hello from athens, greece. coronavirus gave me time to perform an upgrade on my 8v digifant vw cabriolet 2h 1.8. I swapped the head with a 16v KR. All other things remain the same. The one and only problem I have is idling. Obviously, before asking you, I have applied all actions from all other threads. No vaccum leaks, timing is set correctly, CO is ok, idle switches click fine, as well as the WOT switch. Blue temp switch has been changed without altering the idle behaviour. I have bought a new ISV and also a new oxygen sensor. This is the current behaviour I am trying to solve: 1. When the car is cold, idling fluctuates from 1200 to 1600rpm 2. A minute after this fluctuation, it settles at 950rpm 3. When oil temperature gets to 56 degrees (on the MFA display), car raises idle to ~1900rpm steady. It stays like this from then on. Probably it has to do with the setup as shown in the pictures below. If I press on the rubber neck at the end of the ISV when it idles at 1900 rpm, it drops considerably (I press on the spot with the red rectangle). Idle screw doesnt make a difference. https://ibb.co/CnxKyjk https://ibb.co/P9mZDTy Any ideas? Cheers, George
if you havent done so already you need to cap off the small hose to the inlet or 5th injector housing, probably this is giving you a massive air leak. by the way, fitting a 16v head on an 8v block will result in very low compression so its not going to be particularly fast now unless you also strap a turbo on...
Yes the 5th injector is not used in this setup, and is already sealed. As far as compression is concerned, the car does not seem to have low compression. The 2H block of 1781cc is more or less the same as the one used in the KR setup, without the breather hose. The car seems very fast, it will do 0-60 in 8.3secs (GPS measured) and this is the cabriolet version of 93. We have changed the head, cylinders and connecting rods. We used injectors from Fiat Uno Turbo and they deliver quite well (Bosch part number 0280 150 708). Compared to other stock MK2 GTIs, it is certainly faster.
Aha you didnt mention earlier you had also changed the pistons, thats why its all ok. you originally said head only and everything else remains the same, that would have been a problem because the 8v pistons are dished and 16v pistons are flat I see you have a KR 50mm inlet, there is a nipple on the bottom of the inlet between cylinders 1 and 2, which was connected to the breather system originally on the KR. this nipple needs to be capped off if you haven't already done so. the hose on your isv is quite large bore, the 8v hoses are a fair bit narrower so it may just be down to that, perhaps use a cable clamp to gradually restrict the hose till the idle comes down and build a better pipework system for the longer term. maybe base it from the KR setup, 1 hose from the inlet boot across the front of the engine and then over to the 5th injector housing
indeed both the nipple between 1 & 2 as well as the 5th injector are sealed. I will try to restrict the airflow from the ISV to the intake and let you know of the results.
I restricted the airflow from the ISV to the intake, and the car dropped about 800rpm when warm. I thought that the ISV provides the necessary air to the intake, but obviously diameter of the hoses play major role. Two more questions in regards to this: 1. I followed the instructions of setting the timing based on the manual of the 8V. Should I follow the numbers of the 16v timing, and what are these? 2. The secret menu on the MFA, on menu 2, option 1 (the one that says about vacuum to the intake) is about 987. Is this approximately correct, or is it too high? Thanks
1. use the 8v digifant setup procedure, so disconnect blue sender and hold revs at 2.25k rpm, set timing to 6 degrees. you may find it likes a little more ignition advance, 8 degrees is a good start 2. just fired up my abf and its around 450-500mbar, but where have you hooked the MFA vacuum line to?
aha! Is this the vacuum line that goes from the TB to the dash? I disconnected that a few days ago. This is my engine bay. The 8v crankcase ventilation pressure regulating valve has been removed, oil goes to an oil catch tank. https://gifyu.com/image/lDcO
yep thats the one, will be why its reading close to atmospheric pressure so yeah run that to one of the nipples on the brake servo hose and try again
findings after extended lunch break: Even though the hose is more than 1/2 smaller than before, the car, when running hot, it will still idle high. I think the ISV compensates for the air flow restriction. When (aftermarket) air-condition is on, car works at 900rpm, even when running hot. Vacuum on the MFA after the hose has been connected: Idle (at 1800rpm - aircon off) = 326mbar Idle (at 900rpm - aircon on) = 552mbar At 3000rpm driving = 787mbar At 2500rpm driving = 621mbar At 2000rpm driving = 574mbar My wild guess is that the whole problem with high idle is not due to air leaking into the intake. I think the digifant II of the 8v car has different mapping than the 16v. It is getting different info from the inputs (knock sensor, etc) and gives orders thinking this is a low powered 8v. Was there a 16v digifant 2 version, and were all the components similar to the 8v?
You may be right, perhaps the afm needs adjusting a bit? https://itinerant-air-cooled.com/viewtopic.php?f=50&t=7761 in the US when guys do the digifant swap they use the DF1 type ecu instead as its a bit more tunable, the VW Vortex forums have loads of information on this. but you'll probably get a much better result if you bin the lot and go to megasquirt, emerald, dta or similar. much finer control over the engine
Hi! I stumbled upon your posts here, I know it's been quite a while but I've done some similar work on my car during 2020 and I experienced more or less the same issues (and still am mostly) Briefly my setup is as follows GU bottom KR internals and cylinder head ABF intake mani ABF fuel rail/ injectors 76mm TB Digi II Crankshaft breathing is free I did find quite early that restricting the air flow to the isv significantly keeps idle at a proper range. I am talking taking the 18mm hose down to 8mm. A bit of fiddling with the air flow sensor (clockwise, a lot) got the car to a good point actually. Cold starting has been an issue and my workaround has been an electric valve which I installed and with the flip of a switch I let more air into the intake manually. Since that I had no problem cold starting. Now the two main issues of Digi II when it comes to 16v is a high idle and a lean mixture. No matter what I do once the car gets warm.it leans out. I believe that is because firing times are calibrated for 8v, not 16. I don't know or have tested higher fuel pressure and don't know if that would work. I am pretty sure I'm going for a standalone ECU eventually cause I can't seem to find a way to trick it to work better so far. Anyways, nice to know someone else has done this as well, even better if you actually get to see this post after 4 years ☺️
