Out of curiousity, i've been reading info about how some aftermarket TBs can cause split blms because the iac port in the tb opens up to the Throttle body bores. From what i gather its much better to have the iac air directed to only go through the iac port on the manifold.

Now my question is.. i have one 02 sensor on the drivers side. The gen 7 just came with the one so do i have to worry about the split blm issue?

i've read somewhere that you can put a brass fitting on the back of the TB so that the iac air goes where its supposed to like in the stock TB. But if it doesnt affect me i wont bother.

 

http://para.noid.org/~lj/PCM%20Tutor...litBLMinfo.htm


I found out yesturday that I have split BLM issue. Bank 2 is very lean while bank 1 is rich. I'm been reading up on this issue for the past 4 hours. Here are a few more links ..

http://forums.corvetteforum.com/show...ight=split+BLM

http://forums.corvetteforum.com/show...&highlight=BLM

http://para.noid.org/~lj/

http://forums.corvetteforum.com/show...&highlight=BLM

http://forums.corvetteforum.com/show...&highlight=BLM

http://www.corvettemagazine.com/1999...ion/fuelp1.asp

http://forums.corvetteforum.com/show...&highlight=BLM

 

 

 

The Holley i had didnt share the iac port with the main bores like that one so i don't need the brass tubing. I sent my stocker to have a 52mm job done on it so that takes care of it as well. i also appreciate the links but my main question is, how are both sides sending different readings? is one o2 sending a rich condition and the other lean? reason why i ask is I only have 1 o2 on the car, does that mean having split blms is impossible?

 

Are you sure that you have one sensor? All LT1 engines from 92 and up uses two main sensors that the ECM or PCM control fuel trims with. Better look again. If you don't have an aftermarket TB with the incorrect idle air passage, then the split fuel trims can come from a small exhaust leak on the corresponding bank. Any unburned o2 will cause the sensor to indicate a lean condition for that bank, and your ECM will throw more fuel at that bank to correct the condition.

 

Im running a gen 7 dfi and the one 02 you supplied me with Tom. I don't know why but the installer of the harness ( who did a fine job btw - all stock guages working ) chose to wire it with the 1. I believe the other header is plugged. Ill know more details in the next few days when i FINALLy ( ) get the car home. i dont have split blm issue atm i was just curious because we have one sensor. The stock ecu was removed completely along with the harness.

 

I have had slighly split blms from the beggining on my car.Funny thing is the pulses the ECM sends to the injectors are exactly the same for both sides.Long story short it does not make any difference if the pulses are the same IMHO.I wonder if anyone else has noticed this with split BLM's?

 

Besides the splits I am working right now, I have had splits on my 93 (in all these commbinations) with 2 different engine, stock and a 396 LT1. I have had the stock cam, stock injectors, a Hot Cam, 30#svo and a 230/236 cam with 30# injectors. I have also had a stock throttle body (48mm), a modified stock to 52mm, a BBK 58mm and now a AS&M 58mm with the modified air circuit with the mod above. I have also a 95 manifold ported on now since I have had a 396LT1. HHMM, are the manifolds diferent from 92-97 in any of the engines? Also, I have had stock exhaust, shorty headers and Long Tube headers. I think my 93 Vette is designed with split BLMS just for "Steve" misery sake

 

From what i know the LT1s short runners makes this an issue. But since i have 1 o2 bung for the dfi its impossible to have split blms??

 

Depending on what fuel strategy that you choose for your DFI system it is highly unlikely that you would see split trims. One reason is that the DFI system isn't equipped to fuel each bank separately. Howevre in SFI mode it can trim fuel to each cylinder individually. But if you are in batch fire mode, the ECU sends the same amounts of fuel to each bank each time it fires each bank.

Normally in stock LTx engines there are no issues with split fuel trims. I have seen problems when the engines are modified. Headers are a number one culprit of fuel trims issues, because the headers when not installed properly will result in exhaust leaks. When this happens, raw air is sucked into the exhaust system and if its near the o2 sensors then they detect it and the PCM or ECM will correct for a false lean condition on that bank. Another cause of split trims was the forementioned aftermarket TB issue where the idle air port has been machined to allow idle air to enter the main plenum and not to the dedicated idle air port. Another reason comes after a camshaft installation. With longer duration cams, intake reversion occurs and this alone can cause split fuel trims due to the amount of reversion in the intake track.

 

I have yet to see a speed density LT1, stock or modified without split BLM's. Seem's to be nature of the beast.

 

So, with an aftermarket T body, headers (with leaks) and the longer the duration cams, you will see split BLMS?
What about while driving? Does it get better? Or stay split?

 

For what ever reason Steve even with split blms both sides get the same pulses on the injectors so my take is it does not matter on batch SD fire cars.All the cylinders get the same amount of fuel.It would make a difference on post batch fire cars though as it would change the pulses to different cylinders.Batch fires work pretty much like carbs as far as I can tell.And the split remains on all my data logs at all speeds but the car runs fine.

 

Thanks. Mine is more severe as the right is above 150, for example.
I am going to play with the T body , as it is a modified AS&M to allow idle circuitry to be like the facotry intended it to be.
Its just as bad as the Opti, these split BLMs

 

Mine is not that bad but it is the right side too in the low 130's.How are your O2's?AC Delco and not Bosch I hope.

 

I use DENSO 3 wire. I just found my right side O2 had a loose wire. I will rescan tommorow, hopefully I will see a change.

 

AHHH sounds like you found it.Good luck.I forgot you had the heated O2's

 

I sure hope so, as my tuner is probably going to shoot me if I have any more "issues"

 

The Holley i had on the car has a designated port for the iac. The tpis throttle bodies and the callaway unit i now got for my car is similar to that in the pic. WHen i spoke to TPIS about the iac port bleeding air into the main section of the intake they said its not a problem at all and they have many modified cars that have no issues.

I wonder if a big cam might need more air than the idle air ports can provide ? If my 388 needs much more air than those ports can provide i might just forget about putting in a brass tube. Since i only have 1 o2 on one side split BLMs are a non issue i guess.