How does a fuel pump fail/ beginning signs?

[Sunroof]

Not a new story. Car runs great all day, comes to a traffic stop and car dies. Crank til the battery almost dies and nothing. So you pull off the side of the road call for a tow, get notice that its an hour wait for the truck, while no less then eight other Porsche drive by (thanks guys!) without even asking whats wrong and........................the car starts up and runs strong for five minutes then dies again. So the cycle of wait twenty minutes, run five goes on until the tow truck comes. Three cycles.

Is this the sign if a dying fuel pump????????????????????

Oh, and it gets towed home and guess what? I can drive it off the tow truck because it ran for five minutes...........

from what I already know: no fuel relay
one questioned a faulty ground wire once before
pump is rebuilt pierberg (about three years old)
happened on first hot day of the year (85 today)

1973.5T/CIS
2.4 - no thermotime switch (not until 1974)

Is it time to replace the pump?

thanks

Bob

[jcunning]

It definitely could be fuel pump. They can die suddenly or they can die a slow, loud death... I've experienced both.

A fuel pressure test will easily tell you if its the pump or ignition.

[wwest]

Look closely at the fuel pump fuse and fuse holder. The momentary current flow inrush for a pulsating fuel pump can often be 4 times the fuse rating. Over time the HEAT resulting from that high inrush current will cause the fuse clamps to lose their springiness.

The fuse contact with the fuse holder becomes intermittent in exactly the way you describe.

[Sunroof]

I know that the 1973.5T/CIS is quite unique in that the power source at fuse number 7. I have cleaned this area on the fuse block and have ensured the proper amp fuse was installed. What was unique about today was that the car ran flawless with stops and start ups at eight different locations. Can overheating be the problem?

The pierbergs are not Bosch direct replacements, but do a hell of alot of work and seem to hold up okay. I thought my symptoms were of a dieing pump.

[wwest]

Remove the fuse, carefully bend both fuse end holders/clamps inward, toward the opposite holder/clamp. Even rolling out the factory door these fuse holders did not really have enough clamping force, nor electrical contact area, for high current inrush applications.

[Sunroof]

I'll give that a try......................I like that idea..thanks

[emac]

When is the last time you changed the filter?
Ernie

[Deschodt]

Could it be ignition related too ? Gets hot, dies...

My fuel pumps were rather loud before dying... But yeah, any of those things...

[manbridge 74]

Early 74 CIS guy here.... you can't really answer your original question until you know pressure and volume test results.

[E Sully]

The fuel pump is fed from the battery side of fuse 7, so the fuse does not protect the pump. Fuse condition will not affect the pump. It is possible the fuel filter in the engine bay, or the screen inside the tank is clogged. There have been a few cis Threads where the problem has been a clogged fuel or return line. You need to hook up fuel gages and check the volume of gas flow and pressure. It is possible the coil is failing when it gets hot. When it dies you can pull one of the plug wires, put in a spare plug and check for spark. Points and distributor in good shape?
Jims CIS primer gives much information.
911 CIS Primer - Index

[wwest]

Originally Posted by E Sully

The fuel pump is fed from the battery side of fuse 7, so the fuse does not protect the pump. Fuse condition will not affect the pump. It is possible the fuel filter in the engine bay, or the screen inside the tank is clogged. There have been a few cis Threads where the problem has been a clogged fuel or return line. You need to hook up fuel gages and check the volume of gas flow and pressure. It is possible the coil is failing when it gets hot. When it dies you can pull one of the plug wires, put in a spare plug and check for spark. Points and distributor in good shape?
Jims CIS primer gives much information.
911 CIS Primer - Index

Sorry, but I cannot accept the idea that something as potentially volatile as the fuel pump is not properly, adequately fused. My 1978 most certainly is.

[E Sully]

WWest, I am sorry you to hear you cannot accept this. The power to the ignition switch is non fused, and the power from the ignition switch to the fuse block and fuel pump connection is non fused. Porsche engineers did what they did back in 1973, and what they did in later models does not change this.

[T77911S]

mine did the same thing. bad coil/CD(?). this is very easy to trouble shoot.
1 check for spark when it does not start.
2 i think your pumps should run with the key on and engine off.

[T77911S]

Originally Posted by wwest

Sorry, but I cannot accept the idea that something as potentially volatile as the fuel pump is not properly, adequately fused. My 1978 most certainly is.

porsche was not very good at this. only reason i put porsche above lucas is at least porsche's works and they did not make + ground.

look at the headlight circuit on your car. they did nto fuse the wiring until AFTER it ran thru all the switches. they even did this on my 86 930.

[tirwin]

And as far as 1983, any maybe even later, the front condenser fan motor is also unfused. There was a thread recently where a guy's car caught fire when the motor seized. In later models an inline fuse module was added.

[tirwin]

Bob,

That is similar to what my car did when my PermaTune CDI failed in my '83.

I left home and it ran fine. Left it sitting for a couple of hours. Went to start and it cranked but no fire. Swapped fuel pump relay and it started and ran for about 6-7 miles then died on the way home. No spark. Had to call for a tow. If you can get it to start in the driveway and run for a bit maybe you could check for spark when it dies. Could just be the coil.

8 Porsches? Were you at C&O yesterday or maybe the one near Sandy Plains and 92? I was at the one on 92 and I would've stopped if I had seen you. I left around 11.

[Sunroof]

I was all over the place yesterday. I did not go to the C&O off Windward although I drove right by it nor to the 92 event. Most of my driving was up the 400 area with a stop at Lake Lanier. The car died on the south entrance ramp going from 141 to 400.

Most Porsche that drove by me (hood and rear trunk open on my car) were Boxsters or Caymans................

[T77911S]

it would sure be nice if people put where they are. they might get some in person help

[E Sully]

If you checked for spark with a spare spark plug when the engine dies and you get a spark, then fuel delivery would be next.
One check of the pump is to check the total fuel flow. You need to disconnect the return fuel line and the pump should put out 850 ml in 30 seconds. You previously had fuel problems from the tank coating peeling off. It is possible to damage the pump if it ran dry from fuel starvation. The pump is cooled by the gasoline flowing through it. It is also important to check the in tank fuel screen in the center of the tank. You would need to empty the tank to remove it.

[frannyB]

Hi Sunroof,

When I bought my car, the fuel pump would buzz loudly (like an open door buzzer) when it was hot. I replaced the pump and the new one did it too. I had also replaced the fuel filter, but it still buzzed. Then I pulled the screen (which was actually broken) on the bottom of the tank and, oh my... Lots of red sludge down there. I spent the better part of the day cleaning all that out, but after that the pump was/is nice a quiet and all happy again.

I guess my point is that even with all that crap in the tank, the engine never missed a beat. If it wasn't for the buzzing I would have never known...

When your car dies, is it abrupt (like you turned off the ignition, or does it sputter a bit, run lean and then die under load)? My experience is that electrical issues usually die abruptly and fuel is more subtle - just as a rule of thumb... A great exception is a dieing condensor. That will allow the car to run somewhat at idle, but not in the upper RPMs.

I hope you find you solution soon!

Franny