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1956 Coupe DeVille Stalls At Idle When Hot

Started by limikep, June 28, 2016, 11:13:00 AM

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limikep

Hello.  I had my carburetor rebuilt by Daytona Carburetor about a year ago and works great.  I had a starting issue as well and changed the ignition coil and coil resistor (coil was bad).  The car ran great for about 6 months but now after driving 25 miles on a parkway, it stalls when I get back to the garage when it is at idle.  I also have an electric fuel pump on the car.  When the car stalled, I pulled a spark plug wire and inserted a screwdriver in the wire and had someone crank the car.  I did have a spark.  What I notice before is stalls is I get a "humming" noise coming from behind the dash that gets louder as the RPM decrease.  As RPM decease, pressing the gas pedal does not increase RPM and the car stalls.  Sometimes when I try to restart, I get a clicking noise and the whole car looses power as if it has a dead battery.  After a few minutes, all the power returns.  After 20-30 minutes, the car starts again.  I did a complete tune-up about a year ago (points, condenser, wires, distributor cap).  The car is running rich but I do not want to adjust until I solve the stalling issue.  I have never had an issue with vapor lock as I owned the car for 22 years.  I know the fuel has changed a lot since than but car ran well up to carburetor rebuild.  The car has factory A/C if that means anything.  Thank you in advance for any advice.  Michael Pisciotta CLC#11110

CadillacRob

Timeline of problem and when you installed the electronic fuel pump?

If its running rich your pump might be too strong.  On a total side note, does your oil smell like gas?
1950 series 61 sedan
1956 coupe de ville

limikep

I have been using an electric fuel pump since I got it 22 years ago (purchased car with electric fuel pump already installed).  Have changed it twice with current pump in use for about 4 years.  It is running rich because after I installed the rebuilt carburetor, I need to learn how to adjust properly... I am still learning how to adjust air/fuel.  Timeline of problem as described in original text.. about 1 year ago.  Oil does not smell like gas.  Thank you for your feedback and looking forward to hearing more.

Jeff Rosansky CLC #28373

#3
If the car is dead electrically then I would say start there. When it dies, before you even shut the key off, check the voltage at the coil. Dont be concerned if it is low because it it probably has a resistor or resister wire. What happens if you put full voltage to the coil with a jumper wire? Will it run then? We need to determine if it is electrical.
When the car seems dead, is everything dead-headlights, radio, blower fan?
A direct short in the battery could only be showing when hot. Pulling so much current the generator cant keep up. The car starves for electricity. Or a short in the generator when hot. When it dies are the battery/generator extremely hot?
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

CadillacRob

Good thinking Jeff.  I like the electrical failure due to heat theory.  Car cools for half hour and runs fine again.  I like it!
1950 series 61 sedan
1956 coupe de ville

J. Gomez

Michael,
Quote from: limikep on June 28, 2016, 11:13:00 AM
What I notice before is stalls is I get a "humming" noise coming from behind the dash that gets louder as the RPM decrease.  As RPM decease, pressing the gas pedal does not increase RPM and the car stalls. 

Would you expand on the “humming” noise you are hearing? I would take you are inside the cab when you notice the noise. How about from the outside with the hood open, any area in particular?

Quote from: limikep on June 28, 2016, 11:13:00 AM
Sometimes when I try to restart, I get a clicking noise and the whole car looses power as if it has a dead battery.  After a few minutes, all the power returns.  After 20-30 minutes, the car starts again.

That is an indication and condition of a “hot” starter. The solenoid just verily pulls the starter (clicking noise) and extends the +12 to the starter but it won’t energize the starter and it may get stuck. Even if you release the key the starter still stuck and will continue to draw current from the solenoid contact.

You now have a total power lost as the starter is the main drain.

Once the starter cools down a bit it finally releases so power is restore, but since you have drained the battery you still can’t get it starter again. Only once it is cool and the battery recycling back from the heavy power drain it will start normally.

You have the exhaust pipe within inches from the starter and if the pipe is not insulate the radiated heat will cause the starter to get extremely hot.

If you have the Service Manual check Section 10 Fig. 10-14 it would show the insulated exhaust pipes on both sides. They look like flex pipes on the picture, they actually are but slide inside the pipe to isolate the heat.

I would suggest if you experience the same condition of power lost when the car is hot, to immediately removed one of the battery cables, you may see a large spark when the cable is removed.

Good luck..!
J. Gomez
CLC #23082

CadillacRob

For my own knowledge, Im piecing together a 56, where can you get those heat insulators?  If nowhere what can be used?
1950 series 61 sedan
1956 coupe de ville

limikep

You guys are all great and thanks a lot.  I have some work on my end.  I can only hear the humming noise from inside of the car.  The battery is about 6 years old and did go dead once before (had to recharge and might have overcharged?), so it would be a good idea to start with a new battery.  The humming noise could be from the generator/other component when the car begins to starve for electric as stated by Jeff.  I will keep you posted.  Thanks again.  Mike.

J. Gomez

Quote from: CadillacRob on June 29, 2016, 09:24:52 AM
For my own knowledge, Im piecing together a 56, where can you get those heat insulators?  If nowhere what can be used?

Rob,

You may be able to get them from any muffler shops in the length and diameter you may need, or you can get small pieces from any auto parts and weld tacked them together.

The ID for the flex pipe would need to be larger than the exhaust pipe OD to accommodate slide them at the pipe bends.

The air gap in between them should allow a fare heat transfer insulation.

I also know folks with late 195X GMs have wrap the pipes with heat shield insulation wrap and place the flex pipe over for additional shielding.   

HTH
J. Gomez
CLC #23082

Jeff Rosansky CLC #28373

If you have a 6 year old battery then it is time. My original thinking was having a bad battery that only manifested itself when hot could be a problem. It could be an internal short that just sucks the life out if everything. When driving the generator can keep up with the load but at idle, such as pulling into your garage, it cant overcome the load. You then have a low voltage situation and the coil cant produce enough of a spark to keep it running........ remember hi school days when someone had a bad generator. The car would run off the battery but eventually die. Especially if you had lights on or hit rhe brakeas.
However, before you do that I suggest you take voltage checks at various temps. My concern is if you have a runaway gen/regulator issue you could trash a new battery. Either way tho, time for a new one. You can take it to an autoparts place and they can test it for you.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

limikep

Hello all,

I'm back with a follow-up.  Took almost a month to get a GOOD battery from Antique Auto Battery (as the first was defective) than wanted to test drive awhile to get a pattern.  Just to refresh.. after a 25 mile ride on parkway, after backing into garage, the car will stall while idling in garage for about 2 minutes.  Here is the update,  the car does still stall but with the new battery, I do not get that short when I try to restart.  With the old battery, when I tried to restart, the starter would "click" and the car was dead but after a few minutes, the car had power.  What I did this time when the car stalled was I tried to restart but would just crack.  The interior lights and fan did work but when I turned on the headlights they did not come on.  As I stood in front of the car, the lights just came on in about 30 seconds.  The coil resistor on the firewall is very HOT (cannot touch).  It was replaced about a month ago with a NOS original unused and a NOS original unused coil was also replaced.  Should the coil resistor get that hot and if not could that be preventing the restart until the car cools down as the car starts after about 30 minutes.  The back of the coil resistor where the wire filament is covered with the plaster type material is cracked but all the filament is covered.  Thank You.

J. Gomez

Michael,

Quote from: limikep on August 29, 2016, 09:56:37 AM
The coil resistor on the firewall is very HOT (cannot touch).  It was replaced about a month ago with a NOS original unused and a NOS original unused coil was also replaced.  Should the coil resistor get that hot and if not could that be preventing the restart until the car cools down as the car starts after about 30 minutes.  The back of the coil resistor where the wire filament is covered with the plaster type material is cracked but all the filament is covered.  Thank You.

There is obviously something wrong if the ignition coil resistor gets that “HOT”, it should be warm to the touch under normal condition.
Is the coil also hot?

Is the resistor wire correctly, you may need to check with the wiring diagram? -> “pink” wire from the ignition switch to one end, the other end would have a “yellow” from the starter solenoid and one “black” going to the coil “+” side. 

When the engine is running the ignition switch supplies the +12V at the “pink” wire and the resistor drops it down to about +9V up to the ignition coil. While cracking the starter solenoid provide a +12V directly to the ignition coil.

Good luck..!
J. Gomez
CLC #23082

limikep

UPDATE- I finally had the generator rebuilt and after road testing, the problem seems to have gone away.  It appears it was the generator that was causing the problem after driving 25 miles and at idle (when car was hot).  A number of parts were changed (that were all over due), but wanted to do one at a time so I would know which one solved the problem.  It took a few months but I got my answer.  Thanks to all you guys with all your input that put me in the right direction.  Thank You all!

limikep

I have to apologize for not updating everyone regarding the stalling issue.  I did change/rebuild a lot of parts and don't regret it as most if not all were original.  I thought the rebuild of the generator solved the problem, but the issue reappeared.  What I did change and what worked was the inline fuel filter which is installed before my electric fuel pump.  The one I removed, before all this started, to replace with a new one is shown if Figure 1.  The one I replaced it with is shown in Figure 2.  Notice they both have the same part # which is why I didn't think much about it when I changed them.  But there is a big difference.  I cut both open and noticed that the original one is bigger and has a lot more filter material and not so tightly packed where the newer style one is smaller with a lot less filter material packed very tightly with filter material.  I have to assume that when the car got hot, and because the fuel did not flow as freely through the small filter, it created vapor lock.  I purchased a vintage fuel filter as in Figure 1 from EBAY and this solved my problem.  I hope this helps some else.  Bottom line, same part number but different product.


CadillacRob

Limikep, please make sure you rule out all electrical Gremlins through careful testing of components and following a wire diagram.  That super hot resistor is concerning to me.  Did that go away?

Also, as a side note, please make sure all your ground connections are clean shiny metal.
1950 series 61 sedan
1956 coupe de ville

limikep

Rob

Thank you for the follow-up.  The resistor is just warm to the touch, more than likely from the heat under the hood.  Not like it was in the past where I could not touch it.  It had to either be the rebuilt starter, rebuilt generator or the new ignition switch I put in that solved that problem.  Otherwise, the car runs just fine without any stalling issues.

Mike

CadillacRob

Good deal Mike.  Glad you got it sorted.  :)
1950 series 61 sedan
1956 coupe de ville

limikep

I forgot to mention, I also changed the voltage regulator.  So, one of these four parts I changed solved the very hot resistor problem.  I hope this helps someone else.