oldred95

I drive a 95 chevy C1500 yadda yadda 350 TBI and 4L60E. I've been talking to Fast305 about it as he is running a MAF but with a 700R4 and he's had great results. He said the only concern is that the PCM may not be able to process all the data coming in all at once. I've yet to even begin building the air intake system for it but I'm thinking it will be a cadillac bonnet on top of the throttle body, then a 4 inch chrome stack (cheapest route for a chrome finish) to cut up and use for the pipe, some silicone rubber couplings, a 5.3 liter MAF and a vortec 350 air filter for a full size truck and a heat deflector type deal to keep the heat away from the filter. Anyway what I'm wanting to know is more then likely I'll be at college or on at home for the weekend when I end up switching over to the MAF and I'm just concerned it may not work. This is my only mode of transportation so it has to work or be reversible incase it doesn't. And if it does work will it be drivable until I figure out how to get it tuned?


Also is there any way to bench test a MAF? I picked one up at work that is questionable and I put power and ground to the proper pins (I've got the pinout if anyone needs it) and hooked the DVOM to the MAF signal wire and it was putting out 10 volts regaurdless with no air, and with air moving through the sensor. 10 volts seems way too high for a signal but then again this is all new to me. What kind of reading should I be looking for?

dimented24x7

iTrader: (2)

I have code that should both run the MAF and 4L60-E. I made some changes to reduce the total ammount of code thats run for the MAF, so there should be enough time for both. I gave it to fast for testing. Once his time permits and he tests it to make sure it works as advertised, you could then make the change over. If you should happen to run into issues, reversing it would be a matter of loading the stock calibration on and moving a few pins. In addition to adding the MAF, you will also have to tap ahead of your VSS buffer box. The MAF takes the normal VSS input as its output is the same as the buffer box. This allows it to be plug and play. Since this displaces the transmission output speed input, the transmission output shaft speed sensor then needs to be inputted directly to pins F4/F5 if I recall correctly. That input is set up to take the VSS pickup in directly. I have the PCM wired up this way on my TKO so I can have the MPH in my datalogs. Just plug the pickup into those two pins and the PCM does the rest.

Also, the MAFs output is a switching transistor that switches between 180-12,000 Hz. This grounds a pulldown resistor in the PCM, making a 0/5V square wave that triggers the pulse counters/timers. You wont see a voltage with a DVM. The voltage may just be currents traveling around the DVM and internal MAF circuitry, which could possibly damage it. The only true way to verify its working is to plug it into the PCM when you go to make the change over. Youll see the MAF frequency in the ALDL data when using the ADS file for the MAF PCM calibration. Itll typically be around 2.5-3 kHz at idle, 180 Hz engine off.

If you want to bench test it, get a 10 kOhm resistor and a 5V DC power source with a common ground to your 12V DC power source. Hook the resistor to the +5V lead and the other end of the resistor to the MAF input as shown in the schematic below. Once the MAF has +12 VDC power, the MAF will ground the resistor intermittently to make a pulse train. If your DVM has a frequency counter, put one probe on the MAF frequency pin and the other on the gorund. Youll see a variable frequency there as air moves through the MAF.

oldred95

Chris explained it to me the other night now the basic system works. It took a while to figure out the VSSB's role in this. The VSS is directly wired to the TSS pin in the PCM as the TSS pin reads an AC signal which the VSS produces. The VSSB is then used to convert the DC MAF signal to an AC signal that the PCM can then read. I believe thats how it went. As far as the PCM having enough processing power Chris is converting to MPFI and also intends to keep the MAF and switch to a 4L60E and he doesn't think it will be a problem but I don't want to be the ginny pig and be left stranded.

Awww crap, sorry, I hit the damn edit button instead of the quote button next to it. My bad.

dimented24x7

iTrader: (2)

Now for the correct button...

The TIS isnt going to be used. The current TOS is used for the MAF, while the alternate TOS input that accepts AC signals will be used for the TOS. Also, the MAF code isnt currently set up for MPFI. Id have to add additional logic in the DRP interrupt routine to handle batch fire as well as the TBI firing. Currently the software just does the standard ping-pong/80 Hz async.

Chris: Its not a huge ordeal to add in the MPFI, but if possible, the 4L60-E stuff should be tested first before attacking the MFPI side of things.