’92 Ranger - MAF Sensor Question

So the 1992 Ranger I just picked up has a dead miss, apparently at cylinder 5. I’ve done the usual (swapping plugs, swapping wires, testing the coil pack, replacing the fuel filter, switching two opposing wires within one coil pack pair, etc). Haven’t found the source of the problem yet (I think it’s probably a clogged fuel injector at #5), but there was a new wrinkle today.

Whilst changing the oil, cleaning out the air intake butterfly valve (which was absolutely filthy), and looking some things over, I noticed something odd. I tried to “test” the Mass Air Flow (MAF) sensor twice while the truck was running and got different results. I had heard that if you pull the wires off the sensor, the engine should die if it’s operating correctly. On the first try, the motor didn’t die, but the idle did kick down slightly. Thinking that maybe what I had heard about the MAF sensor was wrong, I drove the truck around a bit, then tried again. This time, the engine immediately died when I unplugged the pigtails from the MAF. Started right back up again when I plugged it back in, but at no point was there any change in the miss.

Any thoughts as to whether the MAF could be contributing to the issue I’m having? I know it’s not cheap to replace, so any testing info is also much appreciated. Thanks!

No, MAF issue would not cause specific cylinder to misfire.
Computer doesn't "need" MAF sensor, it is there to fine tune air/fuel mix.
Computer, in this Ranger, is programmed to run a 4 Liter engine so it already "knows" how much air it will suck in at any RPM and throttle position, it's just math, MAF is there to compensate for the WEIGHT of the incoming air, cold air or warm air, sea level or high elevation air weight changes air/fuel mix
Unplugging MAF sensor can stall the engine or not stall it, depends on the software version and Open or Closed loop operation, in my experience it doesn't tell you much when you do this.
Testing MAF voltage found here: http://therangerstation.com/tech_library/CleanMAF.shtml
1992 Ranger will have 4 wire MAF, test C and D wires while engine is running
A and B is the heater circuit and can be tested with just key on.
6-wire MAF had added air temp sensor, 1995 and up Rangers

Did you do a compression test?
That is the first thing to do when a cylinder is misfiring, compression is black and white, can't be intermittent(in most cases, lol)
So once compression is tested you either take it off the table as the problem and move on, OR......... you find out it is the problem and don't waste time and money on spark and fuel issues.

1992 Ranger would usually be running Batch Fire fuel injection, not Sequential fuel injection.
On a V6 engine Batch fire means 3 fuel injectors open at the same time, then the other 3 injectors open the next time, so left and right intakes are kept filled with air/fuel mix, one step up from carburetor.
Each cylinder just sucks in that air/fuel mix when intake valve opens, same as carb engines did.

So a clogged injector running Batch Fire shouldn't cause a specific cylinder to misfire, it would make that Bank(side) of the engine Lean, computer would open injectors longer to compensate so no misfires, and then you would get Lean Code from O2 sensor on that side.

Some 1990-1994 Ranger 4.0l engines did come with Cam Sensors, Calif. models, these would often run Sequential fuel injection for lower emissions, if you don't have a Cam Sensor then it would most likely be running Batch Fire

Most 1995 and up Ranger engines used sequential fuel injection and a clogged injector could cause specific cylinder misfire

Just a quick update for everyone that was kind enough to chime in on the thread and those that come after. Turns out that MAF sensor was just fine (despite being ancient). The problem was my fuel injectors. They were absolutely disgusting. 67 bucks for a rebuilt set of Bosch injectors and I’m up and running with no more vibration. HUZZAH!

Good work

I put a can of injector cleaner(Seafoam) in the gas tank of each of my fuel injected engines once a year, notice a smoother idle after about 1/2-3/4 of a tank on the older engines, and I do run gasoline that's "suppose" to have fuel system cleaner in it all year so..........don't think thats the same thing, lol.

RonD said:

Good work

I put a can of injector cleaner(Seafoam) in the gas tank of each of my fuel injected engines once a year, notice a smoother idle after about 1/2-3/4 of a tank on the older engines, and I do run gasoline that's "suppose" to have fuel system cleaner in it all year so..........don't think thats the same thing, lol.

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Hey thanks, RonD! When I posted last night, it was late and I was excited to have the old girl running right at last, so I only left a quick post. I had actually already done a compression test on the cylinder that wasn’t firing, as well as the others on that side. I’d also tested the coil pack, wires & plugs, replaced the air & fuel filters, tried running a can of Seafoam through the system, and cleaning the butterfly valve inside the air intake plenum.

But man, when I saw the top of the engine, my heart sank a bit. It was covered by an INCH of oily, rotting pine needles. Took my time and carefully blew things off with compressed air and carb cleaner. Cleaned up the inside of the intake and plenum as best I could (which were also gross inside) and pulled the injectors. Several of them were disgusting and I have no idea how the truck was even running, much less driving. Put the new injectors in, installed the new fuel rail and plenum gaskets, hooked everything back up, held my breath, and turned her over. She sounded like a different truck! Really looking forward to giving her the maintenance attention she so badly needs, as she’s obviously been neglected for a while now.

By the way, does anyone know where I can get the two “security bolts” that hold down the MAF sensor? The heads on them basically look like they accept a 7 mm Torx bit with a hole in the center. I found the correct bit to take them out at my local parts store, but alas, they both snapped on me (my MAF sensor is currently held down by zip ties as a result). No Ford dealership nearby, so I’m looking for other options to replace the two screws. Thanks!