95Blackhawk

Hey all,

I cannot figure it out. My MAF goes crazy somewhere above 220 AFGS or so. When I mean crazy, it hits the highest setting then will immediatly drop to almost nothing then back up multiple times in a second. With all my years of doing this, I cannot figure out what is going on.

I am in closed loop but it is as if the car is ignoring the MAF signals as you can plainly see that the 02 reading are still rich up top and don't act as if the MAF is fluctuating. As a reference, I hit the rev limiter and immediately, I get the 02's reading lean because there is no more fuel. Also, the injectors start to become erratic up top. Although not smooth during this event, the injectors are still matching the air flow.

I have confirmed the voltages to and from the MAF per the GM service manual. They are within spec's.


New MAF does exactly the same thing. UPDATE: I changed my PCM with the same program and no change to the issue.

So it has to come down to wiring or power supply. Thinking out loud, the system needs power to heat the elements. As the elements get heated more at higher AFGS, they need more power. Maybe I don't have clean and good power to the MAF?

Please just take a look and you will understand better. It is freaky.

Ben

bobdec

Ben, post it up or email it to me, I'm not a real expert, but maybe something will be there that you glanced over. Is it the RX7 or the '95 M6, if RX7 what year PCM and harness are you using..

WS6T3RROR

Post a log and the tune file, and I will look it over.

95Blackhawk

Cannot figure out posting so I will email to you both. 95 PCM and harness using $EE.

Disregard my BLM's being way off. I have a leak and just did not have time to fix it at the moment. This is probably what put me into cell 18 during the WOT run.

Out of the datamaster file, the only portion you need to focus on is the small WOT run.

Thanks.

WS6T3RROR

Car is not ignoring maf signals, look at your injector bpw and your duty cycle while the maf fluctuates. The o2's aren't reacting because they're still saturated with fuel and vapor and maybe the average fuel air fuel is still ok.

You also need to use the blm locker to keep your wot ratio where you tell it to be.

I am really not trying to get under your skin but your pe values are way off out in left field, and zeroing the rpm pe values will cost you shift recovery and throttle response. Again don't take it the wrong way just my opinion.

I don't see anything in your programming that will cause a problem like you have. Sometimes what can happen is if the maf calibration tables get messed up and if the frequency increases and the afgs decreases it will confuse the pcm and sound like a two step and do what your maf values are doing. However that is not the case here.

My advice is to make sure the maf wires and any high voltage wiring are well away from each other especially the alternator wiring, and any ignition wiring. The problem is likely some induced noise in the line that is only making a difference at high rpm for whatever reason.

95Blackhawk

Thank you so much for the look.

I have BLM locker programmed. I assume locker is not used because it is in cell 18. I assume cell 18 was used because of the bad exhaust leak. don't worry, it always goes to 128 in cell 15 normally.

Yes the BPW is increasing with RPM as it should. However, you did not mention the erratic injector BPW showing up after the MAF starts oscillating wildly. Do you consider this normal or just not a big issue?

What do you mean by "shift recovery" and "throttle response"? Would I gain by doing something different? I have an M6 and my intention is to run the car rich at 12.1 AFR throughout the RPM range and not worry about blowing it up in the hot summer air of 100+F on a road course running WOT over 5K RPM constantly. I know I am going up probably 20 HP but it is worth it knowing the engine has more of a chance to last. My DCR is 9.4 so I am being cautious.

I think your idea of looking at electrical interference is justified. I will do so.

Ben

WS6T3RROR

You misunderstood. Your car is jerking the fueling around to match the maf readings, that is why your bpw is bouncing all over the place. That is also how I know the car is not ignoring the maf. That is why I mentioned it because it is not normal in any way. Some oscillation is normal in the maf reading and the bpw but NOTHING like what you have.

What you can gain by doing something different with pe is you can adjust the air fuel against rpm and then fatten it just a bit before the shift and you can also fatten it up at lower rpm in case its ever down low. Usually makes cars just a bit faster. Probably of no value with the ratios you're running though. Had no idea you were running it that fat on purpose. The reason it helps is the maf is slow to respond to huge changes in airflow so you have to cheat it a little bit for launching a stalled auto and for shift recovery in every case. You are also tangling with the stock fuel pressure regulator which is changing fueling as well.

Since you're road racing, something else that will help you is to keep your timing consistent in the upper rpm ranges. If you're off the throttle a bit in gear so vacuum is high and the timing is hovering up around 40 degrees and you punch it again and the timing drops back to 30 degrees, that is not good for response. Had plenty of experience with m6 guys drag racing bogging like hell out of the hole for similar reasons.

bobdec

Ben, ++ to above posts, 1- make sure your power to MAS +12 (ign) is clean comes from fuse 5 stock, not sure where you tapped into. Ground is the stud in front of the left head, and the yellow signal wire to PCM B19 . 2 - As WS said your timing is dropping from 43 to 30 (starting at record 302) when you hit the throttle. Check your main spark table as you move into the around the 95 kpa/3K rpm area for big drop in timing. 3 - This is minor but looks like TPS=0 voltage is a little high. After your wot run (records 302-398) you can see TPS voltage bouncing between .76 and .78 and the TPS% bouncing between 0% and .8%. Cranking the stop a bit would eliminate the TPS=% bouncing on/off. 4 - You don't seem to be using all of the BLM cells (never enter 12-15), have you adjusted the BLM cell boundaries to match your actual MAP during normal (non WOT) running. 5 - Your O2 switching looks slow look at the trace with just L & R O2 voltage selected the left looks sluggish. 6- Your left side is also reporting lean, but you said you have a leak, take a look at the DM histogram classic view when you get a chance, you are all green (lean) across the board.

bobdec

As a follow up.. I also looks like an open VSS signal is picking up noise and could be messing up the BLM cell 16, 17,18 selection. A graph of you speed shows this. Not sure how you wired the speedometer to the new conversion however I suggest getting the correct VSS pulses to the PCM..it uses VSS (speed) in a few calculations, including IAC follower correction.

95Blackhawk

I am trying to resolve the VSS signal now. Not sure if it is the new PCM or just by chance the sensor went out at the the exact same time I changed to it.

BTW, I resolved the issue by a new connecting better power directly to the MAF. I was getting a 1 volt drop to the MAF and this corrected the situation.

95Blackhawk

Everything resolved. VSS sensor was unplugged. MAF has its own power supply as it should per original design. Everything is good.

bobdec

Sounds good.. looks like just a little more tweaking and she'll be ready to rock.. you plan on a dyno tune after the kinks are all corrected or are you going to do the WOT tuning yourself ?

T/A lt1

So if the vss sensor is umplugged it will cause timing to be altered? I have a Th350 and I am getting trans codes including a vss code so I think it's giving me problems is there any way to correct this thru tunercat?

95Blackhawk

I plan on eventually getting it to the dyno for tuning of timing. I can easily get the AFR correct myself. Probably in November after it cools down here.

bobdec

T/A lt1, The VSS (speed) data is not used for any timing alterations. In a non electric controlled tranny setup it is only used for IAC follower control (prevents stalling & low RPM conditions when coming to a stop), and control of BLM cell selection during TPS=0 conditions (cell 16, 17, 18 selection). None are really critical to performance just minor drive-ability problems at TPS=0 conditions. You can turn off the errors in the TC Switch Table by removing the X in the DTC 72 and 97 selections. Assume your torque converter is does not have PCM lockup control as that is driven by MPH. Scan the TC switch table and disable any TCC or Tranny enable switches and diagnostic codes by removing the X's .