MAF Signal Wire Voltage too high

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S13gPanda
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Joined: Fri Apr 09, 2021 11:16 am
Car: 1990 Nissan 240SX S13 KA24DET
330cc injector
T3 Turbo

MAF Signal Wire Voltage too high

Postby S13gPanda » Mon Apr 12, 2021 4:13 am

Summary: My MAF signal wire voltage is reading 12.4v at idle... it’s suppose to be around .5v — she’s running super rich AFR:10.0 :( help


—Alright I am running an ApexiNeo (KA24det) on a stock manual tran ECU. It allows me too add or subtract fuel per-certain RPM.

I got the car 5 months ago and I haven’t driven it yet. When I got the car she was sitting for a solid 6 months (no drive/ no start)
I basically fixed everything and got the car running, but but ever since I got the car it’s been running stupid rich, and at first I thought it was The fuel map that I had on the apexi neo. But it wasn’t

When I start the car, she’ll go from 14.7 then drop to 10.0 on the AFR gauge. I tried making a tune to where I’m taking out Max fuel and still... rich asf

I then went and checked my MAF and was surprised on what I found and also happy cause it all made since.
———————————————————————————————

1. So at idle, I unplugged the maf and nothing happened. I plugged it back in and nothing happened
2. I then went to go check the voltage on my maf harness, and realized my signal wire was reading off 12.4V at idle and around 9-10V The ignition on
3. The white wire, Which supposedly is supposed to be the power wire, I was reading off .47-50V

So somehow my signal wire is reading with my power wire is supposed to read and vice versa. So now it makes sense why I’m so rich because the ECU thinks there’s so much air coming through

Maf harness:
- White: Power
- Black: Ground
- Black/White: signal

How should I got about this, any advice helps...thanks!


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VStar650CL
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2004 Nissan Altima 2.5 S

Re: MAF Signal Wire Voltage too high

Postby VStar650CL » Mon Apr 12, 2021 6:08 am

Are those readings with the connector loose, or back-probed?

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VStar650CL
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Re: MAF Signal Wire Voltage too high

Postby VStar650CL » Mon Apr 12, 2021 6:20 am

The only one I ever saw like that turned out to be a bad ECM, the power and ground looked fine with the white wire removed but went to about half a volt as soon as you connected it. I presume the MAF power supply in the ECM was the culprit. There's also a quirk with the start signal to the ECM on those old KA's, if the start signal stays hot when the engine isn't cranking it will make the injectors go flat open all the time.

S13gPanda
Posts: 5
Joined: Fri Apr 09, 2021 11:16 am
Car: 1990 Nissan 240SX S13 KA24DET
330cc injector
T3 Turbo

Re: MAF Signal Wire Voltage too high

Postby S13gPanda » Mon Apr 12, 2021 3:02 pm

both, the connector was loose and back-probed

I was thinking about borrowing my friends ECU and checking again

There is also a short in the car so maybe it has something to do with that
Last edited by S13gPanda on Mon Apr 12, 2021 3:08 pm, edited 1 time in total.

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VStar650CL
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2004 Nissan Altima 2.5 S

Re: MAF Signal Wire Voltage too high

Postby VStar650CL » Mon Apr 12, 2021 6:00 pm

Okay, I pulled the WD and you have your wires mixed up. B/W is MAF power and W is signal. Half a volt on W with key-on engine-off is normal, should go to around 1.3~1.5V at idle if the MAF is healthy.

S13gPanda
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Car: 1990 Nissan 240SX S13 KA24DET
330cc injector
T3 Turbo

Re: MAF Signal Wire Voltage too high

Postby S13gPanda » Mon Apr 12, 2021 10:50 pm

Well then that’s correct, I just had them mixed up. I thought the B/W was the signal and white was power.

So what’s the next step from here, do I need to do some re-wiring, or maybe get a new MAF or ECM

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VStar650CL
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2004 Nissan Altima 2.5 S

Re: MAF Signal Wire Voltage too high

Postby VStar650CL » Tue Apr 13, 2021 5:45 am

See what the MAF voltage does with the engine running before you condemn it. They are known to fail, but if it's reading where it should at idle, around 1.4V, then it probably isn't causing your issue. There are a lot of other things that can make you run rich. First, check the coolant sensor, it should read around 800mV (0.8V) when fully warmed up. If it reads high then the ECM will rich the engine because it thinks it's cold. If that's okay, check your O2 sensor. With an actual rich condition, it should read high at a little under 1V. If it reads low or 0V then you may have a bad sensor or sensor harness.

S13gPanda
Posts: 5
Joined: Fri Apr 09, 2021 11:16 am
Car: 1990 Nissan 240SX S13 KA24DET
330cc injector
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Re: MAF Signal Wire Voltage too high

Postby S13gPanda » Tue Apr 13, 2021 6:09 am

Alright sweet, i'm going to run all those test today. I will let you know the results
dont think is this has anything to do with the issue, but when the car was idling i was unplugging and pugging back the MAF and nothing would happen to the engine at all

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VStar650CL
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2004 Nissan Altima 2.5 S

Re: MAF Signal Wire Voltage too high

Postby VStar650CL » Tue Apr 13, 2021 6:57 am

It's entirely possible the MAF is bad, it's just worth ruling it in or out before throwing parts at the problem. ;)

S13gPanda
Posts: 5
Joined: Fri Apr 09, 2021 11:16 am
Car: 1990 Nissan 240SX S13 KA24DET
330cc injector
T3 Turbo

Re: MAF Signal Wire Voltage too high

Postby S13gPanda » Tue Apr 13, 2021 8:09 am

Yea true, i just to do hella diagnostics and ill know whats upp


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