ndj

I presume this low voltage at pin 6 is what is causing my AFM to read half of its expected output. Causing fail-safe mode.
Outside the car the MAF tests correctly, but once connected it outputs .6volts.
I have attached some photos of the FSM that I have been following. There has been some contradictions that make absolutely no sense. For instance, look at the maf circuit and then look at the testing for it....why would there be battery voltage at the pin that outputs final MAF sensor voltage (B)???

WHERE DO I GO FROM HERE...
Link to photos

ndj

I presume this low voltage at pin 6 is what is causing my AFM to read half of its expected output. Causing fail-safe mode.
Outside the car the AFM tests correctly, but once connected it outputs .6volts.
I have attached some photos of the FSM that I have been following. There has been some contradictions that make absolutely no sense. For instance, look at the maf circuit and then look at the testing....why would there be battery voltage at the pin that outputs final AFM sensor voltage (B)???

WHERE DO I GO FROM HERE...

rsfire

Hey, I know this is an older post. But did you have any luck figuring that out? I'm throwing maf code, but maf itself checked out fine when out of the car. But same as you, at key on position it gets .6 to .7V, and running at idle it gets 1.1V. Once my meter is hooked into the system it puts ecu in failsafe mode, so it won't rev past 2K then, but once I remove my voltmeter it revs normally.

ndj

I didn't think anyone really cared about the final outcome considering the lack of responses.
A few things were wrong with this car that was causing fail-safe.
- I had limited understanding of engine management systems. Now Im a pro!
- The multi-meter was the least used tool in my toolbox.
- I bought a replacement AFM from the junkyard. a sensor that could trick the ECU with no codes, yet still cause limp-home mode??? WTH!
-----In order to resolve my problem I had to check everything blindly!
I finally found a lead when I started checking the shielding around wires. Take your multimeter (set to ohms) place one lead on the shielding, and the other on the wire its shielding. Do you receive any resistance? If so, replace. You can make new shielding with Aluminum foil, high temp black tape and lots of patience.
- I checked every wire in the efi harness. Found a problem with the shielding around the AFM Signal Wire. The wire got too hot and lost its insulation, and was grounding out on the shielding. It had no visible defects. I also added another level of protection to this braid of wires, as they route near the turbo charger. The day this car died on me It spent alot of time in boost.
- I then went and bought a new AFM. It had very small differences when measuring the ohms between terminals. Use this for testing
XenonZ31 Sensor Information

Those two things in that order did the final trick! START THERE!
Best of luck to you. Only thing I can figure is the bad wire shorted out the new sensor I got from the junk yard just enough to trick the computer into not throwing the code. It then lead me on a wild goose chase, changing/checking/swapping everything related to fuel and ignition. I know my engine management now. I did some other nifty stuff while I chased the wind.

rsfire

Yeah, I guess when the problem doesn't pertain to you it's hard to care about it. But I like to still post up what happens since it's likely it may happen to someone else down the road. Thanks for writing back, I'm very glad you did!!
So if I'm getting this correctly Wire B, the output voltage has a shield around it huh? I didn't realize that. How far back does the shielding start? I just pulled the rubber boot on the connector back to test voltages but didn't see a shield or anything.

So once I check my shield and the ouput voltage wire, hopefully i'll see some resistance and finally find my problem. Although my issue does not seem as bad as yours. I am getting low voltage, but it's not putting ecu into limp mode, it is just running leaner than it should. It leans out past 18:1 AFR when first giving it throttle then richens up. It also runs around 17:1 cruising 65mph on HWY, but at 75 it would be 14 to 15:1.

I am throwing code 12, which is weird because it wasn't throwing that code a week ago, even though it still had same problem.

And I take it when your output signal was grounding out, it did fry your MAF? You did need a new one?

And just curious, if you hook your voltmeter up to the output wire and a ground what voltage do you get now while idling? I'm wondering what normal is.

rsfire

Wow, a few other nifty things. That doesn't even look like the same engine bay anymore. Dang! Did you gut your intake there?

ndj

Yeah, I guess when the problem doesn't pertain to you it's hard to care about it. But I like to still post up what happens since it's likely it may happen to someone else down the road. Thanks for writing back, I'm very glad you did!!
*I love to help. Your welcome!

So if I'm getting this correctly Wire B, the output voltage has a shield around it huh? I didn't realize that. How far back does the shielding start? I just pulled the rubber boot on the connector back to test voltages but didn't see a shield or anything.
* The shielding starts a few inches back from the connector. It joins with cas and 02 sensor shielding near the ecu. splits again to the 4th plug of the efi harness that does not go into the ecu but rather joins with the main harness through under dash connector.

So once I check my shield and the output voltage wire, hopefully i'll see some resistance and finally find my problem. Although my issue does not seem as bad as yours. I am getting low voltage, but it's not putting ecu into limp mode, it is just running leaner than it should. It leans out past 18:1 AFR when first giving it throttle then richens up. It also runs around 17:1 cruising 65mph on HWY, but at 75 it would be 14 to 15:1.
* Make sure your MM is set to DCV, and not 12v Load test. How does the car run? Have you checked your sparks plugs?
If you are certain of this ratio you could try a calibration if your out of spec per the testing procedure. XenonZcar.com
Whats your gas mileage? I pull 26 mpg hwy/town mix on 91octane ethanol free fuel, no tps sensor.
Do these things...in order.
-download FSM.
-check for additional non-metered air entering engine, aka vacuum leak.
-use the link above to test afm meter from the computer.
-test o2 sensor.
-Check wiring--grounding, insulation check, continuity.
-calibrate AFM


I am throwing code 12, which is weird because it wasn't throwing that code a week ago, even though it still had same problem.
* My wiring issues caused all sorts of funky stuff to show up. If you are throwing code 12, you indeed have a faulty sensor. Repair/replace. I would recommend being safe and check everything that could cause such a failure before throwing in a new one. Remember, I started with this issue. It was an easy fix to pick up a new one and throw it in. I drove half way across the state to get a new one. Only to later realize the new one removed the code and I was still in limp mode. I should of started with my wiring before shorting out a $50 part. Its a total headache, be prepared to devote many hours. Some just opt to replace the whole EFI harness, I picked the more involved route. Thou this might not be your problem.

And I take it when your output signal was grounding out, it did fry your MAF? You did need a new one?
* It made for a faulty sensor that could trick the ecu into thinking it was not the problem. So i did end up starting back over with another one once i fixed my wiring problem.

And just curious, if you hook your voltmeter up to the output wire and a ground what voltage do you get now while idling? I'm wondering what normal is.
* I would need to look into this. Might take several days.

ndj

Crappy picture, but yes the intake is gutted. Tough project without a mill. Nevertheless completed by myself. Took $80 and about 5hrs of labor.

rsfire

Oh ok, so the shield joins with the o2 sensor at one point, I need to double check but I think I recall seeing some frayed shielding or something pretty close to the o2 sensor, probably from where it is spliced into a new sensor, maybe the shielding is contacting some of bare wires where it is spliced.

Though if I have resistance down my wiring, my voltages of my MAF output signal at the connector vs at the ecu plug in should be different correct? Because I was getting the same voltages on both sides of that wire.


Ok I'll take a look and make sure I'm measuring things in the right settings with my MM.
My car runs great for the most part, drives fine, pulls hard full boost. The only thing i would notice if I didn't have a wideband is when I first give it throttle from a low rpm it's a little hesitant. Once I got my wideband I could see that hesitation was indeed a lean backfire. Other than that it runs a little leaner than it should while cruising, but I wouldn't know that if I didn't have the wideband. My plugs are whitish, for sure lean. And I have only done city driving the last couple weeks so hard to say what I got. But last hwy trip it was running much more lean, it got 31mpg on premium.

I plan on doing a pressure check of my intake today or tomorrow. I've checked all my vacuum lines over and over, I only have a few things plugged in anyway.

I'll go ahead and check my calibration too, i was thinking about trying that anyway.
I'll test o2 sensor, although I did try unplugging it to see if it would run better, but no luck.

Ok thanks, no rush to check things, I'm happy just gettting advice. Thanks!!

rsfire

Wow well that's totally worth it doing it yourself huh. Sounds tough. What did you use to gut out the inside?

ndj

It took along time, not really that hard...just slow. I used a right angle grinder, 2 metal cut off wheels, 1 120grit flapper wheel. Mig welded. 5052 3/16" top plate. Once opened things like port matching/honing, enlarging TB should be considered.

ndj

Can I clarify-- Your throwing code 12, but not running in limp-mode?

ndj

Oh ok, so the shield joins with the o2 sensor at one point, I need to double check but I think I recall seeing some frayed shielding or something pretty close to the o2 sensor, probably from where it is spliced into a new sensor, maybe the shielding is contacting some of bare wires where it is spliced.

*It is frayed once it exits the wire its shielding. There are a couple points where shielding can contact bare wires. It's more likely that its contacting the wire its shielding, which would cause inconsistent readings. Only way to know is do the test. T

Though if I have resistance down my wiring, my voltages of my MAF output signal at the connector vs at the ecu plug in should be different correct? Because I was getting the same voltages on both sides of that wire.

*Not necessarily, there could be a short and still maintain similar voltage throughout. This is where you would isolate the circuit and check for high resistance. Now, resistance between the shielding and the wire its shielding would be a bad thing. As that would indicate an insulation failure.

rsfire

Sorry for slow response, no internet at home and this site doesn't work with my phone haha. So anyway, I went through and checked stuff last night.

I checked shielding of the output wire and the output wire itself. When harness is disconnected from ecu I get no continuity between them. But when I plug it into the ecu I get resistance. I would need to go do it again to see how much. I think somewhere in the megaohm region.

I checked for continuity between all the wires from the ecu side as well as the fsm states and no continuity, that checks out fine.
But last step it says to jump D, E, & F then check some of the wires and I should get 0 ohms. I get no continuity instead of 0 ohms. But this step makes no sense to me, if I jump my body ground, self cleaning ecu wire, and battery source wire; why and how would I get a complete circuit when checking a bunch of ecu pins like output voltage, variable resistor, and ecu ground. Am I looking at this wrong or is the FSM wrong?

I did go through and do what I thought would tell me right. Jump ecu ground and signal output, then check those two wires on ecu side and got 0 ohms. No resistance in those 2 wires. I did that to all of the ecu wires and got 0 ohms, so according to that check the wires don't have resistance.

And did you ever find out what the FSM meant in that test you first posted up about. Checking voltage of signal output and ecu ground into connector? Because I think same thing, how could I get batt voltage when it's the signal output that is not even connected to AFM.

rsfire

Oh and after checking all the wires and everything seeming good to me, expect those two steps in FSM I figured my wiring may be ok. So I got a 86 N/A MAF from local junkyard and stuck it in there and immediately driving off I have same lean problem.
Now I'm kicking myself for not checking the MAFs voltage before putting it in car to see if it was already bad or not. But once I got home I checked it. Same deal, .8v now while hooked up to power, and 1.1v to 1.5v while blowing through it rather than 1.6v hooked to power and 2.2-4v while blowing through. So either I randomly got a bad one or I fried another.
So unless some of my wiring stuff I just talked about seems fishy to you, I'm wondering if my ECU is frying the unit.
And random side fact, I did check the MAF before replacing my bad fuel injectors and it was fine. But after I changed them it has been toasted. I can't think of anything that could fry MAF from changing my injectors.

rsfire

And yes, that is correct. I am throwing code 12 but the car is not in limp mode. It drives just fine except for a little lean cruising and it leaning out when I first give it throttle. Maybe the voltages are just not far enough off to throw it into limp mode. It does however put it in limp mode when I hook my voltmeter into the system to read my output while idling, so limp mode does work.

And wow that sounds like a ton of work, but glad to hear no crazy tools are needed to gut that. I need to learn how to weld, I've got a good welder but just haven't used it yet haha. Yours turned out awesome! I'm impressed