1994 Explorer 4.0 EEC-IV (ODB-1), cranks, tries to start but dies right away. If I unplug the MAF it will start and run like crap, but at least I can move it. Exhaust left a black stripe on the curb during diagnosis.

I've looked all around the internet trying to find the answer. I have found others with the same problem, but they either never found the problem, or never came back to post the solution.

I am not a mechanic, I am an electronics and computer tech. A vehicle is just another broken piece of equipment to me. Keep this in mind if I don't use the correct terms.

The only new parts were the fuel pressure regulator, fuel pump/filter/sock, hoses, 1 of the MAF's and plugs and wires, everything else was used from the junkyard or on-line

Let me try and describe what I've done or tested so far.

Fuel pressure regulator changed. I think it was leaking gas to the vacuum line

Fuel filter, pump and sock were changed (store rental meter wasn't sealing good, and gave false readings)

Fuel pressure seems fine, I can't remember the reading, I can measure it if needed (eventually bought my own pressure tester)

Vapor canister hose replaced, the 90 degree elbow

DPFE and rotted hoses replaced, it set a code for this one time.

EGR removed, cleaned a bit, tested with hand vacuum pump and blowing in it. New gasket

IAC removed, cleaned a bit, tested solenoid with 12v power supply, ohms were also in spec. I think new gasket.

When I say "cleaned a bit" I mean I sprayed carb cleaner and maybe used a toothbrush on it, I didn't soak it overnight and it was still black.

Vacuum lines all checked, doesn't seem to have a leak, I think it has at least 25 on the vacuum gauge

ECT and IAT temp sensors checked on both ohms and volts at various temperatures backprobed from the EEC

Engine compartment grounds were all removed, wire brushed and screwed back down.

EEC changed

TPS at like 1v or 1.1v backprobed to EEC, tested ohms sweep with analog meter.

Plugs, wires, coil pack all changed

Ignition module came loose from the frame and was hanging by the wires under the battery compartment, I swapped it out with another and re-attached it to the frame.

I think that's everything I've done, and still same problem.

Before I found it would run with the MAF disconnected, I found I could keep it running by continuously spraying starting fluid into the intake hose that I pulled from the oil filler neck. After a while when it warmed up a bit, I could keep it running by revving it a bit. This is probably when I got the DPFE codes.

I can do the KOEO test and it gives 111 - OK

I have tried to do the KOER test by disconnecting the MAF, warming up the engine, clearing the MAF code, re-connecting the MAF, and starting the test sequence, but it stalls out during the test and won't complete it.

Sometimes it gives a code 157 - Low voltage mass air flow sensor (MAF). The voltage is around 0.55v, I have backprobed this to the EEC.

I have changed the MAF with one I bought on-line (Carquest) and a Ford one from the junkyard, I have cleaned the original by spraying it with MAF cleaner.

I hooked the MAF to a 12v power supply and to my meter. I used a vacuum cleaner hose to pull air across the element and the voltage went up to like 3v or so.

The truck had a K&N high flow air filter, I changed it out to a paper filter. There was a black gook coating on the bottom of the air box, but the MAF housing side of the filter and air box is clean.

There is a hose, about 1.5" in diameter, from the engine to the bottom of the air box, it looks to be a coiled metal spring with a cloth wrapping, kinda like a gas dryer vent hose. It has a hole in it. I don't know what it's for.

That's all I can think of right now. I hope someone can point me in the right direction. I'm at a loss. If you need me to check anything else, let me know and I'll post it to the thread.

Thanks,

Eric.

 

I'd be inclined to suspect you have a pretty significant vacuum leak somewhere after the MAF sensor or a bad misfire. The black soot on the curb from the exhaust would suggest a rich condition. A vacuum leak could cause this if the PCM thinks there's way more air entering the intake and it therefore extends the fuel injector pulse width to increase the amount of fuel.

Since you had the plugs and wires replaced, be sure to make sure all the wires are firmly connected at each end. If they were "economy" spark plug wires, you might want to slide the boots up on the wire and make sure the carbon wire was actually wrapped to contact the connection before being crimped. It's unfortunately not too uncommon for brand new plug wires to have bad crimps where the center conductor doesn't even touch the connector.

You mention that you removed a K&N filter and there was a black gook coating on the bottom. It sounds like someone really over-oiled the filter at at least one point. That would certainly coat the MAF sensor element which can also cause a rich condition. I've experienced that personally. If you have some electrical parts cleaner, or dedicated MAF sensor cleaner, it would be worth cleaning the MAF. However, your description sounds like you have a more significant issue than just a dirty MAF sensor. But still worth taking care of.

The coiled tubing at the bottom of the air box likely connected at one time, or maybe still does, to a heat shield over the nearby exhaust manifold to provided heated air to the intake.

-Rod

 

Ok, someone PM'd me but I can't seem to reply.

I meant to get back here for an update.

Turns out it was the flippin' MAF.

I ordered a module from the Internet, same problem.

I got 2 different ones from the junkyard, same problem.

I noticed a similar truck at the repair shop around the block, so I talked to them and brought mine over.

I had to show them how to get the EEC into test mode with the jumper and gave them some printouts on it.

I think he took the MAF from that truck and stuck it in mine, but it was the WHOLE UNIT metal ring and module TOGETHER. (he scrapped the other truck soon after)

He said he cleaned the throtle body too.

Other posts I read mentioned the high failure rate of these modules, and that they are tuned to the ring assembly.

So if you encounter this problem, keep changing the WHOLE MAF SENSOR ASSEMBLY, RING, GASKETS and all.

And maybe clean the throttle body.

Eventually you'll find a MAF that will work.

The truck is still running good to this day.

Hope this helps.

 

Similar issue for me, and t’s been driving me crazy too. I was thinking it was a vacuum issue as i was getting a MAF low voltage and o2 sensor error codes. I knew i had a LIM leak, so i tore into that job and replaced LIM, UIM, along w/ leaking valve cover's. Replaced plugs/wires while i was at it along with a new EGR valve and tube (due to rust and gaping hole). Two new motorcraft o2 sensors as well. Got it all put back together and it fired right up and idled great! I was like sweet...problem fixed! Then took it for a test drive and same issue. Pushed the accelerator going up a slight hill and it would barely run. Had to pull over and unplug the MAF again. (Vacuum is consistently ~20 idle, and fuel pressure at idle is 28-30 and rises ~40 when accelerator is pressed)

I’m actually on my 3rd MAF now. I replaced 2 MAF units (NAPA, Oreillys) and now just finished replacing 2 MAF assemblys (Hitachi-NAPA/Ford Motorcraft). This last one I tried was a NOS original Ford Motorcraft-had to wait 4 weeks for shipping but finally arrived. I’m not getting any MAF error codes but I reset the PCM and don’t think I drove it enough for it to throw a new code. But when I unplug the dang MAF I can drive it. So it still seems like it’s something with the MAF.

I’ve also tried a different PCM. I was able to find an old 1994 Ford Powertrain/Emissions service manual. It’s about 25 pounds of diagnosis info, so I was gonna try looking at the wiring closer. Took it to one shop so far and they couldn't figure it out. I think all the old guys are no longer around who actually worked on these back in the day. Been a good (but frustrating) learning experience for me and my son, since it's his daily.

Thanks again for posting a follow-up.