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I almost finished the single turbo upgrade (SP57 kit with 720cc fuel system) on a friends car, BUT I'm having problems with the VPC (well I think it's the VPC). The main computer keeps on throwing engine code 31 (Air flow meter error). So I assume the VPC is not doing it's job correctly. Now i've wired it up like the article 'how to hard wire the VPC'. Only four wires and a resistor, easy we all say. Well, I've even asked a friend if he could check it, no wiring problems. So my main question: How do you 'measure' or something if the VPC is actually doing what it should do? I see all kinds of blinking leds on the front. Anyone knows what this is? Anyone know how to 'debug' this situation?

thnx
 
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It is not uncommon for this to occur. Try resetting the ecu if that doesn't work don't worry about it. Its just one of the quirks of changing a car from mass air to speed density.
 

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We have checked and double checked every connection and everything is as it should be according to the article on www.mkiv.com. We still keep the Error 31 Code and adjusting the VPC knobs does not have any effect on the engine behaviour.

The ROM chip has a sticker on it that says JZA80 18B, is this correct?

Should we perhaps try a different value resistor other than 1200Ohm? We measured the stock MAF and it came out 2000Ohm.

We are pretty baffled what to do. We even checked the output of the VPC and this varies with rpm so we think the VPC is fine.

Are we forgetting a wire we should cut or solder?

Flavio
 

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Should we drive the car around before the Error Code 31 disappears or should it not come up at all if everything is working as it should? We have not driven the car, we only started the car in the garage.

Flavio
 
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I had this same problem. I didn't have the resistor correctly installed across the pins on the MAF connector. Make sure the resistor is connected into the contacts properly.

Looking at the pins of the MAF connector with the rectangle notch facing up, the resistor goes into the second and third contacts from the right.
 

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stoker6 said:
I had this same problem. I didn't have the resistor correctly installed across the pins on the MAF connector. Make sure the resistor is connected into the contacts properly.

Looking at the pins of the MAF connector with the rectangle notch facing up, the resistor goes into the second and third contacts from the right.
It is fitted correctly, we have even measured the resistance with a multimeter and it is 1200Ohm.

Flavio
 

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Discussion Starter #10
I've done some extra detail testing on the setup. We tested all pins of the Eprom, they are all ok. Every pin of the eprom makes contact with the VPC.
I've done a sensor check on the pressure sensor. The voltage is ok and it varies with the manifold pressure. Same goes for the yellow wire which goes to the JZA8 ECU. It varies when we rev the car a little.
Any suggestions what I can check more? I don't have a spare VPC or chip here, that's the whole problem. Otherwise it would be cool to check with a different unit.
 
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Hook up the MAF sensor to the connector and see if it goes away. Did you try that?
 

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stoker6 said:
Hook up the MAF sensor to the connector and see if it goes away. Did you try that?
You mean only hooking up or putting it in the air flow as well? This is kinda undoable as the single turbo kit has no space allocated for the MAF.
I can hook it back up no problem but some wires are cut for the extra resistor and the VPC. I don't see why it should work. What is your exact suggestion?
 
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Sorry for the confusion. I did not mean to un-do the VPC. Just hook up the MAF sensor to the conector. This will check your resistive connection that is supposed to simulate the MAF sensor. I just have a feeling that the resistor isn't doing the job it is supposed to. The ECU is sensing no MAF sensor and is spitting out the code. It is a very quick/easy check. Couldn't hurt.

Did you install the resistor at the MAF sensor connector or at the ECU harness?
 

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Unplug the ECU harness and replug it in, I have seen several cases of the actual harness not making good contact on all connectors. This causes all kinds of funny things to happen.
 

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If we can't solve this VPC problem I am thinking of getting rid of the VPC and GCC and using the stock MAF in a blow through setup. Will this have any drawbacks in my situation (SP57 with fuel, hoping for 580rwhp)?

Flavio
 

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Flavio said:
If we can't solve this VPC problem I am thinking of getting rid of the VPC and GCC and using the stock MAF in a blow through setup. Will this have any drawbacks in my situation (SP57 with fuel, hoping for 580rwhp)?

Flavio
Not a bad idea, works for the RX7 TII, unfortunately the Supra's MAF measures what is called a "swirl frequency" rather a WOT (wide open throttle) condition. I guess you could try it? But first try this....
Going off what I've read it seems that your VPC was originally for the previous generation. I take it that you've changed the chip using the JZA80 18B which is correct for your single turbo and all your wiring is correct. (I would still recommend the using the HKS Harness) If you open the VPC controller you will see two sets of (4) switches. Each set has "ON" and "SD" labled on the top row and "1 2 3 4" on the bottom. Starting on the first set of (4) switches closest to the edge.... 1-dn, 2-up, 3-dn, 4-up.
The second set....1-dn, 2-dn, 3-dn, 4-dn.I believe these are the settings for the MKIV TT Supra. Call HKS to verify these settings if that doesn't help. Good Luck
 

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Can't believe this people. Today I did some more debugger. First of all the dipswitched are set correctly, the connections are good etc.etc. We've all checked that.
I removed the resistor that was hardwired to the MAF harness and put the stock MAF back in. I reset the ECU and then checked for codes. First the check engine light was blinking as in "no errors logged" then it started to blink code '31'. MAF error. So even without starting the car, and using the resistor of the MAF I already got a check engine error!
Then I wired the MAF wire back to the ECU (it was connected to the VPC) and checked the codes. No check engine code. Not possible to start the car of course, as the MAF was not in the airflow. But anyways, it was obviously not the wiring, or the main ECU. Problem must be in the VPC.
Last thing I checked was the voltage on the MAF wire. The stock MAF came with something between 0.5 and 0.7 volt, while the output of the VPC (yellow wire) was 7 volts!!!! This was with the car not running, only the keyswitch on 'ON'.
Only question I got left now is, anyone know the range of the MAF signal? What is 'normal' and what's not?
 

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I can't remember for sure, but I thought the MAF only went 0-5V. 7V out of the VPC sounds very suspicious... Sorry I can't be of more help.....

You could check to see if the VPC voltage goes down when you apply vacuum to the sensor or heat the temp sensor.
 

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Seems like a new Rom fitted today solved our problems. Tomorrow we're going for the test drive!
 

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choritsu-shi said:
Not a bad idea, works for the RX7 TII, unfortunately the Supra's MAF measures what is called a "swirl frequency" rather a WOT (wide open throttle) condition. I guess you could try it? But first try this....
The Supra TT's MAF is a hot-wire type, which measures the mass of air by ajusting the voltage needed to keep a Pt wire a certain temp. Your probably thinking of a Karman-vortex MAF which is used by the NA Supra and other cars.

One person has converted their stock MAF to blowthrough, I think without any problems or other changes needed. If you do this, be sure that no oil will get on the MAF, from the PCV system or turbo seals.
 
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