Sign of a dead or dying fuel pump (73.5T - CIS)

[Sunroof]

I learned several many ago that when the fuel pump starts giving up its life it usually kicks a few ounces of fuel when its cooled down before finally coming to an end. At least in that particular episode. That was about three years ago and I changed out that Bosch rebuilt OEM unit for the sleeker retrofitted new fuel pump that needed a whole new set of fittings (nipples and electrical) in order for it to work.

Well, here I am so many years later and my car will not start. It just died in the driveway! So when I turn the key, the CD unit is humming but the fuel pump is screaming like a scalded chicken. No fuel to the engine. No smell of gas, nada.

Before I go on the hunt again for a replacement and believe me the price ranges are crazy, I wanted to get some needed info on what a screaming pump might really indicate (internally speaking). Its a high pitched crazy vibrato, but the poor thing cannot stay on key!! Oh, its one of those Pierburg units. Can it be saved?

Thanks

Bob
73.5T CIS

[Gogar]

Whenever my fuel pump died it would just stop making noise altogether.

I'd suggest that you make sure fuel is actually getting back to the pump; when there's no fuel getting to the pump they just try to push the air and it makes a considerably louder noise than normal. And sends it to the graveyard much much faster!

[ossiblue]

My guess would be worn bearings on the impeller shaft which could cause the rotor to wobble and rub against the sides of the stator--just a guess but worn bearings can cause a screech/scream from friction on something.

BTW, do you still have the pump mounted above the left, rear wheel? If so, this might be a good time to move it forward to the cross beam, if you wish.

Edit: Gogar posted while I was typing and I agree with his idea to check for fuel to the pump first. However, my 73.5 pump made noise before failure so it's good to eliminate the easiest/cheapest cause--lack of fuel to the pump--before junking the old one.

[Sunroof]

Thanks.
The first time the fuel pump failed (It had to be at least seven-nine years old) it just died like a car running out of gas. No big noises that time. During this run, I was smelling light gas vapor for many weeks if not months and thought it was the charcoal filter in the trunk since it was coming from the front at the footwell. It was intermittent. Never drips or anything on the pavement under the car. No issues with acceleration or performance. When I pulled over the smell was never coming from the rear mounted pump or engine area. The pump is mounted near the drivers side wheel well for now. It was always a noisy pump since new, but not quite screaming like it is now.

I have seen many aftermarket units for sale (MSD, Mallory and Holley) to name a few, all claiming to be an OE aftermarket fit. Since they are all continuous flow and twelve volt I guess the only concern is PSI outlay and an internal check valve. I can always mount an external check valve if necessary.

Any suggestions on pump brands or what to look out for? Pump prices are crazy!!

Bob
73.5T

[E Sully]

You may need a new fuel pump, but I agree with Gogar that the first thing to check is fuel flow. Have you made sure the filter screen in the bottom of the tank is clean. The fuel pump is a wet pump where the armature is submerged in gasoline, it is cooled and lubricated by the fuel. If the in tank filter or line is restricted and the pump is running dry, it will make a lot of noise and burn out.

[BK911]

Originally Posted by E Sully

If the in tank filter or line is restricted and the pump is running dry, it will make a lot of noise and burn out.

+2
I would try there first. Sorta sounds like pump cavitation, which will destroy the pump. Fix it now before it is too late.

[shadowjack1]

Sunroof: That filter takes a 22mm allen wrench, which most of us do not have or wish to buy for a one time use. I removed mine over the week end and found that a 7/8" nut will fit the filter just fine with enough of the nut sticking out to allow a 7/8" socket to get a bite on it for easy removal.

[Sunroof]

Thanks all.

Sully......I would agree that taking out the filter is a good idea. The only issue I have is that I have to drain the tank first, which is a real bear, especially if I have no spare 10 gallon tank around to hold the approximately 10 gallons I have in the tank right now! That filter was replaced about three years ago when I refurbished this gas tank.

J. Simms awhile back addressed the issue of the 73.5T fuel tank and installing an in-line filter before the fuel pump to collect any garbage. A fantastic idea. My tank was internally coated twice with "RED KOTE" after being boiled in caustic solution. It is feasible I picked up tank trash in the fuel pump. The other day befothe pump screams I let the fuel go too low before filling it up. I should be drawn and quartered for that since it broke a very important rule of mine (never let it go lower than a quarter).

Shadowjack....I fabricated one of these hex nut fittings when I removed and installed the tank filter. I still have it so it will come in handy. I appreciate the help on that one.

I guess for now the best thing to do is at least run the pump after removing the line to the fuel filter to see if anything is coming through when activated. I can take the pump off as well and bench test it. If I reverse the wire connections, maybe it might run backward and clear anything out. Worth a try. Any comments on that?

Anymore ideas?

Bob

[Jim Sims]

Bob, Information below on prefilter (between the tank and the fuel pump) installed on son's 73.5T. Pump is still at the original location at the back near the engine. Filter has been working for seven plus years - I believe the original plastic filter collected most of the loose debris and the metal one is just there for insurance.

Install a filter in the suction line right before the fuel pump; this will cause a minor pressure drop to the pump but we've done it with my son's 1973.5 CIS T without ill effect. We are currently using a metal housing NAPA Gold fuel filter 3033 in this role. However initially we used an equivalent NAPA fuel filter with a transparent plastic housing (remember this is the suction or low pressure side of the pump so it typically doesn't have much pressure on it and the plastic fuel filter housing). Even though the tank had been cleaned, sealed and flushed there was still significant debris (which we could see through the transparent housing) in this auxilliary fuel filter upstream of the pump.

Jim

[Sunroof]

Thanks Jim.

Where exactly did you mount the NAPA filter? Was it at the location of the fuel pump area? Or was it just aft of the tunnel fuel line connector? If near the fuel pump, I would have to extend my fuel line from the tunnel and construct some sort of mount for the filter. Please let me know what you did in setting this up as this might do the trick is helping to keep the pump goiing longer.

Bob

[Jim Sims]

The filter was mounted near the fuel pump; the was insufficient space at the tunnel exit area to put a filter there. We used extra fuel line to add the filter in line just before the fuel pump. This line was secured with hose clamps - recall this is the low pressure suction side of the system so hose clamps work fine. The filter was secured to existing fuel pump/pump bracket with a couple of robust plastic cable ties. Jim

[Jim Sims]

The filter was mounted near the fuel pump; there was insufficient space at the tunnel exit area to put a filter there. We used extra fuel line to add the filter in line just before the fuel pump. This line was secured with hose clamps - recall this is the low pressure suction side of the system so hose clamps work fine. The filter was secured to existing fuel pump/pump bracket with a couple of robust plastic cable ties. Jim

[Sunroof]

Thanks Jim............

Ready for this?

I ran down into the garage a few moments ago to see if the pump is still making noise. I turned on the key, the pump sounded smooth and with the cold start lever up it started right up!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I am thoroughly convinced after having the same issues with the CD unit, WUR, and now the fuel pump that this car is CURSED. I take a horse shoe with me everytime I go out for a spin these days.

I think my love affair after 40 years with Porsche is slowly coming to an end.........

Whats next?!

Bob

[E Sully]

When you get a chance to empty the tank, I would remove the fuel lines and snake the tank lines to make sure the red coat isn't blocking tha lines and restricting flow. I wouldn't run the pump backwards, there is a check valve and it would just cavitate.

[Jim Sims]

Being a man of science I do not believe in curses but I do believe in the laws of thermodynamics. A '73 is nearing 40 years since manufacture of its components. If you want to keep it as a reliable daily driver all the engine, fuel system and brake system related rubber and electrical parts should be replaced or rebuilt: fuel pump, fuel system accumulator, WUR, engine wiring harness, fuel lines, injectors, ignition distributor, ignition coil, ignition wires, alternator, throttle linkage plastic and rubber elements, shift linkage bushings, brake lines, etc. Jim

[Sunroof]

Your so right Jim, but I am more a victim of Murphy's Law with this car then ever. The airbox, injectors, cold start valve, engine wiring harness, coil, WUR, accumulator, CD unit, fuel hoses, air boot, fuel tank and fuel pump were all replaced or refurbished within the last three-four years with no more than 12K miles driven over that time period. I will hold off on the list of the other major system replacements completed through the years. I am with you on all this. Its not my daily driver.

Proceeding forward, I will take the necessary step to evaluate amount of debris and pump out a pint or two of fuel collected through the fuel level unit on the tank from the bottom to get a visual on particulate in the fuel. If I get a lot of loose red kote sealant I am not going to be too pleased with the folks that refurbished the tank for me. This might take me back to square one on the tank. Last time I checked the Porsche dealer was asking over 1K for a new 73.5T tank.

The inline fuel filter will be the next move after that, but I will have to remove the pump and add the necessary fuel line and mount the new filter appropriately.

Stay tuned.

Bob

[RWebb]

Usually what happens is some guy fixes n-1 out of n problems, and then gets frustrated and sells the car.

The next guy fixes 1 problem and the car runs fine for 10 years...