choogenboom

my 1999 996/4 (51K miles) died hard on the freeway last night 200 miles from home. The failure was immdeiate - engine was running fine, going about 90 MPH, and sudden complete loss of power, glided to stop on roadside. Cranked, caught occasionally and died.

$540 in flatbed fees later its now in my garage and I am debugging. If I spray carb cleaner in the intake it will start, idle smotth for 5-10 seconds and die. Very strong smell of gas so I believe it is running very rich. If I let it sit for a while (10-20 minutes) it will fire up, run rough and die after about 5 seconds. Again, very strong smell of gas. If I apply any throttle at all it bogs down and dies immediately. Usually when an engine is flooded if you let it sit the excess fuel in the cylinders evaporates and the engine will start so I take this bevahior as a second indicator of running rich.

So - any tips on what the problem might be?

Thanks in advance for your help.

Chris

ADDED 10/5/2009
Summary - While I did smell gas in the exhaust it became clear as you will read later in the thread the problem was one of fuel delivery - or more accurately the lack thereof. The cause was a end cap that popped of the venturi pickup in the fuel tank. Once that cap popped off fuel pressure dropped close to zero. Repair was to zip tie the end cap in place - costs about a penny. Alternately you can replace the venturi assembly for $325. Needless to say I liked the zip tie Read on for more detail on the repair.

ADDED 1/17/2012
the in tank quick disconnects failed after the repair. See my new post for more on that subject.

medtech

Sounds like the fuel pump or fuel filter, but others with more experience will chime in.
Try Renntech as well.

Good Luck.

gota911

Chris,

Sorry to hear about the problems. I think medtech is right, sounds like the fuel pump.




BTW - I don't think it's a good idea to have the word "boom" in your screen name if you drive a 996!

OCNYPORSCHE

Sounds like the fuel pump too.

choogenboom

Thanks all for the tips. I think I am being decieved by the smell of gas in the exaust that its flooded as I have to agree that all other symptoms are of fuel starvation. I ran the fuel pump manually and verified it is running - so now need to start checking fuel system pressures. Stay tuned.

blinkwatt

Is there a Check engine light? Was it flashing or solid before your car went caput? What up with no AAA roadside assistance? That's a big towing fee.

OCNYPORSCHE

Chris,

Check on Renntech.org too. There are alot of techs on there that may be able to help more. I remember on an old Toyota Supra I had, there was a vacuum leak that caused the same. The problem may NOT be fuel related.

OCNYPORSCHE

Chris,

Check on Renntech.org too. There are alot of techs on there that may be able to help more. I remember on an old Toyota Supra I had, there was a vacuum leak that caused the same. The problem may NOT be fuel related.

Barn996

I would consider your coil packs might be the culprit. GL

Macster

I assume car's gas tank not empty?

Sounds like a fuel supply problem. You can test fuel flow and pressure. You have to be very careful when working on a car's fuel system though. One mistake can see the car go up in flames, or worse.

You need to learn how to trigger the fuel pump on without having to crank the engine. Then with the fuel line disconnected measure the amount of fuel over a given time. The time and amount is given in the factory manual. I do not have the numbers nor do I have at hand the way to trigger the fuel pump.

Try to make the fuel flow test as long as possible. The pump may deliver fuel for a moment or two then the flow will drop off. If you do a brief test all may look ok but had you let the test go on longer....

Try to route the fuel into say a clean 5 gallon gas can -- plastic so you can see the level and hopefully the can's got graduations on it so you can know where 1 and 2 and 3 and so on gallons are. Using a clean gas can means when the test over you can dump the gas back in the car with no problems.

If flow ok you can test pressure at the fuel rails of the engine. These have pressure test points but the plugs are not reusable. Remove the pressure test point plugs and after the test you have to replace with new ones. You will of course need a proper fuel pressure test gage and the fitting to connect to the fuel rail. A visit to a well-stocked auto parts store, auto tools store, is called for if you do not have the tools.

As with fuel flow and delivery pressure is also called out but I do not have the numbers handy.

Be very sure you button fuel lines back up properly. Before you drive the car be sure you check fuel system for any leaks.

Always remember gas fumes are highly flammable and have plenty of ventilation and no open flames around. When I worked on my car's fuel system I worked on fuel system out in the open away from the garage and house in case car caught fire it didn't spread to garage and house.

Sincerely,

Macster.

choogenboom

thanks for all the tips:

re AAA - I have it, but basic only which includes only 3 miles towing.

OK - did diagnostics today. Pulled the fuel supply lin at the tank, ran the pump, plenty of fuel. Must be clogged filter?? So pulled hose from outlet side of filter, ran pump, plenty of flow! Ok, now what. Put hose into 5 gallon jug (I have 4 of them ready for this phase of the debugging) and started to run the fuel pump to empty the tank. This is where it gets intersting. I know tank has about 14 gallons in it, but flow stops after 7 gallons are pumped. I here bubbling in the gas tank. Turn off pump, wait a few minutes, turn on pump, pumps a few ounces then quits and I hear bubbling in fuel tank. I add a gallon to the tank, turn on pump, it pumps out a gallon and quits, I hear bubbling in the tank.

I open up the tank and I can see tank is about 1/2 full and of note is it is full exactly up to the level of the top of the fuel pump module. It will not pump out any lower than that. Turn on pump and see bubbles coming from rear passenger side corner of the tank, near where the fill tube comes into the tank. I can not specifically see the hose the bubbles are coming from but best I can tell its the larger diameter hose on on the top left of the pump module as viewed from the front of the car.

So - if I had to guess, there is a pressure relief valve that is malfunctioning?

I should note I have a C4 which has the same tank setup as turbos - smaller tank with more stuff jammed into the tank itself to make space for front drivetrain.

Ok - anyone have any tips on where to go from here? Any of this ring a bell with anyone?

Thanks,
Chris

choogenboom

oh - and while I have not pressure tested the pump I am almost sure that when it is pumping that the pressure would be almost zero, but I will verify this soon.

medtech

Ask Loren on Rennlist for a diagram of the tank.

I'm just guessing, but shouldn't there be a hose that goes from the inlet of the pump to the bottom of the tank? Could that have come loose?

htny

Out of curiosity, did you check to see if there were any stored or pending obd codes in the computer?

air, fuel or spark, troubleshoot all independently before going crazy or ordering parts, e.g. pull the MAF off and see if it stays running, watch voltage / examine coils/plugs. If running smooth and then dying cleanly without a lot of stumbling, maybe vac/sai etc? from description I suspect air issues first, then spark then fuel. might be as simple as a bad hose or joint somewhere, inspect all the rubber and plastic!

Good luck, try checking for stored codes and "pending" codes, sometimes incredibly helpful in zeroing in on the problem.

OCNYPORSCHE

Most likely not coil packs. It unlikely that coils would cause the engine to not start, it would just run rough, because you would need a total failure on more than one, which is unlikely. It is a fuel or some other electrical problem.