95Blackhawk

Hey all,

Just up front, I do know what I am doing in calibrating MAFs. I have done it for years and confirmed my prior Hawk engine, with its calibrated MAF, was correct. In that situation, I had to modify the MAF by -12% on the idle side to adding 9% more on the WOT side (meaning it was lean in WOT area before calibration). Reference this sticky to confirm my background: https://www.camaroz28.com/forums/sho...d.php?t=505190

Here is the deal: my current RX7 conversion with the 95 LT1 setup shows the correct calibration requires a reduction of 28.5% from the stock tables to on the WOT end (100 AFGS and up) to get my BLM's to 128 range and eliminate the rich condition I had.

Bottom line, this does not seem right with a reduction of 28.5% in the tables! However the car runs fantastic and makes great power. Injector DC's are reading about where they should and further, the BLM's are equal on each bank. They only thing I can conclude is the heads are more efficient and thus burn more oxygen which shows up as a rich condition with the O2's. I had calibrated this MAF prior when the engine was still a 350 stock headed LT1 and the calibration at that time indicated a 9% reduction at WOT.

Just looking for input...

Ben

JP95ZM6

Well, are you shooting for the WOT A/F ratio that is programmed in? In other words, at WOT the AF is set richer than normal, and if you used BLMs as an indicator, and changed MAF to get to 128, you would be at stoic instead of the desired rich condition. That could take a pretty big change to the MAF table. If I understand correctly - I have only cal'd my MAF for non-wot conditions.

95Blackhawk

I appreciate you taking a shot at this.

I disable PE mode while tuning the MAF so I am at stoich throughout the entire range. I want to shoot for 128 in all BLM's (and I am very close at 127 in the upper end of the MAF tables). Your note regarding PE mode WOT is not an issue here.

JSK333

Different fuel injectors?

BLMs can be affected by a lot of fuel-related things like injector offset, base pulse width, extra pulse width adder, etc. They may show up in a non-linear fashion too.

95Blackhawk

Interesting. No idea if the guy I bought the car from used aftermarket injectors but I will be looking at this closely when I put in my new injectors in the coming weeks.

Thanks for giving me something more to consider.

vettedoctor

i thought that if you are in pe mode the ecm only reads off of the last blm it see's if the car is running lean so if you blm in cell 15 is 140 it is going to add a certian percent of fuel i believe some where around nine percent before it adds the fuel from the pe tables so you would have a pe fuel ratio of 12.1 plus 9 percent for example so the car becomes pig rich. I know my new blms are around 133 all of the time now and the car has no knock with the pe table set to about 12.5. this is on stock timing with 93 octane. The car runs very good and my gas milage went up when i got my blms from 144 to 133. also on my pe table i just subtracted fuel equal across the board in the pe vs rpm table and it seems to work for me.

Airbornec507

I've done the same thing disabling the PE mode and using tuning the MAF in close to 128BLMS. I've probably got about 5-10 more BLM's to go as my long term are around 120 with my short term around 128. I'm a lot closer than I was but so far have changed my calibration about 17% off of Bryan at PCMforless's tune. Maybe I'm having the same issue with the heads I don't know but it is strange as I'm actually about 5 to 10% below the stock settings for the MAF at this time. I get absolutely no spark retard all the way up to 6300 rpm. This being said yes the pcm is shooting for 14.7 A/F ratio so after I get the normal driving around set in real good I'll turn the PE function back on and tune using my wideband for the WOT tables. I'll also verify my MAF tuning with my wideband. The only thing I don't have though is a dyno to actually see what my power output is. Maybee I'll get better gas mileage after I'm done too.

Anyway I do thing the drastic changes in the MAF table are in fact strange. Any input on this from folks who know theoretically what's going on would be nice.

Thanks.

JSK333

Others have mentioned that exhaust temperatures can affect the accuracy of the O2 sensors. So, the same voltage at a higher temp may be a different AFR than at a lower temp. So if the temps are high enough it could be the O2s are reporting richer than it really is.

The other possibility is that the O2s are fouled. They will read richer when they are fouled, which ends up making the engine leaner than it should be.

Airbornec507

Well I've finished my MAF tuning after today but it will be wednesday before I get another chance to hook up the wideband and confirm the A/F ratio. After all the tuning I had to actually lean the MAF out and take fuel away from about 20% to 30% throughout the 4 MAF tables. Of course as mentioned the changes were not quiet perfecty linear. Around Idle and WOT the changes were about 20% fuel taken out and throughout the normal driving range closer to 25% to 30% in some areas. As stated I'll confirm the A/F ratio with a wideband on wednesday and save some other comments until I do so.

JSK333 - I'll check your statement and see how close the pcm is to dialing the A/F to stoich with my wideband on wednesday. The wideband will be connected just after the .O2 sensors that are located after the flange of my LT exhaust. I do have duals with an x-pipe however all readings will be gathered approximately 1 foot prior to the x-pipe for the A/F ratio(widebands) while the .O2 sensors are approximately 1.5 feet from the x-pipe and about 6 inches from the LT header flanges.

Airbornec507

Well, to report my findings of my MAF tuning by checking with my FJO wideband I do have some strange results. While running the check the pcm kept my A/F ratio right around a steady 13.2 plus or minus .2 throughout the rpm range. This is very strange as the entire time I was trying to lean the mixture out via the MAF table to get my BLMs around 128 throughout. The ST BLMs are right on and the LT BLMs are within 5 counts of 128 whether it be above at times or below 128 the LT BLMs do stay close thus confirming that the tune is close enough for the PCM to keep it to what it percieves as stoich.

Now, when I did a WOT run I got extremely lean. I think that is because the pcm saw a slightly rich condition prior to going into PE mode and took some fuel out thus leaning out the mixture while in cell 15. The WOT table is close to stock but the recommended changes by my tuning program(Excell spreadsheet) had me changing my WOT/PE table to almost +50 points from 4800rpm to 7000rpm. I have used this table many times to tune my brother's and my car in the past with very accurate result needing only about 2 or 3 runs to get the desired A/F ratio dead on. Also to not my table 4 in the MAF section maxes out at 433 AFGS at 11216Hz to attain the above BLM results. Now this may be what is playing in to the fact that I have such a high number in the WOT/PE table. Or my FJO wideband needs a little more looking at as far as set up or Wideband accuracy. Based upon what I have presented here could the theory of my MAF tables being adjusted as much actually have this affect on the WOT/PE tables?

JSK333

I assume you have aftermarket injectors? If so, I'd suspect you don't have the correct constant and/or offset values in the tuning, since it's showing the MAF off by that much. Offsets can make a huge difference in BLMs, especially at WOT.

Airbornec507

I have Delphi #38 injectors that are set up as 38.01 lb/hr in the constants table as that is what the injector is rated at with 43psi pressure as per the factory spec card.

As far as offsets go there at two tables, both of which I have not done any tweaking to, the Injector Offset vs Battery Voltage and the Low Pulse Width Injector Offset Adder vs. BPW. Please expound on your reasoning and any tuning background on the injector offsets. Meanwhile I'll also research the subject myself.

JSK333

http://www.teamzr1.com/ubbthreads/ub...at&Number=2794

That's a good link to read to understand the basics. The offsets control when the PCM fires the injectors, based on how long the injectors take to react and open from when they are pulsed.

So you can see how if you have an offset lower in the PCM than what the injector physically does, the injector will end up squirting too late to efficiently match the spark output, and the opposite will happen (squirts too soon) if the offset value is higher than the physical spec. Obviously that will seriously affect combustion efficiency, and thus BLMs/AFR.

Airbornec507

These are the injectors I have:

http://www.racetronix.com/17113798.html

Based upon the link you posted it looks like a lot of trial and error would be used to get the BLMs to settle out on 128. However that would assume that all the MAF values are set back to stock, working the injector offsets first then fine tuning with the MAF values.

My question is that even by doing this how do you know that this type of injector is set correctly without having it tested in some way prior? Is there really any way to find out at this stage with the injectors in the car via BLMs(or is this really just a band-aid approach)?

Comment: I just checked my injector offsets compared to a stock file and it seems that Bryan at PCMforless has added 183 to all my values. Interesting.

lt1srule

when tuning the blms at idle and off idle i adjusted the mass air flow up about 1 full point across the board in table 1 then open the graph and blend every thing so its a fairly smooth transition .i had to go up quit a bit cause the mail order tune was not tuned for my thunderraceing maf ..i started with splits of 128 to151 at idle and off idle after upping the table in the maf table 1 it brought my blms to 134 to 128 then i had to richen my idle fuel tables on the left bank on cyls 3 and 7 cause they were a little lean of course checked with a heat gun to check cyl temps after that data logged the car and its dead on 128s left and right through the whole log never stepped out of 128 ..and all i can say is Wow Unbeleavable ..The clutch won't hold now just slips when i try to accelerate quick ..and i have a zoom clutch rated at 400 horse ..It just showed how much the mail order tune was off Way off ..and the cruising conditions are night and day with no more bucking or cam surg ..It took 3 days to figure every thing out but i am 1 happy camper now ...I never thought i could pick up that much more power fine tuning .Awsome just Awsome..