I have a 1988 F250 460 EFI(bought it new in 88)...has 175k mi. and now has an intermittant problem. After a cold start in am it sometimes stalls within the 1st. 3 miles of driving and then I get several cranks and no starts before it finally starts and then runs fine throughout the rest of the day. It has dual tanks and problem occures with either tank. I have maintained this truck and it is in excellent running condition. I would like to solve this problem before it leaves me stranded in the boonies. Any suggestions?

Jim

Try startig it after it dies by depressing the throttle slightly (10% or so). If it then starts right off, the Idle Air Control motor is sticking. Easy and inexpensive fix.

If it's the IAC motor sticking can it be cleaned and lubed or should I just replace it?

Any other posabilities if it's not the idle air motor?

Since it's a "speed density" EFI system, it *could* be an engine coolant temp sensor or vacuum leak problem too, but that's not common.

You can clean the IAC motor, but that is usually a "patch" and not a fix.

Thanks again for the info and quick response

ModMech, if your out there....this AM iit happened again....2mi. after start up cruising at 40mph....died. I tried to start with pedal slightly depressed as you suggested but still got several cranks and no starts before it finally started. Have ordered a new idle air valve and will pick it up today and see what happens....also maybe some how related....on two ocassions after leaving vehicle parked at work in hot Arizona sun for 10 hrs I got several cranks and no starts at initial start up, but it did eventually start....still think it is air valve?

Jim

No I do not. Since the distance/time element is so similar between the occurances, and that it has given you troubles in 90* weather, I think the Engine Coolant Temp sensor, or it's wiring are defective.

The reason I think that is when you start it, the computer operates the engine in the "warn-up" mode and it switches to "run" on time so that could explain the "2 mile" quitting problem, the computer *thinks* the engine is much warmer than it is, and it's leaning out causing a stall. The no start hot, would be explained by the the computer not adding enough start-up fuel because it thinks the engine it warmer than it is.

The engine coolant temp sensor (ECT) is a two wire sensor, of the Negative Temperature Constant type (hotter is LOWER resistance). Resistance should be about 40,000 ohms at 65*F, and 3,600 ohms at 180*F. So a high resistance in the wiring will also fool the EEC into thinking the engine is much warmer than it really is.

Do I have two coolant temp. sensors....one for the temp. gauge and one for the computer or just one common to both. Coolant temp gauge reading hasn't changed at all.
Jim

Yes, gauge sensor is a one-wire sensor.

ModMech....I changed out the air bypass valve over the weekend and checked out the coolant temp sensor and it checks out ok...but I have nailed down the failure a little more.....it appears to be a time thing....whether I let it idle or drive it after a cold/cold start it dies in 8 minutes is this of any help? Any more suggestions?

Jim

It's having issues when it switches from open loop (warm-up) to closed loop (O2 feedback). It does this on time/temp. New vehicles are on time only, older ones like yours go on both. Since it would warm up quicker while driving, that would explain the two miles driven vs. 8 minutes at idle.

Vacuum leak? If you have a small cacuum leak it will go too lean at idle in closed loop causing a stall, and it can cause extended cranking times hot and cold.

It does it in 8 min...at idle OR driving! I can set my watch by it. Consistant as hell. O2 sensor is fairly new..less than 10k on it. Any particular location I should look for vac. leak? Cold crank and start is immediate...no problem there,just on restart after stall.

I assume a bad connection at O2 senser could caust this also????? If so I will check O2 senser wiring....what do you think?

Also seem to have bypassed the problem the last two mornings by going to WOT (wide open throttle) for a couple of seconds before 8 min. had elapsed.....does this help narrow it down? I appreiciate all the help as I am driving a 16 yr. old truck and cannot afford to go to Ford for service.
Thanks,
Jim

Hmm, going WOT would do two things really. Get the O2s hot enough to work well sooner, and raise the ECT faster. Sounds like the O2s are not "comming up" fast enough in light driving causing it to go lean.

So I should be looking at the O2 sensor and wiring?
I only went to WOT for 2-3 seconds at the most!

Anybody else have any suggestions? Feel free to chime in....I need all the help I can get.
Jim