eatga

I have inherited a 1987 F150 with very low miles on it that has sat for most of it's life. The problem is that it ran great one day and the next day was hard to start and when started had almost no power. I have changed the plugs, plug wires, distributor cap, fuel filter, air filter, fuel regulator and rotor button. I have tested fuel pressure and timing and nothing seems to be out of spec. After extended barely running time, the 7th and 8th cylinder spark plugs are black looking so these are causing the trouble I think. I have tested the injector harness for shorts or breaks as well as the injectors for problems. Nothing shows up bad there. Can the distributor module or EFI computer cause my running problem? I would think that if either one of those were bad, the engine would not run at all. Remember this is the engine where four injectors fire at the same time in banks of two. It gives no engine codes and I am ready to give up. The engine is a 302 and the transmission is an automatic.

RLXXI

1st rule to diagnosing an engine that's not running right is a compression check. Do that and post back your readings.

Just call me Sean

iTrader: (1)

No codes at all? You should get at least one every time.

eatga

I forgot to add that I did do a compression test as well as a cylinder balance test and both results were perfect and within the specs. I also should have stated that the only code I got out of the computer was was the 11 code which I think is the okay code.

Just call me Sean

iTrader: (1)

Yes, 11 is pass but if you didn't get it there would be a problem.

1994Vmax

Failing coolant temp sensor maybe. If it reads enough temp it may not set the check engine light. It causes the problems you describe. The gauge and computer use separate sensors.

eatga

Thanks for the idea. I had a mechanic friend suggest the same thing. Can it be unplugged or connector jumped to trouble shoot it?

1994Vmax

The computer is going to use resistance values from the sensor to determine engine temp. You would need to know what resistance it needs to see for whatever you ambient Temps are so you could start it and see if it runs normal. Unplugging it will net infinity and of course a short is zero. I don't have a chart for the Ford stuff to see what values they use for what. I hate suggesting to throw parts at it but I imagine the sensor is pretty cheap.

eatga

Thanks again for the suggestion and you are right, they are cheap enough to just put one in. I already have the coolant out so it would not be too much trouble to change the sensor out. I believe that my problem has to be electrical because of the quickness the problem developed. It was running perfect the day I shut it off and the next day I tried to start it and had trouble. Could any wire between the distributor and computer cause my problem if a rat or something else chewed it up? I have had to repair a broken injector wire where something chewed it into. I have double checked the plug wiring for proper firing order and looked at the tips of each plug. All are the perfect light gray color except 7 and 8. They are black with the oil look. However, compression on both cylinders is perfect. Like those injectors are not firing. I have checked that all the spark plugs are firing. Since everything is based on the distributor, I do not see how a broken wire could effect just two cylinders. I have in my process changed all the injector around and the same cylinders show the fouled spark plugs.

RLXXI

Very much so on the rodent issue, I have replaced countless injector harnesses due to that very reason, make sure none of that harness has bare wires grounding on surrounding metal surfaces, if the ground pulse wire is shorted it will cause the injector(s) to go full open washing out the cylinder(s)

Two wires per injector and one of them is hot at all times with the key on, the other wires are the ground pulsed circuit from the pcm.


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