Jeep LS swap for the LJ

Little update.
A couple month or so ago the Jeep wouldn't start for my wife. I got home a few hours later and it fired right up. No issues, then it happened again a few weeks later but this time was a no go. I had spark and fuel and the motor was turning over plenty fast.
Messed with a few things and nothing. Then two days later, it just fired up, not confidence inspiring.
Im pretty sure it was a bad ground somewhere but since I was digging into it I decided to pull all the Jeep PCM and wiring out since I'm not using it.
The end result is much cleaner and simpler wiring. I moved the GM PCM to the factory jeep location for better protection against water.



I also took @DaveB advice and wired a 40A relay to run the injectors. It's still triggered off the asd relay and powers my aux fuse block for the GM PCM as well as the injectors.


I also got a stock jeep shifter boot to finish the lakor shift. I might keep it now that it looks half decent. Custom t case shifter label still in place.


Took it for a drive this morning after finishing the rewire and I may have identified the clunk. There is play in the rear cv. Not sure how that happened, it's got less than 5k miles on it. Maybe my opinion angle is off. I never adjusted it after changing the drive train.

I hate it when my opinion angle is off. Seems to be the norm though.

UNSTUCK said:

I hate it when my opinion angle is off. Seems to be the norm though.

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I corrected that twice. Or I thought I did.

glockman said:

Took it for a drive this morning after finishing the rewire and I may have identified the clunk. There is play in the rear cv. Not sure how that happened, it's got less than 5k miles on it. Maybe my opinion angle is off. I never adjusted it after changing the drive train.

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Is it the CV? I had a clunk which turned into a vibration. Luckily I caught it before it got worse. Ended up being the rear driveshaft U joint toasting itself with less than 3k miles. There were no needle bearings left on one trunnion. It was a Tom Woods supplied U joint. Have switched to Spicers.

Glockman, if I could make one suggestion to possibly prevent any future electrical issues, eliminate those POS OEM battery terminal clamps and invest in some good marine or military grade battery connectors. I have seen more issues with those stamped steel battery connectors over the years that usually will lead to starting issues or worse, those intermittent grounding issues and related codes.

Just a suggestion.

Mike

zmotorsports said:

Glockman, if I could make one suggestion to possibly prevent any future electrical issues, eliminate those POS OEM battery terminal clamps and invest in some good marine or military grade battery connectors. I have seen more issues with those stamped steel battery connectors over the years that usually will lead to starting issues or worse, those intermittent grounding issues and related codes.

Just a suggestion.

Mike

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Upgrading battery terminals is a good idea on any rig.

SnwMnkys said:

Is it the CV? I had a clunk which turned into a vibration. Luckily I caught it before it got worse. Ended up being the rear driveshaft U joint toasting itself with less than 3k miles. There were no needle bearings left on one trunnion. It was a Tom Woods supplied U joint. Have switched to Spicers.

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I can feel/hear a clunk when pushing up on the driveshaft. I checked the T-case output flange and it isn't moving. I checked the Axle yoke and it is also solid. The only place left is the CV in the driveshaft. I pulled the shaft and cannot duplicate the clunk on the bench.
It has a vibration at 45-50 that has been getting worse. My pinion is not pointed at the T-case output (it's about 6 degrees off/down) so I'm going to correct that first. I pulled the upper rear control arms and one of the joints is seized, so I'm soaking it in PB blaster in hopes it comes loose and I can lengthen them to correct the pinion angle. I'll report back.

I've had what I thought was a drive shaft clunk that turned out to be a loose control arm bolt. Finally found it when it got loose enough that the axle started rolling under braking power too. Another idea of something to check...

Adjusted the rear uppers to correct the pinion angle. One of my arms was seized so @mesha came through with a new arm same day, what service 😁.
Took it for a 25 mile test just now and the clunk noise is gone!!!
I think the joints in the cv will need to be replaced eventually but having them lined up properly took care of the noise.

Ready for ejs now, oh happy day.

Intermittent no start is back.
Wife drove to drop my son off at school, no problem, shut it off in the driveway and it won't start AGAIN!.
I'm listing this stuff to hopefully help someone else, not to document my obvious incompetence.

Have 55psi of fuel pressure at the rail.
Battery is at 11 volts while cranking.
Cranks strong, can smell gas after cranking for a couple cycles.
Pulled both white plugs that go to the coils (driver and passenger side) They have KO power and ground.
Pulled two plugs from each bank and I have spark at each plug and they are all wet, this makes me think the injector pulse is functioning.
No codes in the ECU.
Checked all grounds and the block is grounded as well as the heads in addition to the actual coils having good grounds.
I am leaning towards crank or cam position sensors.
I wiggled the SH!T out of the harness going into the PCM and nothing. It's possible I have a broken wire somewhere but I just cut 3 feet off the end that gets the most bends going into the PCM plug.
Crank position sensors are pretty common to go on LS engines and cause the engine to die, then restart once it cools down, which is not what I am experiencing. I also see 300-400 RPM on my scanner while cranking, which should mean the sensor is working.
Fuel injector function should mean the crank and cam sensors are syncing but I'm not 100% on that.
Picked up both sensors from Napa today. I will replace both since they aren't too expensive or hard to get to.
I would normally pull out the meter and test them, I hate to through parts at problems, but I have limited time to get it resolved.
Leaving for EJS, maybe in a 4 runner, on Sunday.

I would recommend running only GM crank and cam sensors, rather than parts store brand sensors. Not sure that it'll fix your issue, but it's a step in the right direction.

Do you happen to have HP Tuners? I wonder if you can run a diagnostic check and see if you're getting any codes, when it's cranking without starting.

Greg said:

I would recommend running only GM crank and cam sensors, rather than parts store brand sensors. Not sure that it'll fix your issue, but it's a step in the right direction.

Do you happen to have HP Tuners? I wonder if you can run a diagnostic check and see if you're getting any codes, when it's cranking without starting.

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I bought Delphi sensors. I've had pretty good luck with them in the past.
I have not yet purchased HP Tuners. I need it and this is just one more reason to buy it. I'll probably have it ordered before the end of the day.

Crank or cam sensor should give you a code. You have spark, fuel, and highly likely compression. Really all that's left is timing. Timing doesn't come and go depending on the day. If it ran before it should run again.

Are you getting any back fire or any hits at all?

I'm leaning towards a bad ECM. It's doing all the right stuff, but I'm guessing at the wrong times, sporadically.

You might try hooking up your scanner and check your short term fuel trims. It should be +- 10 If its running too rich you could be flooding it out. My LS is running about -1. Not sure if the scanner will read these while cranking it over.

UNSTUCK said:

Crank or cam sensor should give you a code. You have spark, fuel, and highly likely compression. Really all that's left is timing. Timing doesn't come and go depending on the day. If it ran before it should run again.

Are you getting any back fire or any hits at all?

I'm leaning towards a bad ECM. It's doing all the right stuff, but I'm guessing at the wrong times, sporadically.

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From my interweb learning, intermittent cam or crank sensors can mess up timing without setting a code. I'm hoping it's not an ECU and lots of stuff I've read says they are very rare, fingers crossed.

If the Cam sensor loses ref voltage, it won't throw a code and the engine will run off the crank sensor until you turn it off. I might have a broken wire intermittently causing the sensor to essentially turn off, I'll check ref voltage and ground on both plugs before I replace the sensors. I don't know how else to explain a non running engine with fuel, air and compression as you stated.

DaveB said:

You might try hooking up your scanner and check your short term fuel trims. It should be +- 10 If its running too rich you could be flooding it out. My LS is running about -1. Not sure if the scanner will read these while cranking it over.

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I checked them last night and they weren't updating while it was cranking. I monitored both long and short when it was first running and after I corrected my O2 wiring mistake they have been good. It runs fine, starts fine, drive it around and it never dies, then you shut it off and it won't restart, even after it cools off. Kind of like a power supply that works forever, then fails voltage self test after being power cycled.



And I ordered HP Tuners today.

What color are the connectors are your PCM? Blue/Green or Blue/Red? I have a PCM that will be going to my pops with my old 5.3 when we do that. It is a Green/Blue PCM and tuned with a 4l80, but it may still start your jeep? Might be a useful troubleshooting tool?

RockChucker said:

What color are the connectors are your PCM? Blue/Green or Blue/Red? I have a PCM that will be going to my pops with my old 5.3 when we do that. It is a Green/Blue PCM and tuned with a 4l80, but it may still start your jeep? Might be a useful troubleshooting tool?

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Mine are green blue. I'll hit you up if I don't make any progress tonight. Thanks for the offer.

What 3 things are needed to start an engine?
Don't assume anything.
The butterfly in the throttle body was stuck. Missing air!
Makes sense why it never dies, only would not restart.

Humphhhhh.....Air is so overrated.

glockman said:

What 3 things are needed to start an engine?
Don't assume anything.
The butterfly in the throttle body was stuck. Missing air!
Makes sense why it never dies, only would not restart.

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Nice job sticking with it. What a relief that has to be to have figured it out.