I'm trying to diagnose a crank nostart on a 1968 F-100 i6 240. This is my friend's truck that has been sitting for around 2 or 3 years since it was last running, he said it would usually run fine but had a hard start. Then one day just quit. Since I've never worked on a car this old before, I just wanted to get a few tips on how to proceed.

I put in a new battery and changed the oil. The oil was so thin it was almost like water... I don't know how it got to be like that. I suspect that because there's no spark the basically flooded it over and over and it just drained into the pan and thinned it out. I used 10w-30 conventional because I've heard that synthetic oils will "clean out" and break up the crud and cause even more problems. Some people suggested a heavier oil, I don't know what people are running in these.

Now it appears to me that we don't have spark anywhere. I've basically poured starter fluid in the intake and it hasn't changed a thing as it cranks. I have an HEI spark tester that I use for my other cars, it has no spark on anything, but I don't think it is supposed to work with a car like this. Maybe I'm wrong but I don't trust it. I tried disconnecting the wire from the coil at the distrubtor and holding it about 3/16"-3/8" from ground but it didn't spark. I can't get the spark plugs out because they are bigger than the spark plug socket that I have, but I'm going to try and do that next time I head out there.

It had an MSD Blaster 2 (oil-fired ignition coil) in it that was mounted sideways, the top was craked and popping out and was leaking oil. From what I read those aren't good coils anyway but especially when they get mounted sideways they have problems. I would have got a different coil entirely to replace it but he just went ahead and got another identical MSD Blaster 2. It was like $80. Still, after replacing it, no spark.

The coil has power on +. With the key on its ~11.8V, start its ~10V. What I have read is that it should be 12V to start and 6V to run, to avoid burning the coil up, but I figured I would fix that after I got it to actually start. I suspect that the previous mechanic who was working on it, years ago, was having trouble with diagnosing electrical and just plugged both run and start into the start on the ignition switch. I could try jumping + to the battery for a direct 12V but if it can run on 6V I can't see how that would help. When I measure the resistance across the + and - on the coil it starts at 0.7 Ohms and then drops to 0 as I hold the meter's probes in place. 0.7 is in spec for the coil, and I suppose the decreasing voltage is normal as you hold the probes in place. The resistance from + to the wire is 6.5k Ohms. The package says that it should be 4.5k Ohms. Could that be a cause of no spark? Some people say online that 6.5K is fine.

I found a wiring diagram here but the only thing I can find that is wrong is that the ballast resistor isn't installed for the coil I'm using. Although, I don't know what that symbol inside the distributor is supposed to mean. The distributor housing is grounded all the time... is it supposed to be periodic? I know there's moving parts in there but I don't know much about them past the cap / rotor. Still I suspect the coil because the resistance is out of spec from what's on the box and I can't get it to spark, and the cap / rotor looked OK and when they fail it is more likely to have spark on some plugs but not others, rather than no spark to any plugs.

Anyway. I guess the plan for tomorrow is to get the right size spark plug socket, maybe try jumping the ignition coil to 12V and seeing if that changes anything, then re-replacing the ignition coil. I suppose if its not that I should recheck all the timing.

 

Pop the cap. Points? Watch some vids to see how to deal with them. Might just need to be cleaned up.

if it’s been converted it should be simple to test. Sometimes the parts store will have an accel version of a Pertronix 2.

 

I always thought that the distributor cap/rotor acted as the switch for the spark, never realized there was another mechanical switch underneath. TIL.

There is a tuneup kit on rockauto with a rotor, points, and condenser in it for $6 so forget cleaning it lol. I read points should be gapped to 0.025"-0.027", is that correct? I'm also probably gonna return the new MSD Blaster 2 coil for out of spec and just get a normal one so I don't have to fool around with the resistor.

 

I have never seen a coil go bad so save your money.

Most of the time the points get a crust on them from sitting.
Take some 400 grit same paper and run it thru them then take clean white paper and also run it thru them and see if you get spark then.
I would guess that gap would be good to get it to run but you really should set the points by dwell.

BTW if you put a test light on the neg of the coil with cranking it should blink if the points are working as they should to make spark.
Dave ----

 

Its sparking now after I put in the the new points. I also changed the condenser, distributor cap, and got a working ignition coil. I was going to change the rotor but the one I got on rock auto doesn't fit correctly so I'm just using the old one. But its sparking anyway so that's good. Still not running though, and I don't know if its because the spark is weak because I can't get the points gapped correctly, or if its a fuel problem.

It fires, but it won't run. I almost had it running once, I had the choke lever in (open) and floored the accelerator pedal and it ran for a bit, but when I let off the throttle it died and I couldn't get it to start again. I suspect fuel problems. I can see it pouring fuel into the throttle body so I don't think its fuel pressure. This car has been sitting for 3 years; I've heard that gas can go bad but I've never actually seen it happen before. But I'm going to try and replace the fuel filter and dump a bottle of fuel treatment stuff in the gas tank and see if that works I guess.

Also, the accelerator pedal feels loose. I think the bracket inside where the throttle cable attaches to the pedal is bent, but I don't know what its supposed to look like or if it needs to be replaced. It kinda still works though, it just doesn't do anything for the first few inches of pedal travel, then it will engage the throttle cable. But, I don't really know how those carbs / throttle bodies are supposed to look / be hooked up. Does anyone have diagrams of them? I want to make sure its getting the right amount of air / fuel.

The only other thing I can think of for why it would fire without running is compression

 

I understand your frustration. Air, Fuel, Spark. You are going to drive yourself crazy jumping from one thing to another, ie pedal linkage, compression, etc. etc.
Now that you have spark, get a gauge and set the points to the right gap; do a static timing check, that will get you close to a running parameter.
Drain the old gas. Bad / old gas isn't going to help you at all. Fuel treatment will not overcome bad gas. take the fuel line from the tank off the fuel pump. lightly pressurize the tank with compressed air to force the bad gas out of the tank. Put in fresh fuel and filter..
Remove and clean the bad gas / varnish out of the carb. Set idle mix screws to 2-1/2 turns out for starters.
With all this you will now have air fuel spark and it will start. Bad gas-gummed up carb is probably your biggest problem once you have spark and timing close.
Without the basics of air fuel gas you are going to get nowhere. My 2 C

 

You can pour a little gas down the carb if you think it’s a gas issue, but it sounds like timing or ignition still. If you fill the bowl it should run for 30 secs or so.

if you haven’t already, get a lone wolf/solo adventurer trigger starter so you’re not constantly jumping into the cab. It makes troubleshooting a lot easier.

 

Trying to start / run a motor on old gas is not good.
For now disconnect the line to the fuel pump and plug it so gas dose not leak out for now.
Get a small gas can and set it on the inner fender and long rubber hose and run it from the can to the inlet of the pump for now.
Just be careful that the hose goes to the bottom and not curl back up out of the gas.

You can see if it will start and run but I think we need to look at the points.
Lets see why you cant set the points right? Yes if not set right it will not run good.
You need to set the points rubbing block on the highest part of the dist. shaft cam lobes.
You can get it close with the key or starter button then turn the crank or fan to set it on the lobe.

Do not loosen the screw all the way leave it a little tight. Some points and dist. have a place to use a flat blade screw driver to move / adjust the points to the right gap. If you can find one a matchbook cover works as a feeler gauge. I dont know what the setting is sorry.
Once running you should set the points by dwell with a meter.

With fresh gas and the points set right see if it will start / run and get back to us.
Dave ----

 

Got it going! I drained the fuel, replaced the filter, put in fresh gas with some seafoam for good measure, and replaced the spark plugs / wires. Just took rebuilding the whole ignition system to get it to run 😜

 

Great news! Thanks for coming back and reporting your success. Congratulations on your first old truck tuneup/startup.