Jump to content
SAU Community

Recommended Posts

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.

Link to comment
https://www.sau.com.au/forums/topic/418113-r34-maf-voltage-issue/
Share on other sites

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

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...

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 :)

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

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.

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?

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

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?

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

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

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Had a go at the stuck crush tube this afternoon. Tried things like grips and a chain wrench first but wouldn't just twist straight off. So got to work with a drill. Started small and kept a depth stop on to make sure I didn't drill into the bolt. Made a line of drill holes all the way up and enlarged them. Then a combination of chisel and Dremel to split it all the way up. Levered the split to get oil in there and eventually it gave a bit while levering. Worked it back and forth with loads more oil till it was spinning freely, then with grips I could work it downwards and off. And no significant damage to the bolt (not by me anyway - just the 27 years of rust)
    • Well, I'm tired. I'm tired because about 4PM yesterday, before today's appointment someone immediately bought my bumper. They couldn't get it any other day as they're on the way back to NSW. So I had to do that big GTR conversion I had been planning. Unfortunately, the information on SAU about what you need and how this is done is incomplete. So what should be a simple bolt on affair, yeah, it's not. Did you know if you use all GTR items the bonnet won't close? This little manuever sent me into about 1am the night before trying to dodge a way to get it closed. I will have to revisit this in the next few days  - or maybe not, I may let a body shop figure it out. It all needs to come up and my motivation to pull the bumper off is low. It also seems to hit things in the bay where the GTT bonnet didn't. Yes I used 100% new OEM GTR items. Today, I had the joy of driving to the dyno looking like this: Given I had roughed in the fuel and given sensible but pretty conservative timing, I didn't really bet on having the car drive out any real difference than when it drove in. Sadly due to a miscommunication and laptop fun and games (and almost bricking the dongle, prayers and firmware updates indeed), I ended up using HP Tuner credits to licence the car that was already licenced. So in the end my laptop was used. It turns out my butt dyno is still well calibrated after all this time. The 325kw was on 74% Ethanol, the 313kw line was on 98. The other line is the 'before' line which was 281kw. While the numbers are pretty low, they're pretty in line with what you'd expect. Even if US dynos bump the whole result up about 50KW, gaining 10-15% is similar gains.  The curve of the cam is pretty much spot on with what was discussed as well. All this said, it still feels bad to not see the number you secretly want to see. Even if the car drove great beforehand, and I knew pretty confidently the car would drive out much the same way it drove in due to the nature of a wellish dialled in LS1 not gaining much if anything at all from being tuned from where it was. As expected, the car isn't particularly sensitive to running it at anywhere between 12.0 and 13.0 - And the initial timing at 20deg and 12.0 made 308KW. So 3 degrees of timing, and leaning it out to 12.7 for 5kw, anything above stopped giving any benefit until E85 (which has an additional 2 deg as before). Car itself behaved entirely fine. I found out that 100C = 1.15V! IAT at about 7pm was 19C. I might mess with the bonnet mounting.. but given the REO NEEDS TO BE CHOPPED TO FIT A GTR BAR this is possibly something I may leave gathering (more) dust until it returns to paint jail.
    • It sounds farrrrrrr too cold at your place Duncan... Here I was thinking our 10 degrees overnight is getting cold...
    • oh yeah, reminded this morning....bin lids frozen shut too
    • In my case not, because of total reno. But yeah.
×
×
  • Create New...