LS swap update and questions

[Longhorn84]

@Longhorn84 how many O2 sensors are on your jeep, in your harness? Based on the codes it seems your computer is expecting 2 upstream and 2 downstream if it’s saying bank 2 sensor 2 is throwing code? I had downstream deleted on mine.

I did put all 4 in, two up and two down. I know I have a leak so maybe that's the issue. I'll have a shop weld up the holes and we'll see what happens. The knock low voltage may take more digging, I know I replaced the sensors and harness and the wiring was all redone by Novak on the GM harness, it's all loomed up but I guess I'll have to do some diagnostics on it over the next few days.

 

[lBasket]

It really helps to have a friend working as a tech to get you factory and alldata diagrams and troubleshooting flowcharts for electrical stuff. Its most of the job these days

Do you use alldatatdiy? Is it good for that generation of vehicles?

 

[lBasket]

I did put all 4 in, two up and two down. I know I have a leak so maybe that's the issue. I'll have a shop weld up the holes and we'll see what happens. The knock low voltage may take more digging, I know I replaced the sensors and harness and the wiring was all redone by Novak on the GM harness, it's all loomed up but I guess I'll have to do some diagnostics on it over the next few days.

Not sure how different these engines are but in my truck (2003 6.0 LQ9) I have that code sitting, I replaced sensors and the sub harness, and code didn't go away. Did some further reading and the sensors ground through the metal plate they screw into in the valley and they can get corroded and cause a bad ground for the sensors and cause the CEL. I need to go back in and run a thread tap or cleaner over the studs on that plate I think.

 

[Rickyd]

Do you use alldatatdiy? Is it good for that generation of vehicles?

I have.it isn't as good,but better than chiltons

 

[lBasket]

I have.it isn't as good,but better than chiltons

I liked them back in college, but then they stopped offering the DIY section for a while and when it came back I don't know if it sucks now or its a coincidence on the car I bought. It was literally a full service manual for my saab but the audi I paid for the sub for was complete junk. Couldn't even find info for like transmission fluid capacity.

 

[Rickyd]

Not sure how different these engines are but in my truck (2003 6.0 LQ9) I have that code sitting, I replaced sensors and the sub harness, and code didn't go away. Did some further reading and the sensors ground through the metal plate they screw into in the valley and they can get corroded and cause a bad ground for the sensors and cause the CEL. I need to go back in and run a thread tap or cleaner over the studs on that plate I think.

People will use rtv to cover them and make little dams so water doesn't leak around and corrode them

 

[lBasket]

People will use rtv to cover them and make little dams so water doesn't leak around and corrode them

Yep I did see that, the little halfmoons. I think I did do that this time... but didn't clean off the threads. Which sucks, its a PITA to get down there.

 

[GoldenGorilla]

Ok,that's a good start. I bet a decent obd2 reader could tell if the speed sensor adapter is operating correctly?

The HPT Mpvi also does all the ODBII scanning very well. If you go that route, you don't need a separate scanner.

 

[Longhorn84]

Yep I did see that, the little halfmoons. I think I did do that this time... but didn't clean off the threads. Which sucks, its a PITA to get down there.

Doing some digging on that knock code, seems like it’s super common for this gen of motor and most folks I read still have the issues after replacing the sensors/harness so I agree it must be something like a ground. I’m hoping the exhaust leak is the root cause, maybe the o2/cat codes are causing the engine to actually knock a bit, I think it’s slightly unlikely but I’m going to fix the exhaust leak today (I have a smoke kit and some JB Weld) and clear the codes and see what happens.

 

[GoldenGorilla]

I did put all 4 in, two up and two down. I know I have a leak so maybe that's the issue

If you have a leak at the exhaust manifold, even very small or if there is a mini-cat right below the collector(s), exhaust leaking out = O2 leaking in and it will definitely throw off the upstream sensors and the over-richen fueling. Potentialy to the degree that the fuel is causing carbon buildup or even washing the cylinder walls and getting into the oil. It's not as big an issue with sensors below mini-cats or after the mains as they're not used to calculate fuel trim The final sensors help the system know if the cats are working.

Leaks after the main cat(s) don't matter for the a ECM calculations. They're just annoying.

I'm on team don't throw parts at it.

 

[Longhorn84]

If you have a leak at the exhaust manifold, even very small or if there is a mini-cat right below the collector(s), exhaust leaking out = O2 leaking in and it will definitely throw off the upstream sensors and the over-richen fueling. Potentialy to the degree that the fuel is causing carbon buildup or even washing the cylinder walls and getting into the oil. It's not as big an issue with sensors below mini-cats or after the mains as they're not used to calculate fuel trim The final sensors help the system know if the cats are working.

Leaks after the main cat(s) don't matter for the a ECM calculations. They're just annoying.

I'm on team don't throw parts at it.

I did a bunch of learning about knock sensors last night and here's what I did this AM. I checked the resistance of the knock sensors and both read 100ohms which is within spec, I then checked for voltage coming from sensors when hitting a screwdriver to the block and they put produce similar voltage from what I could see from the naked eye, I then checked the harness side and both leads got 5v reference voltage. So, as far as I can tell, the knock sensors themselves aren't the issue. I guess the voltage they produce could be off of spec, hard to tell without a fancier diagnostics tool that would show the voltage side by side. So, my plan is to JB Weld the exhaust leak today, clear the codes, and see where we are after a bit of driving.

 

[Longhorn84]

I did a bunch of learning about knock sensors last night and here's what I did this AM. I checked the resistance of the knock sensors and both read 100ohms which is within spec, I then checked for voltage coming from sensors when hitting a screwdriver to the block and they put produce similar voltage from what I could see from the naked eye, I then checked the harness side and both leads got 5v reference voltage. So, as far as I can tell, the knock sensors themselves aren't the issue. I guess the voltage they produce could be off of spec, hard to tell without a fancier diagnostics tool that would show the voltage side by side. So, my plan is to JB Weld the exhaust leak today, clear the codes, and see where we are after a bit of driving.

After a bit more watching, I rechecked the voltage coming from the sensors and there is definitely a difference in voltage coming from the different sensors when I tap one large hit on the engine, I think the front sensor is bad which sucks to have to pull the intake. I also put a smoke machine and I have a large leak on the header and the cat and downstream of the cat on the passenger side. More work to do today to try and fix the leak, probably replace the cat, and eventually replace the knock sensors.

 

[lBasket]

After a bit more watching, I rechecked the voltage coming from the sensors and there is definitely a difference in voltage coming from the different sensors when I tap one large hit on the engine, I think the front sensor is bad which sucks to have to pull the intake. I also put a smoke machine and I have a large leak on the header and the cat and downstream of the cat on the passenger side. More work to do today to try and fix the leak, probably replace the cat, and eventually replace the knock sensors.

Clean out the threads and do the RTV dams while you're in there

 

[Wildman]

After a bit more watching, I rechecked the voltage coming from the sensors and there is definitely a difference in voltage coming from the different sensors when I tap one large hit on the engine, I think the front sensor is bad which sucks to have to pull the intake. I also put a smoke machine and I have a large leak on the header and the cat and downstream of the cat on the passenger side. More work to do today to try and fix the leak, probably replace the cat, and eventually replace the knock sensors.

Keep at it and you'll figure it out. It's crazy how one little thing can cause other issues. Header leak & then @ the cat could be causing you to have a lean condition at the O2 sensor.

How hard is it to pull the intake to do the knock sensor?

 

[Longhorn84]

Keep at it and you'll figure it out. It's crazy how one little thing can cause other issues. Header leak & then @ the cat could be causing you to have a lean condition at the O2 sensor.

How hard is it to pull the intake to do the knock sensor?

Hard is relative but it's a big pain on these engines! you have to unhook a lot of wiring, vacuum hoses, gas lines, etc to pull but I bet it's a three hour job. Problem is many folks online do this only to have it happen again shortly after, that's worst case scenario! Header leak is the one I'm not looking forward to, it's a tight fit, I may try jb weld there vs pulling the header, will need a shop to replace the cat and weld up the rest. will keep everyone posted but at least i have a plan and I appreciate the encouragement to get off my butt and get this taken care of.

 

[Wildman]

Hard is relative but it's a big pain on these engines! you have to unhook a lot of wiring, vacuum hoses, gas lines, etc to pull but I bet it's a three hour job. Problem is many folks online do this only to have it happen again shortly after, that's worst case scenario! Header leak is the one I'm not looking forward to, it's a tight fit, I may try jb weld there vs pulling the header, will need a shop to replace the cat and weld up the rest. will keep everyone posted but at least i have a plan and I appreciate the encouragement to get off my butt and get this taken care of.

The LS is not as wide as a Hemi so YES I know about tight fit and the struggle to get to things. I wouldn't suggest JB Welding the exhaust leak on the header no matter how hard it is. I'd get the knock sensor fixed & then the exhaust manifold gasket replaced before I'd have the cat replaced unless you're positive it's bad.

I had the cat clog up on my 5.2 Magnum from what I think was it running too rich for a long period. But it clogged to the point where the engine wouldn't run.

And I seem to remember the issues with the knock sensors so that does SUCK... Seems like you'd want to make sure you followed all the tips possible while you have it apart. I'm glad the Hemi knock sensors are on the sides of the block. The Hemi intake isn't "hard" to pull but it'd be a couple hour job too.

Good luck.

 

[Longhorn84]

The LS is not as wide as a Hemi so YES I know about tight fit and the struggle to get to things. I wouldn't suggest JB Welding the exhaust leak on the header no matter how hard it is. I'd get the knock sensor fixed & then the exhaust manifold gasket replaced before I'd have the cat replaced unless you're positive it's bad.

I had the cat clog up on my 5.2 Magnum from what I think was it running too rich for a long period. But it clogged to the point where the engine wouldn't run.

And I seem to remember the issues with the knock sensors so that does SUCK... Seems like you'd want to make sure you followed all the tips possible while you have it apart. I'm glad the Hemi knock sensors are on the sides of the block. The Hemi intake isn't "hard" to pull but it'd be a couple hour job too.

Good luck.

Thanks, that's the next plan, replace knock sensors/harness and then I agree, I have to remove the header unfortunately and reseal (sanderson headers use high temp silicone vs gasket which is strange but that's what they insist). The cat was pouring smoke out of it when I put a smoke machine up the tailpipe, there is some type of heat shield maybe wrapped around the cat so it's impossible for me to actually see the leak, I'll take it to an exhaust shop and see what they say.

 

[Wildman]

Thanks, that's the next plan, replace knock sensors/harness and then I agree, I have to remove the header unfortunately and reseal (sanderson headers use high temp silicone vs gasket which is strange but that's what they insist). The cat was pouring smoke out of it when I put a smoke machine up the tailpipe, there is some type of heat shield maybe wrapped around the cat so it's impossible for me to actually see the leak, I'll take it to an exhaust shop and see what they say.

I have had GREAT success with Remflex gaskets on my headers so I might not follow Sanderson's instructions this time. Do they offer a reason why they recommend the silicone over a gasket?

Those damn heat shields can be a PITA.

 

[Longhorn84]

Clean out the threads and do the RTV dams while you're in there
View attachment 635477

will do!

 

[Longhorn84]

I have had GREAT success with Remflex gaskets on my headers so I might not follow Sanderson's instructions this time. Do they offer a reason why they recommend the silicone over a gasket?

Those damn heat shields can be a PITA.

From Sanderson:

No Gaskets??? That is correct. Please, do not use a gasket at header flange. A collector gasket, yes.

1. Apply just a thin smear of high temperature silicone on the entire raised surface of the header flange.
2. Let the silicone fully dry (overnight is preferred).
3. Bolt the header to the engine.

If you use a gasket or too much silicone at the cylinder head flange, you will likely experience sealing problems.

Even a clean installation such as the one shown below (with a gasket installed) can have sealing issues if the instructions are not followed. This header flange started leaking a few weeks after this picture was taken.