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Questions and Answers

Volkswagen Jetta Won't Start Or Run

Q. Hi Vince, I own a 1988 Volkswagen Jetta, 5 speed manual transmission with Digifant II ECU. I was driving at 60 mph with rain, when the car just died. It would crank the engine and the fuel pump will work, but not start again, although I had ½ full tank. I towed it to a garage, not the dealer, and they kept it for four or five days but nothing turned out.

Volkswagen Jetta Won't Start Or Run

They mentioned that they were checking fuel pressure, so I suppose they also checked that the fuel regulator and fuel pump valve are doing fine. Common sense suggests that they should have checked that injectors are okay. Anyway, they suggested me going to the dealer. Instead I brought it back home, I'm trying hard to save money.

I checked fuse, changed the fuel pump relay and I worked the pump backwards in case the fuel line was clogged. Nothing. I also performed some electric checks, voltage supply to Digifant control unit, Ignition Control Unit, throttle switches, Idle air stabilizer valve but no good.

I then thought that the Digifant II ECU might have blown off, since it seems exposed to water due to its location. I got it out and opened it but everything looked new. I asked the dealer if they could check the ECU for me, but they said they needed the whole car.

I should mention that the car, after I towed it back, got started for a few seconds and then died, this for a few times. Acceleration would just shut the car down. Previously the car had some small problem starting in cold weather and moving right away, but a bit of acceleration and time would keep it from stalling.

So, what's the new step? Should I start from the air flow sensor, throttle body, intake manifold? Should I check the injectors myself, or rather get a used Digifant II ECU? Is it possible that the pressure regulator/fuel pump valve is faulty and they didn't find out?

Fuel filter is new, spark plugs are new and shortly before the problem I used Valvoline fuel system treatment to get rid of the cold start problem.

Thanks a lot in advance for your response.

A. I could be wrong, but it sounds like you may have a bad fuel pump. The digifant II system has two fuel pumps. A transfer pump located inside the fuel tank and a main fuel pump located underneath the car, just forward of the fuel tank. One or the other may not be working. You can check the fuel pressure to see if you have good pressure and a fuel volume test to see if there is the proper quantity of fuel getting to the engine.

Volkswagen Jetta Won't Start Or Run

To check the fuel pressure remove the fuel pump relay, and install a jumper wire with in-line switch. Hook up a fuel pressure gauge to the fuel system and activate the fuel pump and read the pressure. It should be:

  • 2.5 Bar (36 psi) with vacuum hose to pressure regulator connected.
  • 3.0 Bar (44 psi) with vacuum hose to pressure regulator disconnected.

To check the fuel volume:

Transfer Pump:

Volkswagen Jetta Won't Start Or Run

  • Battery fully charged.
  • Voltage supply okay.
  • Fuel filler cap removed.
  • Remove fuel pump relay.
  • Set in-line switch to OFF position and install in relay socket.
  • Remove black feed hose (1) from fuel sending unit and plug the hose end.
  • Install auxiliary hose (2) onto open connection of sending unit and place the other end in a measuring beaker.
  • Switch in-line switch ON for 10 seconds.
  • There should be a minimum of 300 cc of fuel in ten seconds.

Main Fuel Pump:

Volkswagen Jetta Won't Start Or Run

  • Battery fully charged.
  • Voltage supply okay.
  • Fuel filler cap removed.
  • Transfer pump okay.
  • Fuel filter okay.
  • Disconnect the blue fuel return hose (from the pressure regulator) where it attaches to the main return line near the right shock tower.
  • Place the hose end into a measuring beaker.
  • Switch in-line switch ON for 10 seconds.
  • There should be a minimum of 500 cc fuel in 30 seconds.

Personally, if I find one fuel pump is bad, I would replace both, even more so if it's the transfer pump that went bad.

Additional Information provided courtesy of AllDATA

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