Is Fuel Pump the Problem

[911 FAN]

After driving my 1999 996 Carrera 4 on a 40 mile freeway ride, I parked my car to run errands, when I came back one hour later, the car wouldnt start, I called AAA and they came to jump car, but car wouldnt take a jump. Had it towed to Indy Porsche repair shop. They recharged battery, checked electric system and said it took a charge all electric system appeared good. I explained to them that about 3 weeks ago, the car did the same thing (wouldnt start) but the next morning it started with no problem. They recommend replacing fuel pump to solve problem. Is this a fix for the average driver or should I let them replace fuel pump for me.

[ericinboca]

I'm assuming the car turns over normally, but just doesn't fire off? One symptom of a dying fuel pump is it failing when hot, but once cooled, it will work again.

As it gets progressively worse, you may also start to feel it fail while driving.

Replacing involves removing battery, the tray, etc. to get to the port at the top of the fuel tank. There is a collar nut that calls for a special tool, although if you are creative, it is possible to remove this collar without that tool. From there it is pretty easy. You are supposed to replace the pump with the tank empty. Otherwise you risk sparking, and you have to stick your hands down in to find the locking tabs on the bottom of tank to know where to place and lock in the pump. Risky behavior, but I have replaced with fuel in the tank at the track.

[logray]

It might make sense to test the fuel pump before replacement. It can be tested for both volume/time and pressure.

There are plenty of other reasons for no start such as weak or faulty electrical, sensors, etc. There are also different types of no start... slow crank, no crank, crank without fire, etc... each with their own different plausible causes.

[wvicary]

Is the engine not cranking over fast enough and thats why they thought a boost was needed? The fuel pump has nothing to do with engine cranking speed. I would test the battery and then inspect the ground connections and the positive cable to the starter. There has been a problem with this circuit due to corrosion which leeds to excessive resistance and is worse due to heat soak.

[Loren]

It might make sense to test the fuel pump before replacement. It can be tested for both volume/time and pressure.

There are plenty of other reasons for no start such as weak or faulty electrical, sensors, etc. There are also different types of no start... slow crank, no crank, crank without fire, etc... each with their own different plausible causes.

I agree - an intermittent crankshaft position sensor (CPS) can act the same way. When it fails it tells the DME the engine is not turning so shut off the fuel.

[911 FAN]

Thanks guys I will get in there this weekend to see whats really going on. Im pretty sure its the fuel pump going bad. When I start the car cold and run it...no problem. If I stop and try to restart it when hot it as trouble starting. Since I am not all that mechanically gifted, do you think $966 is too much too pay to have it removed and replaced?

[logray]

Hmmm... if it doesn't restart when hot, not so sure it is the fuel pump... again what is the reasoning/evidence behind that?

There seem to be several more common issues for this such as weak electrical, corroded main engine pos wire, or neg wire, or faulty crank position sensor, etc. Sure fuel pump could be an issue too... but one should rule confirm or deny that before spending $1000 on a repair.

As for the price. The 1999 C4 pump P/N 99662010300 goes for $344 discounted (+ tax/ship). I'm not sure what the book time is, but accessing the pump is not all that difficult on a C2, could be harder on a C4 due to the limited space. Basically on a C2 remove the battery, tray, and gas tank cover. Then remove the level gauge and the fuel pump comes right out. I would guess a couple hour job @ say $125/hr = $250. So total around $600-$700 sounds more like it to me.

Edited November 17, 2011 by logray

[trevorhp]

Just before you rush off to buy a new pump please check the pipework inside the fuel tank.

The two small rubber hoses often split and cause intermittent loss of pressure.

Not easy to see but attached picture shows the problem,

E10 fuel in the UK and Europe affects both rubber hoses and they should be replaced with the correct type of fuel submersible hose.

It is very cheap £5 GBP per metre and easy to fit. (you only need around 20cm)

In the UK it is available from Halfords and other outlets such as NAPA in the USA.