HOW TO: Check, repair and tune your MK2/Corrado 1.8 16v

Discussion in '16-valve' started by rubjonny, Jul 16, 2009.

  1. rubjonny

    rubjonny Administrator Admin

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    Before you start fiddling with anything, the first thing to do is check the overall health of the engine. To start with the ignition system all needs to be tip top, so if its not been done for a while get new plugs, leads, cap and arm. only buy top quality bosch or beru parts from the likes of http://www.gsfcarparts.com/ or http://www.vwspares.co.uk

    Next check the ISV ios buzzing with the ignition on, if not look at the wiring to it and check the ISV control unit behind the centre console. The black wire to the controller should be live ignition on, and the brown/white should be earthed. The earth wire runs to the side of the head. If the ISV is buzzing fine have a look inside, if it looks dirty then you can clean it out by soaking it in petrol or similar. It helps if you can do this with the ignition on and valve buzzing, swish about till black stuff stops coming out of it.

    Look at all your vacuum lines and inlet boots for air leaks, take all the inlet boots and rubber pipes off and check in the folds and under the clamps for splits which can be tricky to spot on the car. Do the same for all the vacuum hoses on the car, try to buy genuine if you want the OE over-braid look as I found cheaper pattern pipes dont last at all. The breather hose get soft with age and split, this can introduce an air leak into the air shrouded injector system. This system is fed by the little pipe from the breather to the inlet/5th injector housing, as a quick check you can cap off the nipple on the inlet/5th inj housing and see if that makes any difference. Then replace the breather when you can, its ok to leave the system capped off while you search as it doesn't make a massive difference. Finally remove the idle screw and check the o'ring and replace if worn. You might struggle to get one on its own I had to buy a big box of random o'rings and picked the closest one. Try to screw it in the same amount roughly as it came out for now, then adjust idle later on when everything has been checked over.

    Give all the wiring in general a good check over at the same time, check plug pins are straight and clean, make sure they are fully seated in the plug housing, peel boots back if fitted to make sure the wire crimps are good round the back, look at spade crimps under boots and in housings are tight, remove any insulation tape you find over wires to check condition of the splices underneath etc. In particular look at the earths to the head and battery as some of them are for the ECU, Ignition amp and ISV controller. Look at the wiring to the 3 sensors on the side of the head, the red/green one is for isv control unit and the blue/white is for the ecu and yellow/red is for the dash temp gauge. Make sure they're clean and spades in good condition, as all 3 are the same rating, one test you can do is swap the dash sender wire over to the others and compare the dash temp reading. If one sensor shows vastly different temp then that one is probably bad. If you need to replace a sensor part number is 049919501 or 027919501. Try to get genuine if you can, the pattern ones often read incorrectly. They're the same as MK1 GTI, early MK2 golf, MK1 Cabrio and Scirocco, plus all MK2/3/Corrado/Passat 16v have at least 1 or 3 depending on what injection system is used. If you have a multimeter you can check the resistance:
    20°c - 1000 ohm
    60°c - 250 ohm
    100°c - 75 ohm
    110°c - 80 ohm
    'too hot' light flashing - 50 ohm

    If the car likes to cut out or you feel it 'hold back' randomly when driving, check the over-run cut-off valve. This is the black plastic thing located behind the airbox, with 2 chunky pipes, a vac hose and a 2 pin plug. The pipes to it are not clamped so sometimes it falls off the inlet, you may want to add some hose clips to prevent this. If thats all good next disconnect the 2 pin plug and see if this stops the problem, if so try another one. Its OK tyo leave it unplugged while you try to find another, just watch the revs if ou lift off from high rpm as its job is to catch and drop the revs slowly back to idle. When off the car jump the valve with 12v and you should feel/hear it click, if the wires start getting hot it has died!

    While you're looking behind the airbox make sure the plugs to the overrun cutoff and cold throttle enrichment valves are the right way round, the larger black & grey plastic overrun valve should have a black/yellow and black/brown wire, the smaller metal cold throttle valve should have a white and black wire.

    The 5th injector should spray fuel when cranking on a cold engine, to test it simply unbolt it from the inlet and point it into a container then crank it over when engine is stone cold. The WUR on the side of the head should be live while the fuel pump is running, red/white is the power and brown is earth. The big brown 2 pin 5th injector thermoswitch at the side of the head at the back should get cranking live to the red/black and the green/white wire needs to have continuity to the 5th injector green/white. The black wire from the 5th injector goes to the 2nd starter motor spade 15a, as does the black wire from the cold throttle enrichment valve behind the airbox. Check the wiring is correct to the 5th injector thermoswitch brown plug as per this picture:
    csvplugs.jpg

    Next check the idle switch, open and close the throttle smooth and gently and you should hear the idle switch click every time it hits the stop. If not check the upper part of the linkage is free as its free floating and can stick. To fix this remove the 13mm nut, arm, spring and 2 plastic washers. Clean it all up then reassemble with some GP grease, taking extra care when assembling as its easy to catch the spring in the washers. Once fixed it should move free and close easily under its own spring power. If the switch still doesnt click undo the 2 screws and adjust its position, you can also bend the upper linkage arm slightly if required. The switch should see ignition live on the black wire, when closed the switch sends 12v to the black/yellow wire to ecu and isv control unit. When the throttle is open the switch sends voltage to the the cold throttle enrichment valve, under hard accelleration the vacuum connection causes the valve to close which then sends 12v to the 5th injector. The system only works on a cold engine as the 5th injector earth path via the thermoswitch on the side of the head is broken when the engine is warm.

    The fuel injectors and/or seals might want replacing if they're original, spray a bit of carb cleaner or similar around the seats while the engine is running. If the note changes then you probably have a leak, new seals are available from GSF and VW Heritage. But before you buy new seals its a good idea to perform a fuel injector spray test, remove all 4 injectors and sit them in 4 equally sized containers. When you come to do the job spray penetrating oil around the seats and give them a little wiggle to encourage it to seep around the seal. Give a firm tug directly backwards to remove them, try not to pull at an angle as you may break the delicate plastic lower seats. Disconnect the black wires from the coil to prevent any chance of a spark. Now go to the fusebox and swap the fuel pump relay with a 17, 18 or 100 x-over live relay (fuel pump is slot 2 CE1, slot 12 CE2) This will power the fuel pumps up with the ignition which helps when diagnosing the fuel system. Pop the rubber boot off the top of the metering head and switch on the ignition, the injectors shouldn't spray any fuel. If they do the metering head is incorrectly adjusted (see further down), faulty, or the injector(s) are faulty.

    Next lift up the metering head flap slowly by hand all the way to the limit of its movement checking the spray pattern on all 4 is a nice cone shape, then lower it slowly to its resting position. Now switch off the ignition and wipe the injector tips, they shouldn't drip for at least 5 minutes. Measure the volume injected is the same for all 4. If any injector shows an issue swap it with one of the others then repeat the test, if the problem moves its a faulty injector, if not its the metering head or fuel line.
    You can fine tune the fuel volumes delivered by undoing the 4 screws next to the fuel line banjo bolts on the metering head, underneath are small adjustment screws. I cant recal which way does what but you'll soon figure it out ;)

    If you need new injectors you can buy brass mercedes injectors from ebay, usually these are a little cheaper than the original steel type. These dont give you any performance benefit though, they're just slightly cheaper. The other thing is they dont have the top hats on the tips you need for the air-shrouding system. You can disable the system by capping the vacvuum nipple on the inlet/5th inj housing as I mentioned earlier, I've run mine with and without the system hooked up and couldnt really tell the difference. With care people have swapped the top hats over, replace the seals for these as well as the main injector seals obviously, dirt cheap. You might want to take the opportunity to replace the insert seals, the brass inserts screw out with a 13mm allen bit (I used a drift with a spanner slipped over it!) Main injector seal is part number 034133557E, top hat seal is 035133557A, insert seals 035133557 and plastic lower seats are 035133554.

    If you're having hot start issues you may be loosing residual pressure after the engine is switched off, 2 main culprits for this a holed diaphragm in the fuel accumulator or the non-return valve in the fuel pump is faulty. The fuel accumulator is very expensive new, but luckily the test for this is easy enough. If you look in the end of the unit there is a small slot head screw, if you can get this undone and you find fuel is leaking out the back you know the diaphragm inside is split and the accumulator needs to be replaced. If not its probably fine so try replacing the non-return valve, the part number is 893906093 and it's relatively cheap. Currently VW Classic are making them again, they can be ordered via the classic parts finder on the VW Heritage website or direct from classic if you prefer.

    Next we need to move onto the metering head, give it a damn good clean especially around the narrowest point of the air flap. The metal disc should pass through it smoothly without sticking when you push down on it gently. Next you need to check the height of the flap to it is flush with the narrowest point of the cone towards the front nearest the fuel metering head. If it needs adjustment you can bend the stop underneath:
    [​IMG]

    Also the flap needs to be central in the hole, you can remove from the car and hold it up to the light or if you have a bright work light you can stick it underneath while you make your adjustments. If you want to remove it for any reason, crack off the injector fuel line bolts and rotate them out of the way of the 3 bolts that hold the fuel metering head to the air flap assembly. Usual precautions here, the system may still be pressurised so hold a rag over the top and put your tab out ;)

    Once off you can remove the airflap assembly without disturbing the other fuel lines. be sure to take care not to knock the metering pin in the base. This is a good time to check the pin in the metering head moves in and out smoothly, there may be some resistance depending on if the fuel pressure is high or not. Another thing to be careful of is depending on the metering head fitted the pin can drop out the bottom if there is still fuel pressure in the system, original vw units have a retaining circlip to prevent this from occurring. You can remove the pin to check for scoring and clean off any deposits, only use fresh petrol for this and take extra precautions to ensure the pin & hole is kept totally spotless ass the tollerances are very fine.

    Non-VW metering head (Porsche) no retainer
    [​IMG]

    VW metering head, with retainer:
    [​IMG]

    Once all this is checked out, if you have access to a set of fuel pressure gauges you can move on to check system pressure, and fine tune the WUR control pressure if you wish:
    https://clubgti.com/forums/index.php?threads/81658/

    Next look at the static timing of the engine. look at the timing belt and tensioner while you're here, if its looking ropey replace it! Timing on these is simples, only the cam and crank to worry about and the marks are clear and easy to find. If at all possible use the flywheel mark to line up the bottom end as its more accurate and the damper ion the crank pulley can allow the mark to drift out. You'll need to get the gearbox bung out anyway so you can do the ignition timing.

    Cam:
    [​IMG]

    Crank: (this is mk3 crank pulley, but mk2 is similar)
    [​IMG]

    Dizzy, make sure the rotor arm is close to the notch, it doesnt have to be perfect we will tune it in a bit:
    [​IMG]

    Flywheel, use the small punch mark to the right:
    [​IMG]

    If you have loosened or replaced the tensioner you want to be able to twist the timing belt about 45 degrees on the longest run with your fingers, unless you have the later 16v auto-tensioner with that you tighten it till the indicator arrow bottoms out, then loosen off till the arrow lines up to the mark then nip the nut up. Once you're happy with the timing marks and belt tension, turn engine over 360 degrees by hand and recheck the marks and tension are still correct. if not, adjust as required. if you take the spark plugs out it makes it much easier to crank the engine over.

    Now check/set the ignition timing, I recommend an inductive pickup timing light as its much easier to fit to the spark lead. you dont need one with an rpm gauge or advance dial though they can be handy. Remove the green bung from the top of the gearbox housing if you haven't already done so, then start the engine and let it warp up to at least 80 degrees. Connect your timing light to spark lead #1, then point it down the hole.

    The large diamond should line up with the arrow on the gearbox housing as in the flywheel pic above, if not loosen the dizzy bolts and twist it slightly till it does. You can usually dial in some extra ignition advance if all is well, the best figure depends on engien health and mods but this is outside of the scope of this guide. I start at 8 degrees and work from there (read: leave it there, and get someone else to fiddle with it further because aint nobody got time fo dat) lol

    Finally we can move onto the idle and CO settings. To put the ISV control unit into setup mode look at the coil -ve terminal, you'll note there is a spade connector on one of the 2 black/red wires. Disconnect this then start the engine, you might find it struggles to idle if so wind out the idle screw a bit till it will run on its own.

    Let the engine warm up then set the idle to around 850-950 rpm, you can use the MFA secret mode trick to get a digital rev gauge as per my digifant guide:
    https://clubgti.com/forums/index.php?threads/124949

    Once you're happy you can try to adjust the CO, I recommend you use pro equipment for this I find the DIY setups a bit hit and miss. You're aiming for a value of around 1.8-2.0% to start with (As with ignition timing the best setting depends on state of tune and engine mods, a proper tuner with a rolling road or well callibrated arse dyno will get you the very best results!)

    To set the co you need a long 3mm alen key, turn it anti-clockwise to lean out the mixture, and clockwise to richen. When you adjust turn it in 1/8th turn increments then remove the allen key and allow it to settle, then carry on with the adjustment. the CO screw is very sensitive! also try not to press down too hard as that will move the air flap and throw out the display on the CO meter for a bit till it stabilises again. Oh and dont rev the engine with the allen key in place, it can jam the air flap. Unlikely to cause any damage but its just not clever lol

    When co is about right the engine should settle to a nice steady idle. if you dont have a CO meter you can attempt to set it by ear, wind the co screw anti-clockwise untill the idle becomes rough or the car wants to stall. then gradually wind the co screw back clockwise 1/8 turn at a time till the idle smooths out. Look at the bonnet steady arm thats a good indication of the smoothness of the idle. Once happy, switch the engine off and plug the red/black wire spade back in.

    Now take it out for a run and when you dip the clutch at high revs, the tacho needle should fall to around 2-3k rpm then smoothly drop to idle, not plummet. If it does then you know the over-run cut-off valve is functioning correctly. If not you may have an air leak, a wiring fault or the idle switch is not adjusted correctly. The over-run valve is the larger black plastic one on the back of the airbox, it should have ign live to the yellow/black wire and the brown/black is a switched earth from the isv control unit. If you jump the valve pins with 12v from the battery it should click audiably, if it doesn't or the wires get hot then the valve is toast!

    Thanks to GVK for modelling his manky fingers in the pics below, and to Kevin Hayward for the original and famous tuning guide which I'm sure everyone who owns a 16v has used before :)
    [​IMG]
    [​IMG]
    [​IMG]
     
    Last edited: Apr 16, 2020
    gvatte likes this.
  2. GTI

    GTI Forum Member

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    "pull off the breather hose and block the airbox hole"

    could somebody clarify exactly what is meant here please? does this mean the breather hose that runs from the front of the block to the back of the airbox? just want to be sure.

    also, if i'm not mistaken, one of the temp senders under the dizzy runs to the ecu (blue/white wire), one to the isv circuit (colour unknown) and the other to the temp guage in the dash (ditto!). again, clarification would be great :).
     
  3. rubjonny

    rubjonny Administrator Admin

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    pull the hose off the side of the airbox and point it somewhere where the gasses from it wont get sucked into the airbox

    3 single pin black sensors on the side of the head which are all the same rating, blue/white for ecu, green/.red for isv controller and red/yel for the dash gauge
     
  4. Tristan Forum Junkie

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    is this the same for 9a powered corrados?
     
  5. rubjonny

    rubjonny Administrator Admin

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  6. Tristan Forum Junkie

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    Thanks RJ!
     
  7. rickygolf83 Forum Member

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    sorry to resurrect this, but if i only need to adjust my mixture (stinks of fuel but passes mot) do i still need to disconnect the red wire at the coil and block off the breather?

    can idles okay, as in around 950 (+- 50) but it feels lumpy and shakes/rocks a bit once warm and gets you high! :lol:
     
  8. rubjonny

    rubjonny Administrator Admin

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    you need to have the lead off, because as you fiddle with the co the idle setting will need to be changed too :thumbup:
     
  9. rickygolf83 Forum Member

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    cheers johnny, might take the car a spin and give it a bash tonight after dinner. its dry up here in glasgow for a change!!! :lol:

    you might have just saved me half an hours labour at the garage!!!

    thanks ! :thumbup:
     
  10. wesley Forum Member

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    Hello, I put a kr into my mk1 and also isv etc so i dont have the red wire at the coil,
    Is there another way off putting the car into adjusting mode?
    Thanks
     
  11. rubjonny

    rubjonny Administrator Admin

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    its got to be there somewhere, the isv control unit needs the red/black to be fitted tyo the coil wire somewhere as this is how it can see the revs.

    start at the control box and follow the red/black to where it goes to, then cut and fit a spade so you can put it in setup mode
     
  12. wesley Forum Member

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    Perfect thanks rj, have it here alright
     
  13. wesley Forum Member

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    Had no luck with this, this evening,
    Every time i disconnected the wire the car would cut out,
    Tried increasing the revs but made no differance?
     
  14. rubjonny

    rubjonny Administrator Admin

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    you arnt disconnecting the main red/black to the fusebox are you? if so, are you using a mk1/2 8v k-jet relay? if so that'll be why, the red/black is the rev counter feed to the fusebox, and the k-jet relay needs this to trigger the pumps.

    if it cuts out just when disconnecting the red/black then the basic settings are out of whack, you are getting the engine up to temperature before disconnecting the wire right?
     
  15. wesley Forum Member

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    Yea im letting it heat up before hand, only disconnecting
    the wire going to the isv relay, even done this at the relay end
    of the loom to be sure, it will stay running if i keep the revs
    Up with my hand on the throttle body.
     
  16. rubjonny

    rubjonny Administrator Admin

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    ok sounds liek you need to tweak the idle and co screws till it will idle, then you can do the full co procedure
     
  17. Paul 16v Forum Member

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    How long does the 3 mm Allen need to be?
     
  18. rubjonny

    rubjonny Administrator Admin

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    longer than a standard allen key, put it that way! you want one of those longer T handle type
     
  19. M7R

    M7R CGTI Regional Host

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    quick random question - I set mine up the other night, but forgot to disconnect the "red lead"... (the garage at the last MOT leaned it right out to 0.3% co!) I have a basic gunston CO machine, so re set it back to 2% with the oil breather removed and air box blocked off. it would stutter a bit when free reved untill it hits about 2500 rpm, and then it would rev up nicely.

    I then reset the emissions again last night with the read lead unplugged, and set the timing (after cleaning the dizzy cap and rotor arm with some wet and dry)

    when I had finsihed setting the emissions it seemed to rev from idle if I blipped the throttle.. however I left it to cool for a bit and then when I came to drive it back into the garage it was stuttering again up to 2500...now the engine was not fully at temp, but the needle was off the stop so it wasnt stone cold.. is this just a querk of the Kjet? or I have i set something up wrong? (its been a few years since I had Kjet and then it was a 8v mk1)

    Karl
     
  20. rubjonny

    rubjonny Administrator Admin

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    the 16v has a cold throttle enrichment system but it probably would have been disabled by then anyway. it certainly shouldnt stutter like that i would start hunting for air leaks and do an injector test
     

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