling for the engine should be finished. Worst case is that I modify the thermostat to be a little cooler but don’t expect that much less than 180 would be necessary.

Note: A great book on the LS1 is “Chevy LS1/LS6 Performance” by Christopher P. Endres (Endres, 2003)

[Fred007]

At this point, with the engine and transmission mounted, the electronics and plumbing ready to go I needed to order the drive shafts. Originally, I had planned on reusing the stock drive shafts, but with the new transmission and transfer case that did not seem possible. I had the folks at the Offroad Toy Store order some Tom Woods drive shafts. The measurement instructions were pretty decent and with the SYE kit I had 1310 c.v. yokes on both the front and rear of the transfer case.

I had thought it would take a while to get the drive shafts but apparently the folks at Tom Woods can fabricate shafts pretty quick. I got the new shafts and they fit perfectly.

[Fred007]

At this time everything was in place to crank up the engine and see how it ran. I had already changed the fluid in the front and rear differentials, transfer case, transmission and engine and with new radiator fluid was ready to give it a whirl. I fully expected that the engine would start the first time I tried as the computer controls the whole process and GM has such a low failure rate on new engines in their plants.

First problem I ran into was that the PCM was turning off when I cranked the engine. I debugged this using the Autotap software and I could see the software loose connection to the PCM when the engine was cranked. This turned out to be a bad choice on my part of the ignition source wire. I had used one of the left over wires from the old harness and tested to make sure it was tied into the ignition. However, this particular wire was one of those that looses power when the engine is cranking. Selecting a different ignition based wire that did not cutout allowed the PCM to continue to operate. This is a foreshadowing of a problem I will describe later.

Second problem, now that the PCM was staying awake during crank, the engine still would not start. I traced this to a fuel supply problem. The old engine had a mechanical pump and I was replacing with an electric pump and knew there could be an issue with the pump not being able to draw the fuel from the tank. I started working on this issue and while the pump I was using was located below the tank itself, it did just not have enough to draw the fuel out of the tank. Even if I solved this by priming the system, I was worried if I ever ran out of gas I would not be able to get it restarted.

After researching this a bit, I knew I had to go with an in-tank electric pump solution. I discovered I had the 20 gallon plastic tank so that was good. I got in touch with the folks at MTS and they had an in-tank solution that promised to deliver enough fuel for the LS1. I ended up dropping the tank and running braided fuel line from the filter/regulator back to the tank and hooking the pump to the PCM. I now had 3/8” braided fuel line from the tank to the engine fuel rail. Testing this setup showed that the pump was working great and delivered fuel to the engine just fine.

At this point, cranking the engine allowed it to start and things looked good. I had a check engine light, which I was prepared for, but used the Autotap software to reset the codes and start over. However, I continued to get the same check engine light. The code was for a problem between the TAC and the PCM so I started to trace this back. The result of this code was that the throttle pedal was not working the first time I started the engine. However, if I used the Autotap software to reset the codes while the engine was running, the throttle pedal would start working. (not a good long term solution…)

Here is where the previous problem with the ignition wire came back to haunt me. The harness I am using needs two main inputs, one from the battery and the other an ignition source. If they are switched the system does not start correctly and you get the problem with the TAC module I was experiencing. I think the problem was that the TAC was powered up before the PCM because I had the wires backwards and the PCM was confused about the state of the TAC. In any event, switching the battery and ignition wires eliminated this problem and the throttle pedal has worked since then.

With the drive shafts installed, and the engine running it was time to see if the Jeep moved at all. In this area I had some good luck as the drive train has just worked since that day without modification. My main concern at this point is sometime hearing a clunk in the back that signifies the Dana 35 has had enough of the V8 and given up the ghost. I do plan on addressing this shortly by swapping in a Ford 8.8.

Here is a view from below, you can see the LS1 truck oil pan and how the engine fits from underneath.


View of the radiator mounting.

[Fred007]

No sooner than I got things running to the point where I could drive it on demand, than I leaned back in the seat and broke the slider and seat riser. Since I was planning on replacing the seats anyway, this seemed like a good time to make that happen. After doing a little research I decided on the Corbeau Neoprene seats. I also ordered a new riser and slider for the driver’s side. Between the seats and the new hardware, I ended up with seats about 2” higher than the stock seats I was used to. Since I am a big guy, sitting in the Jeep on this setup had me looking out the front window right at the top edge of the windshield.

I ended up cutting about 1.75” off the riser supports and cutting the cross braces and welding them back slightly shorter than what they previously were. While this is working, I no longer have the ability to articulate the driver’s seat forward as the cross braces are not quite right and bind up a bit. This summer I plan to make new supports from angle iron, loose the regular riser and ability to articulate the seat. I still have this on the passenger side so am not too worried about it.

[Fred007]

1) BDS 3.5" Lift Kit
2) TrXus Mud Terrain Tire 33x12.50R15LT
Cragar Soft 8 Black 15x10.5 Wheels
3) Ford 8.8 Rear End Swap
4) 4340 Axle swap in front with ARB locker and regear to 3.73
5) Paint

(Every time I hit the gas I wonder about the 35 in the rear...)