I have a 1994 Ranger 2WD, 2.3L, Manual trans...

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I rebuilt this truck for one of my daughters. Engine completely overhauled, all new suspension, tires, etc... It was driven a year or so and was passed down to my son. It's been sitting for a few years until he got his drivers license. It was never driven much, so it really doesn't have that many miles after the rebuild. It has been sitting for the last 2-3 years I'd guess.
The truck ran perfect up until it was stored. Never a problem. No CEL light, no stalling, etc.

We took it out a few days ago to teach him to drive and the truck stalls while you are accelerating, usually in lower gears. The stalls are like switching the ignition key off and on (immediate engine kill and run). I've tried stomping the gas pedal to the floor while it's in the 'stall' and it does nothing. Dead stick. The engine comes back immediately after you let up on the gas pedal, or switch gears. The CEL also keeps going on and off during this stalling phase.

The engine will continue to do this until you can creep it up to highway speeds and only then will it stop stalling. Once you're 'cruising', all is well. I've been able to reproduce the 'stall' in the driveway only once. While in neutral, I revved the engine high and it did cut out once. I have yet to do it again while in the driveway.

Things I've done or tried thus far:
EEC is tossing a code 157 (MAF undervolt) KOEO
EEC is tossing a code 998 (Hard fault) Engine ON
EEC initially tossed codes 543 and 546 (fuel pump circuit issues), but they seemed to have disappeared for the moment. Possibly temporary reset of the CEL. Will know more tomorrow.

The IAC valve is BAD. I removed it to clean and check and found that the coil will activate, but the valve will not move. I can manually move the valve, but it won't while you apply power. So the valve is confirmed DOA. Will this cause the stall? I don't know.

DPFE valve appears to be OK:
Brown/green wire: .62v
Brown/white wire: 5.04v

MAF checks:
Engine OFF:
Battery voltage: 12.8v
Terminal (A): 12.3v (neg VOM lead to battery)
Terminal (B): 12.3v (pos VOM lead to battery)
Terminal (C): 12.35v (pos VOM lead to battery)
Terminal (D): na

Engine RUNNING:
Battery voltage: 14.6v
Terminal (A): 14.62v (neg VOM lead to battery)
Terminal (B): 14.52v (pos VOM lead to battery)
Terminal (C): 14.57v (pos VOM lead to battery)
Terminal (D): .07v at idle, ramps smoothly to about .40v at high RPM. Voltage lowers smoothly when RPM backs down.
Voltage between pins (A) and (B): 14.65v

Seems to me the MAF voltage is indeed too low as the CEL indicates. So what causes a too-low voltage to the MAF?
The signal voltage DOES operate smoothly, so am I looking at a bad MAF?

To look for possible voltage/amperage issues:
I detached the relay box to take a look underneath. Nothing broken or obviously damaged. I pulled on many of the wires but none gave way, so I can assume they are good.
Replaced the positive wire from the battery to the starter relay.
Replaced the positive wire from the relay box to the starter relay.
I used heavy duty 4 gauge welder wire I get from battery shops.

The original wire between the relay box and starter relay did have slightly burned/overheat marks where it attaches to the studs of the relay box, so I figured replacing the wire with a larger one wouldn't hurt. The wiring on early Ford's was never the greatest and most could have certainly gone a gauge or two larger (IMO). I also soldered everything.

I cleaned all grounds that I could find.

Unfortunately none of the wire upgrades and cleaning solved the stalling issue. I didn't think they would, but the upgrades didn't hurt. Nor did they cost me anything as I had the extra wire.

The fuel filter is due for replacement, but I'm pretty certain it's not a fuel issue as the engine stalls and recovers immediately as if you shut the ignition switch off and on or pulled/replaced the EEC relay. A fuel issue would take a few seconds. In fact, i tested that theory and pulled the fuel pump relay while it was running. The engine took a few before it died.

For the love of my sanity... does ANYONE have a clue?
Whatever caused the stalling - happened while it sat. A poltergeist perhaps? Ex-Wife with a voodoo doll?

 

Takes fuel, air, spark & compression to make em run, so whats going missing? When it stalls, are the dash warning lights out, or lit?

 

Thank you for your reply...
Dash lights are ON when it's stalling. Only the engines craps out like you're shutting the key off/on. While in a stall, the moment you lift up on the gas pedal - the engine returns.

I also confirmed today that the EEC relay is NOT dropping out, so that can be ruled out. I made an LED test light and connected it to the output side of the relay to verify if it was losing connection. It wasn't.

This is the strangest problem I've ever had on an engine and I'm just about ready to go full tilt!

The engine dies and recovers too quick to be fuel related, or at least it sure acts that way. And it only does it when you're accelerating in lower gears. You can eventually 'creep' up to highway speeds and it will stop stalling. Likewise, it will run top-notch all day long sitting in the driveway. I've been able to reproduce the stall only once in the driveway while in neutral.
I brought the engine to a very high RPM and it stalled. It quickly recovered just like the other times on the road: back off on the gas pedal and it returns.

I also did checks on the battery and charging systems. I swapped the alternator for a slightly bigger one I had from a 2001 Ranger I used to own. It increased the amperage output by about 7 amps. Nothing to rave about, but I wanted to rule out any issues there. Unfortunately the alternator swap didn't solve the problem (I didn't think it would anyway - but what the hey). I also have a 200 amp alternator, but that's way over kill. If my kid installs a big stereo and amps, he may want that larger alternator.

QUESTION: On these 94 Rangers, should the engine die when I unplug the MAF? I read some cars do and some don't.
My Ranger does NOT die when I unplug the MAF while idling in the driveway. In fact, there is NO change whatsoever when I unplug the MAF. It purrs away in the driveway. Also, the error codes do indicate voltage problems with the MAF. So I'm wondering... IF the engine supposed to die when the MAF is unplugged, could the low voltage somehow be causing it?
The MAF signal voltage does change when you increase/decrease RPMs, but nowhere near the typical 1v to 3v that most apparently show.

 

Oh how the mighty can fall from the littlest things...

The MAF was working, but at a MUCH lower output voltage, so I decided to take the MAF housing off the air box and completely clean it. I already cleaned the MAF itself, but it didn't fix the problem. I took the small plate that's at the end of the MAF housing off and found a spider nest! It looked a lot like cotton. Dunno how this industrious little spider found its way in - but it did

Once I evicted the cotton spider nest, my MAF voltage returned to normal: Around 1v idle and 2.8v snap-throttle. Engine no longer stalls! YAY!

There was enough air flowing through to run OK at idle, but once you got going down the road, the engine would stall. It acted like you turn the ignition off/on quickly. This puzzled me to no end. Maybe the techs have ran into spidery-clogged MAF's before, but I sure the heck haven't!

My guess is (techs - please correct me if I'm wrong):
At idle, there was little air passing through the MAF due to the spider nest, so the computer said there was lower MAF voltage than normal, but not enough to kill anything. Once I went down the road and increased FUEL and AIR demand - the amount of air across the MAF stayed relatively the same, so the computer said WHOA! WRONG MIXTURE! Too much fuel and not enough air, so the mixture was leaned back and killed the engine. Or something to this effect? I think this is why it felt like an electrical stall rather than something else. Perhaps a little of both?

Am I right? Or close?

Why it wouldn't do this consistently in the driveway is still a mystery. I could rev the engine high in neutral and it would not stall (actually it did - but only once). I'm wondering if the speed sensor had something to do with this?

In any event... truck runs beautifully again! Lotsa power and I didn't throw a bunch of unneeded sensors at it like (unfortunately) a lot of people do.

So guys... if your engine is stalling and/or has these symptoms, CHECK that MAF inside and out!

1. Vehicle has sat and/or stored for long periods and has signs of arachnid activity.
2. CEL is on and tossing codes 157, and possibly 543 and 556.
3. Stalls/bucks at lower speeds like the ignition is being turned off/on.
4. When stalling, you can press gas pedal to floor with no results (dead stick).
5. Engine recovers quickly if you lift up on gas pedal.
6. MAF has correct supply voltage, but shows low voltage on signal wire (pin D) at idle and high RPM. (CEL code 157).
7. Engine runs fine in your driveway, but stalls when driven.

Clues:
1. Sat for a long time between operating.
2. Good supply voltage to MAF, but low output on signal wire.



Thanks to everyone who helped out!

Oh and I had a little fun with some photos... Enjoy!

 

Good trouble shooting find, fix feedback & to hear all now seems well & your on the road again. I've heard of a few strands of spider web causing problems, but don't think I've ever seen That much in a MAF sensor!!!

 

I thought this might be a 'doozie' as far as spidey webs are concerned! Certainly one for the techs to study and keep in mind.
The puzzling part is how the little invader got in that far. At no time during storage was the air intake disassembled, so how the heck did he get in? I know the air system is never 100% 'sealed' - but WOW. He found that .01% hole I guess!

 

Check the air box, air filter & air tube fit & condition all the way to the MAF sensor mount.

 

Good to hear you found the source of the problem. That "Check Spider" light is real cool, thanks for the laugh.

You might find some more insight into your problem in this thread: https://www.ford-trucks.com/forums/1...d-pinging.html

Here is the full TSB referenced in the thread: Article No. 98-23-10

 

I added rep points specifically for the "check spider light"

 

Thank you so very much for making this post, and for your diligent research. I had the same symptoms with the same truck, with the same cause. Sometime while sitting, a spider built a nest in there, just not as far back as in yours.


I pulled the fluff out with a pick and it ran perfectly fine again. I owe you a beer.

Ford definitely needs to include a Check Spider light in all vehicles now.

Thanks again!