I have a 383 with a Lunati Vodoo Cam, 36lbs inj, holley steath ram and a custom tune(timing and fuel is supposed to be built in), using 6 degrees of advance(stock) and 48psi of fuel. I started the car and everything is good, blm 128, o2 at about 600-800, and total timing at 24 degrees at idle. As it warms up the o2 starts reading lean and the blm goes to 145-160 and then it pulls error code for maf low. When I give it gas it jumps back down to 128-135blm. Then during driving, ok at accel 128-135blm (total timing is around 34 degrees)the at deccel (no load) jumps to 160blm.

I changed the o2, bumped the fuel from 40psi to 48psi(got a little better) checked for vacuum leaks(good). The charcoal canister is not hooked up.

Any Ideas????

Hmm. First of all, Block Learn has three different cells, or modules that it runs in for different driving modes. There is one for idle or low throttle, one for acceleration or heavy load, and one for part throttle cruise. You can see the ECM switch BLMs(1,2,3) by monitoring BLM on datastream while you drive. Block learn may be different for each BLM according to tuning. Ideally, we want to see 128 accross the board. Noting what Block Learn does as it goes from one BLM to the next can tell us where the deficiency is. High BL in cell 1 is likely unmetered air. High BL in cell 3 is more likely fuel management such as MAF, or fuel supply(clogged injectors, low fuel pressure).

You may want to talk to Rbob on the DIYProm forum about your tune. I don't like burned PROMs because they don't allow the end user to tune fuel or timing maps. Dynamic EFI's EBL converts the stock ECM to be user programmable like my ACCEL DFI is.

What is a dynamic EBL that converts the stock ECM to be user programmable. I am about to try to start doing my own proms and want something versitle. I have three of the speed density cars 90-92 so it makes sense that I learn how to do this instead of hauling cars to Ed Wright. All the info you could give on doing your own programming would be greatly appreciated. allen.bray64@yahoo.com

Whats your engine combo? Having blm range from 128-135 for most load conditions seems perfect to me. Car feel ok while driving?

If you have a big cam, ignore BLM at idle in closed loop. Read plugs instead. Its common to have BLM "off" when at idle with big cam but as long as its stable idle, who cares what the BLM does.

At cruise rpms/loads, thats where you need to focus on BLM and having it in the +/- 5 BLM from 128 is a good range. Minor tweaking to fuel tables will dial it in but if your that close to BLM 128 and INT looks good, then I wouldnt worry about it and just enjoy the motor.


In DECEL mode its suppose to go lean, thats normal. WOT or entering PE mode, BLM goes to 128 usually and stays there. You tune WOT with wideband, plug reading, or you can try to monitor narrow band o2 sensor milivolts and shoot for 900 mv. Thats close to 12.8 to 1 air fuel.

Stock unheated O2 sensors don't read properly around idle when installed downstream on headers. They don't get hot enough. Big cams make it worse. Have you tried a heated O2 sensor?

If the INT is not at it's limit, then it is still able to average stoichiometric, regardless if BLM readings are pegged. If your seeing an error code for MAF low (code 34), the problem is normally a false air detection or a vacuum leak. Check for vacuum leaks, and check your TPS voltage....

I have a dumb question? I am still fighting a error code 34....I have a big cam. I runs great in the powerband (blm 126-132), but its rough when its cold comming off the clutch (not smooth). the tps is .071 at idle(900 - 1000rpm) but o2 sensor not working correctly at idle shows being very lean 44.00 mv and slow increases blm up to 160, but as soon as I give it gas, it starts working perfectly again. Is this due to the cam?