GolfGTIforum.co.uk
Model specific boards => Golf mk2 => Topic started by: GTIrl on 16 July 2005, 13:03
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hi there, does anyone know how a malfunctioning knock sensor would affect the performance of an 8v? and is there a way to test it, or do you just have to switch it out and hope for the best...
the story so far..
my car is intermittently underpowered, backpopping, jerky throttle and noisy like the engine is labouring, also sounds like its fluffing at the exhaust manifold. otherwise (when it runs well), it revs smoothly and is pretty nippy. exhaust sounds loud but fine. so it must be an electrical fault with it being intermittent. but apart from changing all the sensors and everything im stumped. im totally skinted but wondering if it is worth taking it to a vw garage... eeeek!
(timing has been checked, checked again and then rolling roaded and checked again.)
any ideas would be greatfully received
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right best way to test it is to simply run hte car and tap the block with a hammer... this will cause the car's timing to alter and it will be noticeable... if it doesnt make any diference then its probs shagged...
and it sounds like ur ign timing maybe out still check it via the correct procedure and also check for air leaks.. thiis would cause poor running
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thanks for info, i'll try the hammer. one other question tho, if the ecu doesnt get info from the knock sensor does it change the ignition timing automatically? or does a nonfuntioning knock sensor just not make any difference at all? sorry if my questions are a bit dim...
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just tried the hammer trick, i hope i was doing it correctly.. just kinda tapping it on the block? but it made not a parp of difference... and i had my ears out on stalks listening for a change, but nuffin. i guess thats it not working then?
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I had similar intermittent poor running problem, had thought my mixture setting was wrong, however, having re-set it the problem persisited for weeks. Fortunately, I have a spare knock sensor, distributor, air flow meter and coil. I embarked on a process of replacing each of these items. The knock sensor and air flow meter change made no difference, however, on swapping the coil the car returned to its normal healthy state.
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you do have to give it a whack... (within reason!)
but if nothing is happening then it may be fooked! the coil could well be the cause and for the sake of a few bob it maybe worth changing it anyway...
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hmm thats interesting about the coil. wish i had all spare parts lying about... i had another go with the hammer, well actually i got my boyfriend to do it cos i thought maybe i wasnt proficient enough in the art of block hammering... and he did tappety tap on it for a bit, no change, and then all of a sudden it changed and sounded like it might stall, and then went back to normal after 10 seconds or so. so now i dont know if its broken or not/ intermittently broken, or what. blinking thing! i will check out the thought on the coil though, what exactly was your bad running symptoms which turned out to be the coil wellfan?
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GTIrl, Looks like my problem has returned. It is either a loose wire somewhere in the vicinity of my coil or I have another broken coil. My symptoms are similar to yours, most pronounced is a misfire (sounds like the car is spitting out unburnt fuel) the car can also be slow to respond to my foot on the throttle. It is definitely an electrical problem in my situation. Might be worth checking all of your connections in the engine bay.
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Might be a long shot but i once had an electrical problem which turned out to be a problem with my front engine mount. As i was flooring it the engine would lift backwards pulling on the wires causing it to misfire. Changed the engine mount and the problem went away. Its worth a look as all you have to do is put y handbrake on tight then rock the car on and off the clutch in 1st gear or reverse. If the engine tries to climb out of the bay then your mounts most likely foooked.
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wellfan when you blip the accelerator when at idle does it pop pop when coming back down the revs? (when its running badly that is?) and does your brain bleed out of your ears when going up a hill?!
total bummer your problem came back. i was hoping the coil idea might be my saviour. still might be i suppose. all the wires in my engine bay are arranged in a spagetti like fashion, and some had to be re-routed cos they were a bit tight. but there is nothing obviously corroded or bad looking, apart from some of the plastic coating around the knocksensor wire has melted which is why it is suspect. oh for a donor car...
i think my engine mounts are probably not great, but not problematically bad, but ill check it out again, thanks for the suggestions.
The fault isnt as regular as that unfortunately, sometime i start it up and immediately its rubbish, other times its fine. sometimes like the other day when i was overtaking it suddenly started to work well and it was like a turbo boost!!
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Got a spare coil sat in me shed if ya want it GTIrl, ya can have it for the price of postage if its any use to ya?
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thats a very kind offer solarized,. im taking my car to a friend on wednesday to do some tinkering, and also to get mot'd, so if it looks like it could be the coil then i may take you up on your offer. thankyou!
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sorry, a bit of misinformation, apparently i dont have a misfire! i thought maybe thats what the unburnt fuel pop was, but the engine is firing on all cylinders, so maybe its not the coil after all. wednesday am getting a new knock sensor and blue coolant sensor so will see if that helps...
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Try changing your earth straps guys so many problems caused by those little blighters cheapest and most overlooked part imo!! try your hall sender + connections from the dizzy if they have it on 8v sure they do.
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just out of interest.. ive got a new knock sensor and a new blue coolant sensor, new inlet manifold gasket and exhaust manifold gaskets,and fixed all earth straps and timing checked yet again... and its still not better!!! am losing my mind over this, but now wondering if i need a new brain! is it possible that it could be the brain?what else can it be???please help :sad:
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you dont mention if you have changed dizzie rotor arm ht leads and plugs recently had a simular problem and it was just a warn rotor arm.
just a quick check list of things that will bog ya engine down and cause power lose
fuel filter not blocked
air filter not blocked
dizzie plugs etc...
ignition leads and earth leads test this by spraying a light mist of water while the engines running spray a mist over connections and look for archs
compression test for a blow head gasket
only things that this leaves if that didnt work is the igntion/distributer or the fuel injectors
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thanks rain for your suggestion. yes it has new ht leads and plugs distributor cap and rotor arm, they were new about 10 months ago. it is an intermittent problem so cant really be mechanical can it?
also new fuel filter about 2 months ago
compression is slightly down in the middle two cylinders apparently, but nothing worth worrying about.
unfortunatley the bad running is not bad enough to point to something specific, you just notice while driving that it is slightly down on power and it sounds loud when the engine is under load especially around 3000 rpms. it still goes strong and doesnt missfire, its just as if the timing has gone slightly out, and get back pops and a jerky throttle -like when you take your foot off the accelerator it is like putting on the break.these are all things that arent there when its running well..
thinking about a faulty airflow meter now...and am just going to look up what symptoms that would produce
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My airflow meter went a few months ago, however, when it goes it is not an intermittent fault. The poor running remains until you replace the meter. The symptoms when mine went were a distinct lack of power and rough running. My son's Corsa had the same problem with the same symptoms. They are very expensive to buy new, try and get a second hand one from a breaker for about £20. May be your ECU, these can be bought very cheeeply on ebay, I tend to buy one when they are going for a few quid to keep as spares. However, I am not convinced that is your problem, still sounds like an intermittent electrical problem. My problem seemed to disappear after changing my coil, however, it soon returned. I believe I have a loose connection somewhere near my coil. I have since put back the original coil and it is running well again. My problem will undoubtedly return unless I check my wiring.
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if its lack of power all round then its likely to be mfa but if your car is down on power and very loud at 3000rpm is you exhaust ok? mine does something simular because they fit badly and it blows between the joins this causes lose of power when its wide enough but other sysmptoms are popping and rumbling and very loud zorst sounds good but gets on your nerves after a while it also caused my car to shudder and act up maybe the air flow changing as you drive along its worst examining especially if you have just had it fitted recently.
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yeah my exhaust sounds horrible, its a stainless steel magnex system, and seizes periodically around the ball jointy bit that should allow for movement, and then it makes the next joint up fluff, anyhoo thats getting off the subject a little, my exhaust is fine now, all fixed and defitnitely not fluffing or leaking anywhere. my friend who has been helping me with this, well actually doing it all while i stand around passing tools to him, has just suggested that it may be sticking exhaust valves, but ive not to get my hopes up too much incase it isnt. but that would possibly explain why its not got a ryhme or reason and why maybe the electrical route has not borne fruit yet. any thoughts on this?
thanks again for all your help
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I am also thinking AFM problems, the only other thing I can think of is possibly the hall sender is on its way out?
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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.
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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:
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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
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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?
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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
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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? :)
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ah ok, i dont have a lambada probe then :grin:
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?
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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?
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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! :rolleyes:
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"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?"
Where abouts are you? I live in Lanarkshire, not too far away.
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You can get the injectors cleaned in an ultrasound 'bath' not sure how much new ones are, without looking them up on gsf, but i suspect cleaning em would be cheaper. worth a try !
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im near peebles. where are you wellfan? do you have an 8v digifant? would you consider having a look at my car to see what you think?