Hi, i have this 1996 a4 i recently purchased, it went well for the first 2 months and now it wont start or dies after 10 seconds. i took off the whole fuel tank and changed fuel filter, also bashed out tank cause it was badly caved in. it still wouldnt go. i replaced purge valve, still nothing. it cranks but feels like fuel isnt getting up there or not enough of it. i am at the point now where i am considering getting rid of the whole charcoal canister and hooking up hoses with a T joint as i have seen done on other forums. i was wondering if anyone had an idea? i check the atmosphere valve in to the charcoal filter and its fine. last would be that valve next to refuel hole, cant figure out from different forums wether the "out" line from charcoal canister goes to manifold or back to tank. or if pressure is equalized thru same hose.

i have been digging at it for days, please share the knowledge!
thank you

 

One word of caution I will put ouyt there is if the tank has been damaged in caved in I would look to replacing the fuel pump first and foremost. If you pinch off the line into the purge valve in the engine bay and you still have an issue then I it not the EVAP system causing the issue. I would replace the fuel pump and see what issues your still have. As for your charcoal canister I believe one line vents through the LDP and the other goes to the Purge Valve. If you pull off the lines to the charcoal canister and there isn't raw fuel in either line then most lokely you don't have a rollover valve issue or an EVAP issue. It would take a massive failure of the EVAP system and alot of fuel vapors going to the engine to even make it stumble let alone not start. Let me know how things go.. Best of luck..

 

Get a gauge and check your fuel pressure at the fuel rail. It's a lot cheaper than a fuel pump so why not give it a try first.

 

ok, cheers, ill try this tomorrow. the reason i tought it might have been evap system is that i can only start it when replacing purge valve with hose and pumping tank up with electric pump nozzle in filler for a few minutes prior to crankin. if i remove pump it dies, or if i try to connect purge valve. its a brand new one so shouldnt be a problem. also could it be vaccuum system? i looked at it and the hose coming out of tank and to the ball valve right of filler blows air out fine, but it doesnt seem to be sucking in to the "chamber" wether i open or close fuel cap makes no difference. before taking down tank and checking vac pump for clog, does that make any sense to you in relation to my problem? ill let you know once ive checked fuel pressure, and see where i go from there. one thing tho, what pressure would i be looking for?

thank you very much

 

At least 4bar at idle and no lower then 4bar when revving

 

I can't find the process online but here's the basic process from the Haynes manual. Key on, engine off you should have 55-61 PSI. Engine running you should have 46-55 PSI.

Step 7: Relieve fuel pressure. Disconnect fuel supply line from fuel rail and connect fuel pressure gauge with appropriate T-fitting and hose. Cycle the ignition key on and off several times. Note the pressure and compare to what it should be. If fuel pressure is lower than specified, pinch off fuel return line with appropriate pliers.
Step 8: Cycle ignition on and off several times. DO NOT ALLOW FUEL PRESSURE TO RISE ABOVE 85 PSI. If fuel pressure is now above the specified pressure, replace the fuel pressure regulator. If fuel pressure is still lower than specified, check the fuel lines and fuel filter for restrictions. If no restriction is found, remove the fuel pump module and check the fuel strainer for restrictions, check the fuel pipe for leaks, and check the fuel pump wiring for high resistance. If no problems are found, replace the fuel pump.
Step 9: If fuel pressure recorded in step 7 is higher than specified, check the fuel return line for restrictions. If no restrictions are found, replace fuel pressure regulator.
Step 10: If the fuel pressure is within specification, start the engine. With engine running, the fuel pressure should be 5-10 PSI below the pressure recorded in step 7. If it isn't, remove the vacuum hose from the fuel pressure regulator and check that there is 12-14 in-Hg of vacuum. If there is, reconnect the vacuum line to the fuel pressure regulator. If the fuel pressure regulator doesn't decrease the fuel pressure with vacuum applied, replace the fuel pressure regulator.
Step 11: Fuel system hold pressure check. Turn the engine off. Monitor the fuel pressure for 10 minutes. Fuel pressure shouldn't drop below 32 PSI. If it does, there is a leak in the fuel line, fuel injector, fuel pump check valve, or the fuel pressure regulator. To determine the source of the leak, remove the hose pliers from the return line, cycle the ignition to obtain the highest fuel pressure reading, immediately clamp off the fuel supply line between the T-fitting and the fuel rail. If pressure drops below 32 PSI within 10 minutes, the main fuel line is leaking or the fuel pump is defective. If pressure holds, remove the clamp from the supply line, cycle the ignition, and clamp off the return line. If the pressure drops below 32 PSI within 10 minutes, an injector or the fuel rail is leaking. If the pressure holds, remove the clamp from the return line. If the fuel pressure now drops, the fuel pressure regulator is defective.

Sorry for the lengthy post.