Why does my fuel pressure in my cabriolet go up and down ?

85 - 90 lbs

2-3 psi
6 is max

Please have the fuel pressure checked and if that is OK I would suspect a cracked engine air intake hose or a defective Mass Airflow sensor.

Hi there:
You will have to pinpoint what the engine is missing... Spark / Fuel /Compression.

All three of these are tested when the engine is being cranked over. There are two way of checking for fuel. Fuel pressure and fuel trigger. Both are very important and must be present for the engine to start. Fuel pressure is self explanatory. You just hook up the gage and see what the reading is. Fuel trigger is check with a noid light. The injector gets unplugged and the noid light gets plugged in to the injector clip. With the engine cranking over, this light must blink. This is the signal to the injectors from the computer. You can have all the fuel pressure in the world, but it wont matter if the injector is not pulsing gas into the cylinder like it should.

Compression tester, spark tester, fuel pressure gage and noid light are all accessible at your local auto store. All three tests play a very important part in diagnosing a no start condition. Be extremely careful when doing these tests.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

This vw has two fuel pumps one low pressure pump in tank and one high pressure pump under car make sure both are getting power and both are pumping, next try switching out the coolant temp sensor for the computer. The old vw cis fuel injection systems are very complex, so if you don't know what it is don't touch it get a book or better on old vw mechanic! ; )

try pulling down on it while you hit the unlatch,, if it jammed there is too much up pressure for it to release

check your fuel pump or fuel pump relay. When you try to start the car you should hear the fuel pump hum from the rear of the car.

You have apparently broken a timing belt..If the engine and cams are not rotating together, the ecu will not send a spark or fuel. Pull the cam sprocket covers and inspect the belt.

Fuel filter clogged, cheap place to start anyway

there is a pump in the tank ther is one under car.one in take is a pre pump one under car in black plastic housing .make sure fuel pump relay is working.