Scirocco Mk2 K Jet Tinkering

Share what you've done to your v-dub and how you did it.
Post Reply
Posts: 4
Joined: Tue Sep 06, 2011 12:00 am
Location: Elderslie
Drives: T25. T4, Mk2 Scirocco Scala

Scirocco Mk2 K Jet Tinkering

Post by AndyB » Sun Jun 30, 2019 11:57 am

Ok decided was time to run through the K-Jetronic system on my Scirocco to at least get a better understanding and to iron out any niggles the car has. Throughout my journey I found that even the nomenclature of some of the parts on forums, in manuals, at retailers etc is confused, with quite different parts being interchangeably named – so the following is basically the order of the route I took –

The idle stabilisation operates by simply opening and closing a valve that allows air to bypass the throttle butterfly by means of some extra vacuum pipe, regulated by the rpm of the vehicle.
It comprises of a relay in the fuse box (no 57 VW 811905343 Audi 371281425) and a Boost Control Solenoid Valve (026906283B)
The relay has a rev counter/ignition coil feed, an ignition live feed and an earth and an output to the Boost Control Solenoid Valve (basically an on/off gate valve). The pins on the relay are
1 - rev counter/ignition coil feed
15 - ignition live feed
31 - earth
87 - output to Boost Control Solenoid Valve (or idle speed acceleration valve)
relay 57
Inside the relay is an electric circuit board with transistors, capacitor and a mono-stable multi-vibrator, so not your standard open/close mechanical contact switch so I had no idea how to test it ? and I knew I wasn’t measuring a 12v output from it. So I decided to track down a replacement second hand relay in the hope of different results.

The solenoid valve or as VW call it the Idling Speed Boost (N62) (part number 026906283B) is positioned on the offside strut pillar.
Idle boost valve
The valve has the ignition live feed (brown/black wire) from the relay and the other wire (black) which seems to be an earth that runs back to the relay. I took the valve off the car and a crude test was just to blow through the two vacuum ports – my example was closed with no voltage – I applied 12v across the terminals and annoyingly my example was closed with voltage also – so I reasoned a dud solenoid – now to hunt down a replacement – eye wateringly expensive and hard to find a new one and with even used ones blindingly expensive I decided to experiment – I ordered a used solenoid part number 026906283H – a newer part and easily found, same number apart from letter – I knew this newer version had three ports however I reasoned it is not hard to seal off the top port with a little Sikaflex. I had no idea if the original part was a normally closed or normally open solenoid, it was all a guessing game at this stage. The newer arrived and lo and behold the different letter in its part number does mean a whole lot! the solenoid was no use – the polarity of the solenoid was the opposite and the air ports diameter was about a third of the old one.
Part numbers argh !!
So I folded and hunted down the correct part which arrived all shiny courtesy of VWgolf1 in Eire and testing it with 12v I now know the solenoid is normally closed and there is a satisfying click when it energises and opens.

COLD START VALVE (aka the fifth injector)
This again is a simple system where on starting the engine the fifth injector sprays an extra boost of fuel.
cold start valve
The system operates from a temperature switch (probe) screwed into the front engine water manifold – the probe basically acts as an earth which is closed (connected) at low temperature. So I went through the standard procedure to test the electrics as set out in the Haynes and Bentley manuals applying 12v down the line from the fifth injector – No Joy! No spray from injector, testing earth all good and continuity all good, no power – the feed for the power to this system comes from the starter motor as it is only ever used on initial turning of the engine. So down I look at the shiny replacement started motor that some previous owner had installed – yep ignition and battery connected but no terminal spade 15, and yes there hanging in the air disconnected the power lead for the cold start valve.
The power from terminal 15 on the starter should also power the Cold Acceleration Enrichment System which comprises of a series of switches – the throttle switch ( a little electrical reed switch just under the throttle body);
Throttle Switch
a pressure diaphragm switch ( kind of like a little round cone with two wires in the back which is connect by vacuum hose to the throttle vacuum system;
Diaphragm switch
it then uses the thermo time switch as an earth and triggers a squirt of fuel through the fifth injector on hard acceleration.
So.......I considered replacing the starter, then I thought who really needs all this cold start gubbins anyway? Leave it un-plugged = delete and no worries about thermoswitch/fifth injector/diaphragm switch/throttle reed switch. Maybe not every ones solution. Considering though that the Cold Acceleration Enrichment System was a late tweak by VW and probably pre-mid 1980s none of the early Gti engines had it, also it is actually quite common to delete the fifth injector; I wasn’t worried.

So with a car I probably can’t start in the North Pole I moved onto

This is basically a throttle air by-pass – kind of like an automatic accelerator. Inside the body of the valve there is a gate that is open at low temperature, as it heats up from engine temperature combined with a little electric heating element it slowly shuts reducing the air flow. I stripped mines off – and just crudely blew through it to check it was open, I then added 12v across the heater terminal and although the gate shut it still was passing air.
It is a standard Bosch part and they calibrate the rate the gate opens with temperature and the volume of air flow to specific vehicles, the part that was in my Scirocco was Bosch 0280140158 / VW 026133453 which should have 7.5m3/h air and guess what? a completely discontinued part – no surprise.
Being a Bosch part there are literally dozens of variations of this part made for Volvo, Porche, Mercedes, VW, Audi, Ford.
I tried cleaning my part with carb cleaner with no joy – gate valve shut but air still passing. So I found the cheapest replacement I could and found one from a Volvo – part number Bosch 0280140106 – anything without a VW/AUDI/Porche badge seems to be cheaper! I figured even if it had higher air flow would mean higher revs at start up but at least it would close. I was always suspicious of the valve in my car as it made a hissing sound and I realise that was the air passing through it when closed and was in effect adding a little throttle I didn’t want. I have read of people just deleting the valve and manually throttling the car with the pedal during warm up which would guarantee no extra air. Anyways the Volvo part arrived – and yes it has a opening about double the size of the rocco one so I was thinking mega high tick over to start.
Air valve air gaps
Although there is a tiny nut on the back of the part which I loosened and it allows you to vary the plate inside by 2-3mm – so I closed the air gap as best I could on the Volvo part. The thing that annoyed me though was this one was also passing air also after applying 12v and the gate closing – are these things supposed to pass a little air when closed? I seem to read mixed messages on forums – I convinced myself there was no way such a basic slide valve could perfectly seal and out of the two parts I had the Volvo part was in best shape as the little sliding gate in my original part had not only a slide movement but also a slight lateral movement. So fitted it on car.

Was time to move on from the air side and onto the fuelling ( take note I had already stripped down all the throttle body and vac lines a few months ago and cleaned them - if I hadn’t then I would be doing that now)

The injectors were all pretty much welded in place, a homemade extractor and a small crowbar and they were all out.
I lined them all up in my special bottles
Injector measuring
and jumped the fuel relay with a handy old relay I modded with a switch.
Modded fuel relay
To no great surprise, one injector good, one not functioning all, one with a deluge of spray and leaking and last one partially blocked I don’t even understand how this engine managed to run at all with the state of play with these injectors !! I then removed all the injectors and put the fuel lines in my bottles, the great joys all lines were producing the same quantity of fuel telling me that at least the distributor was balanced correctly. I did find that my injector hose to cylinder 4 was fubered at the connection – I opted for a single second hand hose replacement, the car probably needs a new replacement full set in the near future but at £150 I put that expense off to another day. So three new injectors later and a replacement hose a further check and all much better.

Now to get into the nitty gritty and do the absolutely necessary of all K-Jet checks the fuel pressures. I set up pressure gauge in line with the Warm up Regulator fuel feed with the valve on the set up on downstream side.
Pressure Test
Pressure Test set up
1) System Pressure
Basically the maximum pressure from the fuel distributor and pump – with the pressure test line valve closed isolating out the warm up regulator – mines was reading about 70psi – all good.

2) Warm up pressures (control pressures)
Opening the valve and letting the fuel now pass through the Warm up regulator I should get a low pressure which slowly rises as the unit warms up, this pressure actuates a pinion inside the fuel distributor which effectively richens the mixture initially for cold start up. The pressure should stabilize after about 3 minutes to around 50 – 57psi which is the Control Pressure. My system immediately jumped up to 64psi – which has the effect of moving the pinion in the fuel distributor so as I would be getting a lean fuel mix all the time ! - I knew straight away my Warm Up Regulator must be blocked. I removed it and sure enough I could see the gauze filter on the fuel inlet was coated in major gunk. There are four routes to take from here – replace with new £400+, send for recondition £200+, strip and try to clean yourself (£?) or find a used part – I was lucky enough to get one out of a working Scirocco being broken – however it turned out looking at the part number when I received it that it was an earlier Mk1 Golf part and not the later DX engine part
– this according to what literature I could find would mean the Control Pressure would be on the low side for my car – not to be phased – on it went. And testing the pressures saw nice steady increase on warm up over 3 minutes to a control pressure of 53psi.

3) Bleed down pressure
When the car is warm and the engine is shut down the control pressure should bleed down to about 36psi and hold for about half an hour, this gives the fuel lines time to cool and prevents vapour locks in the injector lines. The culprits for a bleed down to zero are the non return valve on the fuel pump, the fuel accumulator, or the system pressure control pin leaking on the fuel distributor. My system held good for half an hour and seemed to be in good shape- however I wasn’t expecting that !!! – as on occasion I have a hot start issue and was thinking this would be the place to find the issue.

Time to tweak the fuel/air – engine oil temperature up above 85C, throttle screw set so my revs about 950rpm – rig up the ancient Hawk tester for exhaust emissions
Hawk Tester
– this is more of an art form than an exact science. I was definitely on the lean side on the Hawk measurement and also popping noises from the exhaust I felt justified now getting the allen key out and onto the fuel distributor turned the screw clockwise to richen up the system. The good old Hawk gauge responded nicely and I set it more by ear than what the gauge said, I maybe went a little rich but hey ho the popping noises subsided.

By no means finished with this system but after the above the car feels smoother, more power and better to drive. I know I will continue to tinker with it.

Post Reply