been playing with the isv , interesting results

[wippy 0]

a couple of days ago i fitted a chip and 70mm pulley and the car started behaving very oddly, sometimes when accelerating the car would pull well through the gears and other times it would pick up fine then loose power.

I checked the boost on the mfa and was getting readings of 1500 from 2000rpm all the way to 6000rpm, my first thought was perhaps it had a boost leak so today i removed all the pipes, intercooler and supercharger outlet box, i cleaned everything up and washed out the intercooler and then put it all back together and made sure everything was tight, i also cleaned up the throttle body and adjusted the boost return valve. I then took it down the road and had exactly the same results 1500 from 2000rpm upwards :roll: .

Just out of curiosity i disconnected the isv plug and took it up the road , instantly boost pressure now read 1700 much better, this got me thinking so i removed the valve and blew into it, im assuming that when it is unplugged the valve would be closed but i could still blow through mine a bit, i plugged it back in and switched on the ignition and blew into it again this time it was easier to blow through so the unit is working as it should, at this point i thought i would just take it off totally and block the hole in the manifold and take it for another drive, this time boost had increased again from 1700 to 1900 just as i would expect for a 70mm pulley.

 

i am sorry for my ignorance now, i am a mechanic but i am new to the g60 set up so any info would be great, am i right in thinking that the isv is also used as an overboost valve if the ecu senses too much boost? if so where does the ecu get its signal for this and what is the trigger pressure? im assuming the sensor in the throttle body pipe is a map sensor so would this be it? is this sensor a known weak point and is it adjustable as you can get in there with a screwdriver and turn it.

 

i am sorry for all the questions but any info would be much appreciated

[Richardshoes 0]

Hi.

You are correct about the isv working as an overboost control. The factory setting is 0.8bar. 11.6psi. I think the ECU signal comes from the vacuum hose from the throttle body and opens the isv fully at anything above 0.8bar.

[Yandards 0]

The ISV only works as an over boost valve in the following circumstances:

 

When knock is detected, via the knock sensor, and depending on the frequency of the knocks it will reduce boost pressure to a max of 0.4 bar to protect the exhaust side of the system.

 

It also acts as a soft limiter on approaching the ECU rev cut-out, from 5600 rpm to 6200 rpm boost pressure is reduced by around 0.1-0.15 bar.

 

It does not use the boost pressure signal sensor as a 'max boost' cut out switch.

 

Please note that on going to full throttle, the full throttle (WoT) microswitch on the throttle body signals the ECU, as part of the ECU process it temporarily shuts the ISV to aid boost pressure increase.

[wippy 0]

thank you very much for your replies, so how do people get round the ecu opening the isv when running a smaller pulley? is this controlled by the main chip in the ecu?

i was having a problem with the car having flat spots around 4000rpm it was not dying but there was a noticable drop in power especially when at wot when the full throttle switch was tripped, the car does not seem affected so badly when its running cool but after 10 miles or so it starts loosing power again, i have checked the timing and replaced the ecu pressure hose and the fuel filter(also checked the fuel pump) and also dissmantled and cleaned the isv ,it did make a big difference but with the isv plugged back in the car still wont make more than 1550 on the mfa boost check and still looses power over 4000rpm, i bought the chip off ebay so there is a possiability that it could be wrong,

i have taken the knock sensor off the engine(but still plugged in) just to check if it was that causing problems but its still there,

the other thing im wondering about is the key way on the crank, sometimes when at low rpms if i put my foot flat down it will be fine but other times i do it i can hear slight pinking, is this a sign of movement?

 

sorry i have so many questions but im just trying to get my head around the problems with the g60

 

thanks in advance for any help :salute:

[JMC 0]

thank you very much for your replies, so how do people get round the ecu opening the isv when running a smaller pulley? is this controlled by the main chip in the ecu?

 

It should only open and bleed off boost if the ECU detects knock, assuming i) the ECU is fine, ii) the ISV is fine, iii) the knock sensor is fine and iV) all the wiring is fine. All big assumptions on G60's.

 

The ISV's can be adjusted as well. There is a small allen key grub screw in the top when you take the hose off (it may well be covered by a yellow threadlock). You can adjust this so that when you blow through it the air flow is minimised - should only need a half twist or so if it's not been done before.

 

However your first port of call should be the chip - any markings on it at all?

[Richardshoes 0]

May be worth getting a Bentley manual. You can test each component following the procedures in there.

[Yandards 0]

If you unplug the knock sensor the engine will go into a 'safe' running mode and will be down on power by using the above mentioned boost pressure limiting method.

 

It does sound like your ebay chip is not up to the task, although if you keep the RPM below 5800 then the ISV will not start to bleed boost back through the return.

 

A 'good' chip will raise the boost return rev limit so that it sits closer to the rev cutout limit of 6200 RPM.

 

The ECU controls the following outputs, fuel injector duration, ISV position and that's it. It uses inputs from the throttle microswitches (idle and WoT), knock sensor, coolant temp sensor (blue one), CO/temp potentiometer, MAP pressure sensor, lambda probe and the hall sender on the distributor.

[jaded2882 0]

The ISV only works as an over boost valve in the following circumstances:

 

When knock is detected, via the knock sensor, and depending on the frequency of the knocks it will reduce boost pressure to a max of 0.4 bar to protect the exhaust side of the system.

 

It also acts as a soft limiter on approaching the ECU rev cut-out, from 5600 rpm to 6200 rpm boost pressure is reduced by around 0.1-0.15 bar.

 

It does not use the boost pressure signal sensor as a 'max boost' cut out switch.

 

Please note that on going to full throttle, the full throttle (WoT) microswitch on the throttle body signals the ECU, as part of the ECU process it temporarily shuts the ISV to aid boost pressure increase.

 

Would this be a good time to ask anyone about their views on the BBM ISV re-route method? :norty:

 

I know this was raised a long time ago and no one ever really came to a conclusion on whether they were safe or effective on modded G60s.

[Richardshoes 0]

I think the below link should answer your queries

http://www.vaglinks.com/Docs/VW/Corrado/VW_Corrado_G60_1.8L_Engine_SelfStudyGuide.pdf

[Yandards 0]

I think the below link should answer your queries

http://www.vaglinks.com/Docs/VW/Corrado/VW_Corrado_G60_1.8L_Engine_SelfStudyGuide.pdf

 

It does but there a few more gems of info that are not in there but in the Corrado dealership video, thinks like reving the engine above a certain limit to put it into the correct mode to enable timing and mixture to be set-up.

 

It is a good place to start and covers the vast majority of need to know stuff though.

[Richardshoes 0]

Where can I get a hold of these VW videos? Cheers.

[wippy 0]

thanks for all your help and info fellas , i will swap the chip back and give that a go

[Yandards 0]

Where can I get a hold of these VW videos? Cheers.

 

Er, you cant really. Its taken me 4 years of trawelling ebay internationally on a daily basis to find it.

[Richardshoes 0]

I take it you have a copy? This may seem a little forward but - can I have a copy?

[jaded2882 0]

I take it you have a copy? This may seem a little forward but - can I have a copy?

 

You could at least take him out for dinner first... :lol:

[wippy 0]

just to clarify lads, my isv is opening at .5 bar, is too much knock/faulty knock sensor the only thing that would cause this?

[Yandards 0]

just to clarify lads, my isv is opening at .5 bar, is too much knock/faulty knock sensor the only thing that would cause this?

 

Yes.

[wippy 0]

right i have just unplugged it totally and it drives exactly the same so im guessing mine has bit the dust

[Yandards 0]

right i have just unplugged it totally and it drives exactly the same so im guessing mine has bit the dust

 

Yeah sounds like it, although when an ISV is 'off' it will sit in a slightly open position, have you disconnected the air hoses and blanked the various holes off?

 

It's also more noticeable at idle if its working, you can try this test too:

 

Find a nice straight piece of road and get up to 60mph in 5th, come completely off the throttle and keep an eye on the rev counter, at around 1900 RPM the ECU will start to fuel the engine and you should feel a slight jerk as the engine comes off overrun. The jerk is due to the fuelling going from fully lean to normal and will require the ISV to operate to control the fuel-air mix as the throttle is still closed. If the car is very jerky and will not settle quickly then ISV is playing up.