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maf sensor problems???


blh0007

Well-Known Member
Joined
Jan 16, 2009
Messages
138
Vehicle Year
1994
Transmission
Automatic
Hey everyone,
I have a 94 ranger 4.0 that is running like crap... it has slowly and gradually gotten worse over time... it dies if i try to rev it and it will only idle rough for 15-30 sec and sputters out. I started with routine maintenance.
replaced plugs, fuel filter, air filter, cleaned maf with proper cleaner. all of these seemed to help some, but the truck still will not run down the road.

I got the idea to try unplugging the maf sensor as a test. The truck runs great with it unplugged...
i went to a salvage yard and picked up a couple of maf sensors with the hopes that one of them would solve the problem... i replaced the maf sensor and the truck ran good for about 20 miles and then started having the same problem again. i've tried 2 maf sensors from the salvage yard the truck still runs like crap.

Does anyone have any ideas?
thanks
 
Does the engine run better cold than warm?

Cold engine is running on preset fuel/air mix(called Open Loop), when it warms up computer uses the sensors to set fuel/air(Closed loop).

Can you test the fuel pressure, engine off-key off, engine off-key on, engine at idle and engine at 2,500 RPM.
35-40psi is the range.
Also check the Fuel Pressure Regulator's(FPR) vacuum line, pull it off and check it for gas smell, the FPR's diaphragm can leak causing raw fuel to be sucked into the intake.

The Coil on these can also be an issue, they can be tested with an OHM meter.

Why does it run better with MAF unplugged?
Well, unplugging the MAF sensor puts the computer in to Open Loop, so it is running preset fuel air and timing, ignoring other sensors as well as the now disconnected MAF.
Since you have a few MAF's I would test them and the wiring for the MAF to the Computer.
Good info here for the tests:
http://www.therangerstation.com/tech_library/CleanMAF.html

Used MAFs can be bad, yes not likely to get two that are bad but odds are not 0 either.

MAF sensor is there to tell the computer how much air the engine is using, if there is a leak between the MAF and throttle plate(air plenum) then computer is getting the wrong data, if there is a vacuum leak then computer is getting the wrong data, unplugging the MAF stops the wrong data going to computer, so MAF may be working fine, there is just unmetered air leaking in from somewhere.

Anytime you disconnect the battery for a few minutes the computer is reset, so it will relearn sensor data, which can take 10-50 miles, and you should reset computer anytime you change a sensor.
 
Last edited:
Running rough

you may want to take the computer out and check the capacitors...when they get old the capacitors will leak... I had the same problem unplugging the maf the truck ran fine...plugged in it ran like crap...mine was the computer capacitors
 
I appreciate the information guys...
I will start looking into some of these options and see if i can figure it out.
 
ok, so i figured i would take a look at the computer capacitors first since it seemed easy enough to pull the computer... i have attached 2 pics of the capacitor that i think may be a problem... but i need some opinions before i go further... this is the only capacitor on the computer that has the black mark and the green oxidation color at the contact points. could it be the problem??
 

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FYI, to anyone who may have similar problems...
looking at the pictures i attached in the previous post.
I took a screw driver and scraped the black burn mark and the oxidation off of the circuitry. Problem solved for now.:yahoo: I think the reason for the problem was a bad ground. At least i know where to start looking if this starts happening again.
later
 
Hey thanks for updating us! I have a similar issue, sometimes. Maybe i'll give this a try. Thanks!!!!!!!!
 

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