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  #31  
Old February 24th, 2021, 14:16
98LimitedLQ4 98LimitedLQ4 is offline
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Re: Swapping a Vortec 6.0LQ4 in my 98

Quote:
Originally Posted by VAhasnoWAVES View Post
turning off VATs, O2s, EGR, etc is very simple with hp tuners. i picked up a refurbed computer with the basic requirements to run the suite for like... $100. youll spend $300 for the MPVI, $100 in credits, another $250 for the pro package if you so choose. but its fun to play with. and i use it to read DTCs all the time.

ultimately youll want someone to tune it once its in the vehicle. so it may be cheaper in the long run to reach out to a tuner to see if they will turn what you dont want, then once you get it running you bring it to them for a dyno or street tuning session. might also be worthwhile welding in bungs for wide band O2s when you are doing the exhaust so they tuner can utilize them. preferably one for each bank, but one after the Y will also suffice.

its worth considering what ECM you intend to use. the truck stuff is big and bulky, but works. i opted for an E40 ECU and a separate TCM for packaging, but that required loading up a start up tune to get things started.

when it comes to harnesses... if you are going to do it yourself, do what you will. LS1 tech is a good resource for figuring things out. but i would rather pay for a new built harness than a thinned down stock harness. a 20 year old harness is likely dry and brittle. a stand alone harness will leave you with 6 wires or so to hook up gauges after plugging it all in, doesnt sound like what you want.

now... getting the factory gauges to work gets complicated, or expensive. you pick. a lot of guys end up just stuffing aftermarket gauges in the factory bezel and being done with it. the issue is getting the GM can bus to talk to the jeep BCM. there is a company that had their LS powered liberty at LS Fest doing passes down the strip. not that it was much of a street vehicle, but they were there to highlight their module they had created to get the GM PCM to talk to the the BCM of other various OEMs.







good news is your not the first one to LS swap a cherokee. plenty of info out there. do some reading, come up with a plan, start getting your feet wet. but keep in mind specific questions get much better answers than generic, "how do i do it?" questions.
Iím hoping to reuse the trucks ECU and TCM since I already have them at my disposal, also they are currently working and the truck runs with everything still in place.
A stand-alone harness would be great, I guess the better question I should have asked was, can I piggy back the Jeep ECU to work the gauges and such and tie it into the GMís ECU?
Finding a tuner to tune on this is kind of a mystery right now, the local LS tuner/dyno shop doesnít want to touch this when itís complete.
Definitely will add some 02 bungs when making the new exhaust.
And looking into a atlas 2 speed to get power to the rears.
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  #32  
Old February 25th, 2021, 07:39
VAhasnoWAVES VAhasnoWAVES is offline
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Re: Swapping a Vortec 6.0LQ4 in my 98

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Originally Posted by 98LimitedLQ4 View Post
Iím hoping to reuse the trucks ECU and TCM since I already have them at my disposal, also they are currently working and the truck runs with everything still in place.
A stand-alone harness would be great, I guess the better question I should have asked was, can I piggy back the Jeep ECU to work the gauges and such and tie it into the GMís ECU?
Finding a tuner to tune on this is kind of a mystery right now, the local LS tuner/dyno shop doesnít want to touch this when itís complete.
Definitely will add some 02 bungs when making the new exhaust.
And looking into a atlas 2 speed to get power to the rears.
i think dakota digital is who you want to talk to about this.
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  #33  
Old March 4th, 2021, 10:21
Rockwood Rockwood is offline
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Re: Swapping a Vortec 6.0LQ4 in my 98

Quote:
Originally Posted by 98LimitedLQ4 View Post
Iím hoping to reuse the trucks ECU and TCM since I already have them at my disposal, also they are currently working and the truck runs with everything still in place.
A stand-alone harness would be great, I guess the better question I should have asked was, can I piggy back the Jeep ECU to work the gauges and such and tie it into the GMís ECU?
Finding a tuner to tune on this is kind of a mystery right now, the local LS tuner/dyno shop doesnít want to touch this when itís complete.
Definitely will add some 02 bungs when making the new exhaust.
And looking into a atlas 2 speed to get power to the rears.
Stock gauges just use the stock computer and install its sensors onto the GM engine. You'll need an adapter for the speedo to work.
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  #34  
Old March 5th, 2021, 19:56
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Skruffy Skruffy is offline
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Swapping a Vortec 6.0LQ4 in my 98

I did a similar swap. LS3 with a 6l80 using Novak mounts. No problem at all with the tunnel clearance. The engine and transmission are actually shorter than the 4.0 with the auto transmission so you will likely need to change your driveshafts.
I have TJ rubicon axles and havenít broken them, yet.
Gauges were an ass pain but are definitely doable. I spent about half of my time sorting out the wiring and gauges during my swap. The Novak tach emulator worked for me but is very sensitive to voltage during startup. If your battery isnít totally full it may not function until it has had a minute to charge, then restart the engine. That has been the case for me anyway. I really wanted to retain the stock interior so was a bit picky with this portion, down to the ac switching.
Search supercharged la3 crammed in an XJ on naxja and you can see the whole process that I followed.
The LS is an amazing engine for the XJ and you will be happy when finished. I have somewhere around 500% more horsepower and 75% better fuel economy. You would crazy not to swap the engines given the chance!
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  #35  
Old March 6th, 2021, 09:42
cdsurf cdsurf is offline
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Re: Swapping a Vortec 6.0LQ4 in my 98

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Originally Posted by Skruffy View Post
I did a similar swap. LS3 with a 6l80 using Novak mounts. No problem at all with the tunnel clearance. The engine and transmission are actually shorter than the 4.0 with the auto transmission so you will likely need to change your driveshafts.
I have TJ rubicon axles and havenít broken them, yet.
Gauges were an ass pain but are definitely doable. I spent about half of my time sorting out the wiring and gauges during my swap. The Novak tach emulator worked for me but is very sensitive to voltage during startup. If your battery isnít totally full it may not function until it has had a minute to charge, then restart the engine. That has been the case for me anyway. I really wanted to retain the stock interior so was a bit picky with this portion, down to the ac switching.
Search supercharged la3 crammed in an XJ on naxja and you can see the whole process that I followed.
The LS is an amazing engine for the XJ and you will be happy when finished. I have somewhere around 500% more horsepower and 75% better fuel economy. You would crazy not to swap the engines given the chance!

Was the AC switching fairly straightforward?
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  #36  
Old March 6th, 2021, 10:55
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Skruffy Skruffy is offline
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Swapping a Vortec 6.0LQ4 in my 98

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Originally Posted by cdsurf View Post
Was the AC switching fairly straightforward?

It was the only thing that got the best of me. The Jeep ecu knows when the hvac is set to ac. It then writes a pin to ground that allows current to flow to the high and low pressure sensors. If they are satisfied that current makes its way back to the ecu, the ecu then sends current to the ac clutch relay and it engages. The problem I had is that the Novak harness needs the same two circuits. I hijacked the hi/low pressure circuit from the XJ and wired into the Novak harness, this is pretty straightforward. The problem then comes from the ac switch on the dash. The actual physical switch itself is this crazy pneumatic/electric amalgamation so tapping into it there potentially could cause other systems to not work. The other problem is that even if you did the Jeep uses a ground to complete the circuit and the GM uses +12v. So even if you did wire in unless you put in a special relay it wouldnít work.
So I put a simple 12v button on my dash that feeds the GM ecu 12v when I want the ac on. I didnít want to do this but was desperate to get everything back together.
The unexpected result was that if the Jeep ac dial was switched to on after 18 seconds the odometer would read no bus. This gremlin took me a while to sort out. Ultimately I took a fused (1 amp) 12v source and fed it to the now unused ac switch sense that satisfies the Jeep ecu and prevents the no bus error.
I have no doubt that there is a way of doing without the added dash switch but I just couldnít dedicate any more time to figuring it out.
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  #37  
Old March 6th, 2021, 13:56
cdsurf cdsurf is offline
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Re: Swapping a Vortec 6.0LQ4 in my 98

Quote:
Originally Posted by Skruffy View Post
It was the only thing that got the best of me. The Jeep ecu knows when the hvac is set to ac. It then writes a pin to ground that allows current to flow to the high and low pressure sensors. If they are satisfied that current makes its way back to the ecu, the ecu then sends current to the ac clutch relay and it engages. The problem I had is that the Novak harness needs the same two circuits. I hijacked the hi/low pressure circuit from the XJ and wired into the Novak harness, this is pretty straightforward. The problem then comes from the ac switch on the dash. The actual physical switch itself is this crazy pneumatic/electric amalgamation so tapping into it there potentially could cause other systems to not work. The other problem is that even if you did the Jeep uses a ground to complete the circuit and the GM uses +12v. So even if you did wire in unless you put in a special relay it wouldnít work.
So I put a simple 12v button on my dash that feeds the GM ecu 12v when I want the ac on. I didnít want to do this but was desperate to get everything back together.
The unexpected result was that if the Jeep ac dial was switched to on after 18 seconds the odometer would read no bus. This gremlin took me a while to sort out. Ultimately I took a fused (1 amp) 12v source and fed it to the now unused ac switch sense that satisfies the Jeep ecu and prevents the no bus error.
I have no doubt that there is a way of doing without the added dash switch but I just couldnít dedicate any more time to figuring it out.

I want to cry while reading this.


I know it's the part that will get me too, especially since I want to go the route of no Jeep PCM. I would love to do some custom hybrid controller based off diagrams I have for the Jeep HVAC controls but it looks like it would be a nightmare.



So far what I've figured out from the XJ's C3 connector:
  • P1 DB/OR wire - A/C Comp. Clutch Relay Control [Output]
  • P2 DB/PK wire - Rad Fan Relay Control [Output]


  • P13 TN wire - Rad Fan Req [Input]
  • P22 DB/WT wire - A/C Switch Sense [Input]
  • P23 LG wire - A/C Select Input [Input]




From what you're saying, I'm thinking that:
  • P22 was the HI/LO pressure circuit you fed directly to the GM PCM
  • P23 was what you had to use a manual switch to replicate for GM PCM/ wired as constant ON for the Jeep PCM
  • P13 unused and left for GM's PCM to manage


I may have 22 & 23 switched because my diagram looks like it has a typo but does this seem right to you?
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  #38  
Old March 6th, 2021, 14:26
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Skruffy Skruffy is offline
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Swapping a Vortec 6.0LQ4 in my 98

Quote:
Originally Posted by cdsurf View Post
I want to cry while reading this.


I know it's the part that will get me too, especially since I want to go the route of no Jeep PCM. I would love to do some custom hybrid controller based off diagrams I have for the Jeep HVAC controls but it looks like it would be a nightmare.



So far what I've figured out from the XJ's C3 connector:
  • P1 DB/OR wire - A/C Comp. Clutch Relay Control [Output]
  • P2 DB/PK wire - Rad Fan Relay Control [Output]


  • P13 TN wire - Rad Fan Req [Input]
  • P22 DB/WT wire - A/C Switch Sense [Input]
  • P23 LG wire - A/C Select Input [Input]




From what you're saying, I'm thinking that:
  • P22 was the HI/LO pressure circuit you fed directly to the GM PCM
  • P23 was what you had to use a manual switch to replicate for GM PCM/ wired as constant ON for the Jeep PCM
  • P13 unused and left for GM's PCM to manage


I may have 22 & 23 switched because my diagram looks like it has a typo but does this seem right to you?

Close
P1 and P2 get replaced by the GM harness so no need to worry about them.
P13 is also covered by the GM harness

P22 DB/WT is the one that is satisfied with the constant 12v.
I bypassed p23 because the Jeep effectively uses that as a ground. You will find that it is always 12v regardless of your Hvac switch position. Instead this is the wire that I ran from a 12v source to my dash switch then to the GM harness.
The only good thing about it this way other than it works is that it also acts as a fan request. Push that button and cooling fans come on.
With this set up any time you push it your ac clutch will engage regardless of the XJ Hvac switch position. Not ideal, and not the cleanest but it works.
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  #39  
Old March 7th, 2021, 21:44
cdsurf cdsurf is offline
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Re: Swapping a Vortec 6.0LQ4 in my 98

Quote:
Originally Posted by Skruffy View Post
Close
P1 and P2 get replaced by the GM harness so no need to worry about them.
P13 is also covered by the GM harness

P22 DB/WT is the one that is satisfied with the constant 12v.
I bypassed p23 because the Jeep effectively uses that as a ground. You will find that it is always 12v regardless of your Hvac switch position. Instead this is the wire that I ran from a 12v source to my dash switch then to the GM harness.
The only good thing about it this way other than it works is that it also acts as a fan request. Push that button and cooling fans come on.
With this set up any time you push it your ac clutch will engage regardless of the XJ Hvac switch position. Not ideal, and not the cleanest but it works.

Interesting. I've thought about it and there may be a solution for pre 2003 PCM's. Cut the LG wire associated with the Jeep's P23 and have it interrupted by a relay's coil pins, then have the relay's switch pins complete a circuit using a 12V source in my case and going to the A/C request wire on the GM ECU. I'm thinking it would be VERY different for you with an E38/E40 ecu since they use serial data.
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  #40  
Old March 8th, 2021, 14:23
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Skruffy Skruffy is offline
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Swapping a Vortec 6.0LQ4 in my 98

I donít know much about XJs that are older than mine but avoiding the serial CANBUS system is a good way to stay out of trouble. I think your relay plan will work and it will be super satisfying to not need to add a circuit like I did.

Give it a shot!
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  #41  
Old March 8th, 2021, 16:57
98LimitedLQ4 98LimitedLQ4 is offline
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Re: Swapping a Vortec 6.0LQ4 in my 98

Rockwood, Iím looking into Dakota Digital, just not a fan of the 0-100 fuel readout they have one their dash panel kit.

Skruffy, thanks for the heads up on trans tunnel clearance. Did you use the stock XJ shifter and console? Iím just going to go with a Holley Terminator X Max harness and tuner since I donít want to mess with weeding out the factory harness and Novak was around $800 to rewire my stock one. This has been placed on the back burner since I have to complete my wifeís 98TJ frame caps, and any day my daughters RE 4.5Ē Super Flex is supposed to get here for her 98 Sport. Yeah Iím going with a 2 spd Atlas so once I get it all in place Iíll have to measure for new driveshafts and putting the 8.8 out back. Hoping to have this all wrapped up by August to take them to Ocean City, MD for Jeep week.
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  #42  
Old March 8th, 2021, 23:12
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Skruffy Skruffy is offline
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Swapping a Vortec 6.0LQ4 in my 98

I used a lokar shifter which took some effort and fabrication to install but is now working properly including tap shifting. Remember though I have a 6L80 so it could be a bit different. I was also forced to replace the tcase shift linkage due to intercede fence with the lokar shifter. For this I used the Novak cable one which is a worthy upgrade for any Cherokee.
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