Looking for ideas. 1991 F250 351W automatic. Bought a year ago- had transmission replaced professionally less than 100 miles ago. Truck ran great. the other day I drove to store and it died- started back up ran for about 5 minutes died again. started after 5 minutes drove home. sat for 5 days- started right up- drove fine for 5 or 6 miles and died.
Has fuel in both tanks but no fuel pressure. did the continuous on test and both fuel pumps work. plenty of pressure at the rail- still won't start.
I have been unable to do the KOEO test yet but will try to post by this afternoon. apparently no spark. power to the coil but not out of the distributer. I am thinking EEC-IV due to the no fuel pump activity but it should start if all else is good-no? neighbor thinks spark control or coil but that doesn't account for the no fuel pump with out grounding. Have already replaced the fuel pump relay.

I'm open to which way to go next- joe

 

what was the results of your test?

 

used the test light method (EEC IV vehicles have two connectors for self testing the system. They are located on the firewall or the left or right front fender. The large connector contains the self test output (STO) and ground (SIG RTN). The small pigtail is the self test input (STI). When the ignition is off there is power to the #4 test port and when the ignition is on there is no power. I assume either I have a complete open or complete short to the EEC-IV module. suggestions?

 

The EEC-IV emits pulses to represent these numeric codes; for example, two pulses, a short pause, then four more pulses would signal a code 24

The EEC-IV has two different test modes, the first mode is called Key On Engine Off, or KOEO. The second mode is called Key On Engine Running, or KOER, and each mode has a specific purpose. The first mode KOEO is designed to test all the sensors and ensure that they are functioning within their parameters. The KOEO mode will also display any startup error codes stored in the KAM. The KOER mode is designed to analyse the engine while it is running. Any sensors that detect abnormal engine functionality or that are operating out of specification will generate error codes. During KOER it is also possible to perform additional tests like the cylinder balance test.

To properly diagnose any problems with your truck you must first ensure that all vacuum hoses, connectors, and sensors are properly connected. Vacuum leaks, missing sensors, corroded, loose, or unplugged connectors will cause diagnosis problems and should be corrected before continuing.

One of the easiest ways to test the EEC-IV is to use the check engine light in the instrument cluster. This method is particularly handy because it requires no special tools and only a small jumper wire to perform the test

To read the codes output by the EEC-IV on your Check Engine light you will count the number of times the light flashes. Each flash of the Check Engine light is one pulse from the EEC-IV. For example if the light were to flash six times, then pause for one half second, then flash six more times this would indicate an error code 66. An error code 66 indicates that no mass air flow signal is present.


Key On Engine Running (KOER) Testing Procedures
After you have corrected any problems in the KOEO test you are now ready to perform the KOER EEC-IV test. This test checks all sensors and engine functions while they are in their normal operating states. This test requires up to three inputs from the driver during the test. The first input requires that the brake pedal be depressed, the second requires that the steering wheel be turned at least one-half turn and then released. Finally on trucks equipped with an Overdrive Cancel Switch (OCS) it must be deactivated, then reactivated.
As with the KOEO test, the KOER test will output codes twice during its display cycle.



Here is a link to the OBD 1 Code list

https://www.truckforums.com/forum/sh...ad.php?t=13475

 

I have been unable to get any results from the truck. There are no codes to read. I have tried with a test light to no avail. when the jumper is placed the check engine light fails to come on. My next attempt will be to un-hook the battery and let it try to reset the EEC-IV. I will post after that has been tried- hopefully it will reset and then it will start.

 

un hooked- replaced battery cable ends with new ends- cleaned the posts- it was un hooked for 15 minutes. same results. Can a frd ealer test the EEC-IV unit if I take it to the dealer?

 

yes Ford could test it for you. If I remember right you should try to leave the battery unplugged for 30 mins.

I know this is a stupid question but I have to ask....do you know if the check engine light works at all ??

 

yes. a week before the problem started I had taken the truck and had the state inspection performed that includes emissions. When they inspected it the guys said it passed with flying colors on emissions and were impressed that a truck that old had such good numbers. This may sound funny but as I drove home feeling all proud of my old truck for doing so well the check engine light came on. I was only about 3 miles from the house and all the gauges indicated good so I drove it on. Upon checking fluids I was a little over a quart low on oil- filled it to the appropriate level and the check engine light went out.

 

Sounds as if your having the same trouble as I am. I have a 1990 F350 with the same engine and sounds about like the same problem. I tryed another computer, but that didn't help. It seems to me that my voltage to the relays is to low to pull the relay in for the fuel pump or the other two relays. The engine cranks like crazy but no a hint of starting. What controls the fuel injectors to spray?

 

I have done some research on the above problem. Here is some possible causes that I have found.

Looose, corroded or broken battery terminals

Fuel not reaching the injectors check for a clogged fuel filter, or lines also make sure the fuel pump is working properly and make sure that the fuel tank vent lines are not kinked or clogged.

dirty or clogged fuel injectors

low cylinder compression...run a compression test

defective ignition coils or broken wires leading to them

damaged ignition components

broken or bad wires in the starting circuit

valve timming off due to timming belt/chain defective or broken

defective MAF sensor

These are some of the possible causes I have discovered that could be the reason your truck is not starting.