semlin
curmudgeon
Ok this is a spinoff from Landtank's MAF conversion thread. I had given up on this as an option and gone back to my obd2 conversion idea but recent events have made this option look feasible.
I have been chatting with Landtank for a while about adapting his MAF system to plug and play replace the 93-94 VAF system. The possible advantages would be a smoother throttle response, smoother idle (dispensing with the FPR vacuum assist), better airflow control and perhaps overcoming the tendency of 93-94s to run lean at w-o-t, especially with a supercharger and, in a perfect world, mileage and horsepower gains from better airflow along the lines that Landtank is projecting for his system. Basically, if it works, you are replacing a 1992 technology mechanical vane system with a 2005 hotwire system. The only limitation would be how responsive the older obd1 ecu, o2 sensors, injectors and TPS would be to the newer technology. That's what you call a "known unknown". I am optimistic based on the fact the obd1 and obd2 ecus in the old supras are basically plug and play (they both use a karman vortex air flow meter). The only significant difference I know of is that the obd1 system has left and right trim on the injectors each controlled by the two upstream o2 sensors.
EricE, who will hopefully chime in, also has a 93-94, and is game to help and make a voltage converter. Which is good because I had pretty much given up on this without him.
the basic technical problems are:
1. according to the FSM the voltage signal on a VAF is 5 to 0v not 0 to 5v as with the MAF
2. we don't know for sure the signal is linear or might have a curve that differs between systems. We strongly suspect it is linear.
3. we don't know if the voltage to airflow scale is the same for the vaf and maf. we do want to test this as best we can.
4. we don't know if the obd1 ecu is dumbed down for low airflow signals because the vaf is not reliable at low airf flow such as idle (the vacuum line on the 93 FPR compensates for this deficiency). Again, we want to test this.
the plan is:
1. verify the voltage signal at various common rpm for a VAF and MAF truck to see if the scale is similar or not. If the scale is different a MAF translator inline between the MAF and voltage converter will be needed (we haven't yet looked over the FSM but any suggestions on how to get that voltage reading easily are appreciated)
2. fabricate a circuit board to convert the voltage signal from a MAF from 0-5v to 5-0v so the OBD1 ECU can read it. This will plug inline between the MAF and the ECU.
3. testbed a stock 97 MAF on a 93 truck. Luckily I have an early 93 ECU spare with the 83,84,85 code that can be fried.
4. if that works look to a variation on landtank's system that will bolt on a 93/94 and be plug and play. I say a variation because I believe there are variations in the OD of the VAF and MAF tubes that will impact on hose fitment.
At this point our main limiting factor is the lack of a participating 95-97 truck near to me in Vancouver or Eric in Seattle. If we had that, we could temporarily cannibilize the MAF to run the tests on the 93 and also figure out any mounting/connection issues we are going to face replacing the VAF with a MAF designed to fit the 95-97 system.
I have been chatting with Landtank for a while about adapting his MAF system to plug and play replace the 93-94 VAF system. The possible advantages would be a smoother throttle response, smoother idle (dispensing with the FPR vacuum assist), better airflow control and perhaps overcoming the tendency of 93-94s to run lean at w-o-t, especially with a supercharger and, in a perfect world, mileage and horsepower gains from better airflow along the lines that Landtank is projecting for his system. Basically, if it works, you are replacing a 1992 technology mechanical vane system with a 2005 hotwire system. The only limitation would be how responsive the older obd1 ecu, o2 sensors, injectors and TPS would be to the newer technology. That's what you call a "known unknown". I am optimistic based on the fact the obd1 and obd2 ecus in the old supras are basically plug and play (they both use a karman vortex air flow meter). The only significant difference I know of is that the obd1 system has left and right trim on the injectors each controlled by the two upstream o2 sensors.
EricE, who will hopefully chime in, also has a 93-94, and is game to help and make a voltage converter. Which is good because I had pretty much given up on this without him.
the basic technical problems are:
1. according to the FSM the voltage signal on a VAF is 5 to 0v not 0 to 5v as with the MAF
2. we don't know for sure the signal is linear or might have a curve that differs between systems. We strongly suspect it is linear.
3. we don't know if the voltage to airflow scale is the same for the vaf and maf. we do want to test this as best we can.
4. we don't know if the obd1 ecu is dumbed down for low airflow signals because the vaf is not reliable at low airf flow such as idle (the vacuum line on the 93 FPR compensates for this deficiency). Again, we want to test this.
the plan is:
1. verify the voltage signal at various common rpm for a VAF and MAF truck to see if the scale is similar or not. If the scale is different a MAF translator inline between the MAF and voltage converter will be needed (we haven't yet looked over the FSM but any suggestions on how to get that voltage reading easily are appreciated)
2. fabricate a circuit board to convert the voltage signal from a MAF from 0-5v to 5-0v so the OBD1 ECU can read it. This will plug inline between the MAF and the ECU.
3. testbed a stock 97 MAF on a 93 truck. Luckily I have an early 93 ECU spare with the 83,84,85 code that can be fried.
4. if that works look to a variation on landtank's system that will bolt on a 93/94 and be plug and play. I say a variation because I believe there are variations in the OD of the VAF and MAF tubes that will impact on hose fitment.
At this point our main limiting factor is the lack of a participating 95-97 truck near to me in Vancouver or Eric in Seattle. If we had that, we could temporarily cannibilize the MAF to run the tests on the 93 and also figure out any mounting/connection issues we are going to face replacing the VAF with a MAF designed to fit the 95-97 system.