K-Jet info and testing.

[86gti]

Still seeing a few people with issues on starting, starvation of fuel in corners etc etc.
All the good and scary things of K-jet. I'm sitting in a Tokyo Appartment with nothing to do so I'll post up some of the tests, tips and tricks with trouble shooting K-Jet Problems

OK! K-Jet (CIS) is not a sware word!

in this thread im going to share some info on the K-jet system.
If yo have any more to add please feel free.


cool vid on the system working here


The first glance at a mechanical Injection system can be a daunting thing!
But with good knowledge of EFI systems etc I took a deep breath and drown myself in all the information i could find on the k-jet Mechanical system. Books, Manuals, Web sites etc.for over 5 years.... and now for some silly reason the K-jet system is something I love and have had many years playing with and doing mods to.
It seems it isnt as bad as you would first think! with a few basic tools and a willingness to learn you can do most of the work yourself (I would sugest anything to do with the fuel distributor/AF meter be done by someone who knows exactly what they are doing tho!!)

Its all pretty simple when you break down the system into Main Parts. from the tank to the injector.
-Fuel Tank
-Fuel Pump
-Pump Relay
-Fuel Accumulator
-Fuel Filter
-System pressure (primary pressure regulator)
-Airflow sensor/Meter
-Fuel Distributor
-Warm up Regulator
-Cold start injector
-Aux Air Valve
-Injectors

the main points you will need to break faults into are.
-Fuel Supply
-Air flow Measurement
-Fuel Metering

In this thread i will go over the basics of each section.
when you know what each part does, it makes it less of a head ache to understand.

THE TANK.....
We all know what that is....Its the part of our car that we spend the most money on!
In Most cases in K-Jet (CIS) cars the tank is a sealed unit. it allows the natural gassing of petrol to help delivery to the pump by slightly pressurising the tank. sometimes when u remove the cap you will hear the pressure pass out (especialy on a hot day).
im led to believe some of the older systems were vented, but on later models this isnt the case.
The MK2 runs a "lift pump"... this supplies fuel to another small tank found under the car ... in it is the Main pump that supplies the rest of the system. (basicly under the driver side rear seat)....
This is sort of like a surge tank set up to always keep pressure to the pump when you are conering, braking accelerating ect.


PUMPS.....
Pick up Pump, Lift pump, transfer pump or what ever you wish to call it is the first pump to pick up the fuel in the tank.
Make shure this is working well...If this doesn't work well it will starve the Main pump and you will find yourself replacing 2 Pumps!!
(been there done that)

Testing this pump is fairly simple.
Find your Fuel pump relay.... This was no where near where it said it was in the bently manual so im guessing the US versions differ a bit from the European vehicles. My relay was stamped number "62" and was in the top row of relays on the left.

when you get it out you will see 2 large pins and 2 or 3 small pins (cant remember how many small ones..but they dont matter at this stage)
where the 2 lage pins fit into the relay holder is where we are looking
Grab a switch (toggle ones are best - 2 pole) solder wires to the poles and fit large spade bits on the end of the wires.
make shure the switch is off and plug the spades into the 2 LARGE slots in the relay holder.
dont turn it on yet!!!!!!(if its not off you will hear the pumps fire up when you plug it in, no harm done, just turn it off quick)

Now, dissconnect the warm up regulator!! you will see this on the front side of the engine block, just unplugs...

have a look under the car driver side just under where the back seat is....
you will see the main pump with a plug going into the top of it. It a std type plug that can be removed by pushing the wire clip at the top and sliding it off.
once you have done that we will find the Lift pump.
take up the carpet in the boot well. to the right and up a little from the spare wheel well you will see a plate with 3 screws in it.
undo them and take the plate off to reveal the top of the pump and Fuel guage sender.you will see 2 hoses, both with arrows.
one points in (returned fuel from system) one pointing out...one pointing out is the one you want...
Take the hose off it, and find another bit of hose that will fit over the outlet.
now we are ready to testthe delivery rate. Grab a mesuring cup that will hold at least 500cc and get ready to let the fuel go into it.
get some one on the switch ( ill do it for a tinnie or 2)...
flick the switch and leave on for 10 seconds
you should get at least 400cc / 13 and a half Oz. into the cup...
If you have..thats good news..if not......................
Replace it before the main pump decides to retire.
Try to use Genuine Bosch parts where ever you can . I am running a high pressure Carter Pump in mine and it seems to work fine although a bit more noise than the Bosch product.

well thats step one of a basic Check up and General over view of the Fuel Tank Section and Transfer pump.

[86gti]

Main Pump

In the MK2, the main pump is located in the smaller tank (reservoir)....
This pump is a roller cell pump, with the fuel entering the pump and being compressed by rotating cells that force it through the pump at high pressure. It will apparently pump upto 8 bar (120 psi) with a delivery rate around 4 to 5 litres per minute .....the system relies on pressure to run well....so this is one of the Main parts of the system.
Within the pump is a pressure relief valve that lifts off its seat at about 8 bar to stop the pressure incase the filter, fuel lines or other things become obstructed. The other end of the pump (out) is where the non-return valve is.... When the voltage to the pump is removed it closes the return and maintains pressure within the system... we get to that later
The operating pressure in the system is approximately 5 bar (75 psi) and at this pressure the current drawn on the pump is around 5 to 8 amps.
Apparently the inside of the pump (armature) will spark etc......!!!! sounds bad when fuel is passing in there...
But absence of Oxygen means no explosion! hahahaha....

To test your deliver rate of the main pump get under the bonnet and find the fuel return hose....
this hose returnes the fuel back to the tank that has been unused.
the K-jet system doesn't Pulse fuel into the manifold like an EFI set up....it is always injecting so there is always fuel being recurculated..
plug the main pump back in where you unpluged it to test the lift pump.......
the return line on mk2 is just infront of the firewall on the driver side (UK car)...

this test also relies on the voltage at the main pump..so low voltage at the pump means a bit less delivery...
.....see what sort of voltage you have at the pump between 10-12v is usuall...

now run the return line into a measuring cup (mid sized) from memory mine held about 17oz.
run the pumps from the switch for 30 sec and turn off.

at 10v you should have around 350-380cm3
at 11v you should have around 500-520cm3
at 12v you should have around 650-670cm3

BTW cm3 is also cc ..........1000cc (cm3) = 1lt etc.

this is where i found a problem with my MK2 about 5 years ago.
all my pressure tests were fine, but my delivery from the main pump was less than half what it should have been...
was hard to start when warm, would miss and carry on allot, and eventualy wouldnt start at all...
new pump had it running better than ever

If you plan on getting more indepth than this i would urge you to get a bently manual... (I got mine from Pitstop book shop in WA)

also please be careful when playing around with fuel, especially at high pressure!!

[86gti]

PUMP RELAY

Tachometric relay...... what that means is it only responds and sends a voltage to the pump when the engine is turning over or actually running. The relay gets its signal from the negative terminal of the coil , this confirms that the engine is turning.
this relay is kind of a safety device... if the vehicle is involved in an accident when there is a possibility of a fuel line being fractured, the engine will stop due to a lack of fuel, the signal from the coil stops and then there is no voltage at the pumps.

if the car wont run, get someone to see if they can hear the pumps going while its turning over....
Early relays will not prime the pump when the ignition is turned on.

My relay was a bit of a bugger to find....my bentley manual said it was somewhere that it wasn't.( U.S Manual)
on my mk2 (UK) it was relay "62" as posted before.

as explaned previously bridge the 2 main pins on the relay with a switch, and a 10 amp fuse in the line too...just to be safe..
flick it on and see if it goes.lol.....

If you relay is screwed a genuine one will cost in the amount of $150-250 AUS.....
If you search the net you will find German made ones that will prime 2 times when you turn the ignition on, but also lift your rev limiter to a little over 7,000RPM for around $35 bux....

[86gti]

FUEL ACCUMULATOR
(next to the main pump on a mk2)

It accumulates fuel......lol.
and it's the first part in the fuel system after the pump.
Its first job is to help smooth out any pulses in the flow of the fuel, this is achieved by passing the fuel through a series of baffles and into a chamber giving it smoth flow. Its other role is to maintain pressure within the system when the fuel pump has been switched off.
This is achieved by the accumulator spring and diaphragm pushing against the fuel.
When engine is running the diaphragm will be against its stop within the spring's chamber. When the engine is stopped and the non return valves close the spring pressure against the diaphragm will maintain the pressure and stop any seepage.
in most data books for this system it is shown that the critical time for maintaining these pressures is between 5 and 20 minutes. After a fang when the engine is switched off the under bonnet temperature increases, causing the fuel in the lines to heat up....this will usually make fuel evaporate.....but maintaining the pressure fixes this problem and will let it start when its been standing with a hot engine.

Quite often the problem with hot start issues, though not always.

[86gti]

FUEL FILTER
(next to the main pump on a mk2)

Very good idea to change this at least every 2 years or so...
as the system is so reliant on pressure and clenlyness, you filter has to be in good condition.
not much to say about this filter....
it looks allot different to normal filters and has screw in fittings in both ends to cope with all the pressure.

[86gti]

The System Pressure basicly how it supplys fuel at differing loads.

System pressure within the system between the fuel pump and the metering head. This pressure is determined by the primary pressure regulator inside the metering head......dont open it!!! unless you are a brainiac in that department and even if you are, where you are working should be cleaner than your kitchen bench!!!!!
When the required pressure is obtained the plunger in the regulator lifts off its seat and excess fuel is returned to the tank.
This system due to the nature of its operation will automatically compensate for different fuel demands under different conditions.
EG... if the fuel requirement is low at engine idle, the plunger will lift and return a greater volume of fuel back to the tank than when the demand is higher, when a smaller amount of fuel is returned.
When the engine is switched off, the fuel pump relay looses the coil negative signals that powers it (mine does sometimes ) and the voltage to the pump is removed: this subsequent loss of pressure will cause the primary pressure regulator to close. This action subsequently blocks the return flow to the tank and helps the accumulator to maintain pressure in the system.

The systems pressure is determined by the tension of the spring reacting against the plunger.....sooooo if a higher pressure is required small shims can be placed behind the spring, changing it's effective length and increasing the pressure. A shim of approximately 2 mm will increase the pressure by about 10 psi ....

In the pressure regulator is the transfer valve. This thingo is operated by the movement of the plunger and opens as the plunger moves off it's seat. The transfer valve's function is to block the return flow of fuel from the warm-up-regulator back to the tank, also helping to maintain residual or holding pressure.

once again, don't touch if you don't know what you are doing.

[86gti]

Air Flow Sensor
The airflow sensor, in most types of K-jet is located on the air filter housing and measures the amount of air entering the engine. The sensor housing is conical in shape into which the airflow sensor plate is fitted. The airflow sensor plate lifts as the throttle is opened by the incoming air.
The amount of lift is proportional to the volume of air entering the engine. The shape and angle of the cone will determine this ratio.
A neutral plate position is normally level with the bottom of the cone, this is adjustable by bending a small clip / spring that acts as a stop at the bottom of the unit. The purpose of this spring is to allow the flap to move beyond its neutral position to allow excessive pressure to escape if the engine was to backfire passing a large volume of air back into the air filter housing.
If the system did not have this, the pressure could split or blow off the rubber air pipe bizzo. Any splits or ill fitting air hoses that allow unmonitored air into the engine require fixing!!!..... been there!!.....
As the airflow lifts the sensor plate this lifts the control plunger - the higher the lift the greater the amount of fuel fed to the injectors.

To adjust the fuel mixture a small 3 mm Allen screw is located within the airflow sensor; this alters the relationship between the sensor arm and the control plunger. Turning the screw clockwise enriches the mixture and vice-versa. It should be noted that the screw should be turned in very small increments and the Allen key should be removed before the engine speed is raised.

Failure to remove the Allen key, before starting the engine, can result in damage to the airflow sensing unit.....so take it out!!!!

[86gti]

The Fuel Distribution Unit
there are many parts to this.........
This 'THING" delivers the propper amount of fuel to the engine via the injectors rin referance to the airflow sensor plate height. As the sensor plate is lifted with inducted air volume, the control plunger is lifted proportionately, exposing small slits within the fuel distributor's barrel assembly. The barrel assembly has a series (one for each cylinder) of small slits that are machined into the barrel, and it is through these openings that the fuel passes in its way to the injector.
The width of these metered slits is only 0.2 mm across and it is this dimension, together with the plunger height, that determines the fuel delivery rate to the injectors. pretty interesting eh? I'd love to meet the person who came up with this!!!!!

At low engine speed the air volume into the engine will be low, this will only raise the plunger a small amount giving the requisite quantity of fuel for these engine conditions. As the throttle is opened and fuel demand is higher, the plate raises, which in turn lifts the plunger and a higher volume of fuel is delivered to the engine to match the air. The lift on the plunger will be proportionate to the air volume, this will however be exaggerated during the warm-up period when additional fuel is required by reducing the pressure acting onto the top of the control plunger.
This pressure is called the control pressure (as it controls the lift of the plunger under different operating temperatures) and is determined by the warm-up-regulator.................something that was dissconected on my mk2 when i got it...interestingly ran fine without it..........

I have some detailed pics in a K-jet bosch manual that i will post up if i can get them scanned in....
book number- 1- 987 - 722 195 (bosch yellow book)....inexpensive book that outlines the whole system if you are interested.....

[86gti]

The Warm-up-Regulator ......
This thing controls the amount of fuel delivered to the engine during it's warm-up period. The pressure acting upon the top of the control plunger varies depending on the engine temperature and provides an effective method of enrichment.
The control pressure is tapped off from the primary pressure circuit in the metering head's lower chamber through a tiny restrictive hole which gives it the ability to differentiate between the two pressures. A flexible pipe then connects the control plunger gallery to the warm-up-regulator and returns back to the metering head to a connection next to the primary pressure regulator's transfer valve. This valve is in the circuit to close the fuel from the control circuit when the engine is off, avoiding the total loss of system pressure while the engine is stationary.

The internals of the warm-up-regulator are quite simple comprising an inlet and outlet port, a stainless steel shim, a bi-metalic heated strip and a spring.

The input to the warm-up-regulator flows into a small chamber in the top of the unit, its return is through a small drilling and back to the metering head. By controlling this return flow it will cause a change in pressure acting on the top of the control plunger. With a cold engine the flow must be fairly free giving it a lower pressure. This will allow a higher lift of the plunger which in turn will enrich the mixture under these conditions. The free flow is obtained by the internal bi-metalic strip exerting a downward pressure on the spring which decreases the pressure acting upon the shim, this lower force allows the fuel to flow almost uninterrupted.

As the bi-metalic strip is heated, by either it's heater element or natural heat soak from the engine, the downward pressure acting on the spring is gradually decreased, increasing the force of the spring, which in turn increases the control pressure.

Typical cold engine control pressure will be as low as 1.0 bar increasing over approx. 10 minutes to around 3.5 bar. Some warm-up-regulators have a vacuum connection that will sense a drop in vacuum and lower the control pressure during these acceleration periods.

The voltage supply to the regulator is from the fuel pump relay, because if the ignition was on without the engine running, all enrichment would be removed as the bi-metalic strip would be heated prematurely and the driver would not benefit from the cold engine enrichment.

The two pipes that connect to the warm-up-regulator have different sized 'banjo unions' to avoid them being connected incorrectly. The control pressures quoted are as an example only and reference should be made to the technical data as these pressures can be specific to the part number located on the unit's housing.
This unit will have a resistance value of approximately 20 to 26 Ohms.

NOTE :- it is important to disconnect the electrical connection to the unit before any pressure testing on the control circuit is performed as this will prematurely heat the bi-metalic strip and cold control pressures will not be available.

[Domel]

Good stuff mate - exactly what forums should be for.

Enjoy Tokyo

Cheers,
Dom