I recently bought a 1981 F-100 with a 300 inline six cylinder. The truck willl turn over but not start. I have checked the timing and it is okay. I have replaced the Duraspark module, ignition switch, distributor pickup coil, ignition coil, plugs, wires, cap and rotor. It has spark but will not start. It is getting fuel. It tries to start but wont. The only unusual thing that I have found is that it will crank in any gear. I thought if the neutral safety switch is bad it will not crank at all. I can't seem to find the problem. Help!

Thanks in advance!

 

OK THIS IS NOT THE CORRECT WAY OF FIXING THIS BUT,
MY PARENTS HAD A TRUCK THAT DID SOMETHING SIMILAR, NOT WANTING TO SPEND ANY CASH AT THE TIME WE JUST CUT THE NEUTRAL SAFTEY SWITCH OUT, SO THAT IT THOUGHT IT WAS IN GEAR ALL OF THE TIME, THE OLD TRUCK RAN FOR YEARS....UNTIL IT HAD A MEETING WITH A LOG TRUCK!

 

Bobby,
Your 81 should not have start in gear protection (neutral safety switch), I think that came out in 83. Try putting some fuel in a small bottle (beer bottle, soft drink, whatever) then with someone cranking, try pouring small amounts of fuel into the carb. Perhaps even though your fuel pump is working, it may not be able to keep up, or it is working intermittently. It's worth a try, and doesn't cost anything.

Good Luck,
Ernie

 

Do not try the above unless you want to grow yourself a new set of eye brows... And, yes you do have a nuetral safty switch. My 80 has one as well as my 70. My 80 has a 351m. I am having the same issue with it. If you do get it running, if you could, drop me a line, and let me know what you did.. Thanks

 

check out your battery cables. I've had sort of a similar problem - the engine was getting some spark, but not enough amps to actually run, especially when wet. I cleaned up the pos. cable right at the battery and haven't had any problems since...Dave

 

Thanks Dave! Actually, I just changed the cables, and am getting the problem.

 

oh, bummer. well good luck and let us know!

Dave

 

Just a suggestion, check and make sure distributor is installed correctly and has the right firing order.

 

Thanks all!! I will check all of these. I did receive a wiring diagram, and noticed on my truck that I do not have a wire going from the batt. side of the coil to the "I" terminal on the starter relay. Maybe I am not getting enough spark?

 

His truck might not have the neutral safety switch. My 82 F100 doesn't have it. Its got the 300 too. Im thinking fuel pump working some of the time and not others, I've had this same prob with my 82 before and it was the fuel pump. Try a small amount of starting fluid down the carb and then try starting it, see if it fires. Or take the fuel line off at the carb and have someone crank the engine, see if your getting fuel out of the line. Fred

 

Neither my 1980 or 1981 have a neutral safety switch, and the wiring is still factory. One is a custom with a 400, the other is an xlt with a 302. As to the burning of eyebrows, there is little difference between starting fluid and gasoline that isn't introduced by the carb. The process works, I've done it dozens of times - and using a little common sense, have had no ill results. It's one way to identify the fuel system as a problem. 1982f100 is also right about doing a flow test at the inlet side of the carb, it works as well. If this doesn't point to the fuel system as the problem, checking your timing would be a good idea.

Good Luck,
Ernie

 

Hey Guys. Thanks for the ideas. I tried re-timing again tonight. Still won't start. I've tried pouring a small amount of gas down the carb and then cranking, still wont start. I have a good stream coming from the pump to the carb and a steady stream coming from the carb jet. I looked at the wiring diagrams and it didn't list a neutral safety switch until '84. The switch on the trans range selector only has two wires so I'm assuming it's just a back-up switch. I think I might try some starting fluid and then do a compression check next.

This one has me baffled. Got good spark, timing light strobing on #1 top dead center and got fuel spraying into the carb. The 300 6 cyl timing is gear to gear so I don't see how it could jump time either. I think I'll take a few days off of it and just think.

 

Maybe this is a crazy idea, open each plug and get a little gas into the cylinder replace plug and crank.......If someone redid the heads before you and the valves are not opening this would prevent gas from entering......
Weird things continue to happen each and every day........................

 

I was wondering if the choke is already in the open positon when you put fuel into the carb? And if so does it close when you try to start it? Also have you tried starting it in the neutral position?

 

Since you say that you just bought it, you might have bad/watery gas. Try using fresh fuel from a gas can. Just disconnect the hose from the tank, and connect a hose into a gas can on the ground.

Also, when you are cranking, does it backfire, cough, sputter, lope or does it just crank over forever. Check the timing by feeling TDC on #1 using a wooden dowel and pull the distributor cap to make sure it is aligned with #1. Don't trust the timing marks. These motors are known for the balancer slipping and moving the mark way off.

Otherwise, just work slowly and methodically and don't just throw parts/money at the problem.