LT1 fuel split
01-13-2013, 03:48 PM
#1
LT1 fuel split We got the 396 together and are working on the tune, and we're stumped on this fuel split.
Bank 1 says it has too much, and bank 2 says lean.
My build:
12.5 CR 396
Stock castings Ported, 2.02/1.60's
Ported LT1 intake
Professional Products 58mm TB
244/254 .640/.640 112HR
I've read about the IAC passage on the aftermarket TB causing a split like this states,
http://www.noid.org/~lj/PCM%20Tutorial/SplitBLMinfo.htm
The Tb blades are opened JUST ENOUGH to keep it from sticking, and I drilled the hole, up to a 3/16.
Still no change.
I changed the spark plugs and allowed it to idle and drove down the road and back then pulled them back out, cylinder 1 & 3 plugs looked great. 5 & 7 were covered with black soot.
It eventually threw a heater circuit code on Bank 1, which I don't see causing a split issue, but I replaced it anyways. I inspected all my O2 wiring/extensions, etc. all ok.
I'm lost on what else to check. Any ideas??
Bank 1 says it has too much, and bank 2 says lean.
My build:
12.5 CR 396
Stock castings Ported, 2.02/1.60's
Ported LT1 intake
Professional Products 58mm TB
244/254 .640/.640 112HR
I've read about the IAC passage on the aftermarket TB causing a split like this states,
http://www.noid.org/~lj/PCM%20Tutorial/SplitBLMinfo.htm
The Tb blades are opened JUST ENOUGH to keep it from sticking, and I drilled the hole, up to a 3/16.
Still no change.
I changed the spark plugs and allowed it to idle and drove down the road and back then pulled them back out, cylinder 1 & 3 plugs looked great. 5 & 7 were covered with black soot.
It eventually threw a heater circuit code on Bank 1, which I don't see causing a split issue, but I replaced it anyways. I inspected all my O2 wiring/extensions, etc. all ok.
I'm lost on what else to check. Any ideas??
01-13-2013, 04:16 PM
#2
Did you seal the IAC circuit?
What you are describing sounds like the air is all coming in the front of the manifold and the front cylinders stealing it before it gets to the back.
Have you moved the injectors around to verify there is not a failure there?
Can try swapping O2s side to side to see if the issue follows them too.
Any chance the rear two on that one side could be sucking oil one way or another? Be it from the lifter valley, or intake studs or we have even seen a "reputable" vendor port heads so thin that under the high vacuum of the intake port the excessively thin aluminum was porous enough for oil to pull through.
I had a set of the blue Felpro intake gaskets go bad and start sucking oil from the lifter valley.
What you are describing sounds like the air is all coming in the front of the manifold and the front cylinders stealing it before it gets to the back.
Have you moved the injectors around to verify there is not a failure there?
Can try swapping O2s side to side to see if the issue follows them too.
Any chance the rear two on that one side could be sucking oil one way or another? Be it from the lifter valley, or intake studs or we have even seen a "reputable" vendor port heads so thin that under the high vacuum of the intake port the excessively thin aluminum was porous enough for oil to pull through.
I had a set of the blue Felpro intake gaskets go bad and start sucking oil from the lifter valley.
01-13-2013, 04:47 PM
#3
Yes. I inserted a tube in the back of the TB to meet the manifold.
I've also swapped O2's. No change.
When it comes to injectors, I monitored the Pulse width a bit earlier and it shows bank 1 Around 4.1, and bank 2 at 3.1, constantly, which confirms the PCM is dumping more fuel. So that leads me away from the injectors.
I've also swapped O2's. No change.
When it comes to injectors, I monitored the Pulse width a bit earlier and it shows bank 1 Around 4.1, and bank 2 at 3.1, constantly, which confirms the PCM is dumping more fuel. So that leads me away from the injectors.
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01-14-2013, 08:00 AM
#13
Not at all unusual to need to tweak those tables some with a cam change, ported heads or intake. However, the PCM is not knowingly going to command one bank, or both, rich enough to blacken the spark plugs. Leaning the individual cylinder fuel correction tables for the side with black plugs will simply drive the BLMs up for that side. As someone already mentioned, swapping sides with O2s are always the first thing to try. Things that will trick the PCM into adding that much fuel (high BLMs) are leaky headers, a poor PCM or O2 ground, or a mis-fire on that side. When you have split fuel trims, the side that looks lean (high fuel trims) is most always the side with the problem. Usually the side with black plugs.
01-14-2013, 06:02 PM
#14
Well I took some carb cleaner to the Bank 1 header, at the header gasket and the readings started to drop drasticly, and went back up as soon as I quit.
So looks like I'll be swapping out the gasket.
But in the mean time while searching for this problem I got the car to idle on its own through the IAC passage hole, lol
I'll update after header gasket swap.
So looks like I'll be swapping out the gasket.
But in the mean time while searching for this problem I got the car to idle on its own through the IAC passage hole, lol
I'll update after header gasket swap.
01-14-2013, 11:26 PM
#15
I am sorry. In my world it is assumed the mechanical stuff is in order before you go chasing your own tail. My bad.
I can think of maybe a hand full of people who have ran wilder combos be it cubic inch's cams, Tricked out intakes headers throttle body's you name it.
One of them even posted here and when I am stumped he is one of my 'Go To' Guy's.
I had yet in all my years had to do all this other crap to get the trims in line. Watch the plugs and trim's and make the adjustments. No drilling here and blocking there.
Makes you wonder how the TPI or even any LSx engine ever runs with out split trims....and yet they do
I can think of maybe a hand full of people who have ran wilder combos be it cubic inch's cams, Tricked out intakes headers throttle body's you name it.
One of them even posted here and when I am stumped he is one of my 'Go To' Guy's.
I had yet in all my years had to do all this other crap to get the trims in line. Watch the plugs and trim's and make the adjustments. No drilling here and blocking there.
Makes you wonder how the TPI or even any LSx engine ever runs with out split trims....and yet they do
01-15-2013, 10:16 AM
#16
TPI cars have only one O2 sensor. Can't have split trims. I see LS cars & trucks, also the '96/'00 305", 350" & 454" trucks with the black PCM all the time with split trims when they have leaky headers, a mis-fire on one side, clogged injectors, vacuum leaks or a poor O2 or PCM ground. Not uncommon at all. Tune enough of those and your going to see them.
01-15-2013, 01:08 PM
#17
TPI cars have only one O2 sensor. Can't have split trims. I see LS cars & trucks, also the '96/'00 305", 350" & 454" trucks with the black PCM all the time with split trims when they have leaky headers, a mis-fire on one side, clogged injectors, vacuum leaks or a poor O2 or PCM ground. Not uncommon at all. Tune enough of those and your going to see them.
01-15-2013, 01:23 PM
#18
Yeah, but you know that the dumber they are the quicker they blame the tuning. The clowns evidently think the two banks each have their own fuel tables. I get more dumb-assed phone calls over this. They just can't accept they have a vehicle problem. "Hey man, it's all new!"
