1996, 302 EFI, 4x4, OBDII, 4R70W, 3.55 open

Truck exhibits occasional stalling, stumbling and missing, both at start-up and when the truck is at normal operating temp. For example, after stopping for a light, pressing on the gas will cause it to bog and nearly die. Letting up on the gas will allow it to idle OK enough to move forward and pull off the road. Shutting down, and restarting usually causes this stalling condition to go away, and the truck will resume operating normally. Problem is more frequent when the engine is cold, and it will exhibit very rough idle and stalling when it is started cold in the morning. Have replaced IAC and TPS and cleaned throttle body. Problem persists. It threw a code for the Crank position sensor after idling very rough and stalling on cold start yesterday. Restarted and ran normally, and the CEL went off on its own after 5 miles of driving.

Have read practically every thread on this board over the last week. Have lots of ideas on what to check, and few tools or experience. Probably have to take it back the the mechanic if I don't find a vaccume line off or something this weekend.

If I were going to do one thing, like the coolant temp sensor, fuel filter, or etc, what should I try. It's cold here and I'll be working outside with a cheap set of sockets and that's about it.

 

I wouldn't worry about the crank code. Do you know anyone with the same model truck? 94-96 5.0L. If so, borrow their mass air meter and try it on your truck. These are classic symptoms of a bad MAF. It won't throw a code, but will run like crap, burn fuel, and stall. MAF sensors are a little pricey, so try another one from another truck first!

Good luck,
Robbie

 

Thanks for the suggestion on that MAF.

I just got done replacing the ECT sensor and reset the computer. It exibited all the symptoms as soon as I started it up. But, I shut it off and restarted it and it ran normally - even seemed to idle smoother. Took it for a drive to allow the computer to re-learn and after 30 miles or so, it did the whole act - so I haven't fixed it yet....

Will search for theads on the MAF see if I can test it before replacing. I'm going to replace the fuel filter tomorrow too.

 

The only test is to try another one. I work for a Ford dealer, and see this all the time on vehicles. Don't waste your time to try and test. Find a known good part and try it on your truck. Trust me.

Robbie

 

Thanks - if I can't find a buddy to swap me his Maf, I'll just buy the part and keep my fingers crossed...

I'll be sure to let everyone know if it works too.

 

i had a 96 eddie bauer 150 and it would run like crap once i changd o2 sensor it was fine ever changed it?

 

I have not yet changed the o2 sensors. The intermittent nature of the symptoms, and the way it will disappear when the engine is shut off and restarted puts the o2 sensors lower on the list of possibilities.

If a new MAF doesn't clear it up, I'm down to EGR and the o2 sensors, however....

(just noticed my radiator has developed an on and off leak too... )

 

sometimes its just cheaper to go to shop. good luck anyways one positive note at least ur doing alot of preventitive maintence.

 

Today I took the maf off the bread box and sprayed the living sin out of it with brake cleaner. Put in my new fuel filter(which was way overdue), and reset the computer.

It sputtered a little a block from home, so, I shut it off and restarted it and then it was good all day. But, I had a feeling "cleaning" the maf was a waste of time.

I let it get cold (3 above 0 right now) and went out to start it - right off the bat it was back to its old self...Once I got it to idle steady, I got under the hood with some carb cleaner to test for vaccume leaks, but didn't find any. Then, for the heck of it, I unplugged the MAF sensor while it was running....

Nothing happened. The idle didn't change at all. I fingered the throttle and it responded no differently than with the MAF connected.

I don't know if that's normal or not and I don't know anyone I could borrow a known good sensor from to test it, though 94-96 trucks drive by my window about every 15.5 seconds --- around here f150s out-number the snowdrifts 2-1.

The other thing is, I haven't done the Koeo or Koer test yet. I think I'll run those tests tonight and see what I find out before I drop $100 on the MAF...

 

You have a bad MAF! No vacuum leaks and unplugging it did nothing. I suggest to get one from the dealer. I know it costs more, but I get bad stuff from Advance and Auto Zone all the time. You can't clean a MAF. Do you know anyone in your area that works for a Ford dealer? Here, I can get parts just above cost.

Robbie

 

I ordered the new MAF this morning, Advance didn't have one in stock. I never thought I might get a bad part from Advance .

Thanks for all your help so far. I do know some people at the Ford Dealership here in town, but since I already ordered it from Advance I feel like I should buy it from them. That, and they did let me use their code reader for free.

Should I really be worried about getting a bad part from them? That would really blow toads!

edit PS - I never did the koeo or koer tests because I couldn't find the wiring harness that my Haynes manual was talking about. I think it was never revised for OBDII systems.

 

The OBDII connector is under the steering column. It is kind of trapezoidal shaped. If I get an electrical part, like a starter or an alternator from Advance, I make them test it before I leave. They might look at me funny, but I tell them it is a lot easier to find out now if it works, not when I bolt it on. Under no circumstances ever buy Advance plug wires. They can be bad out the box. When it comes to computer controlled electronics, I'd stick with the dealer. If it lasted eight or so years from them, the new one should do the same. The parts are cheaper, but if you have to go back and replace them every three months or so, are you coming out on top?

Robbie

 

Replaced the MAF, reset the computer, and the truck idled smoother, and it seemed like the throttle response was better. The truck was warm when I swapped them.

Let it get cold and started it up - and it was great.... for about 5 minutes. Then it did the whole act, choked down and wouldn't run right. Loping, irregular idle, and any throttle would cause it to choke and almost die. Shut it off, restarted immediatly, and it was fine all the rest of tonight.

Anyother suggestions? I'm going to figure out those koer and koeo tests this weekend, and also check the cap and rotor.

Plugs look original, so I'm going to do those too, hopefully. It's cold here and I don't have a plug socket.

Also, it is still doing the teapot whistle when it is really cold. Doesn't seem like it is comming from the belt, and it is different than a belt squeal. It is like a uber-loud teapot whistle. changes pitch with faster idle, and goes away when the rpms come up 500 revs or so. Does not do it at all once warm.

PS) the truck got 11.5 mpg on the last tank, mostly in-town driving 30mph stop and go with several 15-20min warm ups, and mostly in 4x4 due to the ice and snow around here, so excessive fuel consumption is not as big a factor as I thought.

 

Here's another component to this problem.

When I start it up cold, it usually idles high for 30-60 seconds before is drops down to slower idle. Once it drops down is when the problem will occur.

As I have said before, turning the Key to off and then restarting the truck will usually cause the problem to go away until the next time you start it cold.

But here's the interesting part, if you allow the truck to die on its own while it is acting up, and then hit the starter without cycling the ignition through off and back on - the problem will not go away. The truck will start hard and then immediatly try to die.

No matter how many times it dies and you start it, it won't run -- UNTIL, you turn the key to off, and then restart it. YOu don't have to wait a minute, or let it sit for a few counts -- Just cycle the ignition.

If that raises any suggestions I'd appreciate it. Could this be a weak fuel pump? Coil? Fuel Pressure Regulator? I don't know yet if I'm losing spark or if its fuel...

Like I said, I'm planning on doing the plugs, wires, cap and rotor this weekend...

 

Alright, may have been off on the maf, it is hard to diagnose without seeing it. Check to see if the egr valve is hot at idle. If so, check the green vacuum line and see if it does indeed have vacuum applied at idle. If so, follow the green hose to the egr vacuum regulator. It may be the cause. There should be no vacuum at idle, only during cruise. This would explain your problems. Let me know.

Robbie

P.S. Have you tried spraying carb cleaner around everything to check for vacuum leaks? If you have a leak, the engine will smooth out. Also, check fuel pressure. There is what looks like a valve stem on the fuel rail behind the distributor cap. It may or may not have a black cap on it. Fuel pressure should be 35-40psi. Also drive it with the gauge installed. Route it under the hood and attach it to the windshield. Notice if the pressure drops. You may be running lean due to a bad pump. Do you have dual tanks? If so, does the problem happen on both tanks?