Mechanics

F250 ENGINE WILL NOT START

1991 Ford F-250

Engine Mechanical problem
1991 Ford F250 V8 Two Wheel Drive Automatic 159000 miles

The 7.5L engine in my F250, with dual tanks, will not start. I have been troubleshooting it now for a couple of weeks and just can't seem to find anything wrong, and have now run out of ideas. I will provide a list of everything that have tried and the results.

- The engine cranks over nice and hard, so I know the battery and starter are good.
- Both fuel pumps are working, as you can hear them come on when the key is turned on.
- Verified that the fuel pressure is 40 psi at the schrader valve on the fuel rail for both pumps.
- Replaced the fuel pressure regulator, and verified fuel is flowing from the hole when it was off.
- Ignition module tested good at Auto Zone.
- Verified injector solenoid winding resistance on all injectors, they read between 14.9-15.3 ohms, this is cold. Can not test hot as the engine will not start.
- Pulled the connector from all injectors and verified 12 vdc present on the positive wire of each with the key on.
- Verified firing pulses as each injector was plugged in one at a time. No injector caused the pulses to stop. I used your " how to test an injector" article.
- Verified spark at the end of each plug wire.
- Verified that the inertia switch is not tripped.

Spark plugs, wires, rotor, distributor cap, fuel filter, air filter & O2 sensor were all replaced about 6 months ago, and have less then 5000 miles on them.

Thanks for any help you can provide.
Avatar
Matmo
July 11, 2010.



Hi
Try this remove air snorkle open throttle spray CARB cleaner into crank does it fire?
Let me know
Tnaks for donate

Docfixit
Jul 13, 2010.
I did not try this with carb cleaner, but I did try it with starting fluid. It would not start with that either. It was after that, that I started looking into the injectors and verifying if I had spark.

Tiny
Matmo
Jul 13, 2010.
The spark you get at plugs is it 1/4 to 1/2 in. And blue/white?

Docfixit
Jul 14, 2010.
To check the spark I pulled the wire off of each plug, inserted and extra plug that I have, grounded the plug, and then turned over the engine. The spark only goes across the small gap of the plug, it was white in color. So, no it was not 1/4 to 1/2 inch long. Do you have a different method of doing this? Please let me know and I will test it in that manner.

Tiny
Matmo
Jul 14, 2010.
Your method is O.K. So need three things for engine to run fuel, spark and compression. So the question have you checked compression? Did thie problem come sudenly? Any warning signs?

Docfixit
Jul 16, 2010.
Actually I just got the gauge and adapter from Auto Zone to test this. I should be able to perform the test sometime this weekend. I was also reading more material on your site and found a page that mentioned that a blocked exhaust could cause this problem as well. As I am sure that the catalytic converter is the factory original It would not surprise me if this was a problem.

The no start condition just came on suddenly. I have had an issue since the last time I was at lake last year. I accidentally got the muffler under water and it has been hard to start ever since. I usually have to hold the pedal to the floor and then start it, to rev the engine up, otherwise it will start and then die. I will post back once I have checked these two items.

Tiny
Matmo
Jul 16, 2010.
If muffler was under water likely got to CAT and fractured it. This will cause exhaust restriction and hard start

Docfixit
Jul 17, 2010.