Why do I have to unplug my Mass Airflow sensor to get my truck to accelerate??

[streetroddin]

I have been chasing this problem...my Ranger will idle but not accelerate with the mass airflow sensor plugged in, unplug it and it runs and accelerates but hesitates and misses. I have replaced numerous items including the mass air flow three times thinking it was bad...also just replaced the control module with no improvements. The only code it throws is for the mass airflow sensor...I would love some help please, I'm at my witts end...Thanks in advance!

 

[Roert42]

What is the code you are getting?

 

[rubydist]

Well, if you have replaced the mafs and the pcm and still have the same issue, that suggests you have an issue with the wiring between the mafs and the pcm. Of course, you could tell us the actual code so we could help you or we can just keep guessing...

 

[streetroddin]

The code was read and erased by a friend of mine while I was at work, I did buy an OBD1 tester for myself after that, but no codes come up now.
Visibly the wiring is in great shape, I have no clue how to check it with a meter.
After reading in the forums a lot, there are similar issues out there that was resolved by replacing the air charge temp sensor and idle air control valve...I've never been one to simply throw parts at a vehicle till something works, but this truck was bought for me several years back by my late mother and holds sentimental value to me so I'm willing to do so if necessary.

 

[streetroddin]

Ok, today I went ahead and replaced the IAC valve, the PCV and the ACTS...in that order, checking after changing each one to see if there were improvements.
I also sprayed starting fluid on and around the intake and all vacuum lines checking for leaks and there were no leaks... really surprised me to say the least! lol

After the IAC valve, with the MAF sensor plugged in, the truck would idle and revved up with some finesse of the accelerator pedal without dying... so that's an improvement.

After the PVC valve, it ran somewhat smoother, but still not a complete fix.

After the ACTS, no improvements.

So, for an update, the truck will run with hesitation and spits and sputters and has a really bad odor from the exhaust now with the MAF plugged in...
Unplug the MAF and it will literally melt the tires off the truck if you get on it, but still has some hesitation in the acceleration.

It will bug the crap out of me to just drive it with it unplugged, for my sanity I can't stop this journey until the MAF is plugged in and the truck performs as it should...

Any thoughts or help planning my next step will be greatly appreciated.

 

[bobbywalter]

What Intake system?


What air filter? Did you remove the filter and try it? What year? Cali or 49 st emissions?

What are the actual voltages present at the connector?

 

[streetroddin]

What Intake system?


What air filter? Did you remove the filter and try it? What year? Cali or 49 st emissions?

What are the actual voltages present at the connector?

It's a 1993 2wd w/ 4.0 OHV... 49 st emmission, stock intake system
I installed a new Fram air filter, but didn't know to remove it and try it...I will do that tomorrow.
I don't have much electrical knowledge, but will try to check the voltage tomorrow also if I can find the test procedure for it.

 

[rubydist]

If its a 93, you can read the codes if you have a paper clip. Please do that and let us know what they are.

 

[streetroddin]

It's a 1993 2wd w/ 4.0 OHV... 49 st emmission, stock intake system
I installed a new Fram air filter, but didn't know to remove it and try it...I will do that tomorrow.
I don't have much electrical knowledge, but will try to check the voltage tomorrow also if I can find the test procedure for it.

I tried running the truck without the air filter and had no improvement...

Ok, I found this link on testing the MAF

Part 1 -How to Test the Ford Mass Air Flow (MAF) Sensor (easyautodiagnostics.com)

I performed all 4 tests with these results...

Test 1...11.56 volts on wire "A"
Test 2...11.48 volts on wire "B"
Test 3...12.2 volts to 14.15 volts on wire "C" ( engine was surging from approx. 500 to 1800 rpms)
Test 4... voltage increased and decreased smoothly indicating it is working properly

 

[streetroddin]

If its a 93, you can read the codes if you have a paper clip. Please do that and let us know what they are.

I have an OBD1 code reader, so I used that...here are my results with the test condition after the number and the definition of the code in parenthesis following the condition

Test condition key:
O=key off engine off
R=key off engine running
C=continuous memory mode

I was given all these codes during test condition "O" so I am not sure what the codes for the other tests conditions mean...also take note that I have been unplugging the MAF sensor and driving
the truck after installing several of the parts, so some of these codes I am sure resulted from that...

#s given to me in order
159 O,R (MAF sensor fault, above or below normal)
522 O (vehicle not in park or neutral during KOEO)
159
522
10 R (cylinder 1 has a problem)
157 C (MAF sensor fault, low voltage)
212 C (loss of ignition diagnostic monitor signal/SPOUT circuit grounded)
157
212

 

[bobbywalter]

Early 4.0 had bp sensor as well.


The maf needs vehicle power.

But your signal is too high. Should be 1.x volts at idle. So there is a bad wire or pcm voltage converter is bad

 

[bobbywalter]

Signal should be d. Pin 14. Need to back probe it when it's hooked up. One to ground ..one to maf. .2v to .7 idle or koer.


A. Vehicle power
B. Ground to chassis/batt
C. Pcm maf return pin 15

 

[streetroddin]

Early 4.0 had bp sensor as well.


The maf needs vehicle power.

But your signal is too high. Should be 1.x volts at idle. So there is a bad wire or pcm voltage converter is bad

My truck is a non egr valve truck, do they still have bp valves?

Where do I locate the pcm voltage converter?

 

[bobbywalter]

93 won't have bp ...

Your not fixing voltage issue if it's being delivered from board


Non egr is nice.

I have seen bad PC and damaged harness send current down the maf line.

The way I read that ... Was you had current on the harness side of maf line.


That's not good.

What you need to do is confirm actual maf signal voltage at idle. It needs to be plugged in...and you either make a test jumper or back probe.

I am hoping you read it wrong.

 

[streetroddin]

93 won't have bp ...

Your not fixing voltage issue if it's being delivered from board


Non egr is nice.

I have seen bad PC and damaged harness send current down the maf line.

The way I read that ... Was you had current on the harness side of maf line.


That's not good.

What you need to do is confirm actual maf signal voltage at idle. It needs to be plugged in...and you either make a test jumper or back probe.

I am hoping you read it wrong.

Ok, it'll be a few days before I get a chance to perform this test. I work doubles this week and not off till the weekend...thanks, I will post the results once I get it.