Trouble with mass air flow sensor 2003 sport trac

[mostly_broncos]

Hello everyone semi -new user here . I was a member a long time ago when I had a 94 explorer but haven't been back in years and forgot my old ID so I had to create a new one.


I haven't owned an an explorer in 5 years but I am suddenly required to fix one belong to my brother. He is recovering from surgery and can't do much so I volunteered to help him out.

Basically his daughter was driving the vehicle and it died requiring a tow to my house the other day.

Symptoms , very rough idle stalling , many codes . After towing to the house I read out a bunch of 300 misfire codes , a 2197 O2 sensor code air temp code etc. . I didn't have my voltmeter at the time so I decided to unplug the mass air sensor and voila it idled much better but it wasn't derivable . I had an O2 sensor on hand so I replaced the drivers side but it didn't improve much. I had to work so I couldn't touch it for a few days but today I made another run at it .

Now having a meter I decided to test the mass air flow sensor thinking that the way it ran without it might point to it being bad.

It won't run enough to test it with it running so I just began with key on engine off .

I notice right away some tape on the output wire and a bare spot on the IAT sensor output like someone had been at the harness . It was so close to the plug that I went to a bone yard and cut a few harnesses off and got back and pushed the two wires out and replaced them and tried firing it up thinking I might have fixed it, but no such luck.

So I used my meter to test the hot wire found 12 volts , the black (B) wire found a solid ground but when I got to the C wire I'm reading 6 volts !!! I was running out of time for the day but I cleaned the battery terminals and the three grounds right next to the negative post on the radiator support which were nasty.

I'm unable to continue today further. Tomorrow I'll check the ground up near the brain clean it up and if that doesn't work I'll have to check for continuity between the C terminal and the computer plug .

I may have missed some obvious grounds though. Are there more that relate to the brain? I'll check the main ground at the engine end of the negative cable . I think there is one near the wiper motor .

I don't have a wiring diagram which pin is the Mass air ground at the computer plug ? Does that wire have any splices that go elsewhere that may have corroded ? maybe its damaged by someones probing

The mass air still may be bad but without a proper ground how would I know? I don't particularly want to tie that wire to a battery ground and damage anything although if I severed it so ground didn't feed back up the wire to the brain that might be ok .

Any help , suggestions , links to a wiring harness or pinout at the PCM plug would be much appreciated.

 

[mostly_broncos]

Well I did go back out and clean the ground wire and stud next to the ECU at the base of the windshield. Now I'm seeing 7 volts. I should say I was expecting to see 12 I saw 6 then picked up a volt to 7. Thats read off the C pin unplugged from the sensor , I see 12 there with the key off , 7 with the key on. I'm guessing that whatever the MAF is trying to output is cut in half at least and thats why it runs better without it plugged in.

 

[mostly_broncos]

More testing today with 3 different MAF sensors output is 1.6 volts roughly at idle. The MAF signal return ground is erratic with the key off I should be getting the same as the other ground but its a volt less roughly . I pulled the PCM plug and I have continuity from the plug to the sensor . I feel like the wrong ground on the signal return is causing good MAF meters to give too high a voltage at idle leading to too much fuel???

I still feel like this is a ground or power problem somewhere in the harness.