Questions about GM V8 conversion on 98 TJ

[G H D]

Hello all..
im in the process of a chev v8 conversion into my 1998 tj, my goal is
more horsepower and a "sleeper " looker,,,i mean externally very little
evidence of conversion... im wondering if any of you have made the change,? im
going to be using the Holley sniper efi, and am wondering if anyone has had experience
with the signal output for the tachometer, ive been unable to get any satisfactory
information from holley... wondering if someone makes a level converter, my desire
is to keep the dash instrumentation stock appearing..
any help or direction would be really appreciated,

glen

 

[NashvilleTJ]

Hello all..
im in the process of a chev v8 conversion into my 1998 tj, my goal is
more horsepower and a "sleeper " looker,,,i mean externally very little
evidence of conversion... im wondering if any of you have made the change,? im
going to be using the Holley sniper efi, and am wondering if anyone has had experience
with the signal output for the tachometer, ive been unable to get any satisfactory
information from holley... wondering if someone makes a level converter, my desire
is to keep the dash instrumentation stock appearing..
any help or direction would be really appreciated,

glen

What engine are you planning?

 

[macleanflood]

Lots of folks have done LS conversion. Not many have done SBC.

If you're already planning on fuel injection buy a $500 5.3 LS with a computer...or a Suburban/Yukon/Truck with everything you need in terms of LS, wiring and PCM...sell/scrap what you don't need.

Thread 'Jeep TJ LS Swap Guide (Engine, Wiring, Cost & Step-by-Step)'

Dec 20, 2023

Will add pictures, typed this on my computer and all my photos are on my phone so ill go back and edit them in. I will also be adding info as subjects come up and I do more of these.

So you want to go to the dark side discombobulate your TJ and throw a LS motor in your rig? Well its not that difficult and I am going to try and best explain how to do it. Most of my knowledge comes from my personal daily driver 2000 Jeep Wrangler that I have put on roughly 30k miles in the almost 3 years I have had this finished this swap. On this TJ, it has a 5.3 LM7 from a 01 Silverado but I had backed it...

• XCRN
• chevy conversion gm junkyard race motor ls swap v8 swap
• Replies: 234
• Forum: TJ How-to Guides

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-Mac

 

[Abendage]

If you’re going the LS route Novak conversions makes a tach emulator and it can also run the factory cruise.

 

[Obi-Wan]

If you’re going the LS route Novak conversions makes a tach emulator and it can also run the factory cruise.

@G H D , this is the tach emulator being referenced.

I did a Gen III 5.3 in my TJ, and couldn't be happier.

I take that back. a 6.0 would make me happier.


View: https://youtu.be/Jj7MDzNi7vo?si=zeg4xMxoD0lcK64T&t=137

 

[G H D]

What engine are you planning?

an early probably 80's corvette 5,7 litre (350) have totally rebuilt with my own mods
its ready to drop in, just getting to the fine points stage and want to keep instrumentation
original as possible..

 

[GoldenGorilla]

The biggest reason that the LS is more common is that alot of the early adopters were in CA where there are some more stringent rules about engine being from same or newer model year and all the emissions equipment from the donor being retained. Well that and ODBII support makes the stock hardware easier to setup.

Functionally the SBC vs LS doesn't really matter in this context. SBC from 87 and later have roller cams and its much less of an issue to install them in earlier ones than in a TJ 4.0. There's advantages in the factory LS heads, but there are aftermarket SBC heads that can get you to the same results.

As for Holley EFI, a good friend of mine in ABQ is running a a blueprint SBC engine with Sniper II in the Ford coup hotrod his dad built. He's an amazing welder, but not much into auto mechanic work and is working with a shop down there. He's been having issues with the EFI cutting out somewhat randomly and has been working with the shop on the tune. The Sniper EFI system is a CANBUS system, not ODB II, whereas the TJ's JTEC computer was ODB II, but came out prior to the emergence of CANBUS being common in parallel. That may be contributing to the issues getting the two to talk. The TJ gets it's RPM signal off the Crank Position Sensor and the pattern isn't just a single pulse for each rotation.

 

[G H D]

@G H D , this is the tach emulator being referenced.

I did a Gen III 5.3 in my TJ, and couldn't be happier.

I take that back. a 6.0 would make me happier.


View: %5BURL%5Dhttps://youtu.be/Jj7MDzNi7vo?si=zeg4xMxoD0lcK64T&t=137[/URL]

ok.. so using the crank position sensor for the signal input works with this emulator for tach... thats pretty simple thanks glen

 

[GoldenGorilla]

This video has some Pico traces of the crank and cam sensors in a TJ, which probably helps explain why the emulator is probably going to be helpful.

View: https://youtu.be/OF6i5ALkEHI?si=oLFt7xVXCO6OGyan

Or put another way, the signal on a 4.0L flywheel is setup on 120 degree intervals aligning to the 6 cylinder layout while the V-8 signal will be setup on 90 degree intervals.

4.0L Flywheel

 

[G H D]

The biggest reason that the LS is more common is that alot of the early adopters were in CA where there are some more stringent rules about engine being from same or newer model year and all the emissions equipment from the donor being retained. Well that and ODBII support makes the stock hardware easier to setup.

Functionally the SBC vs LS doesn't really matter in this context. SBC from 87 and later have roller cams and its much less of an issue to install them in earlier ones than in a TJ 4.0. There's advantages in the factory LS heads, but there are aftermarket SBC heads that can get you to the same results.

As for Holley EFI, a good friend of mine in ABQ is running a a blueprint SBC engine with Sniper II in the Ford coup hotrod his dad built. He's an amazing welder, but not much into auto mechanic work and is working with a shop down there. He's been having issues with the EFI cutting out somewhat randomly and has been working with the shop on the tune. The Sniper EFI system is a CANBUS system, not ODB II, whereas the TJ's JTEC computer was ODB II, but came out prior to the emergence of CANBUS being common in parallel. That may be contributing to the issues getting the two to talk. The TJ gets it's RPM signal off the Crank Position Sensor and the pattern isn't just a single pulse for each rotation.

my friend that is actually doing the hardware work if installation has had multiple experiences with the holley system and seems to be fairly knowledgable with its quirks so im pretty comfortable with this... thanks for the input. im excited glen

 

[ColoJeep]

The biggest reason that the LS is more common is that alot of the early adopters were in CA where there are some more stringent rules about engine being from same or newer model year and all the emissions equipment from the donor being retained. Well that and ODBII support makes the stock hardware easier to setup.

Functionally the SBC vs LS doesn't really matter in this context. SBC from 87 and later have roller cams and its much less of an issue to install them in earlier ones than in a TJ 4.0. There's advantages in the factory LS heads, but there are aftermarket SBC heads that can get you to the same results.

As for Holley EFI, a good friend of mine in ABQ is running a a blueprint SBC engine with Sniper II in the Ford coup hotrod his dad built. He's an amazing welder, but not much into auto mechanic work and is working with a shop down there. He's been having issues with the EFI cutting out somewhat randomly and has been working with the shop on the tune. The Sniper EFI system is a CANBUS system, not ODB II, whereas the TJ's JTEC computer was ODB II, but came out prior to the emergence of CANBUS being common in parallel. That may be contributing to the issues getting the two to talk. The TJ gets it's RPM signal off the Crank Position Sensor and the pattern isn't just a single pulse for each rotation.

The whole emissions thing takes away a lot of options in areas that have testing , you don't want to be caught , ask any of the rolling coal diesel shop boys.

 

[speeding_infraction]

The whole emissions thing takes away a lot of options in areas that have testing , you don't want to be caught , ask any of the rolling coal diesel shop boys.

I was just saying that the other day, I moved to a free state that doesn't do any of that crap lol. Now, it should be mentioned that rolling coal is generally frowned upon in the diesel community, especially on public roads. Go try and ask for a "smoke tune" on any of the diesel forums, you'll probably get banned but your post would definitely be deleted.

 

[Abendage]

If you're able to make the Sniper output the same tach signal as an LS, this guy got his tach working on his pre-'05 TJ without an emulator. Here's a post I saved from the LS Swap Wranglers FB group.

 

[G H D]

all good info and thanks,,, however im not using a ecm,,, old school with the exception of the Holley efi.
the jeep tj computer will all remain intact,,,all i have to do is make the sensors temp, pressure, rpm ,readable on the
jeep obdI sys.. got it all covered except the tach,,looks like the novak emulator will do the business... otherwise ill build something, digital design is my thing.... glen

 

[Obi-Wan]

If you're able to make the Sniper output the same tach signal as an LS, this guy got his tach working on his pre-'05 TJ without an emulator. Here's a post I saved from the LS Swap Wranglers FB group.

View attachment 681493

Holy moly, That's my old FB post before I locked my account! I changed my name due to a crazy ex. Glad to see it's still helping.

 

[Abendage]

all good info and thanks,,, however im not using a ecm,,, old school with the exception of the Holley efi.
the jeep tj computer will all remain intact,,,all i have to do is make the sensors temp, pressure, rpm ,readable on the
jeep obdI sys.. got it all covered except the tach,,looks like the novak emulator will do the business... otherwise ill build something, digital design is my thing.... glen

I understand that, but you'll need to get the tach signal from somewhere even to feed the emulator. That's why I was saying if you can make the Sniper output the same tach signal as the GM ECM in the post I referenced, you might be able to get by without an emulator. Even with the emulator, its going to be looking for the standard GM tach signal.

 

[Abendage]

Holy moly, That's my old FB post before I locked my account! I changed my name due to a crazy ex. Glad to see it's still helping.

That is awesome! Yes, I had originally planned putting my LS in my '99 TJ and was going to absolutely try that, hence why I saved the post. I ended putting it in my '06 LJ, so ended up not using it and went the emulator route.

 

[speeding_infraction]

Holy moly, That's my old FB post before I locked my account! I changed my name due to a crazy ex. Glad to see it's still helping.

Well perfect, you're just the guy I'm looking for lol. Do you know if this might work for a 1996 xj? I know the whole instrument panel and how it worked changed in 97, but I might as well ask

 

[Obi-Wan]

Well perfect, you're just the guy I'm looking for lol. Do you know if this might work for a 1996 xj? I know the whole instrument panel and how it worked changed in 97, but I might as well ask

I honestly couldn't say. It depends on what type of tach signal the XJ is outputting, and I don't know if it changed between 96 and 97.