knock sensor?

[rubjonny]

I am also thinking AFM problems, the only other thing I can think of is possibly the hall sender is on its way out?

[Rain]

if you have a haynes or simular manual there is a bit on how to afm in there but you need a multimeter if its totally had it take air filter lid off and watch the flap when the car is rev'd if it is stuck open of closed its most likely had it. im sure youll get there in the end intermittant problems are the worst.

[GTIrl]

me again,a couple of questions... what is a hall sender and do i have one on my 8v? i had a look in the haynes manual but only saw the one for the 16v.
also had a good poke about the afm carefully tho! i dont have a multimeter but the metal flap seemed to move pretty consistantly with the revs. it doesnt close at idle like it is when the engine is off? is that right? that was the only thing that made me wonder. apart from that it seemed ok.
the exhaust is as loud as all hell now which is majorly frustrating after all that work doing the exhaust manifold gaskets and no difference. it sounds like its fluffing but isnt.... anyone want to swap their perfectly good car for mine?! :embarassed:

[rubjonny]

The hall sender is inside the dizzy and is what the ecu uses to check & change the ignition advance, you'll have one in your 8v.  Have you actually replaced the knock sensor yet?  When its 'labouring' does it make a very loud tapping noise, if so its pinking which is what the knock sensor is supposed to detect so the ECU can back the timing off a little.
Also what fuel are you using?  If you're using the cheap stuff try a tank of premium 97+ RON fuel, it will help stop the engine pinking!

If that doesn't help the next step is to set the timing, mixture & idle properly:
Run engine to operating temp, proper hot so the fan kicks in at least once
Disconnect the blue temp sender
Rev the engine ofer 2.5 k 4 times to tell ECU to ignore the cold running circuit
Set the timing to 5-8 degrees BTDC @ 2000-2500
Make sure it is within spec, some engines respond to a little advance but the digifant does not because the ECU advances the timing automatically
Once thats done, you'll need a CO meter in the exhaust, the CO content should be at about 1.5
Then adjust the idle to about 800rpm

[Rain]

sounds all good cant for the life of me think of anything else to check maybe the lambada probe in the exhaust but thats a long shot as for the maf flap being slighyly open on idle thats normal if it was closed the engine would choke as it would be getting no air, the more the rev the more it opens. i have to agree with rubjonny if its a digifant then should really run it on 97ron or more optimax being best if you read the manual it says to use 98ron and only use less if its an emergency, if itss a k-jet then it says you should use 98ron but it will run fine on lower, basically listen to the engine if it tends to pink then use super if not wouldnt worry to much as it isnt going to cause the problems you have.

just a silly question but does the car surge ie youll get a burst of power then its gone?

[GTIrl]

hi there, the timing has been adjusted and re-adjusted about 30 times so far! it was out by quite alot the first time and then the rolling road guys did the timing to be sure once and for all. i dont think it pinks, it was pinking before but not since the timing has been done. the brand new knock sensor is on and so is blue coolant temp sensor and we decided to do the manifold gaskets as it sounded like it must be leeking from there. but that made no discernable difference.
it seems to be pretty consistantly crap at the moment,when its labouring the exhaust sounds really boomy and resonates and the throttle is a bit jumpy too.the noise tho keeps falsley pointing at the exhaust but its not rubbing anywhere or anything like that. but bizarrely it has stopped back-popping. you guys are gonna think im making this up. but seriously im not! wish i was!
there was that one time i was over taking that i accelerated hard and then suddenly it kicked in and got fast like a little power booster. after that it ran quite well for a couple of days. sadly it didnt last...
my friend is trying to get an airflow meter from the scrappies along with an ecu. the scrappy wanted 90 quid for the two.. daylight robbery nnnggngnn....
what the heck is a lambada probe.. is it like a flux capacator?!!
thanks again for all your help on this btw

[rubjonny]

Don't think MK2 GTIs got lamda sensors, its so the ECU can monitor the CO output and adjust the mixture accordingly. Think they only got fitted to MK2s with a catalitic converter so don't worry about it unless yours has one

Ok I'm running out of ideas now!  Do you know anyone else with a spare AFM you can try?  Do you live anywhere near Bracknell?

[GTIrl]

ah ok, i dont have a lambada probe then
im up in the scottish borders unfortunatley not near bracknell! i dont think there is anyone around here with a mk2 gti 8v is there?

[monzablue16v]

could be a blocked injector GTIrl I had a blocked one on my Ahem: Astra just had no power and boomed all through the exhaust changed allsorts in the garage (company car ) turned out to be a blocked fuel injector but only happened under load as that's when it was kicking all the fuel in.
running out of ideas rapidly here could be a vaccuum sp? leak?

[GTIrl]

aha! that sounds a likely suspect then. damnit tho cos the injectors were out when we did the manifold.. arg i could have had a look at them then. it is a pain to get to them isnt it? not like in the book where it says 'just pull of the injectors an place in a glass and observe if they spray a perfect cone shape'. its not that easy is it...
but that could be the problem then? it wouldnt make it misfire? that would possibly explain why its totally random intermittentness if it is in varying stages of blockedness?
cheers for the idea, i will check it out if i can or ask my friend to have a look.
it makes me look a bit nuts when i tell people the exhaust gets loud and they look at me like... uhuh, well it is a big exhaust what do you expect...so im glad to know that there is such a thing that does cause an exhaust to boom that isnt the exhausts fault!