I'm hoping that someone can give some insight into the challenge I've having with the ignition system on a '68 F250 Camper Special, 390 block. Here's what's going on; I'm only getting an intermittent spark off the coil when grounded to the exhaust manifold. However, when I turn the key to the off position, it'll spark-to-ground ONE time, then the engine shuts off (since key is turned off). This spark issue seems to be very intermittent. When the engine does operate, (on those occasions), when at an idle, the spark to plug #1 is intermittent (as seen using a timing light). However, when I am able to get it running and I increase throttle, the spark remains consistent. To reiterate, the reason it won't routinely start is because it's not getting spark all the time, BUT on those occasions, when it does fire up, at an idle, it's very rough, and then the engine runs smooth at 1,000 rpm and above. It's as if there's no problem at all with the ignition system. I've already changed... rotor, cap, plugs and wires, ignition switch and fuel filter. . I've not replaced the condenser yet. The points are only about 5 months old. I have the timing set at about 2-4 degrees BTDC. My thoughts... there's a short in one of the low voltage ignition wires, OR the coil is going bad. Has anyone else experienced something like this and are there any recommends?

Thank you in advance!!!

CaptJRS.

 

With the ignition key on you should have a solid 12v at the ignition coil. If you don't, then you'll have to find the bad connector or possibly the ignition switch. It could also be the bushings in the distributor causing the points to move out of position. If you can wiggle the rotor shaft it's probably time for a distributor rebuild or a new one.

 

62Ford, thanks for the recommendation. I'll check voltage and distributor sway tomorrow. One question; the 12V to ground from the coil, which terminal would that be from? I'm guessing the one that goes to the distributor, but I thought I'd ask.

CaptJRS

 

12V goes from the battery to the ignition switch, to the ballast resistor to the coil + terminal. That reminds me that it'll show 6 volts at the coil with the ignition switch on unless the resistor has been bypassed. Then there will be 12V at the coil +. When the ignition is in start position the ballast resistor is bypassed for easier starting, but doesn't sound like that's part of the problem.

The coil - terminal goes to the distributor, which switches the coil on and off.

The ballast resistor keeps the points from burning up too fast.

 

62 FordF250.... Since you replied with some good information, here's what I've done; new coil installed, (so basically, the entire ign system is new). The engine starts, and runs as before. It must have been the coil. HOWEVER, now there's a unusual issue that's occurring. Cylinder 4 misfires at low RPM, but fires great above 1000 RPM. I'm using a timing light and have checked all wires. When the engine "hiccups" it's always related to when cylinder 4 misfires. I've swapped the wires with cylinder 7, which has the power stroke at the same time as #4... the problem transfers to cylinder #7. It's not the plug, nor the cylinder itself. It's as if there's a crack in the distributor cap to where the #4 connection is misfiring but only at low idle (about 500 RPM). Again, at and above 1000, it smooths right out, and fires every time, (as I'm looking at the timing light hooked to #4.

I'm at a loss to figure this one out!

Thanks for your earlier response!

CaptJRS

 

Glad to hear you got it mostly repaired. It sounds like there are only a couple components left to test. You ruled out the cylinder and spark plugs by swapping the wire. It could still be the wire itself, the distributor cap, or the distributor.

Try swapping the wire completely and keeping the firing order the same. If it follows the plug wire, replace it and done. if not, you can try a different cap. Mfg defects do happen. If a different cap doesn't solve it, then it might be distributor time.

 

Exactly what I'm thinking... I think I still have the old cap and could swap it to see what happens. In any case, I have a distributor (electronic) being shipped, so I'll be able to get rid of the points. We're on the same track. Thank you again.

 

If you upgraded the coil to a 12v coil you can permanently bypass the ballast resistor once you get rid of the points. That'll give a hotter spark.

 

Very good. I have a slight worry about slipping in the new distributor and getting it on the correct worm gear. The next project will be a 4bbl carb. Suggestions? (I know it'll require a new intake manifold). The rig has headers, and it's a stroked 360, with 390 cubes. Currently it's a 2bbl. Thoughts?

 

Before you pull the old dist turn the crankshaft (by hand or w/ starter) until you're at TDC power stroke #1. Rotor better be pointed at #1 and that'll make aligning the new dist easy.

The oil pump drive shaft is driven by the bottom of the dist. It's not too bad to get it all lined up, but be careful about dropping the drive shaft.

 

Very good.... Yes, ensure roter is pointed at #1, and rotate crank until piston is at TDC #1. It sounds as if the oil pump is a slotted drive, so, if so, that should make it easier to line up. SO, the next saga. Out for a drive, engine runs great (above 1000 RPM), heats up a bit during the drive, then the engine dies! I let it cool down, started it up, drove it home (about 15 minutes) and it died again as I drove into the driveway. I'm wondering if, when very warm, it's affecting something to where I lose all spark, with the spark back in play after its cooled a bit. More to figure out! Have a great evening. CaptJRS

 

I have seen coils fail when hot. Ignition modules too but I think you still have the points in? Could also be a vapor lock type situation, but not likely.

 

Yes, still have points, but hope to eliminate with the new distributor. Interesting comment about vapor lock and I'd lean that way too, however, the rig ran great all summer, with temperatures fairly high and the engine leaning towards the hot side, but no sign of the engine dying. Now that it's chilly, it dies when warm AND the RPM's drop to an idle. Thunderkiss1065, thanks you for your thoughts! Once I get this sorted out, I'll try to post what the solution was.

 

A bad condenser can sometimes break down when hot, and resume working when it cools off. You said that it was the only component that you had not replaced in the distributor, correct? It is not an expensive part, so replacing it would be a good idea to keep your truck running until your new distributor arrives. While in there, make sure that the grounding wire in the distributor is in good shape and not corroded at the terminals.

 

Thank you bushuna for your reply! Since then, I've also replaced the condenser, to no avail. As it would happen, yesterday, (during a completely different function), I ended up talking to a man who has worked on older cars, and his thought was that one of the distributor lobes is slightly worn. So, when hitting that lobe at low RPM, it'll tend to misfire. All to say, the new distributor is in hand and almost ready to install. I've heard that sometimes some part of the the oil pump may drop when the old distributor is removed. I'm hesitant to install the "pointless" new distributor, but I think that'll be the only way to fix this!!!! Thanks all for the comments.