Trying to diagnose misfires on B2

[243]

Hey guys, the computer lingo "garbage in garbage out" probably applies here so I will try to cover as much background as I can without typing a novel.

I have a 180K mile L59 pulled out of a Yukon a year ago that I drove before I helped pull it, it idled fine, drove fine, made no noises. It is clean inside, bearings look great, replaced gaskets and seals. Oil pressure is 42 at idle and 50 off idle. I have it mounted in a Jeep chassis in the garage and recently installed a factory harness and fuse box to start it.

Plug wires replaced with Standard Motor Products, not what I planned but they are new.

I did swap the MODEC injector plugs with EV6 pigtails and crimped spade connectors assuming I may use the harness again on a different engine.

I flashed the ECM disabling VATS, EGR, EVAP and rear O2's.

Front O2's are hooked up to 8" exhaust stubs that end about 3" after the O2's, pointing straight down (LS3 manifolds).

Re-checked exhaust manifold bolt torque and intake manifold torque after gasket replacement.

Gas tank is from a 97 S10 Blazer with the fuel tank module that puts out 54 psi running, gas 97 octane is fresh and tank is clean.

E85 sensor is hooked up.

Have a radiator hooked up.

Checked for open vacuum ports, none found.

PCV vacuum fitting is cracked, duct taped.

Fuel regulator vacuum fitting is cracked, disconnected and vacuum port is capped.

It didn't start the first time and took three hours to find the little 12ga ground that apparently was for the injectors at the front of the engine. It started but idled rough and rich.

The first issue I started chasing is +25 on LTFT B2 with no improvement after the following, plugs are real black.

1. Swapped coil packs from B1 to B2
2. Swapped O2's from B1 to B2
3. Cleaned injectors
4. Replaced intake manifold gaskets.
5. Reversed O2 and coil packs back to the correct side.
6. Checked plug gap, .035 Delco 41-462
7. Ran compression dry compression test, 1-7 200, 202, 202, 202, 201, 202, 200


Next step was adding channels for misfire and #4 is bad and #6 worse, #2 off and on.


Last log is attached and I appreciate any input in advance.


My thoughts, it should run as it did from the factory, I didn't change anything in the tune other than what is listed above.

My next thought is to swap injector 6 with injector 2 that does not seem to have misfires.

If that does not work, replace the 14 year old coil pack wire harness, they are fairly cheap, but I have already swapped coil packs.


I also have the E85 codes, both high and low voltage and alcohol percent is ~35% when I used 87 octane.

[DrLoch]

Is the distance from the O2 sensor to the end of the pipe the same on both sides? Did you try swapping O2 sensors from side to side? Left side is pulling fuel right side is adding fuel, check your wiring and make sure the sensors aren't swapped.

[243]

Yes, both stubs are within a 1/2" in length frome side to side and O2's are both about 3" from the end of the pipe.

I did swap O2's from B1 to B2 and back again. LTFT issue is consistently on B2.

[DrLoch]

Do you have a WB? If not I would suggest you get one so you can compare what NB's are saying versus what the WB reports. If you have more exhaust tubing temporarily add it the end. Reset your trims under vehicle controls before logging. A miss will make it look lean in which case it will add fuel, which it is, a lot. Try open loop.

[matty b]

You need more exhaust length after the sensors. Reversion will allow big puffs of fresh air to screw up the readings. They will probably read right above 2k, but idle and lower RPM may as well run open loop cause its not gonna read right at all.

[243]

No WB yet, A few hours ago I ordered pipe to weld up a temporary exhaust, 2.5" with a transition to 3" and a 3" single in and out muffler I have in the garage/. It will be about 48" total from the O2's to the end of the muffler.

[243]

I ran multiple scans this evening, initially I swapped 4 and 6 coil and wires not thinking, both have the highest misfire counts. Then I ran it with the O2's disconnected and it was smoother for sure and misfire counts much lower.

Second scan is coil and wire 6 swapped with 1 and O2s plugged in and LTFT on B2 maxed out again.

I can't wait on the exhaust parts, the exhaust in the garage is killing my head.

I am beginning to suspect a wiring harness issue.

[243]

And for grins I flashed the original tune with only VATS disabled to eliminate something I did turning off emissions and it still maxed LTFT's.

[matty b]

You dont even know what youre doing. How bout actually finish the exhaust before attempting to "tune" it and then while youre at it, get a wideband to calibrate it. While those parts are shipping, try using the search function, maybe read the stickies and not run around in circles looking stupid.

I hate sounding harsh, but you are doing absolutely nothing but waste gas, waste time and foul plugs. You cant half ass yourself a properly calibrated motor and you sure as shit arent gonna do it like this.

[243]

I don't think you are being harsh but you are showing your ass, I don't need a WB right now because I am not trying to tune a fk'n thing, it's a totally stock motor and I am trying to diagnose a *mechanical* problem.

Search?

Yep, currently there are 15+ tabs open on my laptop with search terms plugged in such as LTFT, LTFT+25, Mis-fire, Mis-fire LTFT on HPT, LS1Tech and I am reading those threads. I am doing the same seaching Google and sifting through the shit that comes up on random sites.

And I have found countless posts such as this for example...stop fk'n with the TUNE and address the MECHANICAL problem.

There is no doubt in my mind it needs the exhaust, but simple logic would indicate when the exhaust stubs, length, O2 location in the stubs are the same on both sides, it would not be fk'n bloody rich on one side only.

[2xLS1]

Plug in only 1 O2 sensor and with the scanner with KOEO make sure the side unpluged is the one showing 450mv. I've seen many times on swaps the wiring for the L&R O2s get crossed. But you should not be trying to run it at all with open exhaust with any O2s hooked up.

[243]

2x, it's an unmodified factory harness and the O2's are plugged in correctly.

[2xLS1]

I don't care if the harness is modified or not. They can be laid out wrong and crossed. It makes the trims on one bank go - and the other bank go +. I've seen it numerous times. Then you compound the problem with open exhaust. Did you do the test like I said? Or do you just think you know more than the people offering advise?

[243]

KOEO

B1 connected - .451-.456

B2 disconnected - .443-.447

[2xLS1]

KOEO

B1 connected - .451-.456

B2 disconnected - .443-.447

Add B1S2 and B2S2 to your channels and retest

[243]

KOEO

B1S1 connected - .451-.464

B2S1 disconnected - .443-.451

B1S2 disconnected - .443.451 (no O2 sensor)

B2S2 disconnected - .443-.451 (no O2 sensor)

[2xLS1]

Leaving B1S1 connected and B2S1 disconnected run engine for 1 minute then turn off. Then KOEO and report O2 voltages leaving B1S1 connected and B2S1 disconnected.

[243]

B1S1 connected and B2S1 disconnected ran engine for 1 minute then turned off. Voltages leaving B1S1 connected and B2S1 disconnected.

KOEO

B1S1 connected - .000-.516 (climbed steadily for approximately one minute)

B2S1 disconnected - .443-.451

B1S2 disconnected - .443.456 (no O2 sensor)

B2S2 disconnected - .438-.460 (no O2 sensor)

[243]

O2's reconnected, NGK TR-5 plugs and exhaust.

P0141 - O2 Heater Circuit (Bank 1, Sensor 2) (Pending)
P0161 - O2 Heater Circuit (Bank 2, Sensor 2) (Pending)
P0300 - Random Misfire Detected (Pending)
P0327 - Knock Sensor 1 Circuit Low (Bank1) (Pending, Current)

P0443 - Evaporative Emission System Purge Control Valve Circuit (Pending, Current)
P0449 - Evaporative Emission System Vent Control Circuit Intermittent (Pending)
P0452 - Evaporative Emission System Pressure Sensor/Switch Low (Pending, Current, History)
P0463 - Fuel Level Sensor A Circuit High (Pending, Current)
P0522 - Engine Oil Pressure Sensor/Switch Circuit Low (Current)
P0650 - Malfunction Indicator Light Control Circuit (Pending, History)
P0654 - Engine RPM Output Circuit (Pending, History)

P0713 - Transmission Fluid Temperature Sensor A Circuit High (Current, History)
P0740 - Torque Converter Clutch Solenoid Circuit / Open (Pending)
P0748 - Pressure Control Solenoid A Electrical (Pending)
P0753 - Shift Solenoid A Electrical (Pending, Current, History)
P0785 - Shift/Timing Solenoid (SES, Pending, Current)
P0856 - Traction Control Input Signal (Pending, Current, History)

P1689 (SES, Current)
P1810 (Pending, History)
P2761 (Pending)

[243]

Leaving B1S1 connected and B2S1 disconnected run engine for 1 minute then turn off. Then KOEO and report O2 voltages leaving B1S1 connected and B2S1 disconnected.

What is the purpose for checking the voltages?