OT- Ford E350 Diagnosis Help, Please

[Hagler]

Gents,

I have been kicking around this problem with the van that my church owns. I am at a bit a dead-end for fixing it, and I would like some input from you all, if you care to share your thoughts.

It is a 1995 Ford Econoline 350, with 460 V-8, E4OD transmission, and 4-wheel anti-lock brakes. Apparently, for greater than 1 year, this vehicle has been killing at stoplights & stopsigns, with no other performance problems. A very good, trustworthy, local mechanic diagnosed a bad Idle Air Control valve, and replaced it some time ago (many months). The problem has gradually returned. I drove the van, and decided that the throttle body needed cleaning. I cleaned it, and I repaired a cracked MAP sensor hose. I checked the base idle, and tried adjusting it, but the problem persists.

I have cleared the computer's memory, and it has re-learned idle strategy. Shifting has always been good, and accelleration is good. Highway performance is great, and there are no missfires, stumbles, or sluggishness. The church tows trailers with it, and they shuttle around volunteer work crews, too.

Upon further inspection, the problem only occurs as I am rolling to a stop, or as I am rolling to take off from a stop. Sometimes, the engine does not kill. Often enough, removing my foot from the brake pedal (without touching the gas pedal), in order to take off from a stop, is what cause the engine to die. Again: taking my foot off of the brake pedal kills the engine.

There are no codes in the computer's memory. The van was taken to a second local auto repair shop, because all that I can do is speculate about what is wrong with it. After talking to the owner of that shop, I feel that he is selling "preventive maintainance" (major tuneup for a miss that "kills the engine at an idle"), but not really addressing the problem. The van has other issuses (possibly a bad radiator; possibly bad anti-lock brake computer), but none of them appear to be related to the complaint that I was trying to rectify.

I have a couple of ideas, but they are guesses. I do not wish to guess at a solution, and wind up spending money playing parts-changer. I need some educated input. So, I ask you: what would cause this van to run perfectly the majority of the time, but kill when I take my foot off of the brake pedal, without goosing the throttle?

Thank you,
Shawn

[flatnose]

Check all vac lines for an air leak. If they have never been replaced, change them all. A quick check for leaks is to squirt berrymans, or brake cleaner onto vac hoses( you will hear a change in engine rpms if there are leaks).....check intake manifold around the base...also check for air leaks around throttle body etc etc. The idle air control valve is electronically controlled by the computer. The computer gets info from a temp sensor mounted on the motor. Poss bad temp sender? Ford are notorious for bad idle air valves. Take it off and clean it with carb cleaner....the pintle gums up and sticks. You may have another bad idle air valve. (I fitted 2 to the same vehicle in under a year).
It sounds like the motor is very air sensitive... ie a change in vaccuum when using the brakes. Check the vac hose to the brake booster and the other end to the manifold. you can disconnect the booster hose at the manifold, and fit a temp blank off plug. Then roadtest carefully and see if the problem is eliminated.
Dont try and adjust anything. You will lose the factory setting, and all you end up doing is masking over the problem and not fixing it. If you know how to use one, a vac gauge connected to the intake manifold would be a great diagnosis tool.
I would strongly suspect you have an air leak somewhere in the system, or the IAC valve is not operating properly.
If you have adjusted the throttle plate, you will have to readjust it to factory setting.
p.s when using carb spray, run the motor at idle, and keep vapor away from the air intake.
How many miles on that thing? If its over 120000, throw it away....it aint worth fixing.
Good luck.... you will need it.

[flatnose]

The EGR valve also acts up on those things. I am not sure if it has a water heated EGR vave, or vac operated. Make sure the radiator is topped up. Check all the above first. If that does not fix it, check operation of egr valve, and possibly replace it.
If the vehicle has plenty of power for towing and driving uphill, then fuel system pressure and filter are OK.

[RKrodle]

I agree it may be a vacuum problem and it could be in the brake vacuum booster. it does seem strange that it happens when you let off the brakes but I would still suspect the brake vacuum booster. Does the engine idle ok in PARK without the brakes pedal depressed? If not try turning on the A/C and see if it idles up or becomes stable.

[Rusty]

We had a Crown Vic a few years back that would soil the plentum really bad if the oil wasn't kept clean. A rough idle was the result.

If you disconnect the negative battery terminal while you're doing the cleaning the computer will reset it's parameters while you're doing the cleaning. Spray the inside with carb cleaner then let it set a while. Then spray again and brush like mad. Re-connect and carry on.

A good Ford mechanic that used to do my work told me that it's also hard on the vehicle when different people drive it in so many different ways since the computer is always trying to adjust.
Ain't computers great?

[Tycer]

I too would suggest several cans of brake cleaner and spraying everything that hold vac. Pay good attention to the TB and intake manifold gaskets. If you've got a continuous leak and the computer has the A/F mixture adjusted as far as it will go, the added difference of the brake booster might be enough to flip it out.

Also, disconnect the brake booster vac hose and plug it and see if you can duplicate the problem. If the problem goes away without the booster hooked up, our guesses that it's vac related are more likely correct.

Make sure you've got enough leg strength to stop that thing and stay off Gause

[Buffboy]

I'd concentrate on the vacuum booster. Considering the age of the vehicle the booster likely has an internal leak. Most likely at the seal where the brake pedal rod enters the booster.

[kirkwood]

Since you got a lot of advice already on vacuum, let me return to this: the throttle body needs cleaning.

Yes, you cleaned it, but doing it once doesn't necessarily solve the problem. Take it to someone who can do an overnight or over the weekend pressurized throttle body flush and then change the way it is driven. Using it for short hops and then leaving it undriven for days causes glazing to build up. Put it on an annual or bi-annual throttle body cleaning schedule to keep the problem from coming back. Some engines are just more prone to fouling due to the way they are driven.

[Gun Smith]

The torque converter clutch is not unlocking as the van rolls to a stop.

[Hagler]

Gentlemen,

Thank you for the input.

A vaccuum leak has crossed my mind. A bad brake booster has been what I was thinking about. The second shop suggested that, when pressed about the brake pedal issue.

The one possibility that has been in the forefront of mind is this one:

The torque converter clutch is not unlocking as the van rolls to a stop.

I would appreciate any more suggestions, if you have any, gents. I will let you know what develops.

Thanks, again,
Shawn

[JReed]

Gentlemen,

Thank you for the input.

A vaccuum leak has crossed my mind. A bad brake booster has been what I was thinking about. The second shop suggested that, when pressed about the brake pedal issue.

The one possibility that has been in the forefront of mind is this one:

The torque converter clutch is not unlocking as the van rolls to a stop.

I would appreciate any more suggestions, if you have any, gents. I will let you know what develops.

Thanks, again,
Shawn

I dont know about the torque converter. The reason I say that is you said it happens when you leave a stop also I could see the torque converter being the problem if it only died at a stop but it shouldnt be much of an issue on take off. I think a leak in the booster is a good place to start. Does it diesel when it dies or does it just cut out?

[Hagler]

Jeremy,

What I guess I should have said is "inappropriate application" of the torque converter clutch, via faulty signals to/ from the ECM. If the computer engages the TCC at the wrong time (at idle, trans in drive) then it could kill the engine.

What I was thinking is the "Brake On-Off" switch (Ford calls it "BOO"; lets the ECM know if you are pressing the brake pedal) could be faulty, or the Throttle Position Sensor could be on its way out. I mention the TPS, even though I am NOT exercising it, when the killing occurs, because the ECM relies on it for data (vref/ signal return) related to engine operation via throttle angle.

Another possibility is a bad Vehicle Speed Sensor (attached to the speedometer gear). Like the TPS, the VSS gives the ECM data about the van's motion (road speed).

Moving on to the other switches & sensors, I thought of the transmission gear position switch, which tells the ECM which gear the manual selector is in, as possibly being faulty. ...or, a combination of these sensors & switches could be the problem.

The van may be leaving that second repair shop, soon. They want in excess of $1,000 for what amounts to preventive maitainance, and appear uninterested in the reason the van is in their shop. When it gets back to my church, I will pursue the vaccuum booster diagnosis, first. I will rule it out, before trying to tackle more complicated things, or trying to find someone else who we can trust to fix it. "Keep it simple" should be foremost in my mind. Tycer, I will stay off of Gause Blvd., with the brake booster bypassed.

Thanks, again,
Shawn