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R34 Maf Voltage Issue

debusan

By debusan,
in Engines & Forced Induction

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debusan Explorer

debusan

Posted
Posted

Hello,

Back in November I took my car to the tuner.

I am running a power-FC on a 1998 r34 GT-T RB25DET NEO

550 injectors

GT-RS turbine

poncams

Z32 MAF

The car came back but has had issues running very rich (10.0) when cold to 50 Celcius

Once warmed up around 80C the car runs fine (idle 14.7) except that when you punch the gas it studders then engages.

I took the car back to the tuner and he says that it is having an issue he has never seen before. On the data logger when you push the throttle there is a momentary drop in AFM voltage then it raises as it should.

The MAF is brand new and has been tested as fine in another vehicle. All of the other parts are also brand new. Also the engine was just rebuilt.

I went to pick up the car today from the tuner again because he can't seem to figure out the problem. He left me a note that said that he had noticed something. If the car is not turned on and you depress the peddle the AFM voltage and the throttle voltage rise together and at exactly the same value. It seems there may be a crossed wire somewhere or maybe it is supposed to be like that. He said to check the harness. I was wondering if anyone else has heard of a issue like this before. After the initial pause the engine runs fine. It is just the initial push that has problems. Thanks.

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https://www.sau.com.au/forums/topic/418113-r34-maf-voltage-issue/
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paulr33 Grand Master

paulr33

Posted
Posted

agree. MAFS-1 should not change when the car is off and you press the accel pedal

cant be too hard to trace the signal wire when it was spliced at the afm plug, this is where its likely to be wrong

NISMOGTT Collaborator

NISMOGTT

Posted
Posted

before you go looking at all the wiring... have you tried a brand new battery... reason for asking is if it has dropped a cell or 2 then there might not be enough amp's running though...

very simple thing to test and rule out before going to the effort of wire hunting... poor battery can lead to a lot of issues people dont consider...

NISMOGTT Collaborator

NISMOGTT

Posted
Posted

Yeah, but hard to imagine low battery voltage causing the signal from one sensor to appear on the wiring for another.

agreed.. but think about a bad battery and all the warnings a dash will show... i had a bad battery show the oil light, park brake and light bulb warning... replaced battery and all fixed...

as bad battery can show up random things and is a simple thing to check which requires minimal effort... even just leaving the battery on charge over night and check again in the morning... cost nothing to rule it out :)

debusan Explorer

debusan

Posted
  • Author
Posted (edited)

I ran new wires from the MAF directly in to the ECU ports for AIR signal and Signal ground. Same result. So it is not the wiring harness. Does anyone else have a Power-FC in a ER34 that can try this out. Turn the car to on but not engine running put the PFC into monitor mode for AFM and watch the voltage whilst pushing the gas pedal. Any help would be appreciated. Thanks for the replies.

Edited by debusan
debusan Explorer

debusan

Posted
  • Author
Posted

One other comment I would like to make is that my car is an AT/MT conversion. I am well aware that the AT harness has several pins that are not used by the MT or PFC ECU. But as far as I can tell from the wiring diagrams none of the pins in question are different between the AT and MT harness.

paulr33 Grand Master

paulr33

Posted
Posted

why are you using manual powerfc on auto car? you know its not supported right?

but anyway look at ETC, SENSOR SW CHECK and look at the values of MAFS-1 and TPS

do they both change at the same time?

debusan Explorer

debusan

Posted
  • Author
Posted

I do see your point though The AT harness is heaps different and getting a MT harness may un-screw lots of these problems I have attached a shoddy video to show the symptoms on the hand paddle. I appreciate your help

http://www.youtube.com/watch?v=vl7LBBoAFRU&feature=youtu.be

GTSBoy Grand Master

GTSBoy

Posted
Posted

FWIW, the fact that the car has been converted auto to manual shouldn't make any difference. You can run a manual engine with an auto ECU and vice versa. The car won't work well with a manual ecu in auto car because of lack of comms to the TCU, but that doesn't matter. What matters is that all sensors and outputs at the ECU that are involved in running the engine are same same.

It is entirely possible that you have a crossed wire, as we said earlier, or that your PFC has a severe problem. Can you swap in another PFC?

debusan Explorer

debusan

Posted
  • Author
Posted (edited)

Yesterday I tried hard wiring the MAF into the Power FC I had the same result that was with me running all new wires straight from the PFC to the MAF. I don't have another Power FC and its a 1000$ to get another one in there. But if I must buy one then that is the answer. The traction control unit has been disabled. and the valve removed. so it should not be an issue.

Edited by debusan
debusan Explorer

debusan

Posted
  • Author
Posted

So thanks to some info above I have uploaded a video of the PFC switch/test screen that shows the voltage issue in detail. I have a couple more things to check but I am starting to think that the PFC is the culprit as it is the only used part I installed in this car. Guess I need to fork over some cash then.

http://www.youtube.com/watch?v=H31n2YUQjyc&feature=youtu.be

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