76 F-150 4x4, 390 motor, standard tranny.

Ran and drove great yesterday when parked. Today I go out to check the timing and carb (using more gas than usual), and the engine won't crank.
The starter appears to engage, and starts to turn the motor (kinda like the amount you get when you're trying to "bump" the motor to TDC) but then stops. The last time it did this the fuel pump diaphram ruptured and flooded the crank case with gas thus not allowing the starter to turn the motor over.
Checked this, and no gas in the oil
Check the battery with a volt meter and had 12.7 volts, and the engine is not locked up.
Any ideas? I'm guessing starter, but that's just a guess.
Thanks in advance!

 

What happens when you use a booster cable from the battery + Post to the Big LUG on the starter relay (that goes directly to the starter) ?

Try that and report back.

 

Well...that was strange.
The motor turned over, albeit slowly. I then removed the cable, and turned the key. The truck then turned over normally

I'm assuming the intent of the jumper was to bypass the relay?
BTW - I checked the connections earlier and everything was tight.

 

If gas is getting into the motor from the carb dumping excessive gas, it could be hydrolocking, and the gas is slowly getting past the rings (hence the reason it turned slowly, then slowly, but faster) Pop out a couple of spark plugs, inspect for gasoline, try cranking the motor again (key off, trigger from the relay)

 

I forgot to mention..I did pull the number 5 plug and it looked normal (i.e. not fuel soaked or anyting. Looked really good actually).

 

You got me wondering now, even though I checked a plug to rule out hydrolock from the fuel pump....

I guess it could be an intermittent starter issue. Doesn't a starter relay either work or doesn't?

 

Yes, either its on or off, but things can and do go wrong. ALso, you have 7 more other cylinders you can check, that can be hydro locked. It only takes one to cause you issues. If you are bored, put a breaker bar on the crank bolt and turn the motor over by hand. It should turn over with good resistance,and not break your arm while trying.

Also, a volt meter is not an honest test for a battery. I have owned batteries that had 12.7V on them and the minute I hook a load tester to them, they drop to 1.5 volts. You could have a dead cell? Try swapping out the battery with a different one you know is good, it wont hurt to try.

 

I'll check out the battery. I was able to rotate the engine without any issues.
Thanks again.

 

Take all the cables and connections off and clean them up.

remove the relay and brush the back of to remove corrosion and put a thing film of di-electric grease to prevent corrosion when you reattach everything.

Also check the battery cables under the insulatoras they can corrsion under there as well.

This whole area is a hot spot for electrical corrosion

 

Took the battery in today to get tested. It failed 1 out of 3 times. I went ahead and purchased another as the battery was quite old.

Good suggestions Dennis - I'll do as you suggested as well.

 

I had my son put the new battery in. Went out to check it over after he said he was done, and he had it hooked up backwards .

I reconnected the battery correctly and the truck fired right up. However, the next day the battery was dead. Replaced it with another battery I had fully charged. Truck started and ran fine. This morning - same thing...dead battery.

Seems like putting the battery in backwards shorted something out now causing a drain. I'm guessing alternator diodes, but will test to prove it out.
Has anyone else had this happen?

Thanks

 

Reverse polarity ?

Oh No !


pooched Alternator or Voltage regulator.

 

I was under the impression the voltage regulator was part of the alternator?
Is this not the case? Geez - I really need to get to know my truck better.

 

seperate parts but both involved in charging system.

In Later years the VR became integral to the alternator

 

Thanks Dennis.

Do you happen to have a diagram showing charging system you could post up?
Thanks again