Packard Forum Index » V-8 (1955-56)

I've had a similar problem with the 51 that I associated with vapor lock. Not really sure at this point. In very hot weather(90+) the engine would die after sitting through a red light. It would die after crossing the intersection. Sometimes half way down the block. Most of the time if I just kept my foot in it it would pick up again. It would be dead, just like the ignition was shut off, for maybe 4 to 6 seconds. If I pulled over and let the engine stop turning it wouldn't start again. Would have to wait 2 to 3 hours for the thing to cool off. Then it would start right up. I didn't really think this was vapor lock. Did replace the coil with a new one. That didn't help at all. Have had intermittent coils before.

The car still does this on really hot days. I do have all the heat shields in place as well as the insulating washers and gasket on the fuel pump and the insulating gasket under the carb. Had the fuel pump professionally rebuilt. Gas lines are original and properly run and the heat riser is functioning correctly. The timing was checked. The water temp isn't particularly high when the problem occurs.

Any suggestions?

It eternaly surprises me that so few people do not carry a spare coil and condener. Both are easily rigged for quick diagnostics or elusive or intermittent problems.

THis is true of other various parts of a vehicle. With all of the preaching that contiualy goes on about safety, originality, modifications etc. etc. i am continualy amazed at how many people, even experienced gear heads, do not carry or use SPARE PARTS as diagnostic or emegency use supplies. It is nearly absurd not too. Especialy on old iron.

If you see those same hot conditions coming up again, you might add a gallon or so of diesel to a relatively full gas tank and see if the problem goes away or diminishes. This isn't so much a cure as the diesel has other issues, but at least it might help confirm the diagnosis.

A different approach I saw a few days ago was on a '39 Six. It had a large diameter line between the fuel pump and the carburettor. Don't know if the owner did this or if it came to him like that. He says he's never had vapor lock, even when others around are experiencing it.

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This reply is for Bob51:

I was dealing with a Clipper that did the same thing. It would just die without warning and then restart. There was so much worn out on the car that I just scratched my head looking at it. Everytime it quit it wouldn't stay broken long enough to isolate a problem. I've had two modern Dodges that would do the same thing when not fully warm on rainy days. I solved that problem by setting the fast idle up.

Given your car stays broken I would try to isolate the system first. You need three tools: A spark tester, a vacuum gauge and a jumper wire, and a can of ether.

When it quits and won't restart first check the ignition using the spark tester.

If it has spark try a modest breath of either. If the motor kicks then you probably have a fuel problem. Confirm by removing the air cleaner and pumping the accelerator. You should be flooding the motor with fuel.

If both tests don't produce, then check the motor cranking vacuum. Use the jumper wire to bypass the throttle switch. You should have some cranking vacuum. If not then perform a compression test when the motor is hot.

I have seen these problems with leaking fuel pump check valves, worn out ignition switches, bad grounds, air leaks in fuel lines, etc, etc.

Don't underestimate the value of good battery cables. They are pricey to have made but are well worth the money because they save your starter motor as well.

Good Luck

Here is a question about vapor lock: Which side does it affect - the inlet side or the outlet, pressure side? I have always been under the impression it affected the non-pressurized side? It would seem that gasoline under pressure would be less likely to suffer vaporizing. Howard, O_D, anyone?

(o{I}o)

JW, sure - putting the fuel under pressure raises its boiling point and hence makes it more resistant to vaporizing. Everything else being equal (like ambient heat, proximity to hot surfaces, etc.) the least likely place to have vapor lock is in the line between the fuel pump and carb as it is under modest pressure (3-5 psi) much of the time. Most likely is the fuel line from the tank which is under suction as its boiling point will be slightly depressed. The fuel in the carb is under atmostpheric pressure if the percolator valve or vent is functional so it would be a candidate before the fuel line from the pump to the carb, again everything else being equal (which would be really uncommon). Knowing just where the vapor lock occurs would be fundamental to solving the problem. If the carburetor, a stuck (closed) heat riser valve would be a likely culprit.

What Issues do diesel or kerosene have?

Brian, I'm sure you know you need quite higher compression ratios, 16 to 1 and generally much higher, to efficiently extract the power from diesel or kero. So if you add enough diesel to your gasoline to notice the effects, you'll have less power, more visible (black) smoke, a tendency to foul plugs and valve stems, perhaps carbon-up piston tops and rings, etc.

But a fair # of old car owners have reported using it in amounts of about 1 gallon or so per 20 gallons of gasoline without difficulties. Whether they used it long enough for such problems to manifest themselves, or even if they would, is not known to me. Still, my suggestion was just to use it confirm that you have a vapor lock situation, and not as a cure. Having never had a vapor lock problem, I have no first-hand experience with it - just what I've heard and read.

I have often heard that when vapor lock strikes, cooling the fuel pump with water, pop, or half a grapefruit will get you going again. This suggests it occurs in the fuel pump.