The Stovebolt Site Forums The Shop Area The Electrical Bay Intermittent No Spark - Maddening PLEASE HELP

Have a '54 235 still 6 volt that runs smoothly - but when I turn off the key after the engine is well warmed, or after a drive I have no spark until the engine cools down again. If I don't shut off the engine it runs fine, but as soon as I shut it off I cannot start it again, there is no spark. Have had the carb professionally rebuilt, have replaced coil, plug wires, distributor cap, rotor and condenser. Vacuum advance is working fine. Timing is good. Have checked for a short where the negative lead goes through the distributor wall - has no short that I can detect. I've tested the ignition switch. Another thing that is driving me nuts and may be related is that after warming up the engine, when I set the dwell, as the engine keeps running - say 20 minutes, the RPM slowly changes (faster or slower, no discernible pattern) and the dwell (usually) increases. I'm at wits end. HELP!!!

revted47,

With all that you have replaced, it must be almost a new truck. My only question is how are you determining there is no spark. Have you had your wife or a friend turn the key on and crank it over while you hold a plug wire that you have taken off a plug 'near' a grounded engine component.

Is this a standard transmission with a stomp starter. The coil can increase resistance as under-hood temperatures go up and result in this problem...you have replaced the coil. I would have to say that this problem isn't ignition related UNLESS your spark test when warm shows no results.

You listed a whole bunch of stuff you replaced but didn't list points. I'm guessing you just forgot to mention them. A increase in dwell means a decrease in point gap, but again, this shouldn't come and go. Have you taken a voltage reading on the primary side of the coil...the wire from key to coil (+) when the truck is hot.

Verifying that there is absolutely no spark at the plug end when the truck is hot will be the first chore! Good luck.

Stuart

Thanks for the reply - perhaps first of many! Yes, forgot to list the replacement of the points. Yes, have definitely checked for spark by having some one turn the key (in this case) while I check for spark. I've repeated the experiment four times with consistent results = warm engine, shut it off, no spark - wait 30 min. fires right up no problem. But the dwell does increase - then I reset it and sure enough after a while it increases again. Have not taken a voltage reading on the primary side of the coil - will do so tomorrow morning. Assume it should it be 6v. since this is a six volt system. ???

revted47,

Any change in dwell would mean a change in point gap. The only way point gap could change is if they were loose on the breaker plate and this would be a one time deal...and obvious. This is a toughie. Does the starter turn the engine over briskly when the truck is warm? When you replaced the coil, the new one was a 6 volt unit and is wired + to key and - to distributor.

The only component in the ignition system that is heat sensitive is the coil. Everything you are describing screams carburetion, not ignition.

Did the truck do this before all the tune-up work was done? When you replaced the plug wires, did you also replace the coil wire?

Stuart

Again, I appreciate your thoughts - here's what I know so far - The carb was just rebuilt last week by a very well known, reputable guy used by many of the better mechanics in our area. So, if it's a carb problem I'm stumped. Second, I did check voltage to the coil - both on the positive (key) side and the neg. (distributor) side - and I'm getting good solid voltage to the coil, and to the distributor - but there is NO spark. Yes, I did replace both the plug and the coil wires (NAPA parts through out) and I believe I have good solid connections. Regarding the coil - I have replaced it, but this problem occurs with both coils. Ok, last point - was how did it run before the tune-up - well it gradually got worse and worse, so I began replacing stuff, and then it just quit running altogether. Now I've replaced and tuned everything I can think of - so I'm sort of wondering of there is an internal problem in the distributor itself - but I'm not sure what's in the guts of the thing. Am I way off track here? Frustrating thing is that when I fire it up the morning, or after a cooling off period it runs just great!

revted47,

The fact that a new coil made no difference takes that off the list of probable causes. There is nothing in the distributor that would change with a hot engine/cold engine problem. If this is truly a condition brought on by heat, any electrical component would be the first suspect as the resistance goes up as the component warms. The condenser can react to heat, but you have replaced that too.

Obviously, the most common items that would react adversely to heat would be a percolating carburetor or valves that were too tight, but this has nothing to do with a no spark situation.

I don't know what kind of volt tester you have, but I think I would measure the voltage at the + and - side of the coil WHILE someone cranked the engine. The - side should alternate between a positive reading and zero as the points open and close. Do this when the problem would be present.

I know you have checked the point gap using a dwell meter...have you actually set them or checked them with a gap gauge.

If the starter is worn out and marginal, it might be pulling excessive power when you are in a hot start condition. This could mean a weak spark. I know I have stated this a bazillion times before, but I still wonder if you are really getting no ZAP at any plug wire when the engine is hot. This arc probably won't be huge and might be difficult to see...you could find a volunteer to hold the wire while you tried to start it.

Stuart

Do you have a ballast resistor in your ignition? Could cause heat related problems if you do.

revted47,

Your profile info is a tad sparse. From previous posts I gather the subject of this thread is a car, not a truck. The wiring diagram shows the key side of the coil coming from a common post on the gas gauge that is fed by the ignition switch. Is this how you see it?

Stuart

might be in the starter.............being that you have replaced the coil,.............but then that would not address your dwell......up or down rpm.

you got a strange gremlin my friend..

let us know when you find it

Ok, Automark, thanks for your patience with me - sorry I didn't say at the beginning that we are talking about a '54 Chevy 210 Coupe with the original engine, wiring, voltage etc. Now, I've done some more investigation based on your questions. First, yes, the key side of the coil does come from a common post on the gas gauge (and maybe that's the problem - a poor connection there?) Second, yes there is a tad bit of spark. I volunteered, my son turned the key - I got a zap, though not a big one. Finally, I took a voltage reading off the negative (distributor) side of the coil - I mentioned that I had strong voltage - but here's what it reads about 15 volts and drops to 7 volts when points open. How can this be? My VTOM isn't a super expensive model but it has been reliable in all other situations. Incidently my Tack/Dwell and Timing Light are Snap-On equipment in good working order. BTW - yes set the points with feeler gauge then adjusted the dwell from there.

The only way I could see that happening would be if the points and condenser were not grounded. There should be zero volts at the negative side of the coil with the points closed, and battery voltage with them open. What you are decribing would be consistant with a twelve volt system with a ballast resistor, except that the opening and closing of the points is backwards and the readings taken from the + side of the coil rather than the -(distributor side).

Opps, sorry again guys, my mistake - I should have said drops to 7 volts when points close! Now, since the engine has cooled I just went out and started it - and took a voltage reading. Sure enough the voltage drops to zero when the points close. But, when it heats up and the problem returns I get the 7 - 15 volt reading again. Two of you have mentioned a ballast resistor - the only place that might be involved is that I do have a kit that converts the six volts to 12 volts to run a radio/cd player. The radio is connected to the ignition switch.

If the radio is connected to the ignition switch, where is the inverter?

disconnect the radio and see what happens..or by pass the converter..................

The inverter taps off the ignition-coil (+) wire then to radio. Disconnected the radio, - engine warming up, will let you know.

Remove it, as joker advised.

revted47,

Forget about the ballast resistor, it's not used on your system. I would assume this inverter is wired in front of the feed to the radio.

Sometimes you can get lost in voltage readings. The important point is that there is spark when the truck is up to temperature. If there is a flooding condition from a hot carburetor problem combined with marginal spark, the truck probably won't start. Cooling is actually allowing the fuel to evaporate and hence the truck starts.

Next time you drive it and this problem is ripe to happen, before you crank it over, mash the throttle to the floor and hold it there for at least a minute. Then without lifting it, crank the engine over and see what develops.

The voltage readings seem to be gooney..how can a system read 15 volts when it's only a 6 volt system...don't know! Don't get lost here...try the fuel angle first. You can always go back and tackle this voltage thing if the flooding doesn't seem to pan out. Don't give up!

Stuart

Hats Off to Automark! I ain't out of the woods completely, but I'm making progress thanks to your persistence. Part of the problem was indeed flooding and I've got that solved. Another part was that the points (maybe I got a wrong set somehow) would not fully open. I filed a larger slot in the base of the points to allow them to move futher on the cam screw and that solved the dwell problem. I've re-timed it now that the dwell is holding.

The final hurdle is that it now runs rough and not well when accelerating under load. Could it be that one or more of the valves are too tight? Or what? I think I've been over run by a tribe of gremlins - not just one boogie man.

great...Stuart knows his stuff real well, nice to have him and others aboard here..

do you have a pix of your car?

WHat about the distributor itself? If it has worn bushings or gears, the dwell could also change sporatically. As the engine warms up things expand and the oil viscosity changes allowing the parts to relax their fit.

Just a thought.

I've wondered if that distributor needs to be replaced. When I get the money I'll probably put in a Mallory or Pertronix unit. That could be awhile so I've got to make the best of what I have for now.

Hey, here are links to pix of my '54 coupe which we've been discussing) and my 5-window '53. Thanks for your interest:

'54 http://i193.photobucket.com/albums/z298/revted47/Teds54cropped.jpg

'53 http://i193.photobucket.com/albums/z298/revted47/cGlacierPeak53Chev.jpg

nice pix..........thanks for showing.
Fred..

on a side note, i once had a 66 GMC pickup with a 283 in it... i had similiar problems with the dwell "changing" on its own... after several weeks of troubleshooting and messing with it, I found that the plate that holds to points to the distributor shaft housing was cracked, which allowed the plate to move several degrees, this would happen every time is accelerated or decelerated!!!

I've had this exact same problem on a '54 sedan with a 235. I replaced the condensor, points, coil, ignition wires, etc... and when the ehgine would heat up... the ignition system would seemingly just go *puh* and open up. readjusting the points would get me back on the road but when it would cool off, I'd have to readjust the points back to where they were. The timing seemed intermittent.

The problem was exagerated by the 6 volts... and what I found was that I was not securing the points down tight enough with that retainer screw... so when the engine would heat up, it would cause the points to 'slip' and open up. Since 6v has so much more current draw than 12v, there's more heat involved as well. And because I was always fussing around with the points on the side of the road, I in turn was not tightening them down enough because I was so frustrated.

The solution for me was a new set of points, a new screw, WITH a lock washer! Just make sure those points aren't going to travel anywhere.