Re: Re: IML: '55 hesitation

While all of this is absolutely true, if this were happening to my '55 Imperial, I would clean/replace the "stone fuel filter", remove the extra in line filter (as it could be actually restricting fuel flow), and replace the fuel pump and flex-line. This is all assuming that the car had been driven successfully before this happened and since any recent work had been done. If not, then I would also inspect & gap the duel ignition points.

All of these things should be done anyway. The problems with today's fuels that Dick has described have caused fuel pump diaphragms on my cars to prematurely go bad, with similar symptoms. The flex line is a likely culprit. I mention the ignition points since a problem there can lead to similar symptoms, and also, because while in the shop, the mechanic may leave the ignition on (without the engine running) for an extended period, while taking a phone call of a coffee break. This can lead to burned contacts, and a very damaged point set. This happened to me while my car was in the shop for a routine service. My car ran, but not quite correctly. It took months to figure out, but the solution was simple.

At least you have plenty of food for thought.

Paul W.

-----Original Message-----
From: Dick Benjamin <dickb@xxxxxxxxx>
To: mailing-list@xxxxxxxxxxxxxxxx
Sent: Sat, 17 Jun 2006 07:31:25 -0700
Subject: RE: IML: '55 hesitation

This definitely sounds like fuel starvation to me. Given the occurrence in hot weather, I suspect you may be having some vapor lock problems. Modern gasolines are much more likely to develop vapor lock. Another thing that will cause vapor lock, besides the obvious overheated fuel line, is a pinhole leak in the fuel line from the tank to the pump. These leaks are very hard to find because they don’t leak fluid enough to spot or smell, but they do ingest air when the fuel pump is working, producing a vacuum in that line. Any air in the lines at all will lead to vapor lock much more readily than liquid fuel.

I’d approach the problem in steps:

Test your fuel pump output. It should deliver a coffee can full of gas at idle within about 15 seconds, and if you block the output line, it should produce at least 3.5 PSI. This can be done with a hose, a coffee can, and a vacuum gauge (which will also read pressure). Just start the engine and let it idle with the hose on the pump outlet – the engine will idle happily for long enough using the fuel in the float bowl.
If that result is normal, then pressurize your fuel line from the pump back to the tank – don’t exceed a few PSI as the tank can’t take it, but just a small amount of pressure should show up any weak spots on the fuel line. While you’re at it, replace all the fuel hose with SAE30R9 hose – the older stuff isn’t able to stand the new oxygenates – in fact I’d do that anyway, just to make sure. Just buying new hose at the auto parts place may not get you the right stuff – check the marking on the hose. Most stores still stock 30R7, although that is obsolete for modern fuels.
While you are inspecting the fuel line, make note of any place where the fuel line is passing near anything hot – especially the exhaust system, and in the engine compartment, anything near the engine block. If you can, re-rout the lines to where they will be cooled by the air stream, as far away from a source of heat as you can get them.
Some cars seems to have great difficulty with this problem, and it is getting worse as the EPA fiddles with the gas formula – you may have to break down and install an electric booster pump – do it back at the tank area, as low as you can mount it so that the pump will gravity feed from the tank, and stay cool, but keep it safe from road debris. Outside the frame rail, just in front of the rear wheel is usually a good place. You can wire it so that it will only run when you flip a hidden switch, but be sure to wire it through the ignition switch also, so it will go off when you turn off the engine. This will also be a big help to your beleaguered starter, having to crank that Hemi on 6 volts!

This problem doesn’t show up on modern cars, because since sometime in the late 70s, all cars have a vapor return line to the tank from the fuel pump, and since the advent of EFI, cars have circulating fuel in great abundance running through the lines all the time – the tank pump supplies about 5 times the needed quantity of gas, and a return line keeps the excess gas circulating back to the tank, so the fuel in the supply line is always as cool as the fuel in the tank. Next time buy an 81 with EFI – your problems will be gone! ((or at least different?!))

Dick Benjamin

From: mailing-list-owner@xxxxxxxxxxxxxxxx [mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On Behalf Of Jim Poltrock
Sent: Friday, June 16, 2006 11:31 AM
To: mailing-list@xxxxxxxxxxxxxxxx
Subject: IML: '55 hesitation

Hi all-

My ’55 sedan just started hesitating while at cruising speed. It is acting as though it is momentarily starved for gas, then it runs fine, then starved again. If I take my foot off the accelerator pedal and get back on it runs fine again for a bit before it hesitates again.

Since I got her back on the road last fall she has run like a top. It still starts and idles fine- no problems there. And the only time it hesitates is when she is warm and running down the road. I installed a new fuel filter and put a can of Seafoam in the tank (always filled w/93 octane). It has been warm here lately and I wonder if that has anything to do with it. The carb was rebuilt last year and, like I said, she has run fine up until now. I still have the stone filter inline (for looks as the Wix pre-filters for it). The clear bowl is only about 20% full while idling and the stone looks clean.

Any suggestions or input? I have really been enjoying driving the old girl lately (gas prices be damned) and look forward to solving this riddle ASAP. Thanks in advance for any help/direction on this.

Jim Poltrock

Salem, WI.

’55 sedan

Wisteria blue/rhapsody in blue

41k miles