if i have a stock engine and my blm's are at or near 128 either way and i set my % change vs air/fuel ratio at rpm to zero this should give me a air fuel ratio of 12.7 is this correct. I guess this is just a theory because i do not have a wide band but could it be right

 

No. 128 BLM does not mean 12.8:1 AFR. It is a separate range of numbers the PCM uses to correct fueling, completely independent of normal AFR readings.

The % change at WOT tables are based off 14.7:1 AFR. So setting both tables to 0% would give you 14.7:1 AFR at WOT.

 

i understand that i am saying that in theory 128=14.7 and that % change at wot would be correct again in theory on a stock engine. i do not believe that gm dyno tuned every lt1 before it left the factory and that the pe tables are generic tunes at best

 

Oh OK, I think I see what you meant now. You mean only zero the WOT RPM table out, but leave the WOT coolant table stock? If so, then yes, at 80-92*C, the PCM would be shooting for an AFR of about 12.7:1 with the stock tune.

I'm sure you're right, that the factory tune is not ideal; they had to consider long-term safety, which making it extra rich can help to do.

 

that is what i guess but i go as far as to say they have a very generic y body, f body and b body tunes and each is different. But ever engine burns different so if the ecm thanks that the pe table is giving a 12.7 air fuel ratio it be in fact 11.0 to 1 to 13.0 to 1 ratio. I know my car shows long term blm's at 155 area so my car shows very lean at cruse so my car is adding the extra fuel for the block it was last in and is also adding pe fuel which may be making my car burn very rich

 

Yes, this is why several people have disabled PE mode to tune their MAF/VE tables at WOT, to ensure that the commanded AFR at WOT matches real-life. Do a search on here for "WOT AFR Tuning without a Wideband" and you'll see.

With a 155 BLM, you've got some major issues, probably a vacuum or exhaust leak, or constants not set properly in TC.

 

No way that production variances on a '90s engine would lead to that big a difference.

Now when the cars get old and are maintained differently and have widely varying mileage and mods on them, etc. then sure there can be substantial differences.


Which shows that your car has problems due to maintenance, mods, etc., and tells us nothing about the variance in engines as produced.


If your engine is near-stock, you need to stop messing with the tune and fix whatever electromechanical problem is causing the 155 BLMs. If it's not near-stock, then your conclusions about stock engine tunes are just silly.

A signature with list of mods would be helpful...

 

From your previous threads it appears that you replaced the injectors, and presumably then got the 155 BLMs, and then started messing with the MAF tables.


If you had normal BLMs before the injector change, then stop messing with the MAF tables and go back and get the injector constant right first.

 

first it is a 94 vette that is stock other than a msd opti electric waterpump. descreened maf throttle body air foil and k and n air filter the descreened maf and throttle body air foil have been on the car since i bought the car i did not install them. ok so i looked at my data master file and here is what i found most of my long term fuel is between 132 and 142 and my short term is 122 to 130. the only place i saw 155 was in cell 6 and cell 15, cell 6 is off of the throttle rolling down the road and cell 15 is wot so i am guessing my maf calibration has to be off for starters. looking at cell 15. now at idle cell 16 i am at 130 wich is close enough. my idle cell is at 130 so i would say if there is a vacum leak it is very small. but my map reading at idle is 36.6 kpa wich may be a sign of a leak. hmmm maybe i need to check the new msd vacum line.

 

I've reviewed hundreds of data logs for people, and most "stock" setups, with no problems, easilly hold within +/-4% (123-133) on the long term fuel corrections.

Cell 6 is not "off of the throttle rolling down the road". Its corresponds to MAP up to 50kPa, which is not closed throttle. 15 is not necessarily WOT. Its used with MAP as low as 80kPa which is not WOT. But that 155 in Cell 15 will influence the PE mode A/F ratio drastically, if its from anything other than MAF miscalibration.

Replace the screen on the MAF, and restore the MAF calibration table to stock. Then start over.

If you have a "155" anywhere, you have a problem beyond "ever engine burns different"... particularly when working with a stock engine.

 

i do not have the screen for the maf my guess this is what is causing a good bit of my problems. seeing perfect blm's at idle and near perfect in other cells would lead me to believe that because my maf was decreened it is causing the problems. Now the other problem is i do not have another maf to install on the car nor do i have the screen since i bought the car like this. i am going to try and adjust a lot of this out in my maf table what do you guys think

 

The first thing I would do is verify everything about the car, including the fuel pressure. Look at all the sensor inputs on the car and make sure they match what should be happening at the time during logs. Graph the sensor information mass airflow should go up with more tps map should drop, these changes should occur at simillar times and slopes. More extreme changes in tps should cause more extreme changes in map and airflow etc. Also make sure your iac and coolant temp are close with the car off and cold.

It doesnt have to be a vacuum leak to screw up the fuel trims, just air getting in anywhere besides through the maf will screw up the fuel trims good. ie check the elbow. Or an impropper amount of fuel being delivered from injectors not flowing at the specified rate due to weak fuel pressure, from a bad pump or clogged fuel filter.

 

fuel pressure checks at 43 psi seeing that it is just in one or two cells i have to believe there is something going on in those cells maf bad out of cal.

 

Post a log. Otherwise its going to be really difficult for anybody to give you useful advice.

 

I think a used MAF is pretty cheap.