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Experienced all of a sudden rough idle and stalling. Checked codes with Key on Engine off and got a 126 ( Manifold absolute pressure out of range )
But cannot test with engine warmed up and idleing, because it wong stay idleing. I pulled the cover and dont see any disconnected or rotten vacuum lines or in the engine bay either.
Question is, would a code 126 show up without van up to temperature and only doing the key on engine off test?
It is the original map sensor and has never been cleaned and looks like its easy to change but its not that cheap, although what is these days, LOL.
In the service manual PCED they mention a "MAP/BARO Tester" which I think is basically a breakout box for the MAP wiring. With KOEOff they expect VREF to the MAP to be 4 to 6 Volts and the sensor output to be as mentioned in the attached chart. Don't know if this is useful but ?????
The Ford PCED has you testing the Hertz from the sensor and comparing it to an altitude table
That MAP sensor is full of thick film protecting the electronics, just like the TFI module has inside it
That stuff gets sucked out sometimes into the vacuum line
That renders the sensor useless
So, the first step is to check the vacuum line for obstructions
Then
Do the pinpoint tests in the PCED for that code
They will have you reading the actual Hz from the sensor, not voltage
My guess, your sensor is NFG
Very seldom see a MAP sensor code, and when you do, the sensor is generally shot
Here is some of it
If you get through these, I can post the rest
we all learned to just keep a known good map sensor in our tool boxes to cut down the diagnosis time
Right, even in the 90's the new sensors were 100 bucks, I'd get one from a junkyard, most of them last forever
In the service manual PCED they mention a "MAP/BARO Tester" which I think is basically a breakout box for the MAP wiring. With KOEOff they expect VREF to the MAP to be 4 to 6 Volts and the sensor output to be as mentioned in the attached chart. Don't know if this is useful but ?????
Thanks for posting, I was looking at something similar.
The Ford PCED has you testing the Hertz from the sensor and comparing it to an altitude table
That MAP sensor is full of thick film protecting the electronics, just like the TFI module has inside it
That stuff gets sucked out sometimes into the vacuum line
That renders the sensor useless
So, the first step is to check the vacuum line for obstructions
Then
Do the pinpoint tests in the PCED for that code
They will have you reading the actual Hz from the sensor, not voltage
My guess, your sensor is NFG
Very seldom see a MAP sensor code, and when you do, the sensor is generally shot
I was going to check the voltage and vacuum line but then I found that if idle is restored after disconnecting the map plug, then most likely the map is bad, aside from a clogged vacuum line. So I did that and it started idleing and when I plugged it back in it stalled.
I went ahead and picked up a new one, not motorcraft, just a cheapie from oreillys and it worked. Took it for a test drive and runs good now. It was the original map sensor with 254,xxx miles on it.
I was going to check the voltage and vacuum line but then I found that if idle is restored after disconnecting the map plug, then most likely the map is bad, aside from a clogged vacuum line. So I did that and it started idleing and when I plugged it back in it stalled.
That's a new one on me, but I am a factory guy, and basically only know what I was taught, besides what we came up with
Ford should have put that one in the book
They told us to substitute a known good part
Good one
We came up with these You can drive with a dead TFI module with one of these.
That's a new one on me, but I am a factory guy, and basically only know what I was taught, besides what we came up with
Ford should have put that one in the book
They told us to substitute a known good part
Good one
We came up with these You can drive with a dead TFI module with one of these.
This is from an AI generated response. I think it was Gemini but at the time I was reading it, I didnt know thats where it was from, But I also found fairly similiar explanations on a couple websites.
I wish I had one of those TFI cheater things, Ive been stuck a couple times due to a bad TFI Module.
" Unplugging your MAP (Manifold Absolute Pressure) sensor will trigger a Check Engine Light and force your vehicle's computer into a "limp home" default mode. The engine will likely run very richly, causing poor fuel economy, rough idling, hesitation, and potential damage to your catalytic converter.
What Happens When It's Unplugged
When the engine computer (ECU) loses the MAP sensor signal—which tells it how much air/load is entering the engine—several things occur immediately:
Poor Performance & MPG: You will experience a significant drop in fuel efficiency, a loss of engine power, and potentially rough, erratic idling.
Default Settings: The ECU uses pre-programmed "limp mode" maps to guess the engine load, primarily relying on the Throttle Position Sensor (TPS) and engine RPM.
Rich Fuel Mixture: Because the computer can't accurately measure air, it often defaults to a heavily rich fuel mixture to prevent the engine from running too lean (which can cause severe damage)
Why Does This Happen?
The MAP sensor is a primary sensor used to measure the vacuum or pressure inside your intake manifold. The engine computer uses this exact data to determine how much fuel to inject and when to adjust your ignition timing. Without it, the engine operates blindly.
When Mechanics Use This Trick
Mechanics and car enthusiasts may temporarily unplug the sensor for diagnostic purposes.
If a vehicle runs terribly with the sensor plugged in but magically smooths out when unplugged, it usually indicates the MAP sensor itself is faulty, sending bad data to the computer.
However, it is never recommended to drive a vehicle long-term with the MAP sensor disconnected. "
I still had my factory MAP, I hope I kept it, I replaced it when I was chasing codes, turned out the ECM was bad, so everything replaced likely was still good, distributor had to be replaced because only one screw was available to retain the cap, don't know who the other was broken off, really worried about the replacement, most are 50/50 on if its good or not, no quality control in China. I miss when Motorcraft parts were made in Mexico. LoL
Keep a check on you little plastic vacuum lines, they can crack and go unnoticed, tho the MAP one is thick enough to be impressively resilient, unlike the others going to the emission switches.
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