So here are a few questions that I need answered.
1.) Using TunerPro, why when I lock the BLM to 128 don't they lock?
2.) What would a vacuum leak after the MAF before throttle do? How about after the throttle?

Reason for number 2 is that the BLM's are acting really strange. The MAF is descreened but I didn't think it would be that big a deal with the 383. So anyways, it's surging really bad on cold starts and here's something that might be contributing; 15.6 commanded idle AFR. What gives? Where is this value so I can change it. It starts and stalls every time it's a fresh start and it's bugging me big time. I believe there's a leak for the following reason; The air flow is inversaly proportional to the BLM's. Ex) 1000rpm MAF's reporting 8gms (doesn't that seem low) and BLM of 128 but climbs to 156 and the engine IS running rich and ruff in open loop. Same RPM but 20gms and the BLM is lower, like 140. No matter how much tuning I do with the MAF table and scalors it still climbs which is making me believe it's a vacuum leak.
Also, right when closed loop kicks in on a cold engine start the thing idles great but only for a few moments... while the BLMs are still around 128. Once they climb it bogs, stall saver, surge, surge, surge, stall. It feels great once it changes the BLM cell but at idle and anytime there's low air flow it wants to stall. This is an Accel SuperRam so it wouldn't suprise me if it's a leak, just this is the first time I've had so much difficulty with a MAF tune.

 

A vacuum leak post maf will cause the motor to run lean as that will be air that isnt accounted for by the maf. This will get steadily worse with decreasing rpms/loads and at idle as a large portion of the air taken in wont be passing by the MAF.

As far as the blms at idle, IIRC, there is an idling mV bias added into the O2 volts in the MAF cars. This bias can only be achieved through the BLMs as there is no VE table. With mine the BLMs will be around 118-120 with similar airflows and as soon as it goes to idle theyll float up to around 137. Best I can tell is taht its due to the bias. Either that or the headers cooling down and causing the O2 to get sluggish or something.

Finally, Id try bumping up the MAF table at low flow values. I was having a problem with the lower part of my MAF table being undercalibrated. The engine would stumble on those and immediatly want to die because it would go real lean. The stall saver would kick in and push the engine up to higher values on the table. It would settle down and come back to the lower part of the table and want to die again. This would repeat endlessly. I added some flow into the lower parts of the table to more closely match the actual flow and the problem went away. It could also be the other way around. Too rich. Or even some other problem.

I dont know about the actual tuner issues your having. As you probably know, the MAF ecm doesnt use actual AFRs but rather a bunch of multipliers. so you may not be getting the AFRs interprited right in the datalogs.

That and the stupid split flow tables/scalars where two things I didnt like about the MAF ecms. To me it was alot easier to use one 16 bit MAF table and perform an inverse AFR lookup before the PW was calculated. The GM stuff definatly isnt user friendly.

 

Well here's a little more info, I tried richening open loop by setting the injector constant to 22# as aposed to the actual 24 and still no luck. Even went so far as to max out the MAF #1 and #2 tables to richen things up, still nothing.
What is a normal air flow for a sbc at idle?
I'm wondering if we should just go to the $32 mask and see how things perform. We stuck the stock memcal in and it was better (because it said 19# inj constant maybe?) but still stalls lean which it shouldn't.
Also, the idle AFR is 15.4-15.6 when in open loop even on a cold start but all the % open loop tables are positive values. EGR, Air pump are all disabled and I just can't figure out this commanded 15.6 AFR (viewed with Diacom).
He tried propane to find a leak but nothing, changed the MAF, nothing. Also, the pump and filter are good because part throttle and WOT are excellent, it's just this damn idle which you would think as the easier thing to tune. I did everything with the Romulator and no change... I'm banging my head on this one.

 

Idle will be the worst area for an 8 bit MAF ecm. The resolution is the lowest at low flows so there will be some variance in the fueling. I dont think its enough to explain what your seeing but its another thing thatll be working against you. Also, the airflow is very low at idle so there may be other effects there as well.

As far as the airflow goes, I pull around 8-9 g/s at 750 rpm. 8 g/s @1k does seem a little low for a 383, but with a hot cam that may be all its really pulling.

I also dont know about the 15.6 commanded AFR. That may be a mistake in how the value is interpreted.

Shot in the dark here but maybe its too much fuel. The sudden start, stall sounds like maybe an issue with too much fuel when the engine transitions from the crank PW to the MAF.

 

JPrevost

There is a thread about a "Known" gasket problem. It is the #8 and #6 port that mates the manifold to the runner. The leak is caused by a mis-cut EGR port. (Top of port) I you spray some carb cleaner from drivers side of car, under the plenum aimed at that back passengerside runner, you will get an idle sputter. I had to make my own gasket to solve this.

 

That gasket problem would cause an immediate idle problem when first installed right? Is it possible it would get worse over time? I installed a set of new gaskets on my SR last summer but the idle was pretty good for the whole summer and this winter. Now it's just horrid.

 

SHould have done it from the start, you have other issues I would guess. I would still check though.