Cabby Info - Fuel System

Updated: 24-Apr-2024

General troubleshooting and DIY guides can be found under the above dropdown menus. For fuel system-specific troubleshooting & DIY guides, please refer to the individual fuel system sections.

Note: "CIS" has been replaced throughout most of this website with "K-Jetronic". K-Jetronic is the system's actual name (used everywhere outside North America), which is one type of continuous injection system.

Factory Fuel Systems

Pierburg/Solex, or Keihin carburetion

Bosch K-Jetronic

Digifant

Bosch KE-Jetronic No Icon

Diesel

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, K-Jetronic 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. K-Jetronic, 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 K-Jetronic. Slight horsepower gains can be achieved with Digifant by simply "chipping it", where K-Jetronic 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 K-Jetronic 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 K-Jetronic (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!!!

warningNote: If you participate in online car forums/groups, 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 K-Jetronic 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 KE-Jetronic people too if you can, because they often forget that K-lambda exists and the two do not share the same components.

K-Jetronic

Digifant

Carburetors

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

Carb Faults - Common Carburetor Issues: Carb Download

For complete information on carburetors, including troubleshooting and repairing, please refer to the Haynes manuals (prior Internet forum links have gone dead and/or require membership to access).

Caburetor parts

Swapping Fuel Injection for Carburetion

Why would you want to??! Many folks who want to do this "backwards" swap have K-Jetronic 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 K-Jetronic!), 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

Locations

Carburetor

K-Jetronic Filters

K-Jetronic ~ up to chassis E_11290 (up to model year 1984.5)

K-Jetronic ~ from chassis E_11291 (from model year 1984.5)

Digifant ~ 1990-1993

Fuel expansion tank (mounted to fuel tank above fuel pump on 1984½-1993 Cabriolets)

Fuel Pumps

Fuel pump & sender guide: Fuel Pump Download

Tap here for in-tank fuel pump replacement. Tap here for main fuel pump replacement.

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

Help Icons No AttributionFuel pump issues

Fuel Pump Relays

K-Jetronic:


Digifant:


Help Icons No AttributionRelay is Excessively Hot or Burning Up

If your fuel pump relay is getting excessively hot and/or is constantly burning up, consider splitting the circuit. The reasons for the relay burning up: The electrical load creates heat. The heat causes expansion, increasing the resistance, which adds to the load, creating more heat. It is a vicious cycle until the relay's circuitry can no longer handle it and burns up. This can be a continuous issue in cars with a 3-wire (electrically heated) O2 sensor, as this is an added load on the fuse 5 circuit compared to the 1-wire cars. If the relay is not built to handle the load, which is the case with some replacement relays, it will burn up.

Help Icons No AttributionTroubleshooting Procedure

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 the terminals listed 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).

* 1983-1993: You can also install the horn relay (stamped 53 in position 6) as a quick bypass method — this will determine immediately if the fuel pump relay is faulty and/or get you home if it failed out on the road. Warning: This should be temporary only as this will force the pumps to run continuously when the key is in the "on" position, eliminating the safety cut-out should an accident occur.

Fuel Injectors

Fuel injector guide (K-Jet & Digifant): Injector Download

K-Jetronic:

Fuel Tank & Gas Caps

Fuel Tank: 1979-1984 (up to VIN E_11290)

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


Fuel Tank: 1984½-1993 (from VIN E_11291)

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

The Spectra VW5A tank is manufactured to OE 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 VW5A 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.

Help Icons No AttributionRunning 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!

Help Icons No AttributionThe Fuel Tank is Leaking

Take your Cabriolet to your local Volkswagen dealer, or preferred independent shop, for a gas tank inspection. If the tank is leaking, particularly at seam welds, the gas tank will need to be repaired or replaced.

warning While the original fuel tank was under recall for a seam leak, and while recalls never technically expire, manufacturers are only obligated to repair/replace the defective component within 10 years of the recall start date. This means that no Cabriolet qualifies for any recall work.

Fuel/Gas Caps

Factory gas cap guide: Gas Cap Download

Fuel Hose

warning When replacing the in-tank fuel pump and/or its hoses, use 5/16" or 8mm ID submersible-rated hose! If you use regular fuel hose, it will begin cracking and disintigrating in short time.

warning1984½ to 1993: The connecting hose between the fuel pump and metal pipe (going to the white filter/expansion tank) is 11mm at the pump end, 9mm at the pipe end.

VW part #533201543 is too long for this location on Cabriolets unless the upper connecting hose is lengthened.

Gasoline

Minimum Required Octane for Countries Using the AKI Octane Rating Method

Minimum Required Octane for Countries Using the RON Rating Method

Tap here for more gasoline information.

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