MAF plugged in starts and dies, unplugged it runs

[Chris_1]

Hi guys, got a little problem I could use some input on. - '94 ranger xlt s/cab 4x4 auto; starts great dies in seconds. Unplug the maf starts and idles but won't rev up. Original maf, 1 known to be working used maf and a brand new one - same thing. plugs, wires, fuel pump and fuel filter all newer or new. Fuel pump running when you turn the key. Power at greeen/yellow wire under relay - on at start and run ; power through inertia switch.
I have a full set of known to be working sensors, wiring and pcm, thought I would just start changing things 'till something works - any thoughts on the most likely culprits to start with?
Did just pull the transfer case to clean the governor (1-2 upshift delay when cold, which cleaning the governor fixed) and replaced the fuel pump on Monday, truck worked great till Friday morning when this problem started (or maybe I had an early version of this problem and changed the fuel pump for no reason, but what the heck it's new now).
Going to start randomly changing sensors and such tomorrow, so if anybody has any opinions, I would certainly appreciate your input.

 

[Rangerman49]

MAF issue

Hi guys, got a little problem I could use some input on. - '94 ranger xlt s/cab 4x4 auto; starts great dies in seconds. Unplug the maf starts and idles but won't rev up. Original maf, 1 known to be working used maf and a brand new one - same thing. plugs, wires, fuel pump and fuel filter all newer or new. Fuel pump running when you turn the key. Power at greeen/yellow wire under relay - on at start and run ; power through inertia switch.
I have a full set of known to be working sensors, wiring and pcm, thought I would just start changing things 'till something works - any thoughts on the most likely culprits to start with?
Did just pull the transfer case to clean the governor (1-2 upshift delay when cold, which cleaning the governor fixed) and replaced the fuel pump on Monday, truck worked great till Friday morning when this problem started (or maybe I had an early version of this problem and changed the fuel pump for no reason, but what the heck it's new now).
Going to start randomly changing sensors and such tomorrow, so if anybody has any opinions, I would certainly appreciate your input.

Might want to test the TPS, here's a video. The test would be the same as the Ranger..The TPS and MAF work together.

http://www.youtube.com/watch?v=svh5VsWIEkQ

 

[RonD]

Well the O2 sensors are not "on-line" until engine warms up, so they are off the table of suspects.

Did you test the MAF voltages per these instructions:
http://www.therangerstation.com/tech_library/CleanMAF.html

If you have a can of Starting Fluid can you spray some in the intake when engine starts to die.
If engine still dies then Spark is being cut off.
If engine continues to run then Fuel is what was being cut off.

When cold the computer is running in Open Loop, so only a few sensors are being used.
MAF, TPS, ECT, ACT(air temp).
The CKP(crank sensor) tells the computer the engine is turning so to turn on the fuel and spark, but these usually work or don't, can't see it working for a few seconds.

Check the pressure regulator on the fuel rail, it has a vacuum line, remove this line and check for gas or gas smell, if there is gas then diaphragm has a leak and raw fuel is flooding the engine, via the vacuum line.

The IAC(idle air control) valve sets the idle by allowing more or less air into the intake, if this isn't working and closed then there wouldn't be enough air to idle, engine would start and die, or barely idle if warm.

 

[Andy D]

Take it somewhere and see if it is throwing any codes before throwing anymore parts at it.

 

[Chris_1]

Problem solved ! (fingers crossed)

Thanks to the guys who contributed ideas here. Just a quick update; after going through the whole air and fuel systems, replacing a few questionable parts along the way (each of which made the truck work a little better, and are a good idea anyway) we finally worked our way back through the system, checking voltages and pressure readings the end result seems to be that the cheaper Part Source/ Canadian Tire 2 week old fuel pump just wasn't producing enough pressure (only 10-15 lbs.) It was enough to fool you because it was pumping and would make the truck run but not well. Replaced that with A NAPA OEM pump and pressure at the rail shot to 35 PSI and the truck ran like a dream ! Lesson learned - you get what you pay for.
Not a total waste of time experience though, because we learned a lot of in depth stuff about just what makes this puppy run and what stops it cold. Got rid of a lot of dirty old 20 year old parts that should have been replaced a long time ago !
Thanks again to the people who tried to help and the people who posted info about their problems and solutions. Really helped a lot having technical info as close as the computer screen.

 

[RonD]

Good job tracking it down

Thanks for posting the results.

New parts does not mean "it works" anymore, new now means never tested

 

[Andy D]

Good job tracking it down

Thanks for posting the results.

New parts does not mean "it works" anymore, new now means never tested

Yah, no foolin' If you pull parts off a junker , you at least know that they worked at one time