Hello Ford Truck Enthusiasts. My 1st post here. Wanted to start by saying thank you for all the information you have provided me so far. All the past posts and technical help to other members has been a great help to me to find test procedures for my truck and check things off my list.


My problem.
I have a 1996 F150 4.9 I6. only 60k on it. 5spd. that will start after sitting for a day and depending on how cool it got the night before, determines how long the truck will run. Generally 30sec to 2 minutes before you are no longer able to give any throttle, and then it will stumble, sputter and die. Will attempt to restart, and it runs for 5-8 revolutions (guessing) and then dies. Problem started suddenly. Went to the store, came out, and it would hardly run. No past issues.


What we have done:
Fixed a couple obvious broken vacuum lines
Cleaned the IAC valve and throttle body
Replaced the MAP sensor (with a used one) but no change
Replaced the pick up coil in the distributor (motorcraft - pressed the distributor apart and back together to make sure we didn't have reman part troubles)
Replaced the ignition coil (motorcraft)
Replaced the Ignition Control Module on the fenderwell
2 Fuel filters (theorized the 1st one could have clogged up in the 1st couple minutes of running.. we were wrong)


Tested the TPS - seemed to have a nice clean swing within the specified voltage range.
Cleaned and tested the MAF - has power and ground. Seemed to show nice clean readings
Tested the intake air temp sensor. Had good resistance change as temp changed (put it in the freezer)
Fuel pressure seems to be roughly 50psi on both front and rear fuel pumps.
Swapped around the fuel pump and trailer brake relays. (no change)
Coolant temp sensor shows 25ohms cold, and ~12ohms around the time it dies (seems to be functioning)
Both O2s show .3V cold, and steadily drop down to .2V the time that it dies. (probing the blk wire with a volt meter)
KOEO battery voltage is 12.4. and 13.9 engine running.


I saw tonight that I have a P1351 High input code stored. I had previously had about every code possible stored as we were unplugging sensors while the truck was running / starting in an attempt to see if 1 made a significant difference. We are guessing it's running long enough to go into closed loop, and is then looking for an input, and seeing one it doesn't like.


Not sure what to do next here, besides throw tune up parts at it, or spend more time hunting a vacuum leak. I am a little gun shy to throw any more parts at it without some better test data. Any help you guys can provide would be greatly appreciated. I used to be a technician, so feel free to put me through the ringer on tests.

 

robster1213, I am sorry that I cannot help you, but wanted to welcome you to the forum. I am sure others who drive and maintain the newer F.I. engines will come to your assistance.


You might also want to join and post on this forum: http://www.fordsix.com/forum/viewforum.php?f=2

 

Try a wiggle the wiring harness test!

Looks like you've covered most of the items, but I'd investigate what that P1351 High input thing. My first thought with anything EFI is change the O2 sensors... I heard typically they should be swapped out every spark plug change (or was it every 2nd spark plug swap?), anyway you've measured both so I'm outta idears.

 

I have moved the harness around, and can't get it to make a difference. I have ohm'd wires and haven't found anything yet.. still hunting.
I pulled a spark plug to take a reading, and the plug was broken internally and badly worn. So I decided to break down and buy a set of plugs, wires, cap, and rotor. When the truck is running (cold) it runs much stronger now. But as soon as it has been running a minute to 2 mins. it stumbles, and dies. Will still operate at WOT which points me to it being a closed loop problem.
When I was at Oreilly's the guy at the counter selling the plugs and wires told me some folklore about the coolant temp sensor having a bad spot in it, and it showing a high ohm value as the temp was increasing, showing the computer the "coolant temp was at -40F!" Anyway I put my meter on it to watch it as it warmed up that evening, and one of the leads off my mulit -meter got caught in the fan and broke the top of the coolant temp sensor off.. OOPS. So We get to test his theory anyway.

 

UPDATE:
I found a thread you guys have about failing PCMs ECUs whatever you choose to call the computer. So I decided to pull the ECU out and look for leaky caps. Discovered this truck has a remanufactured motorcraft ECU. Makes me worry I have been chasing issues tied to the ECU.
I borrowed multi-meter from a buddy that can read hertz. Tested the MAP sensor and it has good ground. Has 5V source voltage.. but no output from the signal wire. Same goes for the other used MAP I bought.
According to the MAP test, I had a bad MAP sensor, and bought another bad, used MAP. Question is: have any of you guys used the replacement style maps the auto parts stores are using now? These 1996 F150s 4.9s have 2 vacuum lines going to the map sensor, but those lines go down to some port tubes on the EGR tube. I have never seen anything like that before. Have you just plugged the old lines and run a new line to the intake manifold?

 

Turns out the 1996 F150 4.9 does not appear to use a MAP sensor. What I replaced and had been testing was a DPFE sensor for the EGR system. I found a test for the DPFE sensor and tested it with a hand vacuum pump, and it tested good. I pulled the EGR tube off the intake manifold and taped over the hole with duct tape in a hope to test the EGR system and seal off that vacuum leak if there was one. Thought was: maybe it was sucking large amounts of exhaust gas at idle, if the EGR vacuum actuator was not working correctly. Didn't make a difference...
Tested the EGR vacuum actuator just since I was there and had the vacuum pump out.. Actuator tested good. Re-tested Fuel pressure, MAF, TPS, coolant temp sensor, O2s. Everything tests out very well. Would like to get the O2s a little warmer, but can't get the engine to run that long.
Thinking it's time to replace the ECU. You guys having any experience with the Cardone brand ECUs, they seem like the affordable route. I don't have much experience with them though.

 

Reaad a bit, and was going to say the MAP is a DPFE sensor which indicates to the PCM if a failure in the EGR occured (either by user or other...).

'96 is an OBDII setup, is there a diags tool you can use to watch what it does when it does run?

 

I only have a scan tool to pull codes. I don't have one that will show live data. Not sure if 96' supported all the live data or not. I have a couple more buddies I can check with for a scan tool, that will show live data, and see whats there.

 

FIXED! It was the ECU (computer)


After putting a meter on the coil to watch RPM as it was getting a signal to fire as the engine just died. It seemed as though there was fuel pressure, but the injector pulse was gone from the ECU to the injectors. Checked resistance across the injectors to make sure I didn't have a shorted injector or some odd thing there that was possibly feeding a short back into the ECU. All checked out fine. Verified I had a pulse out of the PIP at all times. Hooked the meter up to in (hrtz) and verified I had a pulse as it died. Signal seemed consistent with dying engine rpm each time. I guess the other test would have been to spray starter fluid in the intake as it died, and watch it come back to life. ( I didn't try that)
Oreilly had that Cardone reman ECU. Actually was a genuine motorcraft Ford ECU that had been repaired through their process and tested, I didn't take it apart to investigate. New (reman) ECU and she's back on the road. Hope this helps someone out in the future, whos trying to diagnose a bad ECU on one of these old trucks.

 

I knew it!

well, not really... butt glad you got it figured out! Considering you ruled out everything else