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Odd Problem - Dying Out after 15 minutes

5K views 40 replies 14 participants last post by  Steptoe 
#1 ·
Hello again. Maybe some day I'll be able to contribute but for now I just have questions...

I've got a 69Z (302) that I recently put a restored distibutor and new plugs (gapped to 39) into. I set the dwell at 30deg, timing at 12deg initial (vacuum and all-in timing look good) and the car runs great.

Today I was finally able to take it for what I thought was going to be an extended cruise but when I got 15 minutes from the house it died out at a stop light. It felt like it ran out of gas. I cranked it for a few seconds and nothing...dead.

I pushed it into a parking lot and cranked it over again. It was getting plenty of gas. I took off a spark plug wire and tested spark with a screw driver and the car wanted to start. I put the plug wire back on and boom...it starts right up.

So I turn around and head for home. I get two blocks from the house and the same thing happens. Sure enough, I pull my trusty screw driver out, stick it in the plug wire, get a couple sparks and she starts right up again.

The battery is very weak/old and needs to be replaced but when I check the 'system' with a battery meter, everything is charging at 14.5v consistently.

I thought for sure I burned out the points but it started up again after "the screw driver trick". What the hell is happening?
 
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#2 ·
IMHO it sounds like either a carb float or fuel supply issue or you would be smelling and saying she was flooded. Could also be trash in the tank that gets sucked up to the inlet, then after she starves and dies, it floats back up or away from the inlet screen. Could be weak diaphragm on a mechanical fuel-pump

Could also be heat soak but you would have had to wait longer to get a restart.
 
#3 · (Edited)
Thanks for the reply...I'm almost certain it's not flooding. I don't smell any gas and it starts right up (without even pumping the pedal) after I pull the plug wire and stick a screw driver in there. I checked and double checked the float setting because of another problem I was having with the carb earlier.

I forgot to mention that the battery is so bad that I've had to jump the thing after it dies out. Basically, the car dies, the battery has enough juice to crank the motor for about 5 seconds and then its dead and I need to jump it.

Could a weak battery cause this? That seems too simple. Like I said, once its running it charges at 14.5v consistently.
 
#4 ·
I just spent a little time checking some things...I let the car warm up in the driveway.

-Dwell is set to 30*
-Initial timing (vac adv plugged) was set to 19* so I set it back to 12*. I think I may have messed that up last time becuase I didn't check again after I tightened the dist. I checked it this time and it stayed at 12*. The cent. and vac timing look good.
-Float level is good.
-Idle was high (1100rpm) but is now 850rpm.
-I'm getting 8hg manifold vac at idle and 0hg at vac adv. Vac adv # goes up to 4-5hg when I tap the gas. I'm pretty sure there are no leaks...the car dies out right away when I cover the carb.

Another note: I recently changed the pushrods to CompCams Magnums. I set the lash using the CRG method to .026 and then double checked.

Could the lash be suspect? Are things expanding too much when it reaches a certain temp and valves not seating as expected?
 
#5 · (Edited)
You need Air, Fuel and Spark, and you seem to have those in the right combination. If your vehicle is standard electrical system once started you can disconnect the battery and have it run just fine off the Alternator.

If the battery is weak pull it, charge it to full then put it back in and see if in a few days of non use if it has lost charge. If so you may have an aftermarket radio or alarm system draining power, or an FOE device such as glove box or trunk light that is on all the time most likely draining juice.

If you have no loss, then run it and see if the Alternator is charging it. If that works out to debug the real issue I would run it in the driveway at various rpms for an extended period of time and see if she stall out on you. Without moving you can duplicate fuel delivery scenarios, but you might find a church parking lot to see if power loads are also involved.

I would also take a moment to check all my engine ignition system wiring for cracks, splices and loose connections, also check your coil, as it maybe responsible or your points set is bad.
 
#7 ·
If the carb has fuel (just check for squirter) then most likely ignition is intermittent. I did have the crap in the fuel line issue mentioned above and it pretty much acts as described - bowl was low enough squirters could not squirt a couple times in a row - they will squirt once depending on carb.

If standard breaker point, and it takes 15 minutes to occur and "fixes" itself a few minutes later, most likely thermal in nature.

Coil is a good one, broken wire internally at terminal most likely. Ballast wire is the other likely culprit - dissipates heat to do its job.

Bypass ballast wire, swap coils - should eliminate ignition sources.
 
#8 ·
I was searching around and did find a few posts that point to the coil or condenser.

When I check the spark, the color of the spark is yellow. I think is should be bluish in color.

Did some more searching and found that yellow spark could be a bad condenser or coil so I am going to change the coil, condenser and points.

Does that make sense?
 
#11 ·
A loose wire in the system providing power to the ignition will do this. I had a bike I could ride for a while and it would quit. Them it would start and run fine. Loose wire.

Bad coil? Seems unlikely.
Points? Bad condenser is a thought.
Electronic ignition? Maybe something there doesn't like heat.

Just a few ideas...
 
#12 ·
I would said is your condenser, by you taking the plug wire off and ground it it creates higher resistance and it will actually give you a hotter spark. also I think you should gap your plugs at 35 and replace that battery.
 
#13 ·
Wasn't there a post a while back, same symptoms, coil was overheating after running 15 minutes.
Yep...
Used be common years go dropping car engines into boats...run fine for 5 or 10 minutes on land then head out for a day fishing...15 /20 mins the engie dies...play with pionts, plugs for a while then mysteriously it fires up, and runs as if nothing has happened and 10 mins later dies...and keeps doing it
The reason... any old coast gaurd guy will tell u, is they droped the engine in, dizzy coil etc,,, But DID NOT also swap the ballist resister wire , or the ballist resister cermic resistor...in other words running a 6 volt coil on a 12 v system
And if one runs a 12v coil on a ballist system the same thing happens
Generally over here coils have a stamp / part number on the bottom, and somewhere there will be a 6 or a 12 indicating the type of coil.
So check the coil, and check the voltage at the ign wire to the coil.
 
#14 ·
About 10 bucks gets you a ballast resistor. Install it and see if it goes away. If it does you wire is bad and you can replace it or just leave the resistor on.
 
#20 ·
Try this. My 67 had this same exact issue and did the same thing and the ballast resistor fixed it. If it does your resistnace wire has gone bad and is allowing more voltage to the coil and over heating it.

If you don't want to cut wires to test this most ballast resistors are flat connection fit and your connections can easly be rigged up to see if it works. If it does just keep the resistor or go into the harness and replace the wire or buy a new harness. I am not sure the if the restance wire runs through the firewall connection and into the underdash harness. If it does or does not you could install the ballist resistor under the dash and then it's hidden. Also just put in small micro swith inline and you have handy anti theft device??
 
#15 ·
Been a while but finally got around to trying some things out...

I replaced the battery, points, condenser and coil but the issue remains. The coil is a Delco reproduction from D&R.

I'm going to follow Steptoe's instructions and check the voltage at the ign wire->coil but have a few questions.

-Should the voltage be checked while the car is running?
-Should the voltage be 6v or 12v?
-Where/What is the ballist wire?
-How do I know if the ballist wire is bad?
-How do I know if a ceramic resistor should be installed?
-Where do I get a ceramic resistor? Are there specs?

Thanks again for the help.
 
#19 ·
I'm not sure if this is a fuel or electrical problem. How can I check if this is a fuel problem? The carb was just rebuilt/restored by a well respected vendor on this site.

I just checked the voltage to the coil with the key in the on position and car not running and got 6.5V so I assume I don't need a ceramic ballast.

I'd love to have someone who knows what the hell they are doing take a look. I live about 25 min west of Chicago.

Thanks.
 
#22 ·
I'll give that a shot Joe. Does your car have points and a stock harness with the resistor wire along with the ballast resistor?
Mine was totaly stock with points ....and it had this "exact" same issue. It was almost like clock work when it would die. Let it sit and fired right back up and then in 10-15 minutes it would die.

After I added the ballast resistor then yes at the time it did have a stock harness with the resistor wire along with the ballast resistor.

I installed the ballist resistor and then later (about 6 months) went to a pertronix but still kept the resistor and the harness the same. The problem never happened again, I have now installed an HEI dist since putting the car back together and removed the resistor.
 
#23 ·
Tried the ballast resistor this evening and the car won't start with it in place. Only getting 2volts with ignition on. The car sounds lik it's going to start and immediately dies. Starts right up when remove the resistor.

Any other suggestions?
 
#24 ·
Bypass your you ignition on wire to the ballast in side that you resistor wire is feeding. Going strait to battery power will work to test with.

See if it starts, if it does and stays running there has to be a feed wire issue to the coil. If not I am totally lost because as i said before mine did the same exact thing. I am no electrical guy but I have to think your issue lies in the resistor wire.
 
#25 ·
Wire resistance can be checked by disconnecting a battery cable and the wires to the coil + terminal. Turn ign switch to IGN, take an ohmmeter and measure resistance from alt BATT stud to the cloth covered wire at the coil; 1.8-2.0 ohms.

The OE coil wire is cloth covered and only goes from the firewall connector to the coil.
Coils do get hot, however, one should be able to grab the coil for about 5 seconds, any hotter, as in frying an egg, is too hot - less than half a second holding the coil.

With OE wiring design, the resistive wire is more than enough, and after reaching operating engine temperature, your 6.5 volts measured is normal with engine running. Engine off, point set open, you will read battery voltage, no current flowing. Close the points, current flows, about 6 amps, coil will get hot and 6-9 volts is normal.

You can wire in a test light to the ign circuit, maybe run the light inside, to observe power to the coil. If the light retains its brillance and engine quits, swap in the older 'cooler' coil and test start. If it starts, bad coil, or maybe too much dwell, set for 30°, or 0.019" gap.

Also, there could be other hidden problems in the ign circuit, ie, ign sw itself as in burnt contacts between battery and ign, or, a dirty electrical connection at the battery junction block or horn relay buss bar or firewall connector. Current going through a resistive joint heats up, provides more resistance and reduces output voltage through the same interface.

Food for thought. BTW, coil high tension wire 1/4 inch away from ground, the spark should be blue in color - "Blue is best."
 
#26 ·
There you go Mr. Walsh ! Our resident electrical Wizzard has spoken spec,s meter readings etc. etc .When it comes to volts amps and wires he is one smart cookie and i would expect nothing less of him, a very knowledgable and thorough man. I can,t add anything more to that one , and NO he didn,t pay me to say that, and yes i can be bought for the right price LOL especially in this economy. Alex:D
 
#29 ·
Hey Everett,
I re-read your post a few more times and it starting to sink in. The electrical stuff is foreign to me so I'm naturally a bit afraid of it.

I'm not sure I understant the following statement...

"Also, there could be other hidden problems in the ign circuit, ie, ign sw itself as in burnt contacts between battery and ign, or, a dirty electrical connection at the battery junction block or horn relay buss bar or firewall connector. Current going through a resistive joint heats up, provides more resistance and reduces output voltage through the same interface."

Where are the contacts between the battery and ign? Where is the battery junction block (is this the little 1"x1" block on the fire wall behind the battery)? What is the horn relay buss.

You post is greatly appreciated.

Lastly...my spark is a dull yellow.

Gracias.
 
#32 ·
I'm not sure I understant the following statement..."Also, there could be other hidden problems in the ign circuit, ie, ign sw itself as in burnt contacts between battery and ign, or, a dirty electrical connection at the battery junction block or horn relay buss bar or firewall connector. Current going through a resistive joint heats up, provides more resistance and reduces output voltage through the same interface." Gracias.
Follow the red lead from the clamp, fusible link, the short section from clamp tothe junction block, yes, the little 1"X1" block. Fusible links can corrode inside the insulation, any lumps in the insulation? Broken strands within or at any crimped termination.

The interface of terminals laying onto a mounting surface can be a high resistance joint, wire brush clean and reassemble.

Follow the red lead from the battery junction block across the radiator support to the horn relay buss bar and see there is another orange lead on the same bar. Orange lead is a fusible link. Disassemble and wire brush, check insulation for lumps - corrosion, reassemble. From the hr buss bar, there is another lead giong to alternator and to the firewall connection. Another place(s) for resistance. Once inside the dash, the red lead is crimped and splits, one leg to headlamp switch and fuse panel, BATT, the other to ign switch.

Any one of these connections can be resistive. Generally, a voltage measurement from the battery post to most any circuit in the electrical system, there should be less than 0.5 volts difference. Any measurement more, and a resitive joint is in the path. Same is true for negative side of circuits. Got to have a good return path also. Alt case should be grounded as well, there is alot of paint between the neg post and case.

Tip: connect the ground cable to battery to the block rather than the alt bracket, less resistance. Alum intake manifolds, if equipped, do not conduct current as well as iron.
 
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