MAF Dropout
- Thread starter TurboGeezer
- Start date
TurboGeezer
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- Jul 19, 2001
Root of the Problem.........
Just thinking once again about the root of the MAF dropout problem and wondering:
Is it an "electrical overload"........meaning the ECM just cannot "read" the frequency signal if it is over 140 Hz ??
.....or is it that there is no table entry to tell the ECM what to do when the signal frequency is over 140 Hz ??
This is assuming that the upper limit of the MAF signal range is 140 Hz..........seems like I remember that the MAF opperates in a frequency range of like 0 - 140 Hz.
If it is just a table lookup, then could the table cross-references be adjusted so that say anything above 1792 "counts" would still refer to 255 g/sec ??
TG
Just thinking once again about the root of the MAF dropout problem and wondering:
Is it an "electrical overload"........meaning the ECM just cannot "read" the frequency signal if it is over 140 Hz ??
.....or is it that there is no table entry to tell the ECM what to do when the signal frequency is over 140 Hz ??
This is assuming that the upper limit of the MAF signal range is 140 Hz..........seems like I remember that the MAF opperates in a frequency range of like 0 - 140 Hz.
If it is just a table lookup, then could the table cross-references be adjusted so that say anything above 1792 "counts" would still refer to 255 g/sec ??
TG
This is not an easy question to answer but I'll give it a shot. (Not sure how much of this coding stuff you're into).
OK, first the addresses that get loaded by the ROM program when it calculates airflow are:
$A9 = 8 bit # representing the current MAF table value
$AA = 8 bit # representing the current MAF table scaler
$AB = 16 bit # representing the current airflow
To make a "Max MAF Lock", you need to make $A9 and $AA both = FF. Now $AB should be set to FF00. (I haven't figured out yet why this is better than FFFF, but this is the value the factory programmers used.) After each Ref Pulse, the ROM code will calc the actual airflow or the dropped out airflow, if it occurs. Your code will change these numbers to 255 for as long as you want to.
$A9 is used to calc LV8, $AA is used to calc injector pw, and $AB is used alot but primarily by the ROM code that reads the MAF. (It needs to know if the airflow has increased or decreased.)
Now, (the answer to your question) the first place in the PROM code one of these is used is $3A03. This is the LV8 calculation. So, I would suggest putting your jump to the Max MAF routine before here. Or make the LV8 = FF in the same routine and put the jump in later. Just do it before the BLM code that starts at $3C46 and you should be okay.
Do you see why its not an easy question to anwer? Too many variables. Unless you're looking for some special condition to turn Max MAF on, you only need to set the numbers from one place in the program.
TurboGeezer
New Member
- Joined
- Jul 19, 2001
MAF Lock Locations............
Thanks Dennis,
I guess what I was really asking was: Where is the best place in the PROM code to begin replacing the MAF value in order to cover all of the bases?? You have answered that for me and I appreciate it.
TG
Thanks Dennis,
I guess what I was really asking was: Where is the best place in the PROM code to begin replacing the MAF value in order to cover all of the bases?? You have answered that for me and I appreciate it.
TG
turbobob924
Member
- Joined
- May 28, 2001
maybe this applies to my probom
turbobob924
Member
- Joined
- May 28, 2001
I have bad MAF drop/ noise/ interference that after tracing wires replacing connectors, MAF, ECM still persists.
I hate when that happens!!
Is this happening on the GN or the "transplant"? It sounds like you replaced the most likely causes and still no good. Strange. My first thought is check for good ground connection. The engine needs it and the ecm needs it for all the sensors.
Since you've already swapped ecm's I have to ask, do you have another chip you can try just for troubleshooting? Whenever things go crazy on my car, I switch back to the stock chip because I know it's dependable (I make my own chips and sometimes very strange things happen). You need another chip that you know is reliable.
Oh, and which scan tool are you using to show the maf dropout.
Is this happening on the GN or the "transplant"? It sounds like you replaced the most likely causes and still no good. Strange. My first thought is check for good ground connection. The engine needs it and the ecm needs it for all the sensors.
Since you've already swapped ecm's I have to ask, do you have another chip you can try just for troubleshooting? Whenever things go crazy on my car, I switch back to the stock chip because I know it's dependable (I make my own chips and sometimes very strange things happen). You need another chip that you know is reliable.
Oh, and which scan tool are you using to show the maf dropout.
turbobob924
Member
- Joined
- May 28, 2001
The MAF drop out happens in the mostly stock GN. I have a hacked up harness in my hybrid and never had any problems with the MAF!
I have had this problem with the stock chip and 30lb injectors and the MSD 50's and extender chip.
Thanks for you ideas and input!
\DS shows the bad drop out. Turbolink shows some but since there are less frames per second not as bad,
I just ordered a powerlogger and hope to get better data!
I have had this problem with the stock chip and 30lb injectors and the MSD 50's and extender chip.
Thanks for you ideas and input!
\DS shows the bad drop out. Turbolink shows some but since there are less frames per second not as bad,
I just ordered a powerlogger and hope to get better data!
If you are seeing this with an extender chip, then almost by definition it cannot be traditional maf dropout due to the stock maf outputting a frequency higher than the ecm can handle - the translator and extender chip combo take care of all that. Definitely start tracing and checking the power and ground to the maf/translator, and the signal wire to the ecm. Maybe you have a fusible link going bad, or a broken wire in the harness, or a broken wire at the ring terminals on the ground wires on the back of the passenger head - that last one happened to me and caused intermittent maf issues until I finally found it.
turbobob924
Member
- Joined
- May 28, 2001
Thanks for the ideas. I bought a ground strecher kit from caspers. I will install it this wekend.
I had already put a relay on the 12 power line to the maf and new ground to the frame and it does nto seem to have fixed it.
I had already put a relay on the 12 power line to the maf and new ground to the frame and it does nto seem to have fixed it.
turbobob924
Member
- Joined
- May 28, 2001
I put a relay on it in case I had intermittent 12 volts to the MAF.
.Truer, but the body is explicitly connected to the engine and used as ground for the dash and all lights, while the frame is not.
True Carl, BUT, and IMHO, the reason there are so many people having "funky" electrical issues is because they are grounding things to the body, and assuming the body to block ground is "good". In many cases it isn't. Or is less than ideal. Grounding to the frame is even worse!
It's always best to have a REAL GOOD method of grounding the body to the block. Large braded cables from body to block are one good method, there are many more.
turbobob924
Member
- Joined
- May 28, 2001
Im hooking you the ground stretcher kit and running the 12 volt source back to the battery. I'm going to run the MAF ground wire back to the ground stretcher kit.
