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K-jet resources

Thought I'd add this disclaimer.
Before you start to mess about with anything confirm that both the in tank pump and the under car pump are working.
If both are working, you then need to check the pressure at the engine bay. If you aren't getting the fuel pressure at the front of the car nothing else will matter.
Any K-Jet Owner should invest in a fuel pressure testing kit.

Copied across from the old site:

So over the past 18 months of ownership I've built up a good resource for K-jet stuff and found a couple of options for reconditioned parts. Not cheap, but not ridiculous either.

Reconditioned K-Jet components:
Welcome to ATP - The Home of Electronic Remanufacturing Since 1988

KMI have been remanufacturing Bosch K-Jetronic Fuel Injection since 1982

The price list from KMI as it doesn't show on their website but I contacted them recently. Correct as of January 2015:

The cost of an exchange Warm up Regulator is £132.00 + vat. Customers own unit rebuild.
The cost of an exchange Fuel Distributor is £300.00 + vat. Customers own unit rebuild.
The cost of a new Aux Air Valve is £169.00 + vat.
The cost of a new Accumulator is £154.00 + vat.
The cost of a new Injector is £34.00 + vat.

[EDIT] there are 2 types of injector. I had the other type at £56 each!  :'(

Also NEW genuine stock:

Bosch classic parts site (you'll need to active Google Translate in Chrome)

Bosch classic parts online shop

K-Jet General Resources:

And not forgetting the legendary RubJohonnys' HOW TO: Tune your MK2/Corrado 1.8 16v guide

And much as I dislike pushing people away to other forums as I think this one is the best, occasionally you find valuable content elsewhere

A pretty good, and interesting K-Jet build project:...

And my fav... a mk1, but still a perios Turbo'ed K-Jet

Documents and PDFs:
[size=150]NEW DOCUMENTS ADDED 05/01/2016[/size]
Bosch K-Jetronic Injection Guide (Word .docx)

DIY Warm Up Regulator repair guide (PDF)

V.A.G. Service guide. K- Jetronic SSP 44 - German (PDF)

K-Jet Pressure Test Specifications (PDF)

K-Jet Factory Manual (PDF)

[size=150]NEW DOCUMENTS ADDED 10/05/2016[/size]
Bosch K-Jetronic and KE-Jetronic mechanical fuel injection systems HAYNES supplement, for XR3 RS turbo, but much the same applies:

Same as above but Golf specific for 8v (RP engine code?)

K-Jet Tricks - Part 1

K-Jet Tricks - Part 2

The beginnings of Fuel Injection

Basic Training - Part 1

Basic Training - Part 2

K-Jet Help for Hot Start

I'll add more as I sort them out, TomRich sent me a bunch of stuff, in the meanwhile PM me if you want more info.

Re: K-jet resources

Reply #1
Quick addition to this. I've just been in touch with Mark Carter of

He dose the under car fuel lines for MK1, and he should have Mk2 K-jet stuff available shortly.

As a guide price this is what's listed as an example for the Mk1 set up.

£45 for the pump to accumulator
£27 for fuel line to filter (braided)
£30 for accumulator to supply line (curly braided)
£45 for filter to metering head.

My rebuild is going to expensive but I'm very dedicated to it now.

Re: K-jet resources

Reply #2
Update: Here are the filter pipes.

Accumulator To Fuel Filter 191201218 £36.50
Pump To Accumulator 191201373 £30.00
Pump To Engine Bay 191201374 £39.50

Manufactured by the company that supplied VW in the first place to the original specification, which is a shame in a way as they're only zinc plated rather than stainless steel which would have been nicer.

Re: K-jet resources

Reply #5
Fuel supply
The fuel pump operates continuously while the engine is running, excess fuel being returned to the fuel tank. The pump is operated when the ignition switch is in the START position. Once the starter is released, a switch which is connected to the air plate, prevents the pump from operating unless the engine is running.
The fuel line to the fuel supply valve incorporates a filter and also a fuel accumulator. The function of the accumulator is to maintain pressure in the fuel system after the engine has been switched off and so give good hot restarting.
Associated with the accumulator is a pressure regulator which is an integral part of the fuel metering device. When the engine is switched off, the pressure regulator lets the pressure to the injection valves fall rapidly to cut off the fuel flow through them and so prevent the engine from “dieseling” or “running on”. The valve closes at just below the opening pressure of the injector valves and this pressure is then maintained by the accumulator.

Fuel distributor
The fuel distributor is mounted on the air metering device and is controlled by the vertical movement of the airflow sensor plate. It comprises a spool valve which moves vertically in a sleeve, the sleeve having as many vertical slots around its circumference as there are cylinders on the engine. The spool valve is adjusted to hydraulic pressure on the upper end and this balances the pressure on the air plate which is applied to the bottom of the valve by a plunger. As the spool valve rises and falls, it uncovers a greater or lesser length of metering slot and so controls the volume of fuel fed to each injector.
Each metering slot has a differential pressure valve, which ensures that the difference in pressure between the two sides of the slot is always the same. Because the drop in pressure across the metering slot is unaffected by the length of slot exposed, the amount of fuel flowing depends only on the exposed area of the slots.

Cold start valve (5th Injector)
The cold start valve is mounted in the inlet manifold and sprays additional fuel into the manifold during cold starting. The valve is solenoid operated and is controlled by a thermotime switch in the engine cooling system. The thermotime switch is actuated for a period which depends upon coolant temperature, the period decreasing with rise in coolant temperature. If the coolant temperature is high enough for the engine not to need additional fuel for starting, the switch does not operate.

Warm-up regulator - WUR (Control Pressure Valve - CPR)
While warming up, the engine needs a richer mixture to compensate for fuel which condenses on the cold walls of the inlet manifold and cylinder walls. It also needs more fuel to compensate for power lost because of increased friction losses and increased oil drag in a cold engine. The mixture is made richer during warming up by the warm-up regulator. This is a pressure regulator which lowers the pressure applied to the control plunger of the fuel regulator during warm-up. This reduced pressure causes the airflow plate to rise higher than it would do otherwise, thus uncovering a greater length of metering slot and making the mixture richer. The valve is operated by a bi-metallic strip which is heated by an electric heater. When the engine is cold, the bi-metallic strip presses against the delivery valve spring to reduce the pressure on the diaphragm and enlarge the discharge cross-section. This increase in cross-section results in a lowering of the pressure fed to the control plunger.

Auxiliary air device
Compensation for power lost by greater friction is achieved by feeding a larger volume of fuel/air mixture to the engine than is supplied by the normal opening of the throttle. The auxiliary air device bypasses the throttle with a channel having a variable aperture valve in it. The aperture is varied by a pivoted plate controlled by a spring and a bi-metallic strip.
During cold starting, the channel is open and increases the volume of air passing to the engine. As the bi-metallic strip bends, it allows a control spring to pull the plate over the aperture until at normal operating temperature the aperture is closed.

Cold acceleration enrichment
This system is fitted to later models only. When the engine is cold (below 35°C), acceleration is improved by briefly enriching the fuel mixture for a period of approximately 0.4 seconds. This cold acceleration enrichment will only operate if the thermotime switch, the diaphragm pressure switch and the throttle valve switch are shut off.

Temperature sensor
From March 1986, a temperature sensor is located between injectors 1 and 2. After switching off the ignition, this switches on the cooling fan when the temperature of the cylinder head exceeds 110°C. A time relay is incorporated in the circuit. This switches off the function between ten and twelve minutes after switching off the ignition.

Re: K-jet resources

Reply #6
A few new PDFs added in original post.

Also, interesting article on finding air vacuum leaks in engines which mentions carb-cleaners, propane and smoke generators:

However this does talk about MAF sensors, on-board computers, exhaust-gas oxygen sensors and check engine lights :lol: what is all this mumbo jumbo? but hey the principle still applies.

Anyway, cut out all that crap, and the fact this is basically a sales pitch for an expensive bit of equipment and I've copied and pasted the important bit here in case the link ever dies.

The Carb-Cleaner Trick

Here's how we old-line mechanics learned to chase leaks: To keep the engine computer from richening up the mix, pull the wire on the throttle position sensor or some other handy sensor that will keep the engine in open­-loop mode, where the computer just uses hard-coded default values for the amount of fuel instead of dithering the values around to stay near that golden 14.7:1 ratio.

This is analogous to the situation in a carbureted car (or motorcycle, or any other IC engine that doesn't have a computer). Start the engine and let it idle. Now spray aerosol carb cleaner onto the suspected leak. Yes, this is dangerous, especially if you consider your eyebrows important. There's not supposed to be an ignition source on the engine anywhere, but once in a blue moon, a stray spark or an overheated exhaust manifold can make the carb cleaner flare up. You've been warned.

The combustible carb cleaner will be sucked into the leak, and the engine will pick up its idle speed momentarily—and probably run on all cylinders if it's been misfiring. We quickly learned to use short, directed puffs of carb cleaner to localize the leak.

Another option is to use an unlit propane torch to prospect for leaks. A piece of hose shoved over the torch's valve outlet will let you poke around the engine bay. When the combustible propane is sucked into the lean-running engine, it will smooth out and speed up slightly. Similarly, you can spray water or motor oil onto a suspected leak and achieve the same end. When the water gets sucked into the leak, it momentarily interrupts the extra O2 stream, and the engine's idle will change.

Re: K-jet resources

Reply #7
Anyone with 20 minutes to spare, watch this  :D :

Found a new resource today:

An american based company that offer a sales and refurbishment service similar to KMI, however among their website pages are a bunch of technical articles for set up, testing and analysis.

I'll be reading through and making pointers to anything significant that I find.

If you want to test your k-jet system you'll need a pressure testing kit. Ideally you only need a few key bit and if you can match the sizes can make one yourself. Unfortunately since Photobucket has shafted nearly every forum details on this are limited.

I managed to get this kit:

It's a universal kit so about 75% of it I'll never use, I got it cheap as it had a few components missing unfortunately the bits missing were from the 25% I did need but I went into Pirtek and managed to get the connectors I needed to hook it up.

Instructions in using it and the values to be looking for should all be in the documents already listed in this thread.

This retails for about £70 on eBay, note the connections are American standard - which was what gave the guy in Pirtek a headache when he was trying to help me out. But as long as you get the full kit it doesn't really matter how the bits of it connect. Smaller kits are available on eBay but they don't contain the tap you'd need so it's an option to get one of those £15-20 kits and then try and customize it to what you need.

Re: K-jet resources

Reply #8
A bit more useful info, it's a Capri, but you can ignore that. This diagram helps define where some of the key bits are and how they relate to the full system.

The following text is also Capri related and take from here: Please take into account the values and references to locations or precise configuration may not be correct for VW Golf or Jetta, but the correct information is published in the post prior to this one in this thread.

I've copied and pasted to ensure this info isn't lost if that link ever goes down. But all credit goes to the original publisher.

NOTE:- whilst working on any fuel system, care and attention should be taken to avoid the petrol coming in contact with any source of ignition, this can include: hot engine components, High Tension (HT) sparks and smoking.

This article is taken from a Capri Club International Magazine (May 1999) and was written by: Ian Coulson Aff.IMI.Technical Advisor

"We Unravel The Mystery"

I have been working in the motor trade for almost 10 years years now, and have been working with K-Jetronic for 8 of them. Most of the information I will use comes from course notes I have from attending the Ford Service Training College at Daventry on the Bosch K-Jetronic fuel injection system training course.

I have since moved on from working at a Ford main dealer to a Volkswagen Audi dealer in York, and attending the K-Jetronic training course at the V.A.G training centre at Milton Keynes, as the same system was fitted across the VW Audi range. It is probably the first fuel injection system that was used by a number of motor manufacturers and on the whole, is pretty reliable. it is quite a basic, mechanical system, as opposed to the more technical electronic engine management systems available noe, and as such, is open to wear, corrosion and sticking of components and requires a certain amount of adjusting and cleaning to keep it working in the way Mr. Bosch intended.

General Description

Fuel is supplied from the tank by an electric fuel pump. It passes through to the fuel accumulator, up to the fuel filter, where it then passes to the metering head. Air drawn in by the engine lifts the sensor plate, which in turn is connected to the control plunger inside the metering head.

As this lifts inside it's chamber, pressurised fuel is passed to the injectors, the amount being governed by the amount of air lifting the sensor plate, which sprays continuously on the back of the inlet valves inside the engine. As the valve opens, the air and the sprayed fuel pass into the combustion chamber and ignition takes place.

Firstly, the fuel system.

Fuel Pump

The fuel pump is located at the rear of the car on the drivers side. It is fastened on the side of the tank in a rubber housing to cut down on noise. I tis fed by a rubber pipe which is connected to the fuel tank directly.

It must receive 12 volts to make it work, so it has 2 electrical terminals on it's forward facing end. It is fitted with 2 valves inside, one is the safety valve wich, in the event of a blockage in the system, will release fuel back to the inlet side, and a non-return valve. This keeps fuel in the system ahead of the pump after the engine hads been switched off.

Fuel passes through the body of the pump and out through the cantral union on it's forward facing end and up to the fuel accumulator.


The fuel pump is a sealed unit and cannot be repired. If it fails, it can give a few symptoms, the most obvious being that the car will not start at all. If it becomes noisy, this is an indication that all is not well. It can cause jerky running when under heavy load when accelerating and even misfiring when revving up when stationary. If it shorts out inside, it will blow the fuse. This is mounted under the dash on the drivers side, but I will cover this more in the elecrical system section.

Only basic tools are required to change the pump, being a 19mm spanner for the fuel pipe union, a screwdriver for the fuel pipe clip and an 8mm spanner or socket to remove the bracket from the fuel tank. You will also need something to plug the supply pipe from the tank otherwise you will get a petrol bath! Not recommended.

Fuel Accumulator

This is also located at the rear of the car, just above the fuel tank. It is a metal housing with 2 fuel pipes bolted into one end and a small breather hole at the other. Inside is a large spring, a diaphragm and a steel plate with a fuel feed hole through it.

Fuel, pressurised by the fuel pump, enters the fuel accumulator and forces the diaphragm against its spring to its stop. It remains in this position all the time the engine is running. When the engine and consequently the fuel pump is switched off, the diaphragm is allowed to return under spring pressure, trapping the residual pressure in the system rather like a tyre valve. It will retain this pressure for about 20 minutes. It is fitted to keep pressure in the system so the fuel, when switcing off a hot engine, does not vapourise causing hot starting difficulties.


The fuel accumulator is a sealed unit and is not repairable. The spring inside is very strong, so the unit should not be cut open as injury could result.

The 'holding pressure' which this unit provides is difficult to check without the specialist gauges, but no doubt a garage would undertake this for you. The only thing you can really do is to check that the breather hole has not become blocked. Fuel then passes up the engine bay to the fuel filter which is a silver cylindrical object bolted to the passenger side inner wing. If it gets blocked, it can cause the same symptoms as a faulty fuel pump and can be checked by doing a fuel pump delivery rate check which I will describe later.

Metering Head / Fuel Distributor

So the heart of the system - the metering head or fuel distributor as it is sometimes known. This is mounted right at the front of the engine bay on the passenger side and has a host of black pipes leading to and from it. Fuel enters the metering head from the fuel filter, via the union on the passenger side nearest the large black air ducting. Inside it passes into a central chamber. As the plunger travels up the chamber, it uncovers a series of slots which are connected to the unions on its top, which are connect to the fuel injectors in the engine.

The more of these slots it uncovers, the more fuel passes to the injectors. The plunger is connected to an arm which has a large disk on it. If you remove the large black air duct, this disk can be visible. It is bolted to the arm sensor plate and housing. The air drawn in by the engine lifts this sensor plate and, as it is connected to the plunger, also allows more fuel to the injectors. The more air is drawn in, the higher the plate moves so the higher the plunger moves - uncovers more slots and allows more fuel to the injectors.


The fuel metering head should not be stripped down as it is a very finely machined unit and can be damaged easily. The only real problem that I have encountered with it is of it sticking due to corrosion on it caused by water in the fuel. A good fuel system cleaner added to a tank of fuel will usually cure most problems with it.

The air sensor plate on the other hand can be adjusted. First, it should be clean. it should be cantral in its housing and it should be set at the correct height. The edge of the sensor plate should be level with the start of the cone shaped section of the housing.

If this is incorrectly set, not central and catching on the side of the housing or dirty, it will cause the fel/air ratio to be wrong for the whole engine rev range leading to poor starting, lack of power, flatspots and high fuel consumtion.

After cleaning, raise the sensor plate right up and underneath is a metal 'R' shaped spring. Bend this spring up or down to acheive the correct height. If it is not central, undo the 10mm bolt in the centre and pass a feeler blade around its edge until it centralises itself. After adjusting, it will be necessary to have idle speed and mixture reset using a CO meter. Again, most garages would carry this out for you.


These are monted underneath the ribbed air chamber on to of the engine and are secured in the inlet manifold. They release a finely atomised spray in a cone shape, contiuously - the amount depending on the position of the plunger in the metering head.


Again, they are a sealed unit, but they can be cleaned by fuel system cleaner as described previously. If they get dirt in them or the spring goes weak, they can give an incorrect spray pattern causing a reduction of power in the associated cylinder. the main fault with injectors is 'dribbling'. When the engine is switched off, pressure is still in the system - thanks to the accumulator.

If the injector is not seating properly due to dirt or wear, it will allow fuel to dribble into the cylinder, wetting the lug and more importantly reducing the holding pressure. This can cause various hot starting problems, mainly starting on 4 or 5 cylinders, then clearing after a rev. This can be checked by running the engine and then removing the injectors with the pipes still attached and placing them on some tissue paper and watching to see if they are damp.

The Warm-up-Regulator

This is mounted right at the front of the engine with 2 fuel pipes bolted to it, with different size unions and a grey electrical plug. Basically, it is the 'choke'. It provides a richer mixture for cold starting and during the warm up phase. Fuel passes to it from the central union on the metering head. When the engine is cold, the warm up regulator is open, allowing fuel to pass through it. This reduces the pressure acting downwards on the plunger in the metering head, allowing it to lift higher than normal so allowing more fuel to the injectors and giving a richer mixture. As it heats up, by engine temperature and its heating element inside, it closes off slowly causing higher pressure to act on top of the plunger, forcing it down again, so weakening off the mixture. This pressure is called 'control pressure' and again needs the special gauges to check it.


Behind the larger of the 2 unions is a metal gauze filter. If this gets blocked, it causes the warm up regulator to remain closed, causing very bad flatspots and poor acceleration during the warm up phase, just like trying to drive without using the choke. It can be cleaned out using clean petrol. It also has a vacuum connection to it. This is for full load enrichment. At full load, engine vacuum is low, which opens the valve slightly, reducing the pressure on the control plunger and giving a slightly richer mixture.

The Electrical System

There are various switches, valves and realysin the K-Jetronic fuel injection system, so I will try and describe their function and how to test them.

Fuel Pump Relay

This is to be found under the dash on the drivers side, above the bonnet release handle along with a few other relays. It si pink in colour and has 5 terminals. The brown wire is connecte to earth, the red wire is connected to battery live via a 20 amp fuse which is mounted next to the relay, the black wire is fed with ignition live, the green wire is from the coil terminal 1 with a pulsed live to tell the relay the engine is running and the last terminal has 2 wires going to it. They are both black with a red tracer, the thickest of which goes to the fuel pump. The other wire goes to the heating element of the warm up regulator and the auxiliary air valve, whose operation I will cover shortly. Just switching on the ignition will not not cause the fuel pump relay, and consequently the fuel pump to switch on. It must receive a pulse from the coil before it will work. This is a safety device so in the event of an accident when the engine is stalled but the ignition is left on, the fuel pump is automatically switched off to reduce the risk of fire.

for test purposes, the 4 pin heated rear window relay can be substituted for the fuel pump relay to make the pump run with just the ignition on. This relay is in the same place as the fuel pump relay and is black in colour and has a red 16 amp fuse on top of it, under the plastic cover. I must stress that this must ONLY be done when doing the fuel pump delivery test. This test is described later.

Auxiliary Air Valve

This provides the fast idle during the warm up phase and is bolted to the front of the ribbed air chamber with 2 black pipes going to it, one from each side and a black electrical plug. When the engineis cold, the valve is open. You can check this by removing both pipes from it. You should be able to see through it. It allows air into the engine without it going through the throttle valve almost like an air leak. This extra air, coupled with the extra fuel allowed in by the warm up regulator, gives increased idle and mixture to run the cold engine.

As it warms up, it slowly closes until when hot it is closed completely. This can be checked by squeezing one of the hoses. If the engine is cold, the revs must drop; if the engine is hot it should not affect the speed.

It is heated by the engine and also by a heating element - hence the electrical plug. It is a 2 pin plug, one connection being earth,the other being live via the fuel pump relay. This can be checked with a tes light or meter. The resistance of the heating coil can be checked. This is done by unplugging the electrical plug and putting an ohmeter across the 2 terminals of the valve. It should be approximately 40 ohms. The electrical plug to the warm up regulator can be checked for voltage and resistance in exactly the same way although the resistance of its heating element is only 25 ohms.

Thermo-Time Switch & Cold Start Injector

I have linked these 2 items as they work hand in hand with each other. The thermo-time switch is a large brass switch screwed into the water jacket at the very front of the engine and has a brown electrical plug. It has 2 wires going to it, one from the starter motor i.e. only live when the starter is cranking and the other goes to the cold start injector.

The cold start injector is bolted onto the drivers side of the ribbed air chamber and has a fuel pipe and a blue electrical plug. This also gets a live from the starter motor and gets its earth via the contacts inside the thermo-time switch. this can be checked with a meter or test light as previously described.

To check the valve itself, it should be removed from the air chamber and placed in a measuring container. It should spray for between 1 and 8 seconds dependant on temperature (it will not spray at all over 40 degrees C) and should give a fine conical spray. It should not 'dribble' at all once the valve has shut down. this test should be carried out with the coil lead removed and the engine cranked on the starter.

There is an extra item fitted to the Capri injection, which you may have heard 'clicking' from time to time. this is the 'impulse module' and is a 4 pin relay mounted under the dash near the fuel pump relay.

When the engine is cranked when it is hot, if it does not start after 2 seconds, the impulse module provides an earth to the cold start valve inthe form of a pulse, making it spray fuel to aid starting. It pulses for 1 second and then switches off and then pulses at 1 second intervals until starting takes place.

Fuel Pump Delivery Rate

The fuel pump delivery rate is checked at the return line at the fuel metering head. It is checked here because it not only checks the pressure from the pump, bit it also checks to see if there are any blockages on the way. For example, the fuel filter maybe.The return line union is on the passenger side of the metering head and is the larger of the 2 unions side by side and has an arrow on it pointing away from the metering head. Attach a pipe of approximately 2 feet long to the short rubber hose coming from the union and place it in a measuring container, then substitute the fuel pump relay with the heated rear window relay and switch on the ignition. The fuel pump should deliver a minimum of 750cc of fuel in 30 seconds. If this is not obtained, check the voltage of the fuel pump. A minimum of 11.5 volts is required and if this is OK, repeat the test at the fuel filter inlet pipe. If the required amount of fuel is obtained then the fuel filter must be partially blocked.

This is basically the K-Jetronic fuel injection system.

I hope I have covered all the problem areas and lifted some of the mist surrounding this system. It is quite straightforward in its operation, providing diagnosis and testing is acrried out logically and one step at a time.

Just to close, this system is quite reliable and as such, you should not jump to the conclusion that there is something wrong with it when the car is difficult to start or is not running quite right. You must always check the basics first. Check the idle and mixture, spark plugs can cause all sorts of problems if they are worn or are cracked. Plug leads can also cause problems, especially in damp weather. if the engine earth strap is broken or the contacts dirty, then the starter can demand extra current so not leaving enough for the spark to be sufficient for cold starting. Basic items such as these should be checked prior to diving into the injection system.

Happy diagnosing and keep the legend alive. Ian Coulson Aff.I.M.I. Technical Advisor.

Thought I'd add this link to this thread:

Replacement under car fuel pump housing.

Not cheap, but not that expensive either when you consider what a used plastic one goes for. And this is going to be a lifetime replacement - fit and forget!

Thanks to DaleR32 for the heads up, to see the test fit go here:

[Update 05/06/2020]
Now sold by Mark Carter of Classic VW either a the housing:

Or a complete kit, including pipework, pump, accumulator and filter:

Pipes, pumps etc all sold individually too. If you need advise give Mark a message, contact details are on the website.

Re: K-jet resources

Reply #9
brilliant this! many thanks indeed!!