Not to worry, if this works we will need to replace that hose anyway (with a '95 version). hehe. but yeah, I disconnect it both sides when I do anything with the air cleaner or VAF.
93-94 truck VAF to MAF conversion project (1 Viewer)
- Thread starter semlin
- Start date
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Not to worry, if this works we will need to replace that hose anyway (with a '95 version). hehe. but yeah, I disconnect it both sides when I do anything with the air cleaner or VAF.
I actually got my own MAF installed on my own truck this Sunday. Let me know where to mail out my stock unit.
Rick
Rick
I'll be the guinea pig. I'll be ready to test with the MAF in about a week.
Good to see this is still moving along, but I thought this was suggested already in post #4 and #14. Oh well, I guess.
I'll need an address to get that MAF out to you.
MAF
Not sure if this of intrest but HKS used to sell a kit for the MR2 turbo )vane presure converter and fuel cut defenser) Replaces the toyota VAF with their own MAP sensor.
Not sure if this of intrest but HKS used to sell a kit for the MR2 turbo )vane presure converter and fuel cut defenser) Replaces the toyota VAF with their own MAP sensor.
I tried to further test the converter over the weekend. I wanted to use the output of the VAF as a method to obtain variable voltages between 0 and 5V. What I found is if I turned on the ignition (car off) and moved the VAF from resting (closed) then the fuel pump would kick on and pump fuel into my cylinders. Any fuse I pulled to try and stop that also cut the voltage to the VAF. If anyone knows of a way to make that work w/o pumping fuel (and w/o removing the rear seats to get at the fuel pump) then let me know.
I guess the next step would be to rig the VAF and MAF in tandom with both in the system (truck running off VAF) and test the output of the VAF and MAF together. I only had a little time to look at doing that and it looks like the plumbing is going to be difficult. I’ll work something out, I just need to spend more time at it.
I guess the next step would be to rig the VAF and MAF in tandom with both in the system (truck running off VAF) and test the output of the VAF and MAF together. I only had a little time to look at doing that and it looks like the plumbing is going to be difficult. I’ll work something out, I just need to spend more time at it.
I tried pulling 5 different fuses/links. Every one of them would kill the fuel pump but would also kill the power to the VAF. Supplying power and ground to the VAF would certainly do it and I might just end up going that route.
I did some testing side by side last night. The truck was rigged to run off the VAF as normal. I used dryer hose and ducted the stock MAF in between the VAF and the intake. The MAF was then wired with power, grounds, THA (from the truck). The output of the MAF went into the converter and I measured output from the converter at the same time I measured VAF output. The result is here:
The MAF reading at 3000rpm is completely wacky but I didn’t have time to explore it. I also failed to take a reading of the unconverted MAF at that point so I don’t know if it was the MAF itself giving a weird reading or the converter. I was completely downheartened after doing the tests but upon reviewing the chart today I am less so. IF I can figure out what caused the anomalous reading at 3K rpm and fix it then the graph looks fine. I say that because I SHOULD be able to add a resistor or two to the design and linearly reduce all output of the converter by 1.5 Volts. If that is done then the plots almost completely overlap (assuming I can fix the one at 3K rpm).
I intended to do testing first w/o the THA wired up. Long story short I had the MAF wired backwards and spent a long time trying to figure that out. By the time I discovered that and corrected it I had also connected THA to the truck to see if that solved my problem. So note that the THA was also connected to the VAF. I took no measurements from the THA to see if it varied over time or was a constant signal (eg. +5 or grnd or +12 etc). If it was a constant signal then it wouldn’t cause any problems with my MAF readings. But if it varies over time and if that is driven by the VAF then it could cause wacky readings from my MAF if the MAF uses it as a point of reference. That is what I need to test next time when I try it again.
It took me 3-4 hrs to do all this because the ducting takes considerable time to get right and sealed. I am not looking forward to doing it again but it looks like that is what is needed to figure out the 3K rpm reading.
The MAF reading at 3000rpm is completely wacky but I didn’t have time to explore it. I also failed to take a reading of the unconverted MAF at that point so I don’t know if it was the MAF itself giving a weird reading or the converter. I was completely downheartened after doing the tests but upon reviewing the chart today I am less so. IF I can figure out what caused the anomalous reading at 3K rpm and fix it then the graph looks fine. I say that because I SHOULD be able to add a resistor or two to the design and linearly reduce all output of the converter by 1.5 Volts. If that is done then the plots almost completely overlap (assuming I can fix the one at 3K rpm).
I intended to do testing first w/o the THA wired up. Long story short I had the MAF wired backwards and spent a long time trying to figure that out. By the time I discovered that and corrected it I had also connected THA to the truck to see if that solved my problem. So note that the THA was also connected to the VAF. I took no measurements from the THA to see if it varied over time or was a constant signal (eg. +5 or grnd or +12 etc). If it was a constant signal then it wouldn’t cause any problems with my MAF readings. But if it varies over time and if that is driven by the VAF then it could cause wacky readings from my MAF if the MAF uses it as a point of reference. That is what I need to test next time when I try it again.
It took me 3-4 hrs to do all this because the ducting takes considerable time to get right and sealed. I am not looking forward to doing it again but it looks like that is what is needed to figure out the 3K rpm reading.
I think I am going to give up on this project. Both because the technical hurdles are mounting but also because my truck is running excellent and I don’t really need the performance boost anymore. After doing the HG, O2 sensors, and timing mod my truck is running superb…better than it ever has. I am happy with its performance right now. Also the converter is getting more complicated. I did try and bring the output voltage down by means of a voltage divider but it is not perfect. I was able to match the first two data points exactly but as the voltage went down (RPMs increased) the two paths (real VAF v.s. converted MAF) diverged a bit. So, to do it right we would really need to go the more complicated route of using a PIC (micro computer) to do the conversion. As such the converter gets much more complicated. Not only because the cost of parts goes from $1 to $10 but also because one then has to write code to handle all the ADC and DAC. Totally doable but much more difficult.
semlin
curmudgeon
- Thread starter
- #95
eric,
did you figure out the 3000 rpm surge?
let's not give up yet. but for the 3000 rpm issue you may actually already be there notwithstanding the voltage adjustment doesn't track all the way. I am quite skeptical about a varying voltage adjustment when we don't electronically understand why this divergance occurs. It could just be that the VAF is less accurate at reading higher air flow, especially as it gets older. the knock on the VAF system has always been a tendency to let the motor run lean at high rpm. my take would be to make the adjustment at say 1500 rpm and then run the truck and see if it runs lean or rich and adjust the adjustment accordingly.
if you are definitely out but willing to send me your test materials, I would be willing to take it from here (assumign landtank will lend me his maf as well). My plan would be to try to resolve the 3000rpm surge issue then run the system with the maf and the voltage converter at a fixed adjustment installed at a shop hooked up to sensors to get some stochiometric readings. I'd like to see how the motor is actually performing. If it looks good then I would splice an a/f meter into the o2 sensors and road test the maf. I would maybe come back to you for wiring advice from time to time if you were willing...
incidentally my truck also ran great after the h/g and the same mods other than non stock timing, and still does. The motivating factors for me are fuel economy, slightly more power and the possibility of adding a blower without running lean. i still see this as a worthwhile mod and it would seem there are some out there who would agree given the number who have purchased landtank's maf mod even though their trucks already had better airflow mapping than our 93/94s.
did you figure out the 3000 rpm surge?
let's not give up yet. but for the 3000 rpm issue you may actually already be there notwithstanding the voltage adjustment doesn't track all the way. I am quite skeptical about a varying voltage adjustment when we don't electronically understand why this divergance occurs. It could just be that the VAF is less accurate at reading higher air flow, especially as it gets older. the knock on the VAF system has always been a tendency to let the motor run lean at high rpm. my take would be to make the adjustment at say 1500 rpm and then run the truck and see if it runs lean or rich and adjust the adjustment accordingly.
if you are definitely out but willing to send me your test materials, I would be willing to take it from here (assumign landtank will lend me his maf as well). My plan would be to try to resolve the 3000rpm surge issue then run the system with the maf and the voltage converter at a fixed adjustment installed at a shop hooked up to sensors to get some stochiometric readings. I'd like to see how the motor is actually performing. If it looks good then I would splice an a/f meter into the o2 sensors and road test the maf. I would maybe come back to you for wiring advice from time to time if you were willing...
incidentally my truck also ran great after the h/g and the same mods other than non stock timing, and still does. The motivating factors for me are fuel economy, slightly more power and the possibility of adding a blower without running lean. i still see this as a worthwhile mod and it would seem there are some out there who would agree given the number who have purchased landtank's maf mod even though their trucks already had better airflow mapping than our 93/94s.
I am willing to hand over the reigns to you. Assuming Landtank will lend you the MAF, I can send you that along with my converter. I modified the converter on paper (to bring the voltage output down 1.5V) but I can do it for real before I send it to you.
I never did resolve the wild reading at 3000RPM.
I never did resolve the wild reading at 3000RPM.
do what you want with my MAF. I don't need it any more.
Keep me/us in the loop. I MAY be able to get some expert help on this. I will talk to our ECU programmers this week and bring hime the charts and numbers.
BTW I'm sure you guys already know this but the VAF system is supposed to be a Bosch made system. Not sure if that helps the research or not.
BTW I'm sure you guys already know this but the VAF system is supposed to be a Bosch made system. Not sure if that helps the research or not.
