Causes For High Afm Signal Voltage?

[wlspn]

Hi all,

Recently dropped an RB25 in my R32 & since first start has never run right.

Is overfueling a stupid amount on idle, (7ms injector pulse width) to the point where it cant be driven due to the amount of smoke & hunting issues (due to mixture I believe...) Thanks to this has been off road for months!

Runs best (but still not perfect) when cold-started but as soon as throttle is touched, even slightly & released, starts pouring smoke & idling like a POS!

Unsure of AFM signal voltage when cold & running half decent but I know after throttle has been touched & its started really putting the fuel in that the AFM signal voltage is around 2v+ on idle!

Car runs good in limp mode with AFM unplugged.

Basically just want ideas of what could cause voltage to be so high?

This is obviously telling ECU more air is entering the engine than what actually is & is causing my problem...

Things I have tried so far include:

*Swapping AFM

*Swapping ECU

*Checking AFM wires for short-circuit

*Measuring resistance of AFM wires back to ECU plug (& ECCS relay)

*Checking battery output voltage

*Checking all earths (battery, body, engine, ECU, etc)

Probably some stuff that Ive missed but will add later...

In the meantime if anyone has anything to add please help me out!

Am even willing to pay for correct information...

Yes, if you solve my problem I will send you money!

[R31Nismoid]

What is the voltage @ the outlet of the AFM (start of the wiring) vs what the ECU is seeing @ the harness?

Is the 2V @ BOTH ends?? (doesnt sound like you've checked the wirings directly out of the AFM).

If so, then do you know 110% that the other AFM you tried was decent/correct model because it sounds like it's not if the above is 2V @ both ends, it can only be the AFM.

Also, have you tried putting you AFM into another car?

[Moodles2]

R32 or R33 ecu?

[wlspn]

R31 Nismoid: Will double-check but 99% sure voltage is same at AFM & at ECU

Tried another pink-label AFM but had been sitting around for years so unsure of condition, fitted my old RB20 green label AFM (& plug, with a 12v earth)

which I know was working only months ago on my RB20

No, havent tried swapping AFM into another car...

Moodles2: Standard R33 ECU. Have tried 2 other R33 ECUs as well...

Edited November 27, 2009 by wlspn

[R31Nismoid]

Ok check it and let us know - the old AFM from the shed or whatever could well be stuffed too.

I've seen crappy AFM's under and over volt on a few occasions, it is normally undervolting, however i did have one AFM that was always .7V higher for some reason (it was stuffed as well)

[wlspn]

Hey mate, just double-checked voltages & they are the same at AFM as at ECU.

Tried mine, another pink label & a green label (with modified wiring to work) & all coming up roughly the same... & as I said I know for sure the green label worked as it was on my RB20 for years & been out for a few months only...

Any other thoughts or ideas?

P.S-On tests I done just then, pink label cold-start voltage was around 1.5v at idle, tapped throttle & jumped to around 2v

Green label (cold-ish) was 1.45v, throttle touched 1.95v

From previous testing if I dont touch throttle at all it creeps up really slowly until its on 2v...

Edited November 27, 2009 by wlspn

[wlspn]

Also thought I should note, just then I checked voltage at ECU, went under bonnet & checked voltage at AFM plug, gave it a small rev at throttle-body & checked voltage again. Could tell as soon as I released throttle that voltage would be up as you can actually hear that the AFM is sucking in more air! Quite a suction noise for idle...

[Adriano]

Why dont you check the diagnostic trouble codes

[wlspn]

Oh yeah, should have mentioned that. No fault codes... Diagnostics read all OK (code 55 or whatever it is)

[battery]

the ecu will run different maps depending on temperature, if you unplug the 2 wire plug to the sensor on the plenum the ECU will assume a normal 80c temperature.

might be something to try...

[R31Nismoid]

Also thought I should note, just then I checked voltage at ECU, went under bonnet & checked voltage at AFM plug, gave it a small rev at throttle-body & checked voltage again. Could tell as soon as I released throttle that voltage would be up as you can actually hear that the AFM is sucking in more air! Quite a suction noise for idle...

1.3-1.5 is a tad high, but not 'super' high.

It is looking like a TPS issue. If you kick the RPM and it sits higher than it was previous, that would not be AFM, rather the TPS not reading correctly.

[wlspn]

1.3-1.5v is the voltage when I first start it & its running sort of OK but still not the best...

Then when you tap throttle, goes to 2v & stays there even after throttle is released.

Also as I mentioned even if throttle is not touched voltage will still slowly creep up until it gets to 2v.

Have tried disconnecting TPS when its running crap, measuring voltages at TPS & ECU + checked resistance of TPS wires back to ECU, etc

If I can get hold of another one I will try it though as I havent actually replaced it at all

[robots]

Hey, did you find out what was wrong ? My car is driving me nuts. Very similar stuff.

[paulr33]

are you sure the AFM is the issue here, the AFM will follow the engine

it sounds like the AAC valve is opening and staying open

this would explain why your AFM value increase and then pegs at 2v

whilst the AAC is open, more air comes into the engine

[wlspn]

I suppose the only way to check this would be to replace the whole AAC unit with a working item?

Might give that a shot if I can get hold of one... Cleaned it before the engine went in but cant guarantee it hasnt jammed...

[Adriano]

Is it idling high? Have you checked the ignition timing, as if it is overly retarded, then the ecu will be trying to raise the idle causing high AFM voltages, though it shouldnt run that rich

[STATUS]

upgraded turbo, throttle body and your plenum change has most likely freaked the ecu out a bit much, some cars are fine (at idle and cruise) others just dont wanna play ball, but without seeing it your guess is as good as mine sorry. Duane at hi-torque knows his stuff so im sure he will have it sorted asap.

[MrR33666]

possible coolant temp sensor if faulty it will send signal to ecu saying engine still cold causing overfueling when warmed up

have seen a couple on other makes of cars that where faulty but not bringing up a fault code.

hard to say withouy a data list on a scanner though.

Edited January 12, 2010 by MrR33666

[wlspn]

Is it idling high? Have you checked the ignition timing, as if it is overly retarded, then the ecu will be trying to raise the idle causing high AFM voltages, though it shouldnt run that rich

No. once it warms up it revs are hunting, very erratic idle... Warmer it gets the worse it is. Once its hot it just wants to stall. Even holding the throttle steady the revs are always changing. Yes, have checked timing, sitting at 20 degrees.

upgraded turbo, throttle body and your plenum change has most likely freaked the ecu out a bit much, some cars are fine (at idle and cruise) others just dont wanna play ball, but without seeing it your guess is as good as mine sorry. Duane at hi-torque knows his stuff so im sure he will have it sorted asap.

OK, thanks mate, just figure another opinion never hurts. Yes, Duane seems to know his stuff. Hope he will be able to help me out...

possible coolant temp sensor if faulty it will send signal to ecu saying engine still cold causing overfueling when warmed up

have seen a couple on other makes of cars that where faulty but not bringing up a fault code.

hard to say withouy a data list on a scanner though.

No, have checked voltages & resistances as well as replacing with a known working item.

Thanks for all the input though guys. Will be sure to post up what was wrong when I finally find out...

[robots]

It shouldn't run too differently with different intake and stuff. Throttle body maybe.

My rb25 could idle and run fine with greddy intake, bigger turbo on factory stuff.