allcool

delete duplicate post

allcool

Ya, try to avoid stuffing anything down the tank filler neck. Lots of delicate stuff in there to get damaged.

Do what DJ suggested first.
IMHO,,, do not waste your time on 'what ifs'..
At this point, doing anything other than trying to locate the test port and put your advanced auto parts loaner test gauge on it is a waste of your time imo.
Lets try and eliminate the fuel pump/fuel delivery first.
Go from there... troubleshoot with a logical step by step process of elimination.



JMO

Stringy

Thanks Alcohol, I'll take your advice.

We don't have those rental/loan shops over here in the UK - as far as I know.

I might be able to borrow something from work, or just buy one for £20 or so.

Re the test port - via the engine compartment, I presume, what if anything needs to be removed to get to it.
The car is a cabriolet, if that makes a difference.

allcool

If you can't get a fuel pressure test gauge, a refrigeration/AC manifold gauge set works good to test fuel pressure, just can't use the car134quick connect adapters. Have to use regular spin on refrigeration gauge hose ends with schrader depressor, used with almost all refrigerants r12/r22/r410/r402/r407/etc. Use low side gauge, hose should go right on the schrader valve test port...

I've also got a cab 996.1 & 996.2, don't need to remove anything to access FPTP.

As facing the engine from back of car, look to the right bank between the engine bay body and engine. Look a little farther in towards the right side front of engine, you should see the FuelPressurRegulator on the fuel rail hanging there on side of engine. Look a few inches down the fuel rail and you'll see the cap on the schrader valve FP test port.

Clean off any dirt/debris on cap with squirt of brake clean and blowgun/rag, then unscrew the cap and screw on the hose. If using refrig gauge set, make sure manifold gauge low & hi side handles are shut tight. Turn on key to start position but don't start car. Read max fuel pressure. If pressure is within specs,, great. Next, start car and do the same reading watching gauge, if still good, rev engine too 2500rpm or so and keep at a steady rpm, read pressure. If all the above FP pressure are in spec, 1 last test to rule out a FP problem. Do a fuel volume test if all pressures are in spec. That will rule out the fuel pump/fuel delivery system, or not. Report back what you find.... Or ask a trusted shop to test FP for you if you don't feel confident doing this...

JALFYI, if you want to remove fuel from tank, put a long hose on FuelPressureTestPort fitting, and other end of hose in 5 gallon gas can. in a few minutes it will be half full.

theprf

I can almost guarantee that there is a burst hose inside the fuel tank.
Access to the fuel pump is by removing the plastic "hat" located in the frunk. Then disconnect three fuel lines and one electrical fitting. Unscrew the big plastic nut and lift out the white piece enough to unplug the electrical connection and the duplex fuel lines that are connected on the bottom. Remove the rubber gasket. Reach inside the fuel tank and unplug the two jet pumps, two connections per jet pump. The jet pumps can stay inside the tank. Then reach inside the tank and disconnect the black corrugated hose from the fuel filler pipe - it simply pulls off. Turn the fuel pump 1/8 turn counter clockwise and pull the whole mess out of the tank.
You are going to find a short black rubber hose that has a split in it. Replace this with SUBMERSIBLE fuel hose.

You mechanic should be able to do this in an hour or so for about $10 in parts. The Porsche dealer will want to replace the entire fuel pump for about $600.

Stringy

Is this the type of tester for the job?
https://www.ebay.co.uk/itm/265214345356

So is the theory that the height position of that pipe is related to my half-tank full failure?

allcool

Not familiar with that particular kit, but if it says it screws on a schrader test port, Ya, that kit should do it. Looks like it has plenty of adapters.

You'll probably find exactly what theprf suggested in his above post about burst hoses in the tank connections to fuel pump, seen that posted here before.

Probably still a good idea to check fuel pump pressure before you tear it all apart, as its a very easy/fast test, just to get a baseline. Suppose pressure could be affected by where the split in the line is located and tank fuel level.? Bottom line, it still has to come apart regardless of FP.

Would like to hear theprf's opinion on 'once you're in there' if he would recommend changing out a 25 year old pump and all hoses,? or just do the fuel line repair and call it a day...? He has experience with the same tank in your c4 and knows the best way to proceed for sure...

jmo

theprf

I would not bother changing the fuel pump unless there are issues with fueling at maximum engine load. In other words, running lean at the torque peak. The accordion hoses seem to last forever.
I think, perhaps, the latest fuel pump revision may have all accordion hoses. If so that may be a valid reason to spend all the extra money to change it out.

And, yes, the location of the split and how much fuel in the tank can let the engine run slightly. I have had this line split at least 3 times. Once the car would idle but any throttle made the engine die immediately. The second time it would drive up to around 35 mph but no faster. All the other times it was running flawlessly then suddenly quit and could not be restarted. I have replaced this fuel line on the side of the highway and twice at the track.

De Jeeper

All this ^^^^ is why i said check the pressure. It will tell u if u have to open up the tank. In a c4 its very east yo get to the pump and sender. My gt3 pump burst the hose too because it has a secondary pick up and its a similar design as a turbo pump. On the new pump that hose is accordian vinyl. If u do have a burst hose u have to get "submersable" hose. Standard line will not last and even the correct stuff fails eventually. Amazon does sell the accordian vinyl for cheap and i think its 8mm but u will want to verify. Its what i used to repair my old pump and its now my spare.

My pump...died on track and would not restart.

Stringy

Thanks for the very clear explanation of where the test point is - I have now located it:
As you can see, it looks fairly nasty in there.
The tester is on order too, should arrive in a day or so.
Do I read that I need a replacement cap? Can I find those on ebay?

De Jeeper

Cap is reusable no need to buy another.

Stringy

My tester just arrived.
It tells me 45PSI with the ignition on, and 47PSI with the engine running.
I don't have much time to do more tonight, but tomorrow I thought I would...
Use the bleed button and tube on the gauge to bleed out 5 litres of fuel - more than I topped up with.
Then see what the gauge says, and if it still starts.

Let me know what you think guys,

allcool

Good to know 45-47psi...
Porsche 996 Essential Companion book gives 3.8 bar +/- 0.2 bar or 55psi +/- 3psi.

regardless, at this point I'd do exactly as theprf suggested. Time to get ur hand wet....

Stringy

Hello again guys, I need some more advice...
Today I thought I would bleed out some fuel (via the gauge) to see if the pressure went bad with less fuel in the tank.

When I switched in the ignition there was no pressure, actually maybe 10psi.
Thinking I hadn't screwed the Schrader in enough - it is quite stiff - I switched off, then tightened, then switched on again.
I saw pressure - the 45-47 that I had seen previously.
I then pressed the bleed button and pressure went to zero, and stayed there when I released the bleed.

I switched the ignition on and off again a few times, but no pressure.
I then used my scanner to activate 'Fuel pump relay final stage'
With that I heard the pump run and I now see 50psi on the gauge - a little higher.
What is going on?

Should the pump run all the time? Does it switch off when up to pressure?
Is there something wrong with that pressure switch - if there is one?

More info...
I tried to start the car with the zero pressure and it started, and the pressure went up to the 45-47.
With it running I could bleed fuel out and the gauge would return to pressure.
When I switched off, bled the pressure to zero, and turned ignition on again - I saw the usual pressure. When I bled that, it did not return.
So I guess the pump runs for a short time when ignition on, but does not keep the pump running - makes sense I suppose.

I'll get on with my tank level thing using the scanner.

Stringy

OK. So with the pump relay activated by the scanner, I bled fuel into a can.
After what must be a few litres, there was a whining from the pump, and the pressure started fluctuating - sometimes down to 20psi.
So I think that proves that, as you say, I need to get my hands into the tank.

I could carry on bleeding and see if pressure goes to zero.
I could pour the fuel back into the tank and see if it recovers.
However, I think I'll just get on with it.