93-94 truck VAF to MAF conversion project (2 Viewers)

[landtank]

I am still proceeding under the assumption it will work.

This is the only way to roll with this kind of stuff. If it doesn't work you then analyze why and adapt.

My first try with the MAF housing worked but not all that well.

The second try was better but still not where it should have been.

The third one was the charm.

All totaled, about 5 months of work. So don't get discouraged if the first try is a dud.

 

[semlin]

i agree to a point with just trying it, but since we will not have the benefit pf real time obd2 feedback data I would be nervous about roadtesting. There is a potential for it to run very lean under load if the curve tracing the VAF's voltage response to airflow is much steeper than the MAF response as appears from the preliminary no-load data. We will hopefully get a CEL code to warn us before there is any engine damage, but I am also pretty sure you can cook one of these motors without throwing a CEL code.

the other risk is damaging the ECU with a PCB product/design/voltage error. As I said, I have a spare working 93 ECU and am willing to be the testbed for that reason. Eric, let me know your preference. I think one of us should put up a separate thread looking for a 97 in our areas and just temporarily cannibalize (assuming you agree there is no risk to the borrowed MAF from this test). I know of two 97s owner members in Bellingham who might be willing. maybe you and I could meet there and do it together?

if it appears to work at idle, I would say the safest course is to take it to a tuner shop and hook it up on a dyno and scope and then load test. Does anyone have a cheaper suggestion on how to test it to see what kind of stochiometric performance we get?

 

[landtank]

evaluating it will be tough. Just because the truck runs properly it doesn't mean it's optimized.

What I focused on was the Fuel trim. This basically tells you how close you are to ideal. But then you have to account for altitude as well as that influences the Fuel trim.

What I did was to determine what the Fuel trim was for the stock unit and then mimic it with the modded one.

I'm not sure how to retrieve that info from your ECM.

 

[semlin]

here is a good discussion from a mitsubishi tuner guy on a MAF conversion process with some discussion on doing it with obd1 vehicles. the ARC box adjusting the MAF signal is like a MAF translator, but also note the ARM LED monitor box for the o2 sensors monitoring rich or lean. there is also a discussion a fair ways down on obd1 that suggests the best way to track fuel trim may be a datalogger.

http://www.stealth316.com/2-arc2tuning.htm

 

[EricE]

What about an emissions test? Will that tell us what we need? Those are easy to get around here and reletively inexpensive.

 

[landtank]

I've been thinking about this and the best idea that I've come up with is to mount both unit's in tandem on a running engine.

Basically leave the stock VAF in place and wired into the ECM so the truck will run. Then cut into the air tube or more likely make a substitute tube that will allow the stock MAF to be inserted between the VAF and throttle body.

Now wire the MAF with 12v and ground and monitor the VAF and translated MAF signals with the engine running. This would allow you to also drive the vehicle and ensure similar output during load situations.

I'm heading out in a few minutes to pick up the MAF housings so my stock MAF will be available on Monday for shipping.

 

[EricE]

I've been thinking about this and the best idea that I've come up with is to mount both unit's in tandem on a running engine.

Basically leave the stock VAF in place and wired into the ECM so the truck will run. Then cut into the air tube or more likely make a substitute tube that will allow the stock MAF to be inserted between the VAF and throttle body.

Now wire the MAF with 12v and ground and monitor the VAF and translated MAF signals with the engine running. This would allow you to also drive the vehicle and ensure similar output during load situations.

I'm heading out in a few minutes to pick up the MAF housings so my stock MAF will be available on Monday for shipping.

What you suggest is possible with the exception that I/we have no way to log data while driving. I have no data logging period. So far, I have just set the truck at a certain RPM while parked and checked the V with a Digital Multi Meter (DMM). I have thought about some V meter interface to my CarComputer to allow me to log Voltages but I still wouldn't have RPM or anything since I don't have ODBII. No, whatever we do to test is going to have to be in the realm of an emissions test or Dyno or something with the MAF installed as the trucks meter.

 

[landtank]

With what i proposed all that would be needed is to watch two VOMs and make sure they read the same.

The VAF and MAF produce a voltage indicating a volume of air. It's the ECM which uses that in relation with the IAT to calculate lbs of air.

The IAT sensors between the two systems are the same, so if we get the VAF and MAF to indicate the same then it should be correct.

Remember, this is after you have the PCB built and installed so both readings should be identical.

 

[EricE]

With what i proposed all that would be needed is to watch two VOMs and make sure they read the same.

The VAF and MAF produce a voltage indicating a volume of air. It's the ECM which uses that in relation with the IAT to calculate lbs of air.

The IAT sensors between the two systems are the same, so if we get the VAF and MAF to indicate the same then it should be correct.

Remember, this is after you have the PCB built and installed so both readings should be identical.

True. Its an idea. Run three wires into the cab from the MAF and VAF. Common Grnd, sensor wire for MAF, sensor wire for VAF. One person drives while another takes the readings. If you insure you are at constant RPM when the readings are taken then you can compare. Even better is two DMMs and just watch/log the outputs.

 

[semlin]

we could put the VAF inline in a 97 with obd2 software and a laptop inside the cab and a volt meter on the VAF output. we could manually log the VAF voltage based on the ob2 displayed rpm on the laptop and then go back and compare the voltage output exactly. I do have a tentative donor 97 lined up.

the problem I see is that this still doesn't get us fuel trim info for the 93 and I think this is essential. it is highly unlikely the voltages will line up so what we really need to know is whether the 93/94 ecu can adapt to the new signal.

we have a 3 minute dino emissions test here running at speeds up to 60 mph, It costs $22 a time but the only data they give you is hc/nox/co emissions in g/km graphed in realtime against the speed of the vehicle. about all I can think of doing with that would be running a 97 through and then running a stock 93 through and then a converted 93 through using the 97 maf and comparing the three. you'd pick up obvious problems with running lean with nox emission spikes.

 

[landtank]

the problem I see is that this still doesn't get us fuel trim info for the 93 and I think this is essential. it is highly unlikely the voltages will line up so what we really need to know is whether the 93/94 ecu can adapt to the new signal.

It doesn't give fuel trim but I don't think it matters. As long as that when the MAF signal is translated it's indicating the same value for a given air flow the ECM should respond in the same way. We just need to be conscience of the fact that the MAF will be more accurate at the extremes and try to avoid duplicating those errors.

 

[landtank]

we could put the VAF inline in a 97 with obd2 software and a laptop inside the cab and a volt meter on the VAF output. we could manually log the VAF voltage based on the ob2 displayed rpm on the laptop and then go back and compare the voltage output exactly. I do have a tentative donor 97 lined up.

This might be a better first step. This will show us where and by how much the VAF is off. The best candidate might be my modded MAF as it has the broadest range of accuracy.

 

[semlin]

edit: responding to the idea of mapping the voltages one way or the other.

ok, well if you are still holding out hope the vaf and maf signals match that makes sense. my own view from the data we have so far is that the voltage signal will not match. we have two choices then: one, build another box to tweak the MAF signal; or two, see if the ECU can adapt to the different signal without any help. my thought is we are already at the stage of making this decision and the second approach is the one we should try first.

however, if we do still want to test the voltages under load, your idea is very sound and the only tweak i propose is to run the test twice, reversing the meters each time, to allow for equipment differences.

 

[vt92]

Very interesting thread. Has anyone successfully tried this mod on a Toyota Pickup w/ the 22RE? I didn't see any references to the conversion in the pickup forum.

 

[landtank]

I'm still processing this info and the one thing that has me concerned is that we are working with 13 year old VAFs. We don't know how much the ECM is already compensating for age. So if we evaluate the two how do we decern from an expected varience and one from age?

 

[knorrena]

Could you not reset the ecu (remove fuse) and use a scanner to track its trims over a period of time? A plot of this would be insightful I think.

Karl

 

[EricE]

I soldered up the converter last night. Initial tests are positive but I had no way to generate variable voltages so I could make some kind of line graph. Next I'll hook it onto my VAF and use the VAFs output to generate the different voltages so I can plot in-V v.s. out-V. I probably won't get to this untill after this weekend as I am getting ready for a camping trip. The boundry conditions certainly tested well though. 5V in = .02V out. 0V in = 4.98V out. 2.5V in = 2.5V out. The .02 is a limitation of the op-amp I used but I doubt that will cause any harm.

 

[semlin]

eric that sounds great. do you plan to remove the vaf and manually move the measuring plate or are you going to hook up the box in parallel to the working ecu?

 

[EricE]

eric that sounds great. do you plan to remove the vaf and manually move the measuring plate or are you going to hook up the box in parallel to the working ecu?

Well, I had just planned on tapping into the VAF wires (Ill need to do this at some point anyway) and using the installed VAF signals for the converter testing. But if the VAF will operate with just the ignition on and engine off then I'll do that as it would be much easier. good thought.

 

[semlin]

yup look back in this thread at the fsm excerpts i posted. one shows measuring plate open/closed measurement voltages. Incidentily, I am assuming you know to be very careful with the big rubber intake hose to avoid cracking it and with the VAF connector wire spring, particularly as we'll be doing this a lot. I usually disconnect the airfilter box cover then loosen the hose at the throttle body and pop it off.