holidaysedan

no a/c... what is the correct Fuel pump? Mine seems to have had a rebuilt pump with no glass bowl for a 1955-56 324 engine put on my '58 Super 88 at some point (AC 4317) ... anyone know what is the correct AC pump?

Tedd Thompson

I have two original AC Delco fuel pumps that have glass filter bowls and dual out let for vacuum for 1955" and the number on both is 24317. I don't know if that would work on a 58 or not as the 58 has a different cam (don't know if the fuel pump lobe is different or not) or what the difference AC or not brings to the problem. Some of the replacement pumps do not have the diaphragm for vacuum is that your problem or are you looking for a correct looking, numbers matching thing rather than some thing that will just work?... Tedd

holidaysedan

I'm trying to ascertain the correct original pump. I have a feeling the rebuilt 4317 was put on for expediency, probably because that's what the auto parts store had. According to Fusick it should take a 4540 which has no glass bowl and the inlets/outlets are in the same position as my no glass bowl (incorrect?) replacement. That may be what I should go with but like to make sure.

Rocketowner

Fusicks does say that a '58 without A/C should be a 4540 with no glass Bowl . Larry

TheDon

My 57 takes a 4317 w/glass bowl. I somehow got a 4540 as a spare but I have now use the 4317 on my 1957. Still need a 4540?

Ozzie

The 1958 Oldsmobile chassis parts book says that part number 5593934 had a strainer and glass bowl and fit 1955, 1956, 1957 (type 1), and 1958 without A/C. Fusick shows the 1955 & 1956 as type 4317, and the 1957 & 1958 as type 4646.
GM part number 5621650 had the pulsator diaphragm and fit 1958 with A/C. This is probably the one designated 4540 at Fusick.
The 1958 Oldsmobile shop manual shows both pumps, and designates the bowl style for the non A/C cars and the pulsator type for the A/C cars. The pulsator type pump used a separate inline type filter and a fuel return line to the tank to "reduce fuel pressure build up when the float needle valve is closed".
The only difference I can remember between the type 4317 and the 4646 was the filter in the bowl. The 4317 had either the "stacked" brass thin rings or the brass screen, while the later 4646 had a real filter in the bowl. The real filter worked better; this was probably why the parts book only showed the one pump and let it supercede the 4317 type. My '55 came from the factory with the earlier 4317 type. During a rebuild I changed to the "real" filter.
So to answer your question, my guess is that it should be the 4646, but any of the other ones would work just as well (if you use an inline filter for the pulsator pump or the 4317 with the brass metal strainers).
The performance specs are the same for the pumps (5-6 PSI @ 1800 RPM).

holidaysedan

It's confusing as heck, my non-A/C '58 came with a 4317 that has no glass bowl (but is supposed to), and it looks identical to the 4540 (which is supposed to be for A/C cars) that I got off ebay last week, which looks identical and has the same configuration of lines as the one on my car, so will give it a try.

Ozzie

You are correct that it is very confusing, and since some of the casting parts will interchange the number shown on the pump may not be matched with its original components when considering a rebuilt pump.

Tedd Thompson

I'm also confused as my pumps for my 55 are marked with the steal tab still attached with 24317. What is the deal with the number 2 in front of the 4317? Both have glass bowls.I've not seen the #2 anywhere else mentioned....confused... Tedd

Mark57

My 57 has an M3416 glass bowl pump which I was told was from a 61 Olds. which crosses to an AC 6585…more confusion…

Mark

Rockabilly Hooligan

Hello...To add more confusion to this discussion (LOL) I recently bought an 58 Olds 88 with a 371 (without factory AC). My friend and I rebuilt the engine and existing fuel pump (4646). Finally got the engine going but the fuel pump we rebuilt leaks oil from the bottom gasket. I pulled off and plan replace with with a spare a bought off Ebay a few months back.

The backup spare I bought off Ebay a while back because it looked identical to my 4646. Now that I need to use it, I see that it is a 4540 (not 4646) with an Glass Bowl fuel filter on bottom. Looking at Fusick's catalog, the 4540 (designed for 58 with AC) should not come with an glass bowl fuel filer because it is designed to work with an external fuel filter to support a 371 with factory AC.

Question is..Will a 4540 with a Glass Bowl Fuel filter work on my 371 and provide the vacuum required to support my wiper motor, brake booster, etc?

Ozzie

I'm a bit confused when you say that it leaks oil from the bottom gasket. What exactly are you calling the bottom gasket? The only "oil exposed" gasket I know about is the one between the body of the pump and the engine approximately mid-height on the pump. Below that is the fuel diaphragm. Below that is a gasket for the glass bowl on the fuel filter equipped pumps or the pulsator diaphragm on the pumps without the filter.
Be careful when using the numbers to identify the pumps. Some vendors and rebuilders have misapplied them adding chaos to confusion. It's safer to describe the physical characteristics of the pumps.
The big difference is the fuel filtering and the air dome/pulsator diaphragm. In 1958 the cars with factory installed A/C used the pulsator diaphragm and the separate fuel filter. The other cars used the glass bowl filter.
The good news is that the vacuum capabilities of either pump should be the same and should work on your engine.
The bad news is that the vacuum portion of the pump was there to supplement engine vacuum to get some wiper movement under heavy acceleration in the rain, but still wasn't wonderful even when the pump performed perfectly. This is what led to the change to electric wipers in 1959.

Rockabilly Hooligan

Ozzie. Thanks for info. The bottom gasket I referring to is the one that is used to seal the bottom part of the unit with numerous screws. Identical looking to top one I spoke to a rebuilder who specialises in older fuel pumps. He said that one of the internal seals could fail and let oil into bottom part of unit. On the 4540 fuel pump I found an metal tab that states 4646 RB. It appears someone rebuilt an 4540 base unit into an 4646 unit.

Still not clear on the difference between an regular vs pulsator diaphragm and need for an separate fuel filter for cars with factory AC.

Regards

Erol

Ozzie

The rebuilder is correct. If the seal on the fuel diaphragm's "stem" fails, engine oil can migrate down to the top of the fuel diaphragm. This is the area with the numerous screws. In 1957 they started a transition from the older style pumps which used the glass bowl with strainer or filter and the air dome to the pumps with the pulsator diaphragm and the in-line filter between the pump and the carburetor. The pulsator diaphragm and the air dome served the same purpose. That is to smooth out the fuel pulsations that were felt by the needle/seat in the carburetor. It is similar to the air domes added to the plumbing in your house to reduce the water hammer. When they added the pulsator diaphragm they had to do the in-line filter to provide for fuel filtering that was eliminated by removal of the glass bowl. If I'm remembering correctly, this was also when they started the fuel tank return lines for the A/C cars which became the "norm" in subsequent years to minimize the occurrence of vapor lock due to the added heat.

Rockabilly Hooligan

Ozzie.. Good info. Thanks for explaining to this Olds rookie. when you say "Air Dome" are you referring to the CO2 cannister device that is used to prevent vapor lock?

As stated earlier I removed leaking oil 4646 and installed my spare "4646" (converted 4540 with glass bowl filter). Cranked engine and could not get fuel into the bowl nor up to carburetor . I pulled off and verified by manual pumping that I am getting suction and air flow at all the ports. I reinstalled but left all lines unconnected . Plan to crank engine over and see I am getting same suction/air flow results in the morning.

Tank is full. I see gas at the end of the line from tank. Is there anyway to install the pump arm wrong into block so that it's not moving up and down as engine turns? If not what could be preventing pump from pulling fuel and pushing it up to carb?

Ozzie

The air dome is not a CO2 anything. It is a hollow cylinder containing air on the fuel discharge side of the pump. I don't know how it would do anything to help vapor lock.

If you have the pump installed on the engine, with the bolts "snugged up" correctly, I assume that the pump arm is correctly contacting the fuel pump eccentric. Of course if the eccentric is loose or the timing chain is broken the arm will not be moved. These shortfalls are not "usual". Keep in mind that the discharge side of the pump works under pressure while the suction side works as a vacuum. Leaks on the pressure side show up as spilled gasoline; but leaks on the suction side (all the way back to the tank) often don't show up as anything except that the pump won't pump. Since you see fuel at the end of the line from the tank it might mean that the pump is not pumping for some reason. If it's a rebuilt pump that's very possible. Rebuilt doesn't guarantee that it works. You can test the pump outside of the car if desired.

Rockabilly Hooligan

Got it. Thanks for info