6.0 LS running poorly

wizzo · Jul 27, 2015

6.0 LQ4 has EFI live tune and drive by wire. Engine was freshened up probably two years ago. Running problems started a few weekends ago at Harlan, we had ridden all the weekend and then Saturday night on Jagger it started to stumble/ hesitate/ miss right off of idle. You could push through it but the power was lacking. Got it home and put a snap on solis? scan tool on it. It was running rich and smoking a little. Had a code for the heater circuit in an 02 sensor but that was it. I put new plugs in it. Took it to a county fair race event and it was really running bad. So at that point, I put two new 02 sensors in it. Took it to another fair race event and it ran better but still not right. Now I'm getting a P0171 Chevrolet Fuel Trim System Lean Bank 1. Put a new fuel filter in it. Went to GMP this past weekend and swapped the MAF and MAP sensors and no change. Unplugged the MAP for a bit and it ran pretty good for a while but then back to the same deal. When I was on hellavator (for those that don't know, it's a rock slab and the transition at the bottom is rough so you bounce up onto the rock slab and try to climb up) as soon as the rear hit to bounce up, I would loose all throttle. The engine wouldn't die but when i hit that bump it was like there was no throttle input. Another thing I noticed this weekend was that the engine was running up at 210 and it normally runs 180.

What I have replaced:
New plugs
New 02's
New fuel filter
Swapped MAF & MAP sensors

We've checked the fuel pressure with gauge on rail multiple times
checked for vacuum leaks by spraying cleaner all over engine
ran a crank/ cam position variation relearn
checked fuel trims, etc. pretty much any test you can do on my buddies snap on scanner

What is also weird is that it will not pick up miss fires or throw miss fire codes.

Any thoughts?

muddinmetal · Jul 27, 2015

wizzo said:
6.0 LQ4 has EFI live tune and drive by wire. Engine was freshened up probably two years ago. Running problems started a few weekends ago at Harlan, we had ridden all the weekend and then Saturday night on Jagger it started to stumble/ hesitate/ miss right off of idle. You could push through it but the power was lacking. Got it home and put a snap on solis? scan tool on it. It was running rich and smoking a little. Had a code for the heater circuit in an 02 sensor but that was it. I put new plugs in it. Took it to a county fair race event and it was really running bad. So at that point, I put two new 02 sensors in it. Took it to another fair race event and it ran better but still not right. Now I'm getting a P0171 Chevrolet Fuel Trim System Lean Bank 1. Put a new fuel filter in it. Went to GMP this past weekend and swapped the MAF and MAP sensors and no change. Unplugged the MAP for a bit and it ran pretty good for a while but then back to the same deal. When I was on hellavator (for those that don't know, it's a rock slab and the transition at the bottom is rough so you bounce up onto the rock slab and try to climb up) as soon as the rear hit to bounce up, I would loose all throttle. The engine wouldn't die but when i hit that bump it was like there was no throttle input.

What I have replaced:
New plugs
New 02's
New fuel filter
Swapped MAF & MAP sensors

We've checked the fuel pressure with gauge on rail multiple times
checked for vacuum leaks by spraying cleaner all over engine
ran a crank/ cam position variation relearn
checked fuel trims, etc. pretty much any test you can do on my buddies snap on scanner

What is also weird is that it will not pick up miss fires or throw miss fire codes.

Any thoughts?

Check your oil level and let me know what it looks like. How did the old plugs look?

wizzo · Jul 27, 2015

Just checked, oil level is good. Oil looks good, I can get a pic if needed. It doesn't look milky or metallic. Are you looking for anything particular? Plugs looked like they were well used, nothing out of ordinary.

Another thing I noticed this weekend was that the engine was running up at 210 and it normally runs 180

zjtrey · Jul 27, 2015

what is the condition of your injectors? sounds like it could be a dirty one or multiple dirty ones not spraying enough fuel causing the lean condition

muddinmetal · Jul 27, 2015

zjtrey said:
what is the condition of your injectors? sounds like it could be a dirty one or multiple dirty ones not spraying enough fuel causing the lean condition

Which would also increase cylinder temps, thus raising the coolant temp, but it would typically show a misfire on the cylinder with the funky injector.

Pm me your #, I have an idea to try

wizzo · Jul 27, 2015

zjtrey said:
what is the condition of your injectors? sounds like it could be a dirty one or multiple dirty ones not spraying enough fuel causing the lean condition

I'm not sure yet. We did some sort of injector test and they show to all be in the same range. I'd have to ask exactly what kind of test we did on my buddies scan tool.

I've seen your link to cleaning injectors and that may be where i'm heading.

matth_85 · Jul 27, 2015

Have you tried the fuel filter? Possible even if you have that trash has worked it's way past it in the line and is settling on the injectors.

I had a 4runner that had the exact same symptoms and it had sand in the rails.

Team Willys · Jul 27, 2015

Could be a number of things. If you can load it up by holding the brakes and get on the gas some maybe you can get it to misfire consistently. Then have a buddy unplug the coils one at a time to isolate which cylinder(s) is the culprit. We had a supercharged 6.0 act up at AOP on the 4th and it turned out that somehow a piece of trash made it to the last injector in the rail and clogged it up. It would only be noticeable under low rpm high load conditions but sounded fine up top and at idle.

wizzo · Jul 27, 2015

matth_85 said:
Have you tried the fuel filter? Possible even if you have that trash has worked it's way past it in the line and is settling on the injectors.

I had a 4runner that had the exact same symptoms and it had sand in the rails.

Yes, I replaced the fuel filter, inspected the pump but pressures are good, also checked flow out of the tank and it is good there as well.

KyTrash · Jul 27, 2015

Are you still using you knock sensors or did you delete them ?

wizzo · Jul 27, 2015

KyTrash said:
Are you still using you knock sensors or did you delete them ?

still running knocks

pholmann · Jul 27, 2015

Unplug em and see what happens

matth_85 · Jul 27, 2015

wizzo said:
Yes, I replaced the fuel filter, inspected the pump but pressures are good, also checked flow out of the tank and it is good there as well.

Check from filter to rail, and the rail. My issue was in the rail. Sand was getting on the tops of the injectors and would have a stumble off idle. It would come alive after a second and run fine until the sand collected again.

KyTrash · Jul 27, 2015

Chris , do you have water standing around the knock sensors ?

wizzo · Jul 27, 2015

KyTrash said:
Chris , do you have water standing around the knock sensors ?

I won't say no, b/c honestly I don't know. I would doubt it b/c I put some of that grey GM silicone/rtv on the black plastic covers when i dropped the harness down in

zjtrey · Jul 27, 2015

have you checked for intake leaks? I know its a fairly common problem on these motors in the stock configurations so maybe its worth a quick starter fluid spray test… just a .02 thought

redneckengineered · Jul 27, 2015

Make sure it's not throwing the "junk ****" code. That could be your problem. Maybe it doesn't like spinning them new mud tars.

74_Chevota · Jul 27, 2015

redneckengineered said:
Maybe it doesn't like spinning them new mud tars.

I have nothing of value to add, but Im pretty sure this is the truth. :****:

wizzo · Jul 27, 2015

zjtrey said:
have you checked for intake leaks? I know its a fairly common problem on these motors in the stock configurations so maybe its worth a quick starter fluid spray test… just a .02 thought

I've tried the starter fluid test twice. only place i can't get to is under the intake. So I can't completely rule out the intake leak idea

redneckengineered said:
Make sure it's not throwing the "junk ****" code. That could be your problem. Maybe it doesn't like spinning them new mud tars.

74_Chevota said:
I have nothing of value to add, but Im pretty sure this is the truth. :****:

I have not seen the "broke ass digger" code show up yet. But you are right, the buggy may be rejecting the new dig tires. But honestly I thought it would be the LP 60 screaming for mercy!

jccarter1 · Jul 27, 2015

Have you checked the fuel pressure when it I running and driving had one do this one time and the pump was getting weak it would run fine at idle but when you got on it the motor would stumble until the fuel pump would catch up if it drops below 55 it won't be happy hope it helps