Ford MAF Problem

It’s a 1999 ford econoline with 5.4L. 4 wire MAF. vehicle came in for an enhanced inspection, was wrecked in the front (they repaired it) but it needed more repairs. Along the way, noticed that the MAF was unplugged. If plugged in the van would die with any throttle. I asked if they wanted me to diag/repair it, they said OK. Had codes P0102 MAF circuit low and P1100 MAF sensor intermittent. But also, it was unplugged. So…

Live data showed the sensor voltage was very low. Not getting much higher than a 1 or 1.5v no matter how much throttle. At idle, bouncing from 0-.3v. But the MAFg/s PID showed it stuck at 4.57 no matter how much throttle. Occasionally would quick spike under throttle, but mostly dead stuck at 4.57g/s

I checked 12v and grounds with it plugged in. I jumped 5v to the signal and it changed on scan tool. So I put a sensor in it. Still same issue, the g/s stuck at 4.57. Volt meter across sensor signal and ground wire is reading the same voltage as shown on the scan tool data. I can’t figure why the g/s is stuck at 4.57. Even though the voltage does change some (although not enough). to me the voltage is ALSO lower than it should be, but really confused as to why the g/s is fixed even when the voltage changes. is the PCM in a default mode? maybe from the MAF being unplugged for so long? thats where I am leaning next. going to try leaving the battery disconnected for an extended period of time. But wondering if anybody had experience with this. Possibly an issue with the PCM?

attached picture shows the voltage fluctuating, and the g/s mostly fixed. occasional jump/spike. unfortunately I did not capture that pic with the TP PID so you can see when I am giving it gas. but I think it gets the point across. fluctuating MAF voltage (although, fluctuating enough??) but no fluctuation in the g/s

thanks for any help!

The ECM probably knows the signal doesn't make sense, and so it won't calculate a g/s figure. Is this a 5-volt pull-down design like GM's? Can you tell us what each of the wires does as per the wiring diagram? You should scope the signal wire.

If the replacement MAF is a cheap one it very well may be bad.

Signal's probably a pull-up guessing from that DTC description.

Check the voltage of the MAF signal wire at the PCM/ECM at idle and W.O.T. Compare that to the readings on the same wire at the MAF sensor. If the same then assume the new MAF is bad, ssuming your power and 2 grounds at the MAF are still good with vehicle running and connector plugged in to MAF (back-probed).

You should also check the PIDS of the other air/fuel control sensors to make sure they're normal (T.P.S., MAP, ECT, IAT).

When you jumped 5v to the signal wire, does the scan tool show 5v?

Wow, I had checked the box to get notifications for this thread, but didnt get any. didnt realize I was getting all these awesome responses, otherwise I would have responded sooner!

The MAF sensor is designed like the one in this video that Paul did:

Yes, when I jump voltage, the voltage on the scan tool changes. that is why I am assuming circuit integrity is good. yes, I realize the right thing to do is to scope at both ends of the wire, but jumping voltage and reading on scan tool was my quick way to do it. I didnt have much time as the van was already at my shop for a long time for other repairs, and the MAF was something thrown in at the end before she quickly needed to pick it up.

I did try unplugging battery for extended period of time, and jumping cables together, incase pcm was in some sort of default mode. but that didnt try anything

yes power and grounds are good, tested with plugged in back-probed, and voltage drop tested.

I am open to the idea of the MAF being bad. but neither symptoms NOR voltage readings changed one bit.

unfortunately, this van did need to leave friday morning. So it left with the MAF unplugged. customer is aware of everything. She came from a ways away because not many shops perform the PA Enhanced Inspections like I do. So she has another mechanic near her she said no problem she will take it to him. But if its the same guy who put the front end of her van together, I dont think hes going to figure it out either, and it will probably end up back here, especially since she was very happy with all the service she received here.

So would love to keep the conversation going, but testing put on hold until the van comes back, if it comes back. thank you guys!!

If scan tool showed 5v when you jumped 5v at the sensor plugged in, then...

Check for blockages by the MAF sensor or upstream in the air tube.
Then assume a bad MAF. It seems like you've checked the whole system. Some electronic parts need to be OE.