MAF Signal Voltage Insanity

[Xit40]

I've been having issues getting my S2 RB25DET started and running properly in my S13. The problem I'm dealing with now is the maf signal voltage signal is off the chart high (for reference it has an E60 maf). At the moment it's about 9.85 volts with the car ignition in the on position. I know it should be about .3 volts.

Here's what I have checked so far:
1. Got the FSM and went thru the whole Air Flow Meter testing. Ground and Signal have continuity. Power is also good to the maf 12.8 volts.
2. Took the MAF out of the car and tested it directly with battery power via the FSM testing precedure. With power and ground attached the signal reads .2 volts and when you blow thru it, depending on how hard you blow, it reads linearly anywhere from 1.3 - 2.2 (this is just me blowing thru it directly on the hot wire). So in the end the MAF tests good on it's own.
3. Bought a second E60 MAF before I started testing, which is in the car now and it also tested good before I put it in.
4. Pulled the wires for the MAF back into the cabin as far as I could without removing the ECU plug and pulling it out thru the firewall. It's shielded with new continuous wire all the way back (No breaks, kinks, splices, etc anywhere along the shielding or power wire).
5. The car does start and run in limp mode with the MAF unplugged.
6. I have also set the CAS and TPS in the correct positions. The key is still on the CAS exhaust cam. I set the TPS via the FSM service procedure by testing the resistance.

Today I plan on removing my battery from the trunk and wiring it directly to my distribution block in the engine bay temporarily to remove any possible interference it's causing with any wires. Has anyone experienced wires picking up voltage from the battery positive cable when it's run thru the passenger compartment? I'll admit I don't know a whole lot about electricity and it's properties but that just seems like it shouldn't be possible.

If that doesn't help I plan on pulling the ecu plug out thru the firewall and tracing the MAF wires all the way back to the ecu plug. I'm kinda at a loss here where this power is coming from and I would appreciate any insight or thoughts anyone one has. Thanks

[julio]

Have you tried testing the signal wire of the maf plug while it is unplugged? It should be zero. Sounds like your wiring is funky.

[Xit40]

Moved the battery up front and used the stock grounding location with no success. Same problem.

There is no voltage when the MAF is unplugged. The car starts and runs in limp mode as it should.

Is there any way this could be some kinda ECU problem like a short internally or something? I am about to take the ECU plug and everything out and unwrap it all. Lots of fun when it's 94 and a heat index of 104. It's like death outside

[Blown240sx]

Your wiring has to be wrong because the MAF will only send out 5 volts MAX to the ECU. If your getting %+ volts on the signal wire then something is crossed.

Im surprised you havnt burned anything up yet.

[Xit40]

The wiring is completely correct. I am 1000% sure of that. I just finished pulling the maf wires all the way back to the ECU harness connector. Pin 26 goes to the ground, Pin 27 goes to the 5 volt signal. Verified by eye and continuity test. No breaks in the shielded wire at all, properly shielded all the way back and grounded. I'm at a loss.

[julio]

There is no voltage when the MAF is unplugged. The car starts and runs in limp mode as it should.

Just to be painfully clear (I'm not trying to question your skills here), you checked the signal wire on the maf plug for voltage while it was unplugged and running in limp mode?

Also, does this maf have an additional shielded ground that goes back to the ECU like other nissan mafs'? e.g. Power, ground, shielded ground, shielded 5.0VDC signal?

[Xit40]

I know the MAF will only put out 5.0 volts that's why I described it as insane. Makes no sense what-so-ever.

I tested the connection at the ECU with the MAF unplugged and the car in the ON position. There was no signal. I never tested it while it was running in limp mode.

The E60 MAF has only three connections: Power, Ground and 5 Volt Signal. The power is run separately unshielded. The ground and signal wire are run together in shielded wire which is then grounded thru the ECU grounding plug to the chassis body. The wiring doesn't run near anything else in the engine bay either besides the O2 sensor for a small time which is also shielded.

I'm buying new shielded wire and rewiring the whole thing. If that doesn't solve the problem then I don't know what's going on.

[whoareu]

i had a similiar issue. if i were you, i would get about 15' of sheilded wire and just rerun the maf wires. that way you know they are done right. thats what i did and it fixed the problem what ever it was.

[Xit40]

i had a similiar issue. if i were you, i would get about 15' of sheilded wire and just rerun the maf wires. that way you know they are done right. thats what i did and it fixed the problem what ever it was.

Yep. That's what I'm in the process of doing now. I sent a minion to the store for me to pick up dual shielded wire and some electrical tape to redo the dang thing. I just wish I could do the soldering inside where it's a nice 70 degrees rather than outside where it's 95. Everything will be triple checked, soldered and heat shrinked again. What a PITA. I'll give results when I'm done.

[Xit40]

Finished the rewire and cleaned up all the wiring at and around the ECU plug today. Got everything installed back in as it should be, bolted down, plugged in, etc. Hooked the battery back up, put the key in the on position and bam 9.85 volts again....CRAP.

So as I'm sitting there dumbfounded thinking everything over: I know it's wired right, grounded correctly, brand spanking new shielded wire and everything; I walk into my basement and pull out the extra ECU that came with my front clip. Yes, that's right, when I ordered the front clip they sent an extra ECU because the original one had a small dent on one of the covers. It was only cosmetic damage, but hey that was nice of them. I'll gladly take extra free parts whenever the opportunity arises.

I originally checked both ECU numbers, even though RB25DET M/T was clearly printed on both ECU's, and found them to both be good ECU for my motor. Sweet. So I plug in the alternate ECU and bam.... .28volts with the car on the on position. I have no idea what kinda hokum is going on with the first ECU I tried but there is obviously some kinda short internally or some other nonsense wrong with it. Thank god I had the extra ECU or I don't know what I would have done.