What effect will running an EPROM chip for a MAFT have on a stock MAF car??

[90 GSX]

A while back when I had only limited knowledge of DSM cars I replaced my bad 90 ECU with 91 EPROM ECU that was already socketed and chipped. I did all the wiring fixes and the coil pack and gauge cluster and all of that... The good thing about the chip was that it was tuned for the 550cc injectors that I am running. However, the sticker on the chip says "Dual Image 550cc MAFT." Before I say why I am asking this question, please give me your take on what would happen given those variables. Thanks.

 

[steve]

Depends on how the MAFT code was done. Some guys lock the temp and barometric pressure variables in the ECU since the MAFT doesn't use them. Running a stock MAF that way will lead to tuning problems when the outside temps change.

The chip looks like it was custom for somebody's setup and is of questionable value to anybody else. You'll save yourself a lot of problems by replacing it unless you want to go through it and figure out all the differences.

Steve

 

[90 GSX]

Thanks for the answer steve. I guess generally a MAFT tune is the same as a stock MAF but in my case, I have found something peculiar. My car runs lean at basically all times. My o2 voltage at WOT is around 0.80-0.82 and of course some knock accompanies that because it's so lean. I just realized that my barometer reading is frozen at 1.00 bar (I saw it at 0.99 bar last night but it was at 1.00 bar today). Does it generally sit around that value or has it been locked in the computer by the EPROM??? I'm assuming this is the source of my problems since everything on my car is super tight and done right.

 

[steve]

I just realized that my barometer reading is frozen at 1.00 bar (I saw it at 0.99 bar last night but it was at 1.00 bar today). Does it generally sit around that value or has it been locked in the computer by the EPROM?

If it was unlocked it would track the changed in outside barometric pressure. I set MMCd to English units so what I see is 14.something and sometimes into the 13s when a storm is coming. Also watch your intake air temps. Those will change pretty quickly once your car starts to warm up.


Check your fuel trims to see how lean or rich the ECU thinks things are in closed loop.

Steve

 

[90 GSX]

The air temperature moves around as the car warms up. The barometer stays at 1.00 bar, I have seen it at 0.99 bar as well. Not sure if that tells you anything...

However, the car does run quite lean. Trims are all between 110-120% depending on where I'm doing most of my driving. The car has absolutely not a single boost leak, I mean I literally set this thing up perfectly and went through it with a fine tooth comb. Why would it be so lean?

 

[imdrax]

I didn't want to start a brand new thread with the same exact question so i popped this one back to life. Trying to tune a friend's 93 AWD and we just picked up an EPROM with a chip for 750cc's, MAFT "2x KARMAN TO LOG DOUBLE HZ""%30 expanded custom timing maps for 93 octane", and the IAT and BARO have been locked. If we are running 750's with a 2g mas is it even going to be possible to tune the car? Also can someone explain to me the 2x hertz and what it does and %30 expanded timing map?

 

[tkelly27]

In stock configuration the ECU only looks at ~1500hz. When you double this, you get twice the airflow capabilities. The timing maps sound like they have been adjusted for this extended hz reading, as timing is based off of RPM and airflow.

If the chips have the IAT and BARO locked to a certain value I doubt the MAS will read properly. The Karman vortex style mass air sensors require these other two sensors. The hotwire GM unit does not, and this is typically locked with a signal from the MAFT to the ECU. Sounds like they setup the chip so it would require less wiring from the MAFT.

 

[imdrax]

Thanks for the reply, By looking at the keydiver site i was able to answer some of my questions, but i am still confused on what exactly the 2g MAS or ECU will do with a locked BARO reading? What exactly does the ecu or maf use the BARO reading to adjust? Does it use BARO to fine tune fuel for changes in atmospheric pressure such as a rise in elevation? The OP mentioned his BARO was solid at 1 bar so if i live at sea level (which i do) does that mean as long as we are not pushing the car 100% at different altitudes or extremely cold nights we should be ok? Not really trying to spend 100 on a new chip just to modify one setting. One last question would be that if the since the 2g mas flows about 20% more air and the chip is set up for just a MAFT does that mean i would still need to compensate for that extra airflow by starting my afc settings around +20?

 

[steve]

In stock configuration the ECU only looks at ~1500hz. When you double this, you get twice the airflow capabilities. The timing maps sound like they have been adjusted for this extended hz reading, as timing is based off of RPM and airflow.

The ECU keeps track of a lot more airflow that that. The issue is that the datalogging interface uses 8 bit values and the way the MAF HZ is stored caps the value at 1606HZ. The 2X option just doubles the range of the airflow that can be reported, the actual airflow capability is untouched.

If the chips have the IAT and BARO locked to a certain value I doubt the MAS will read properly. The Karman vortex style mass air sensors require these other two sensors. The hotwire GM unit does not, and this is typically locked with a signal from the MAFT to the ECU. Sounds like they setup the chip so it would require less wiring from the MAFT.

The MAFT always sends its fixed IAT and Barometric pressure values to the ECU. Some MAFT chips will free up these two for other analog inputs and program constants (lock them) for the values instead of reading them.

 

[imdrax]

The MAFT always sends its fixed IAT and Barometric pressure values to the ECU. Some MAFT chips will free up these two for other analog inputs and program constants (lock them) for the values instead of reading them.

Great, but what does that mean in terms of me running a 2g MAS with these values locked? Does it mean the 2g mas will be sending the IAT and BARO readings to the ecu but the ecu will just be "ignoring" them and just use the locked values? If so what does the ecu use these values to make adjustments for? Im only trying to figure out if by having the values locked is going to cause me major headaches trying to tune the car.

 

[steve]

Depends on the chip. Like I said not all MAFT chips ignore the two incoming signals.

If your chip does then your going to have a problem because with a real MAF you need to know the actual pressure and temp to calculate air density so that the volume measurement that the MAF makes can be converted to air mass for the fueling calculations.

If you bought the chip from Jeff he will tell you if the inputs are ignored to make then available for logging other things. If you didn't then your on your own.