'61 stumbling/stalling after acceleration

[David Greenburg]

A few weeks ago I added an electric fuel pump for priming purposes on my '61 (it only operates when the switch is held down). The car seemed to run fine, as it always has, in low-speed local driving. But I recently took it out on the highway and put my foot into it merging and accelerating up to 70 or so. The acceleration was smooth, but then I had to slow down for my exit and by the time I came to a stop at the end of the ramp, the car was stumbling badly, feeling like it was on the verge of stalling. But I made it through the intersection and into the nearby parking lot of my destination, by which time it was running better. On the way home I tried accelerating briskly on a 45 mph surface road. Again the car started stumbling, and as I approached a red light, it actually stalled. I pulled over and was then able to restart the car and continue home (10 minutes) without issue. My understanding is that the fuel tank was replaced about 13 years ago, when the car was recommissioned after many years of storage, and the mechanical fuel pump was rebuilt about 2 years ago

Could the passive electric pump be causing these issues? It seems unlikely to me, because even hard acceleration is normal; there is no roughness or hesitation suggesting fuel starvation. It seems more likely that it could be a fuel filter or pinched fuel line issue. I should mention that there is an in-line "metal can" filter installed by a prior owner in the rubber fuel line leaving the tank and prior to the electric pump.   

[Clewisiii]

When you say it only functions when switch is held down do you mean engine cranking.

Can you explain Passive fuel pump.
I assume it would cause an obstruction in the fuel system if it only functions when cranking.

When the mechanical fuel pump changes in vacuum pressure between different RPMs i wonder if that is affecting a passive pump that is just sitting in the system.

[dn010]

There are many of us here who have electric fuel pumps installed along with the mechanical pump, just to aid in filling the carb/starting. It is most likely not your problem. Time to check hoses, filters and carb.

[David Greenburg]

By "passive" I was referring to to a pump that is only "on" for priming/cranking; when you let off the switch it stops.  Although the switch is wired so that if you push it the other way, it stays on, for vapor lock situations.

[Clewisiii]

By "passive" I was referring to to a pump that is only "on" for priming/cranking; when you let off the switch it stops.  Although the switch is wired so that if you push it the other way, it stays on, for vapor lock situations.

So that was what i was wondering. Does it allow free flow when it is off. Or does it slow down or block fuel when it is off. I think the others who run these run full time while key is on.

[James Landi]

Sharing a couple of experiences with Cadillac fuel systems.  I believe by the late 1950's GM (now gm) finally put the fuel pump where it always belonged, on the underside of the engine block.  The "long tail" consequences of the bad design with fuel pumps on top of the oil filter tube,  is that many of us believe fuel pump delivery is an issue for all old Cadillacs--- did your car have an issue that you're trying to solve?  IT'S NOT the originally designed fuel delivery system, IF, and ONLY if it's in reasonable condition.  I owned a 61 Convertible from 1965 through 1973, a 196O for several years, and a '67 from 1970 through '85 .. NEVER EVER had a problem with start up in hot or cold weather and daily drove these cars-- ran up hundreds  of thousands of miles and ran them until they were junk.  Carl is likely on to your problem.  I recently replaced an electric fuel pump for my boat's 3 cylinder generator...an AMAZON purchase.  It failed after a month and about 25 hours... when I looked at the AMAZON reviews, they were highly mixed, with way too many purchasers complaining of newly installed failed pumps.  BOTTOM LINE: The fuel delivery design for 1961 is perfect, and you DON'T want to install an electric pump because you simply don't need an electric pump.  Yes, a well designed electric pump will act as a pass through when not engaged, but one of those little, cheap ones will not permit sufficient fuel to pass through, as Carl suggests.  When you're needing power from the engine, your newly installed pump is restricting the flow.  Take the pump out-- your problem will disappear.     (unless, of course, your fuel lines have a small pin hole, or your car's fuel pump is failing)-- those items need to be repaired, and an electric pump is masking a potential disaster-- i.e. fire caused by fuel line leaks or worse a rupture in the fuel pump that's passing gasoline into the crankcase.   

[Lexi]

That is why I installed my electric pump on it's own fuel line. It "T" intersects after the mechanical pump (which remains operational). I only use the E pump to assist in starting the car after it has sat for a while, to reduce wear on the starter motor. I also installed a kill switch which allows me to turn off the E pump after it has primed the carburetor. I have found that there is no need for it to run the car as the mechanical pump works fine. But the E pump is also there for emergency use.

I have been told that it may not be good to run the E pump through the OEM pump (if operational). Perhaps someone can comment further on that. One reason perhaps why some purge the inside of the mechanical pump, so E pumped fuel just flows through without the original pump being used. So in that case, the mechanical pump's body remains just for OEM appearance and judging.

After about 11 years I am still satisfied with my separate line system as described. Clay/Lexi

[Jeff Rosansky CLC #28373]

My thinking is fuel lines.
The new pump probably provides a little restriction-- It has to because fuel flows through it.
I'm thinking that you have slightly compromised fuel lines. They work just fine under normal circumstances, but now the mechanical has to suck a little harder. So air is being introduced.
Try this-Cap off the fuel line at the pump, and then disconnect it at the mechanical (you are isolating the fuel line between the electric and mechanical). Then fill the line with mineral spirits or similar, and blow shop air in the line. Let it sit pressurized for a few minutes, then look at it. Any moisture on the line? How about under the clips? If there is moisture, then liquid is getting out. If liquid can get out, air can get in.

[dn010]

People run mechanical and electric pumps together all the time. Many people do this for track use too, it is not unheard of and they certainly work together whether the electric pump is on full time with the mechanical while driving around the track or just used to prime the lines. I can easily pull fuel through my electric pump when needed just by using a suction bulb in the end of a hose at the carb. If you have a check valve installed, that could change things. My money is on something else.

[James Landi]

David,

Please be advised, while most folks don't experience a leaking,ruptured diaphragm in the mechanical fuel pump, that can happen, especially if the pump is ancient and you're using an electric pump that pressurizes the original, mechanically compromised pump--- folks have destroyed their engines diluting the crankcase oil with gas... on boats, when this happens, there's a crank case explosion.  As I've stated above, if your '61 is stalling and starving for fuel without the addition an electric fuel pump, THEN you have a leak in the fuel lines, or a failing mechanical pump.  On the older Cadillacs with the pump mounted high on the engine, an installation like Lexi/CLay's makes sense.

[David Greenburg]

Happy ending on this one. As Dan posited, and I had hoped, the problem was either a pinched fuel line and/or a restricted filter. I replaced the metal in-line filter that had been added at the tank as well as the glass bowl element, and also replaced the rubber fuel line running from the electric pump over the axle and to the metal line with a longer piece to avoid the pinch. Car drove beautifully after that; more smoothly and powerful than it had before, the way that you would expect a 28k-mile to run. I suspect that the in-line filter was somewhat clogged, and the installation of the electric pump jostled the filter and made it worse. I don't know how long the in-line filter had been there, and I wasn't even aware of it until recently. My guess is that it was installed when the car was recommissioned after its 30+ year nap, around 15 years and 10k miles ago based on my understanding of its history.

James- I am aware of the issue of "always on" electric pumps flooding the crankcase and   unfortunately have experienced worse- a fire from a failed glass in-line filter that continued to be fed by the electric pump. But this pump is used for priming only, and the mechanical pump was recently rebuilt.

[Lexi]

Happy ending on this one. As Dan posited, and I had hoped, the problem was either a pinched fuel line and/or a restricted filter. I replaced the metal in-line filter that had been added at the tank as well as the glass bowl element, and also replaced the rubber fuel line running from the electric pump over the axle and to the metal line with a longer piece to avoid the pinch. Car drove beautifully after that; more smoothly and powerful than it had before, the way that you would expect a 28k-mile to run. I suspect that the in-line filter was somewhat clogged, and the installation of the electric pump jostled the filter and made it worse. I don't know how long the in-line filter had been there, and I wasn't even aware of it until recently. My guess is that it was installed when the car was recommissioned after its 30+ year nap, around 15 years and 10k miles ago based on my understanding of its history.

James- I am aware of the issue of "always on" electric pumps flooding the crankcase and   unfortunately have experienced worse- a fire from a failed glass in-line filter that continued to be fed by the electric pump. But this pump is used for priming only, and the mechanical pump was recently rebuilt.

Sorry to hear about that David. The glass bowl filters I suspect are more dangerous to use. That said, they MUST be routinely inspected and with their (now) paper replacement element and gasket being changed yearly. Part of this process MUST include properly cleaning the gasket/glass contact surfaces to ensure cleanliness. Everything must be seated properly to ensure a tight seal. Some of our cars have these glass filter bowls sitting up in the middle of the engine area where all the heat is. Probably not a good place for the engineers to have originally placed these components. I wouldn't move them lower in case of road debris damaging the glass. If done, better to replace with a more robust system. Clay/Lexi

[David Greenburg]

Clay- the fire incident was not caused by the stock glass bowl filter; it was one of those aftermarket glass in-line filters that is essentially a glass tube with fittings on the end installed in place of the stock glass bowl. One end came loose and started leaking and dripped into the generator. I do inspect the stock glass bowls (and other fittings, especially on the Eldorado) regularly, although in my experience the stock filters  are pretty leak-resistant once they are seated correctly.

[Lexi]

Oh yeah, one of those. That said, regular maintanence on the original glass ones is imperative. I think a sight glass anywhere in the fuel system, just leaves more room for failure and for Murphy's Law to rear it's ugly head. Ocassionally it is interesting to cut into a filter, including and especially oil filters when changed, just to see what they have been trapping. Clay/Lexi

[Jeff Rosansky CLC #28373]

If you replace the element in the glass bowl, replace the gaskets too.

[Lexi]

I have found that both seats of where the gasket comes into contact with, both the glass and the metal housing, must be cleaned as well to obtain a precise fit. Probably gunk/varnish on the the gasket as well, so always replace it, rather than re-use. Clay/Lexi

[Clewisiii]

I know this conversation has walked a bit. And David said his fire was not caused by the factory filter bowl.

Here is my collection of spares.



I did have a leak in the one on the left, but it was not from the glass. It was the brass outlet fitting. I could not get it to stop leaking under pressure. I could not figure out if it was the brass itself, or if it was the threads in the cast housing.


I want to collect more brass fittings to build up the spares. 

[David Greenburg]

I'm resurrecting this thread since the problem has returned in a slightly way. Generally the car runs great, including accelerating briskly in suburban driving. However at freeway speeds after a few miles running at 70 or so, the car dramatically loses power and will barely run 45-50.  It feels like it might actually stall, although it hasn't, at least not yet. A couple of times when this has happened I have pulled over and looked under the hood for anything inappropriate, by which time the car is idling smoothly. Yesterday I was setting out on a trip to Napa when this problem occurred about 10 minutes into the trip. Rather than pushing my luck, after stopping to check under the hood I decided to turn around and take a different car. After a few minutes, the problem returned. I turned on the electric pump in its "on" mode, as opposed to the momentary mode used for priming, and the car ran fine on the rest of the ride home on the electric pump.

This sure sounds to me like fuel starvation from a weak but still functional pump. In my original post I mentioned that the mechanical pump had been rebuilt relatively recently. But time flies as we're getting old, and a check of the records reveals that it was almost 8 years (although only about 4000 miles) ago. Is that a normal lifespan for a quality rebuild these days? It was done by one of the well-known rebuilders, supposedly using ethanol-resistant parts etc. I know some have suggested that making a mechanical pump pull through an electric pump can cause fuel delivery problems, but this install was done by a pro who has installed many of these on old Cads, including on my '60, where it works great, even with the thirsty tri-power.

[dadscad]

Hello David. I had the same fittings leaking on the factory fuel filter on my 63. Teflon tape didn't do the job, it always leaked a little. I finally solved the problem by cleaning all of the Teflon tape out of the threads of the filter body and fittings. I applied a fuel compatible non hardening sealer to the fittings and installed them into the filter body. That was decades ago and they are still leak free.

[35-709]

Almost textbook for a fuel filter.  When you stop for a little while the crud restricting the filter migrates away from it, but then comes back soon when the engine is restarted.  Could be the electric pump has enough extra "push" to get sufficient gas through the restricted filter and make the engine run normally.  An idling engine requires little fuel.