Factory Fuel Systems

Pierburg/Solex, or Keihin carburetion

• Years: 1979-1993
• Fuel system controlled by a carburetor
• Locales: outside North America; no Cabriolet was ever sold in North America with a carburetor due to strict emissions requirements.

Bosch CIS using K-Jetronic Fuel Management

• Years: 1980-1993 (up to 1989 in North America)
• Mechanical fuel injection system.  There are two types of CIS K-Jetronic installed in Cabriolets: CIS-basic and CIS-Lambda.  CIS-basic does not use an oxygen sensor and catalyst (but uses an EGR system in most cases).  CIS-Lambda uses an oxygen sensor, catalytic converter and a Jetronic controller; it is often referred to as Ku-Jetronic to differentiate the two systems.
• Because CIS is a continuous injection system, fuel is built up at the intake valve until the valve opens allowing fuel to enter the combustion chamber.
• Additional info: In North America, only 1980 Cabriolets initially sold outside California received CIS-basic.  All other 1980-1989 (up to 1993 outside North America) Cabriolets used CIS-Lambda.
• Locales: worldwide

Digifant

• Years: 1990-1993
• Electronic fuel injection system.  Digifant is Volkswagen's in-house variant of the Bosch L-Jetronic fuel management system.  There are two types: Digifant I and Digifant II.  Digifant I uses adaptive controls to comply with California emissions requirements and has OBD I diagnostics.  Digifant I was installed only in Cabriolets initially sold in California; all other Cabriolets use Digifant II.
• Digifant is a  pulsed injection system; therefore, fuel does not enter the combustion chamber until just before the intake valve opens.
• Additional info: If the 5th digit in the VIN is "B" it's Digifant II, if it's "C" it's Digifant I and should have a check engine light on the dash.
• Locales: worldwide

Bosch CIS using KE-Jetronic (aka CIS-E, mechanical fuel injection with electronic controls) was never installed in Cabriolets!  The main difference between CIS-Lambda and CIS-E: CIS-E uses a differential pressure regulator, a diaphragm pressure regulator, an idle air stabilizer valve and knock sensor; CIS-Lambda does not have any of that. Both systems utilize Jetronic control units and oxygen sensor systems, but that's where the similarities end.  Do not let anyone, or any web site, convince you that your factory-original Cabriolet has CIS-E!  Many CIS-basic afficionados are spreading incorrect information regarding CIS-E; they do not understand the differences between CIS, CIS-Lambda and CIS-E.

Diesel: A small number of diesel Cabriolets were, reportedly, sent to the UK in the early '80s; these GLD models were the only diesel Cabriolets ever produced (if the rumors are true) and are extremely rare today.

Which system is better? One system is not necessarily "better" than the other, but each has its dis/advantages and quirks.  Carburetors are known to be a pain in the ass, especially the stock units, but those who know how to work with them can fine-tune them, upgrade them and receive many years of enjoyment from them.  As for fuel injection, CIS is said to be easier to work on and troubleshoot and contains less expensive parts than the Digifant because Digifant is computerized and relies on electronic sensors and other devices to work properly.  CIS, however, because it's a mechanical fuel injection system, is said to be more finicky than Digifant and requires fine-tuning to run perfectly.  Digifant engines produce a bit more horsepower stock than CIS.  Slight horsepower gains can be achieved with Digifant by simply "chipping it", where CIS requires mechanical upgrades.  Proper maintenance is the key to a nearly problem-free car, no matter what fuel system it has.

Furthermore, many folks out there proclaim CIS to be "the devil's work" and that Digifant is the "bee's knees".  I read it over and over again and I'm tired of it.  They both have their pitfalls, they both have pluses, and they both are a nightmare if previous owners have performed some of their own witchcraft on them.  Just because it's CIS (or Digifant, for that matter) should not prevent you from owning the car of your dreams.  Some people will suggest going so far as to do an engine swap.  An engine swap is fine, if that's what you ultimately want to do, but you'll still have a fuel system to contend with.  The bottom line for all fuel injection systems is to learn how they work!!!

Note: If you participate in online car forums, educate yourself on a) which system is in your Cabriolet, b) which system is in the other Cabriolets, and c) if need be, ask the person requesting help what system is in his/her car before answering.  Time and again Digifant people will provide incorrect information to CIS people, and vice versa.  This only adds to the confusion and, more importantly, frustration to the person trying to solve a problem.  Pass this mantra on to the CIS-E people too if you can, because they often forget that CIS-Lambda exists and the two do not share the same components.

CIS

Digifant

Digifant idle adjustment

Digifant Tune-up

Symptoms of a faulty ISV (idle stabilizer valve)

Diagnosing a Faulty Digifant ECU

Improving Cold-Air Intake

Testing the Airflow Sensor

Single Fuel Pump Conversion

Component Diagram

Cold-starting and/or cold running issues? Replace the blue coolant temp sensor.

Carburetors

Original, stock carburetors are Pierburg/Solex (Keihin was optional):

• 2E2
• 2E3
• 34-PICT-5
• 34-PICT-6
• 34-PICT-7

Pierburg/Solex FAQ

Weber FAQ

Swapping Fuel Injection for Carburetion

Why would you want to??!  Many folks who want to do this "backwards" swap have CIS fuel injection that they can't get running right.  Being fed up, they think it'd just be simpler to switch out to carbs.  The truth is, with a properly tuned fuel injection system, you will get better fuel economy, actually have less headaches (carburetors are more finicky than CIS!), and will have a better-running car.  If your Cabriolet is your daily-driver, it's advised that you simply get your fuel injection properly tuned.  If your car is not a daily-driver and/or you are committed to the carb conversion, click here for items you'll need.

Fuel Filters

Fuel Pumps

Fuel injected Cabriolets from 1984* to 1993 have 2 electric fuel pumps.  The main fuel pump is located beneath the car, passenger side, in front of the gas tank.  The second pump, called a transfer pump, is located inside the gas tank; access to this pump is on the passenger side under the rear seat.  Both of these pumps are wired to the fuse/relay panel.  If a pump fails to operate, check the fuse and relay first (i.e. check the voltage at the pumps).

* Only about half of the 1984 models have in-tank fuel pumps.  Those cars with a full-size spare tire in the trunk do not have in-tank fuel pumps; those with "donut" spare tires have in-tank fuel transfer pumps (from VIN E_11291).

A fuel pump check valve is connected to the main fuel pump.  This device helps in preventing vapor lock and helps maintain fuel system pressure after the engine stops.  On CIS engines, this part can be replaced independent of the pump; on Digifant engines, the check valve is part of the fuel pump and cannot be replaced separately.

NOTE: A CIS external fuel pump can be used on a Digifant system when need be, but a Digifant external fuel pump cannot be used on a CIS system. The Digifant fuel pump does not produce enough fuel pressure required by the CIS system to run efficiently.

Fuel pump issues

• Whining sound: When you hear the infamous fuel pump whine, one or both fuel pumps are on their death-beds.  In most instances, and especially on 1984.5+ CIS cars, both fuel pumps should be replaced at the same time (unless one pump was recently replaced and proves to be good).  If the whine is being heard outside the car, this is an indication that the internal pump is dead/faulty and, as a result, the main pump is working harder to supply fuel to the engine.  Nine times out of ten, when only one whiny pump is replaced, 1) problems will still exist and the second pump then needs to be replaced; or 2) you'll simply be buying time and will need to replace the other pump sometime within the next year.  If you continue to drive the car with the whine, you will most definitely need to replace both fuel pumps.  When replacing the pumps, make sure that the electrical connections are clean (including the wiring).

• Car dies when hot: If the car dies, or tries to stall (sputters) when the engine is warm/hot, it's possible that the fuel pumps are overheating (this is especially true if the fuel tank is low on fuel).  This is usually an indication that the fuel pumps are on their way out.  On CIS cars, it's advised that you replace both pumps at the same time, unless one pump was recently replaced (or if the car has no transfer pump).  Nine times out of ten, when only one pump is replaced, problems still exist and the second pump then needs to be replaced.  On Digifant cars, replace the in-tank transfer pump and then test the main pump; if the main pump proves to be lacking fuel pressure, replace it as well.  When replacing the pumps, make sure that the electrical connections are clean (including the wiring).

Jumping the Fuel Pump Relay

Jumping the fuel pump relay is a troubleshooting technique to narrow down the cause of fuel-related starting and/or running issues.  To jump the fuel pump relay, pull the relay out and place a fused jumper wire between terminals 30 and 87 on the relay panel (more info below).  1980-1982: Jump terminals 2 (red wire) and 8 (red/yellow wire) on the remote socket (remove the fuel pump relay, but leave the harness in place).

Additional information:

Jump terminals 30 and 87.  If the pumps run, the wiring to and from the pumps is fine.

Jump terminals 15 and 87 and turn the ignition key to "on" (not "start").  If the pumps run, the ignition wiring is good.

Connect terminal 31 to ground and check for continuity.  If there is continuity, the ground connections are good.

If all of the above tests are passed, that leaves the ignition coil feed to check (consult your repair manual for instructions).

Fuel Injectors

Fuel injectors clogged and/or old and dirty?  Don't have the cash to buy new ones?  Here's an injector cleaning method courtesy of "Southcross" of VWvortex.com:

Using a can of carburetor cleaner...

1. "Spray clean the outside of the injectors, including special attention to the tip.
2. Insert spray tube all the way into the rear of the injector, spray "through" the injector.  As the injector crud gets cleaned out, you will see the spray pattern change, spray until you have a normal spray cone.
3. Let dry and insert back into the car."

Click here to see a trick to installing new O-rings onto CIS injectors.

Fuel Tank

1979-1984 (up to VIN E_11290)

These Cabriolets do use the same fuel tank as the hard-tops Rabbits/Golf I's.

Capacity: 10.6 gallons

1984.5-1993 (from VIN E_11291)

These Cabriolets do not use the same fuel tank as the hard-tops; these cars use Cabriolet-specific fuel tanks.

Capacity: 13.8 gallons

The Spectra Tank replacement (VW5A) is about the only one you'll find in North America for the 1984.5-1993 Cabriolets.  It is manufactured to OEM specifications and is a direct replacement.  The only difference you'll find when shopping around is price and how it is packaged for delivery.

There has been some talk of making sure that there are baffles in the fuel tank prior to ordering one.  Baffles prevent fuel starvation during hard cornering when the fuel level is low.  The Spectra Tank replacement does not have baffles, and neither did the original tanks from the factory.  The in-tank transfer pump (low pressure, high volume), to a degree, takes the place of tank baffles on the 1984.5-1993 Cabriolets.  If you're driving the car hard into corners all the time when the tank is low on fuel (i.e. when there is only a gallon or so left), or driving it at all when the tank is nearly empty, in time you'll burn up the in-tank transfer fuel pump and will end up with a fuel pressure and/or running problem.

Replacing the fuel tank

Yes, you'll need to drop the rear axle beam in order to replace the tank.  

Running the Fuel Tank Dry

Nine times out of ten, when the tank is allowed to run dry, the in-tank fuel pump is damaged; therefore, replacing the in-tank fuel pump is the only solution.  The longer you drive with a damaged in-tank fuel pump, the harder the external fuel pump has to work and will ultimately lead to its demise.  When replacing the fuel pumps, replace the fuel filter at the same time as a precautionary measure. There is also a filter screen attached to the in-tank pump; make sure this is clean or new when checking or replacing the in-tank pump.  And: Let this be a lesson and warning to never, ever let the gas tank run dry!

The Fuel Tank is Leaking

Take your Cabriolet to your local Volkswagen dealer for a gas tank inspection; certain years of Cabriolets had a recall on the tanks which is still honored by Volkswagen (by USA law).  Click here for further information.  If your Cabriolet is not covered by the recall, the gas tank will need to be repaired or replaced.

Gasoline

Minimum Required Octane for Countries Using the (R+M)/2 Octane Rating Method

EJ, EN, JH, 2H engines: Unleaded 87

Minimum Required Octane for Countries Using the RON Rating Method

JH, 2H, EW, JB, FA, FN, FV, JB, EM, GG, GH, HK, HN, EW, EX engines: Unleaded 91

EG engine: Unleaded 95

DX, KT, JJ engines: Unleaded 98

Click here for more gasoline information.