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Voltage At All 3 Afm Wires With Ignition On...

wlspn

By wlspn,
in Engines & Forced Induction

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wlspn Proficient

wlspn

Posted
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Hey guys,

No doubt some of you may have read about my RB25 overfuelling (I know, I know, those of you who have are probly ALMOST as sick of it as me...

Anyway I keep testing things & results keep changing! At first car idled like crap, after a LONG time, found disconnecting AFM made it stop smoking & hunting (although it still smelt rich & obviously is in limp mode) Had around 1v at orange/blue AFM wire at this stage...

Then all of a sudden one day it started fine! Thought problems were solved until I gave it a rev & found it was in limp mode. Found AFM wires had to be wiggled & held a certain way for AFM to connect properly & when it did it started hunting again, voltage at orange/blue pin on idle was 2.4v!

NOW, car wont start at all, so checked voltage with ignition on only...

Black/white trace has 12.4v

White/blue trace has 11.1v

Orange/blue trace has 9.9v

Surely these wires shouldnt have voltage (or not so high) with only ignition on? If anyone knows for sure, would be great...

This car is starting to drive me bloody nuts!

wlspn Proficient

wlspn

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Ok, had an ECU in the car borrowed from someone (to eliminate my ECU as being problem) & obviously it wasnt too happy as car wouldnt start or run with it in place... Put my ECU back in & no longer has voltage at all pins but still has around 2v at orange/blue wire on idle... Should be around 1.4v as far as I know? Any ideas what could be causing high voltage? Obviously the ECU sort of thinks its pulling in more air than it should on idle so its adding extra fuel... (last time I had a scantool on, injector pulse was 7ms at idle)

Will check resistance of each wire back to ECU & report back in a few minutes... Damn its hot too!

battery Mentor

battery

Posted
Posted

might be an idea to unplug both ends of the loom and check resistance between the wires, there might be a short somewhere.

its my understanding that on a cold start under 3k rpm the afm won't have much effect on anything the temp sensor does however.

but this is all irrelevant if the car is not even starting now.

who did the wiring?

wlspn Proficient

wlspn

Posted
  • Author
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Have just done that, as written above. Car is also running now but still reading 2v at signal wire on idle which is still a touch high... Temp sensor has been swapped for a known working unit & temp sensor wires have also been resistance checked back to ECU plug.

Wiring was done by a member on here. Nothing he has done could cause this however... Have no doubts in his work...

battery Mentor

battery

Posted
Posted
Have just done that, as written above. Car is also running now but still reading 2v at signal wire on idle which is still a touch high... Temp sensor has been swapped for a known working unit & temp sensor wires have also been resistance checked back to ECU plug.

Wiring was done by a member on here. Nothing he has done could cause this however... Have no doubts in his work...

still not quite sure you understand what i said, just to make sure im saying put probe on one end of white/blue and the other probe on the orange/blue, you should get infinity if not you have a short, i would also check them between ground too.

the guy who did the wiring may have done a good job but maybe when the loom was installed it got damaged on a sharp edge etc..

battery Mentor

battery

Posted
Posted
Have just done that, as written above. Car is also running now but still reading 2v at signal wire on idle which is still a touch high... Temp sensor has been swapped for a known working unit & temp sensor wires have also been resistance checked back to ECU plug.

Wiring was done by a member on here. Nothing he has done could cause this however... Have no doubts in his work...

still not quite sure you understand what i said, just to make sure im saying put probe on one end of white/blue and the other probe on the orange/blue, you should get infinity if not you have a short, i would also check them between ground too.

the guy who did the wiring may have done a good job but maybe when the loom was installed it got damaged on a sharp edge etc..

wlspn Proficient

wlspn

Posted
  • Author
Posted

OK got ya mate. Sorry, when you said unplug both ends of loom, was assuming you meant to test resistance between AFM plug & ECU pin...

Will give that a shot. Anything is possible... Open to any thoughts at the moment as Im just running out of ideas & things to check...

daisu Mentor

daisu

Posted
Posted

One of them should be ground, one should be 12V supply (should be able to measure this with the AFM disconnected) and the other should be a 0-5V signal from the AFM.

Definitely sounds like either a grounding issue or the loom has been pinched and the wires are shorting.

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