Hey guys, I would first off like to apologize for joining the group for the sole purpose to ask this question. I usually tend to answer all of my questions by browsing this site and others, but this problem baffles me and everyone I talk to. I'd appreciate any guidance you guys can throw my way.

I have a 1993 F-150 short bed single cab with a 302 and an AOD. Over the past couple of months, I've had a harder and harder time getting this thing to run right. It started off as just a rough idle and bad gas mileage so I changed the plugs to Motorcraft coppers with a gap of .054 (it originally had bosch platinum 4). I changed the distributor cap and rotor as well. I also took this time to buy a timing light and make sure the truch was at 10 degrees BTDC since I had been bumping the timing around prior in an effort to help the truck run a little better. After this, the truck would not idle period. I had to break the wax and turn up the idle screw to bring the RPMs up to about 800 so it would idle and then problem kinda solved. I drove it a couple days and it got in this habbit of dying at stop signs and crappy idleing while cold. Once it died, I would have to let it sit for about 45 minutes before it would start again. The overwhelming smell of gas led me to believe I was flooding it when it died). I did some more research and came to the conclusion that the PIP sensor was likely bad. After a week of driving with 2 feet, I was able to drive back home and install the PIP sensor. When I couldnt get the gear off due to lack of a press, I bought the entire distributor to save myself some trouble. It did great after this. It would idle at all lights and drive normally. I was even able to bring the idle adjustment screw back some. This lasted for a few days and then it was back to hard starting and kinda pumping the gas. Once I got it running though, all seemed fine. I still had no problems at lights and stop signs. I changed the ICM and that had no effect at all. I drove another day or two and changed the ignition coil. Still no effect, and then 3 days ago I drove to class and after an hour out of class I came out to a truck that would not even try to start. It would turn over all day long and I could smell loads of fuel so I decided to change the PCM. I fought for a day or so to find the right one but I succeded in getting a numbers matching computer. I installed it and then tried to crank my truck. I had spark and I had fuel but I had to wrong combinations or something and it took me 2 hours and a cop car with jumper cables to get it to start. At first it would start with me pumping the gas and then die. Then it would start and immediately die over and over. Finally It started and idled fine but would die when I put it in gear. I held the RPM at about 1500 and shifted to gear and it still died. 30 minutes later it started and i was able to drive it home. The next morning it craked just fine and took me to work. 5 hours later it cranked just fine and took me to McDonalds. 20 minutes later it wouldnt start just as it had done two days before with the old PCM. I got a ride to work and then 6 hours later I came back and it started just fine. I brought it to work and killed it in the parking lot and then waited a minute and it cranked just fine. I waited 20 minutes and it wouldnt crank anymore. I waited 2 hours and it cranked just fine..... I think you can see the pattern now.

Assuming the pattern holds true, It should bring me to work in an hour and then after sitting for 5 hours it should crank and let me drive home. Once it cranks I am driving 130 miles to my dad's house with a 1600 square foot shop and any tool you can imagine to test all connections in fine detail over then next two days. Dad has a tow dolly on standby if I don't make it. I would appreciate any suggestions on where to concentrate my efforts. Thanks!

Note: Truck is stock except for a K&N intake and exhaust with one cat delete. I have the EGR valve disconnected at the moment and O2 sensor is still there. It has 140,000 miles on it and I'm the second owner after a 85 year old gentleman that bought it new. I've been driving it now for 3 years and I take really really good care of her. Also, I am an AutoZone employee when not in class so all replaced parts are Duralast Gold (I also realize some of our parts are crap).

 

You would probably get more responses in the pre 97 forum. This is mostly for the
modulars.

 

Your request is in the wrong forum but here is some insight on your problem.
One is your lack of knowledge about how the system works.
It's not your fault but just to let you know.
Begin by saying your IAC or intake air controller is not functiong to control idle speeds.
Never set the throttle stop up to fix an idle problem.
Next, there are several sensors that are fed from the same 5 volt supply out of the ECM.
They all have a common return back to the ECM supply.
If there is a ground, open or short at one of the other sensors the truck will not start because it can affect all the others supplied from the same source.
Next, pumping the throttle has no effect on gas supply.
The only effect you can cause is holding the throtle wide open.
This shuts off the fuel to the injectors and with the throttle wide open passes air to dry up the cylinders to get out of a flooded condition.
To check this all out, you need to be looking at voltage supplied to the "TPS" feed. To do this you measure between it's feed and it's return and NOT to ground because the supply is floating or isolated from ground for special reasons.
Once you find the fault and fix it, set the throttle stop back so the motor idles at about 500 rpm with the connector removed from the IAC while the motor is at idle. If you remove it before hand the motor likely will not start.
Same as your present problem.
Make the voltage measurements at the IAC first. Look for about 5 volts across the leads. The third lead is the signal back to the ECM telling it how far open the throttle is.
Bottom line is I think you have a harness or plugup intermittant issue to find.
There are other ways to test and also look at the codes for posible leads.
One is called a wiggle test, to detect harness intermittants but it gets to involved for this format.

Good luck.

 

I just noticed being in the wrong forum. Could a moderator please move my thread to the correct forum?

 

Thank you for the info. I agree I am ignorant to the ways of these "newer" systems and sensors. I'm slowly learning however. I did suspect a shorted iac today so I disconnected it and cranked my truck. It ran fine and then half way to work it was as if someone turned the ignition off and it died. This marks the first time it has died on me while moving.

 

Your truck runs on the EEC version of ECM and program.
That version is now 3 versions obsolete. It has a 3 digit trouble code output.
Your AOD trasmission told me what version you have. It's not an electric control type.
The next version was PCM driven OBDII from 97 to 2003.
The latest system is the CAN OBDII system from 2004 to the present.
Good luck.

 

I found out the problem after getting to the shop and tracing the electrical. I had two problems. First, the IAC was shorted out and second the PIP sensor that I just replaced had gone out again. After a trip to AutoZone to exchange my warranty parts and a little timing. All is well!

 

Good to hear of your quick success.
Knowing how those systems work; I was pretty sure there was an electical issue to be uncovered by voltage test and inspections.
The PIP is equivelient to the crank sensor in the later motors.
If it goes faulty nothing works.
Good luck.