Formula WS6

iTrader: (17)

What I've got
97 lt1 stock bottom end
LE 2.2 heads / cam
58 mm tb


My problem
PCM is adding, on average, 10-15% more fuel(short term) on bank 2 and the long term fuel trim is maxed @+ 25% . Bank 1 is pulling fuel at idle as it always does and it's long term is -10 to-17%.
B1 injector pulse width is 3.3 ms at idle
B2 is at 5.8 ms at idle

This all started last fall when I threw a code for bank 2 high voltage. Figured no big deal swapped out both o2 sensors as preventative. Still there

What I've done
Cyl leak down. All within 5% of each other
Injector balance test. Perfect
Checked for good spark on all 8. All good
Readjusted all the rockers to be safe
Swapped out o2 extensions to see if there is a short. Good
Swapped plugs. Still there
I was getting an occasional high voltage spike on my bank 2 rear o2 sim. Disconnected both of them cause they're disabled anyways. Still there
Sprayed carb cleaner and traced vac lines with propane. Still there
fuel pressure is 38@ idle w/ vacuum and 45 without( old holly fpr)
all injectors ohm out within .1 of each other.( 30lb svo)

My thoughts without throwing unnecessary parts at it

Possible maf
Possible PCM
Short in the engine harness
Pull the intake to visually check the intake gaskets for vac leaks

Here is a pic of the plugs from 2-8

Why 2 and 4 look decent and 6 n 8 look like **** is beyond me. Bank 1 look like I just installed them
my first thought when looking at the plugs, with the thought that all 4 cyl are getting the same amount of fuel, is 2 and 4 have a vac leak of some sort. To me, The added fuel explains 6 and 8 being rich.

Any other ideas?

Rob94hawk

iTrader: (1)

You have an aftermarket fuel pump and regulator?

Formula WS6

iTrader: (17)

holly fpr and a walbro 255( about 7 years old and 20k miles on it)

Rob94hawk

iTrader: (1)

Did you throw this post over at the tuning section?

Formula WS6

iTrader: (17)

no, I'll copy and past it, thanks

Alex94TAGT

There are only so many things I can think of that would affect only two cylinders. Are those rear plugs carbon fouled or oil fouled?

Without further information, my best guesses:

You've checked for external vacuum leaks around the intake manifold, but you could still be leaking internally from the lifter-valley side. Poor sealing of the intake gaskets could be sucking oil into the rear two cylinders, fouling out the plugs, as well as creating a false lean condition on that bank from the poor combustion (oil isn't known for its high octane rating). Computer responds to the excess oxygen in the exhaust by adding fuel to that bank to compensate (as oxygen sensors can only detect oxygen -- not unburnt fuel), thus causing the LTFTs to diverge.

That, or bad valve guides / seals allowing the same thing. (Incidentally, my LE2 heads are back at Lloyds for a few bad guides after only 10K miles on new K-line inserts.)

You've already checked the health of the piston rings. Perhaps you could move the injectors to the other bank and see if the condition follows.

Formula WS6

iTrader: (17)

thanks for responding Alex

the rear plugs are definately fuel fouled. the motor doesn't burn a drop of oil. I thought about poor sealing of the intake on the valley side. It's certainly not ruled out but I popped the oil cap and opened up propane into the oil fill for about 30 seconds with no definative change in pulse width or fuel trims.( potentially very dumb, I know but I'm kinda desperate for an awnser).

ANTICOP RAM AIR

iTrader: (7)

move youre injectors around.. my friend bought an lt1 cheap as hell with a stuck injector...Id pull one of them and move it.. see if the problem follows the injector...It did with his.. it did the same ****..

Alex94TAGT

Okay. Well, if you haven't already, go ahead and re-torqure the rear intake bolts on that side just for kicks -- see if they've backed out at all. I believe the torque specs are around 30-35 lbs-ft.

Do you have access to noid lights to test the injectors in operation? The injectors are always supplied +12VDC, and the PCM just decides when to ground them out. I dont believe the computer is engineered to adjust individual cylinder pulsewidths outside of adjusting fuel injector constants/offsets within the programming. Not sure what else could hang them open unless they are sticking, which is why I mention moving them around to see if the condition follows. Perhaps you could check the wiring (DVM continuity check) between the injector and the PCM pinouts -- make sure nothing is grounding out when it isn't supposed to.

What brand of oxygen sensors are you running? Don't say Bosch.

[EDIT] I should probably mention that split block learns are thought to be connected to aftermarket throttle bodies' IAC passages and stop-screw positioning, but that doesn't explain your *two* fouled cylinders.

Formula WS6

iTrader: (17)

I wanna say the injector balance test I did would have made that evident, but I have seen outragous problems with cars. for the test I pressurize the fuel system, record the psi and then I pulse the injector with my tool for 3 seconds at a 10 milisecond interval, record the ending fuel pressure and compare all of the differences. I did it for all of em and everyone were identical.

ANTICOP RAM AIR

iTrader: (7)

if the pcm is adding fuel, isnt that what it does in open loop? Is that what you mean by "short term" Why would Inj pulse be different between banks... isnt 2ms a long time in pulse time? Im no tuner so this is a learning time for me too... where are your o2s in relation to the collector/head...?

96famaro

Do this it don't cost you anything just a little bit of your time. But before you do i would get a stethoscope (its cheap plus very useful tool) and check the injectors. Listen to them at idle if they tick, they should. As rpms climb they will start ticking at a faster rate. Ernest

ANTICOP RAM AIR

iTrader: (7)

Could the injector be lazy? it seems like if you get a spike on that side of the harness, then its because whatever its sending a signal to is having a hard time dissipating it.... (guessing) When you did the test, how did you do it? Can you monitor these while you drive? Do you have a data-logger?

Formula WS6

iTrader: (17)

I actually tested the pcm operation of the injectors tonight with my noid lights and all 8 were firing/pulsing at the same intensity.

I had delphi o2's and switched out to ngk's.

I was going to ohm the injector and 02 harness tonight but I was tearing up in the garage from the exhaust and I still had the door open. lol

good point... I did notice while it was in open loop, the pulse width and short term were identical untill it went into closed loop. o2's are surprisingly behaving fairly normal and are located in the header collectors. they're gen 2 LPP's

injectors are firing...that's for sure

I can datalog but at idle is when it's most noticable

Alex94TAGT

No. In control systems vernacular, "open-loop" refers to when there is no sensor feedback being used for error correction. Only in closed-loop operation does the PCM use oxygen sensor feedback for fuel corrections.

To be clear, open/closed loop only refers to sensor feedback. The PCM is obviously still using sensors to calculate fueling in open loop, but there is no error-checking / correction as in closed-loop mode.
The PCM's "learned" fueling correction tables are referred to as short-term and long-term fuel trim. They are useful in determining when the PCM is adding (BLM>128) or subtracting (BLM<128) fuel based on oxygen sensor feedback.
Understand that the entire point of computer-controlled engine management is simply to control injector pulsewidths. We have two fuel-monitoring oxygen sensors -- one on each bank -- which are used to make fuel corrections on their respective bank of the engine. Think of it as two separate feedback loops. As such, scanners/dataloggers report left and right bank injector pulsewidths, left and right bank short-term fuel trim, left and right bank long-term fuel trim, etc.

Injector pulsewidths between 1~2 milliseconds (mS) are normal for a stock LT1 at idle. The value depends on fueling requirements of the engine at hand, injector size/duty cycle, fuel pressure, engine load and RPM, etc. The OPs numbers are indeed abnormally high on Bank 2.

Clear as mud now?

Alex94TAGT

Welp, I'm out of ideas. You're doing everything I would be doing in that situation. I'll let others step in -- hope you get it figured out!

05HD

Fix the idle passage in your throttle body?

Formula WS6

iTrader: (17)

fix it how? please elaborate. nothing has changed with the setup in over 2 years

05HD

Here is a decent thread about what I am referring to- https://ls1tech.com/forums/lt1-lt4-m...an-oem-tb.html

Another possibility I didn't see mentioned here is a fuel pressure regulator leaking past the diaphragm into the vacuum hose.

Formula WS6

iTrader: (17)

already been checked. fpr is all good. upon pulling the vac line, when the pressure jumps, fuel trims drop slightly but on both banks to compensate for the higher pressure which is what I'd expect.