Fuel System

General Infoexpand_more

Factory Fuel Systems  expand_more

General Info Carburetors

K-Jetronic  expand_more

General Info DIY Guides & Tips Troubleshooting

Digifant  expand_more

General Info DIY Guides & Tips Troubleshooting

Swapping Injection to Carbs Fuel Filters Fuel Pumps Fuel Pump Relays Fuel Injectors Fuel Tank Gas Caps Fuel Hose Gasoline

Troubleshootingexpand_more

Fuel Pump Issues Hot or Burned Up Fuel Pump Relay Jumping Fuel Pump Relay Running Fuel Tank Dry Fuel Tank Leaking Head Gasket Failure Engine Wear OBD I Diagnostics Cruise Control Doesn't Work

DIY Guidesexpand_more

Which System Do I Have? Which Injectors Do I Need? Draining The Fuel Tank Replacing The Fuel Tank Replacig The In-tank Fuel Pump Replacing Fuel Pumps Fuse 5 Circuit Split Improving Airflow into Airbox

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Updated: 25-July-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

• 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 K-Jetronic

• Years: 1980-1993 (up to 1989 in North America)
• Mechanical continuous injection system (CIS). There are two types of K-Jetronic (K-Jet for short) installed in Cabriolets: basic and lambda. K-Jet basic does not use an oxygen sensor and catalyst (but uses an EGR system in most cases). K-Jet lambda uses an oxygen sensor, catalytic converter, and an oxygen sensor control unit. The former is often referred to as K-basic, while the latter is often referred to as K-lambda (or Kλ-Jetronic, λ being the Greek letter/symbol for lambda) to differentiate the two systems.
• Because K-Jet 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 K-basic. All other 1980-1989 Cabriolets used K-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 from ca. 1991 onward; 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 and uses a coil pack.
• Locales: worldwide

Bosch KE-Jetronic

• Mechanical fuel injection with electronic controls
• KE-Jetronic was never, ever factory-installed in Cabriolets! Never, never, never... ever!!
• The main difference between K-lambda and KE-Jetronic: KE uses a differential pressure regulator, a diaphragm pressure regulator, an idle air stabilizer valve and knock sensor; K-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 KE-Jetronic! Many K-basic afficionados are spreading incorrect information regarding KE; they do not understand the differences between K-basic, K-lambda and KE.

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, 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!!!

Note: 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):

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

Carb Faults - Common Carburetor Issues:

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

• K-Jetronic fuel filter is in the engine compartment, mounted to the driver's side fender between the battery and coolant tank.


• Digifant fuel filter is located under the car, near the main fuel pump.

Carburetor

• Volkswagen part #251 201 511G

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

• Volkswagen part #431 133 511
• Bosch #0 450 905 021
• Mann #WK 618
• Mahle #KL5
• NAPA Gold/Wix #33008

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

• Volkswagen part #431 133 511D
• Bosch #0 450 905 401
• Mann #WK 830/6
• NAPA Gold/Wix #33156
• Note: Fuel filter #893-133-511 is listed in the VW parts catalog and on parts sites. This is incorrect! This filter is a Golf II (Mk2) filter and is too large to properly fit the Cabriolets. For 1984½-1993 Cabriolets with K-Jetronic, use the part number(s) above to order the correct filter.

Digifant ~ 1990-1993

• Volkswagen part #1H0 201 511A
• Bosch #0 450 905 030
• Mann # 830/7
• Fram #G3829
• Purolater #F60146
• AC/Delco #GF358
• NAPA Gold/Wix #33179

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

• Also referred to as swirl pot, fuel sump, fuel reservoir, fuel filter
• Purpose: To keep fuel available to the main pump at all times, including during hard cornering with low fuel tank level (in-tank pump will briefly starve, main pump will not).
• Volkswagen part #533 201 511A

Fuel Pumps

Fuel pump & sender guide:

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.

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+ K-Jetronic 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:
  • It's worn out
  • It's internally faulty
  • Fuel starvation (transfer pump not working well enough/at all, reversed fuel lines on the transfer pump, reversed wires on transfer pump, pinched/clogged fuel line, clogged fuel expansion reservoir/swirl pot, clogged transfer pump screen, etc.)
  • Too much resistance in the circuit and/or not enough voltage at the pump - this can be caused by a faulty pump and/or faulty fuel pump relay and/or faulty grounds


• 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 K-Jetronic cars, it's advised that you replace both pumps at the same time, unless one pump was recently replaced (does not apply 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).

Main fuel pump volume – minimum specificatios

• K-Jetronic:
  • 26 fluid ounces (760 ml) within 30 seconds and 12V pump voltage
  • 16 fluid ounces (463 ml) within 30 seconds and 10V pump voltage
• Digifant:
  • 10 fluid ounces (300 ml) within 30 seconds

In-tank fuel transfer pump volume – minimum specification

• 10 fluid ounces (300 ml) within 10 seconds

Fuel Pump Relays

K-Jetronic:

• Complete relay guide:

• WARNING: Do not buy KAE brand fuel pump relays! All versions for 1983+ cars are now built with incorrect circuit boards! See the guide linked above for more info.
• WARNING: Do NOT buy fuel pump relays from rockauto.com. You are taking great risk in receiving a junk relay.


• Fuel pump priming (pumps run for 2 seconds when key is turned to "on") is controlled by the fuel pump relay, which has a cut-out function. If the relay does not receive a ground signal from the coil, 12V power to the pumps is cut, and the pumps shut off.

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Digifant:

• Bentley diagram shows a 5-pin relay; this is incorrect. Digifant fuel pump relay is 4-pin (part #191906383 or 191906383C).


• Fuel pump priming (pumps run for 2 seconds when key is turned to "on") is controlled by the Digifant ECU, not the fuel pump relay. If the pumps do not prime, or run continuously, suspect a faulty fuel pump relay, faulty Digifant power supply relay (#141951253B), faulty wiring/ground, faulty ECU.

---

Relay 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.

Troubleshooting 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).

• 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 (31b or 1) to check — consult your repair manual for instructions.

* 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):

K-Jetronic:

• K-Jetronic injector cleaning guide:

• Opening injector pressure is 46.4 to 55.11 psi. Injector flow rate is dependent on fuel distributor and CPR.


• Trick to installing new O-rings onto injectors:

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.

• Part numbers:
• 171201075P: Carburetor
• 171201075Q: Fuel injection


• Capacity: 10.6 gallons


• Spectra replacement tank: VW4B

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.

• Part numbers:
• 155201075B or 155201075C


• Capacity: 13.8 gallons


• Spectra replacement tank: VW5A

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.

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, 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.

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:

Fuel Hose

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.

1984½ 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 #171201543B
• Manufacturer part #1115656100

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

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

Tap here for more gasoline information.