LT1 Restomod Worst Split BLM Possible

As the title says, I've got a 95 LT1 shoved into a 71 buick. Standalone harness from PSI as I was too lazy to rework the factory one. Car starts and idles "decently enough". But datalogging tells a different story. If I can figure out how I'll attach the two eehack logs. First is of everything attached second is on SD without an intake tract as I thought maybe a vacuum leak could somehow cause this or possibly the maf being bad....no dice though.

It's dumping fuel like there's no tomorrow on one side while pulling all fuel from the other, so much so that it's fueling out the exhaust 105/160 split and only stops there because that's where it's locked. I know split BLMs is pretty common on the LT1s without an exact cause but I just recently got the ole lay off notice and I'm not about to start throwing parts at it like most do in this situation. So here I am, hat in hand, hoping you guys can point me in a direction. It'd only make sense that it'd be a sticky injector or a lazy/dead O2 correct?(Didn't get a chance to swap o2 side to side) Or am I missing something? EGR/AIR/CCP all tuned out. Also has been lightly tuned for the long tubes on it. Short of the headers/ intake, it's stock iron/iron/internals for the time being, as I was hoping to get it running right before going any further with her. Thanks in advance, this car has been a long running thorn in my side.

-LT

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Make sure the throttle blades are closed as much as possible. The proper air distribution at idle relies on the internal passages from the IAC motor to the intake ports.

Try running at a higher rpm like 2000rpm for a while then drop to idle again.

Check to see if the bank 1 and bank 2 O2 sensors are swapped. Also, try unplugging them to see how the engine runs in open loop. If it's still dumping fuel, then you will know to check the injectors.

Do you have the VSS or EVAP hooked up? I read here http://fbodytech.com/tutorials/charc...er-purge-evap/ That steps need to be made if you don't have VSS or EVAP to allow the PCM to use the useful BLM cells (1-15) and not the special idle cells (16-18). You might be stuck in 16-18 all the time since the PCM isnt getting a CCP input or VSS input and thinks you're not moving

Make sure the O2 sensors aren't swapped or the injector banks aren't swapped.

As soon as you touch the throttle whats happens?
On my 87 blackbox when I had the injector or O2 sensor banks mixed up I had full sp[lit BLMs and they would continue to split and eventually would send flames out of my sidepipes at idle, then as soon as I touched the throttle the BLMS would start equal again and then immediatlely drift into the split again.
There is individual cylinder Idle Mixture Tuning on the LT1.

An injector balance test where you select individual injectors to fire solved my issues. I was commanding the right side of the engine and injectoirs on the opposite bank would fire.

peace
Hog

FYI: If you have flash capabilities why not make a basic bin for free at:

http://fbodytech.com/bin-files-2/fre...uning-service/

is it aftermarket throttle body or stock?also bad optispark on the way out causes lots of strange issues with an lt1.

Quote:

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Originally Posted by jetblack93

is it aftermarket throttle body or stock?also bad optispark on the way out causes lots of strange issues with an lt1.

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I'm sadly starting to get to the point of saying bad opti. I would have grabbed a skip white to just check, but they don't seem to carry them anymore and the other cheap optis are all junk. Leaving me not wanting to spend 500$ on a maybe. It's a stock TB. But here's an update guys, sorry for disappearing for a few days. Anyhow....

I fixed the split BLMs for most part. Got them down to about +/- 8 max at idle from side to side. But I'm still running into the PCM trying to pull fuel from both sides now (<115), and at the same time I'm getting hesitation and then an intake backfire when i blip the throttle hard from idle. Soo the question is, should I pull some fueling from it? Add some? Is this instead a mechanical issue?

The engine and heads are original but only have about 70-80k on them and were always an auto car, so I'm not suspecting....or atleast trying not to....valves being shot. I've played both ways with the CCP having it active as well as tuning out the special cells....since, well, if you tune those out it still runs/idles just without 16-18cells.

New parts thrown in in just the recent-
New o2s
New plugs
New wires
Swapped to another MAF I had...granted it's an Fbody maf, but I swapped in the appropriate tables into the tune.
Intake seals. Also smoked the intake just on the offchance I had leaks
New opti intermediate harness.
Valve seals

New datalog from eehack is attached(idle and a few runs up and sitting at mid rpms, also ran up in drive(wheels in air)) I'll add my tune as well in case I did something stupid which is very very possible. I think I've got this down to one of three things. Either coil, opti, or injectors. Coil only has about 5hrs runtime on it, but is about 8yrs old(sat on a shelf since my first lt1) So if anyone can narrow this down even more it'd be awesome. If I roll into the throttle she screams and blms even out. But if I try to just jump into it it'll pop through the intake. The idle wants to hunt a bit too about 100rpm or so, but since new plugs/different maf it's calmed down a bit.

As always, Thanks in advance
-LT


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Edit for early morning thought, is this possibly the ICM? I only ask since it didn't get swapped with the newer coil and I'm not really certain what a failing but not yet dead ICM does.

This seems to be a good Opti.

http://www.saccitycorvette.com/AIPOptiSpark.html

From your post, I'm not convinced it's the Opti though.

the only part of an opti that would cause a blm split would be the cap (as in a point burning off and having weak spark in that cylinder as a result)

if you suspect that, take it apart and have a look

i doubt it too

Hey, I'm not going to argue in hopes of the opti being shot. That money can be spent better in other places. I'm still probably going to pull it and cap to check the sensor for visible corrosion/moisture. But I'm thinking my first move is to pull fuel rail. Prime it and look for leaks and then run the starter through a rev with containers and see if i have a noticeable leak or sticking injectors. My other move is resetting valve lash. It really just feels like the spark or fuel isn't fast enough to catch up with the massive influx of air on low end hard throttle.
If all else fails I'll just try to tune around this with adding subtracting fuel and see if i can get it close.