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Model specific boards => Golf mk3 => Topic started by: B.I.G DUB on 25 August 2006, 20:24
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has anyone else had this problem? i had the auto electrician out and he reckoned it was something to do with the lambada sensor having a heater matrix in it that does something to emissions,i replaced the lambada and he said that should cure the problem,but hasnt! the car is a mk3 vr6 1994. this is causing concern as it seems to do it at awkward times,like when over taking,but then does it when im going slow just general driving! somebody plz help as im really worried,is there any chance it could be an earth or something along those lines? any help would be a great help as i am now stumped! :huh:
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its defo the right fuse? had a guy who bought 8 fuses before he realised! :shocked:
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i think so?its a higher amp than the 20 that was in it,around 30 amp to try and prolong the mileage im getting,and to see if whats causing the problem actually breaks. really weird?! :huh:
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Have you replaced the relays?
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relays? replaced 1 of them,is there more linked to it? :huh:
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Just had a look at a current flow (wiring) diagram for you VR.
The fuse SHOULD be a 20A, be very careful putting a higher amperage in place of it as it could bu99er up the wiring etc further up the line :shocked: ( remember VW put in a 20A for this exact reason )
This fuse only supplies the lambda probe heater[ G1/8], the fuel pump [M/2] (obviously) there should be nothing else unless someones been connecting wires in the wrong places. :undecided:
Are the wires down by the plug for the lambda sensor OK and not chafing on any thing?
Other than that the fuel pump wiring needs to be checked out and even the pump it's self :undecided:
N.B. G1/8 and M/2 refer to the plugs on the back of the relayplate ( or some may say fusebox )
eg G = plug location on relay plate 1= terminal this circuit uses in plug 8= how may terminals the plug actually has :wink: :nerd:
Hope this has helped in some way and not confused. :wink:
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it all makes sense except that last paragraph,not sure what u mean? i will put a 20 amp in it now so it is all back to normal.i thought that that wires might be chaffing near to the plug itself so i wrapped the wires in insulting tape to see if that would work but it still happened! the car can go 2miles and stop from cold,i'll replace the fuse and then it will do 25-35 miles before it goes again!? :huh: thanks for all the advice tho, :wink:
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Defo sounds like a damaged wire somewhere, 1st thing I'd do is unplug the lambda probe and see if it still does it! THe car will run with a default map with the probe unplugged, so you wont get quite as much power/economy but it should still run fine.
If that doesn't solve it the problem lies with the pump or wiring! Lift up the boot carpet and the metal disc in the boot floor. Follow the wiring from the pump as far as you can checking for kinked or bare wires along the way.
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Check your fuel filter as well .
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There is no default backup setting if the oxygen sensor is unplugged, so not sure that is a good idea. If you do unplug it, then only leave it unplugged for short periods, otherwise the catalyer could be damaged.
My money is on the fuel pump itself being faulty.
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Our Polo ran fine without, are you sure?
I would have thought it would switch to 'limp' mode. I'm sure VW would have designed the ECU not to kill the cat if the lambda is disconnected...
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Check this
http://www.gti-vr6.net/library/engine/vr6_technical_manual.html
Its a pretty accurate guide. I would say the cat would probably be ok as the other sensors should supply the ECU with enough information. However the oxygen sensor is a safeguard, so i would leave it unplugged for to long...
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I found this in that guide:
There is no substitute function for oxygen sensor (G39). If signal fails, no oxygen sensor regulation takes place.
I take that to mean the ECU uses a fallback map :)
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I found this in that guide:
There is no substitute function for oxygen sensor (G39). If signal fails, no oxygen sensor regulation takes place.
I take that to mean the ECU uses a fallback map :)
I took that as meaning what it says, no regulation takes place, in other words the ecu uses other sensors for fuel injection calculation.
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well yes obviously, but its still going to need a default value for the lambda output, you can't complete a complex mathematical equation with a completly missing value ;)
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well yes obviously, but its still going to need a default value for the lambda output, you can't complete a complex mathematical equation with a completly missing value ;)
Thats what the guide is saying if you read the whole lot.
The lambda does not have a default value, unlike some of the other sensors.
When some sensors are faulty, a different sensor reading is used instead, some sensors just have a default value when faulty, and some like the lambda is bypassed when there is no reading.
Like i said, unplug it, but don't leave it unplugged for too long.
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Exactly, it doesn't say anything about substitute senor feeds being used if the lambda isn't working, so it must use a default fuel map!
If you have a complex fuel equasion to calculate how much fuel you should use for any given ammount of air, you cant just remove the value recieved from the lambda and expect it to work, you need to use a default fuel map value of some kind instead.
The lambda output is used to tune the map to exactly the correct air/fuel ratio at any given time, without it, a default fuel map is used, as per any ECU driven injection system which has no lambda.
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If you say so.
I took it to mean the opposite, no regulation means the sensor is ignored.
If there is an air flow meter, inlet air temp sensor,throttle potentiometer, engine speed sensor, cam position sensor etc etc.. of course the ECU will be able to calculate fuel injection and timing.
Up to you at the end of the day, i wouldn't unplug it for long.
Whether you are right or i am is regardless, you can't have a 'safe' value for an oxygen sensor.
What i'm saying is i wouldn't want to guarantee that the cat won't get damaged.
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well how does the 9a 2.0 16v manage without a lambda then ;)
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big dub's on his Hols, but we've replaced the lambada sensor, the cat, the fuel pump relays, pretty much everything barr the fuel pump, my next suggestion is for him to change the fuel filter, as these allways get well clogged, maybbe it's this restricting fuel flow, resulting in the fuel pump struggling, then popping the fuse???
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yup thats what I'd try next, but GTI filters usually don't get blocked unless you've filled up with some dodgy fuel.
I'm putting my money on a damaged wire somewhere!
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well how does the 9a 2.0 16v manage without a lambda then ;)
Is that a 9A using k-jet or a 9A using ke-motronic?
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As for the fuse popping problem, trace all the wiring as Jonny says, if it is fine, change the fuel pump.
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It doesn't matter :grin:
It works like this:
You have a complex fuel injection map equation, which involves feeds from the MAF, inlet air temp sensor, RPM, Hall sensor, coolant temp sensor, etc to get your final figure for how much the injectors should open at any given time, and exactly when the spark should occur. Then AFTER this is worked out, the feed from the lambda is used to adjust the final result. If the lamda is not present, no adjustment occurs, as it says in that guide.
Remember, the lambda isn't even used right after a cold start!
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Thats right, the lambda is only there to fine tune the mixture, basically to protect the catalyser, hence why an engine can run without it.
Cheers you've just proven my point really.
BTW if you use a 9A with k-jet then that won't even use an ECU, so it does matter what system is used.
KE-motronic uses an ECU, however it is a completely different fuel injection system to the motronic system used on the AAA engine.
Do your homework :grin:
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There is no default backup setting if the oxygen sensor is unplugged, so not sure that is a good idea. If you do unplug it, then only leave it unplugged for short periods, otherwise the catalyer could be damaged.
My money is on the fuel pump itself being faulty.
eh? YOU are the one that said it had no default map?
I said it doesn't matter what 2.0 16v I was talking about because I was trying to make you see that no lambda isn't the end of the world for a cat, its fine without one. As you say it catches any other problems with the injection system, but it will still run fine without and wont damage the cat unless something else is wrong. I know the K & KE Jet are completly different to the VR6 system, please don't try to make me sound like an idiot ;)
The default fuel map will NOT damage the lambda on its own. I have no idea what point you were trying to make really! :grin:
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how do all im back! like hardcore said we tried everything,the sparky disconnected a wire from the lambda to see if that would cure the problem and for a couple of journeys it seemed to work,then started popping them again! i have stuck a fair bit of injection cleaner thru it to try and clean the fuel lines but the last time i used my vr it was still doing it,cats been changed along with lambda. i reckon u might be right with the loose wire.is it possible that there could be an earth thats causing the problem,just a thought coz if u wire an amp up and dont earth it properly,the fuses pop!? thanks for all the advice and help and i will check all the wires from the pump back as far as i can. :wink: please keep helping as i have had to drive my mums corsa for the last week!!!!! :embarassed:
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There is no default backup setting if the oxygen sensor is unplugged, so not sure that is a good idea. If you do unplug it, then only leave it unplugged for short periods, otherwise the catalyer could be damaged.
My money is on the fuel pump itself being faulty.
eh? YOU are the one that said it had no default map?
I said it doesn't matter what 2.0 16v I was talking about because I was trying to make you see that no lambda isn't the end of the world for a cat, its fine without one. As you say it catches any other problems with the injection system, but it will still run fine without and wont damage the cat unless something else is wrong. I know the K & KE Jet are completly different to the VR6 system, please don't try to make me sound like an idiot ;)
The default fuel map will NOT damage the lambda on its own. I have no idea what point you were trying to make really! :grin:
Right lets start from the beginning again.
If the lambda has no signal then you said that the ECU runs off a default map.
For the ECU to run off a default map, you need either a back up sensor/s for the ecu to make the calculation, or a default setting for the sensor.
In this case the lambda has no back up sensor/s, neither does it have a default reading.
So as i said in the first place, which is exactly what that guide says, no signal means no regulation, basically meaning the ECU will ignore the sensor.
I'm not saying that if you unplug the lambda that you will deffo ruin the catalyser. It just something i wouldn't risk myself in the long term because that sensor is basically there to protect it.
I'm not trying to make you out as an idiot, just pointing out what i think mate, don't take it so personally :laugh:
If you read through the whole lot again i think we are basically saying the same thing anyway :grin:
We both agree that the engine can run without the lambda sensor, we both agree that the map will be slightly different, as there is no lambda input.
What we are effectively disagreeing about is whether the lambda has a default setting, or whether it is just completely ignored.
The map could be the same or just a modified one with the lambda sensor ignored, i think it is probably the same standard map with the lambda ignored, what i don't agree with you about is that the lambda has a default setting, as it doesn't.
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Yeah I know, I just thought that 'do your homework' was a bit below the belt :wink: :tongue:
Yeah I can see now we were saying the same thing, I think I should wind my neck in :grin:
by 'default map' I mean the ecu has a standard map whish does not need the lambda sensor. Not that there is a default value for the lambda, just that without one, it doesn't matter. i.e. the lambda output isn't an essential part of the fuel/air calaculation the ECU uses. If it was, removing it would ruin the air/fuel ratio and prevent the engine from running.
As we can see from various sources the output from the lambda is ignored and no substitute sensor readings are used, the lambda output is only used to adjust the engine map. Which when you think about it is all it can do, since the reading from the lambda is basically telling the ecu what happened the last time it calculated the air/fuel ratio, since it is sensing the output from the last combustion cycle.
<bang> nope sorry to rich! <bang> thats a wee bit lean... <bang> yeah thats it! <bang> spot on woo you rock <bang> etc.. :grin:
All you had to say was 'I wouldn't leave it disconnected too long, it may damage the CAT' :tongue:
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cool,now u got that out the way,anymore advice please people! :wink:
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Yeah I know, I just thought that 'do your homework' was a bit below the belt :wink: :tongue:
Yeah I can see now we were saying the same thing, I think I should wind my neck in :grin:
by 'default map' I mean the ecu has a standard map whish does not need the lambda sensor. Not that there is a default value for the lambda, just that without one, it doesn't matter. i.e. the lambda output isn't an essential part of the fuel/air calaculation the ECU uses. If it was, removing it would ruin the air/fuel ratio and prevent the engine from running.
As we can see from various sources the output from the lambda is ignored and no substitute sensor readings are used, the lambda output is only used to adjust the engine map. Which when you think about it is all it can do, since the reading from the lambda is basically telling the ecu what happened the last time it calculated the air/fuel ratio, since it is sensing the output from the last combustion cycle.
<bang> nope sorry to rich! <bang> thats a wee bit lean... <bang> yeah thats it! <bang> spot on woo you rock <bang> etc.. :grin:
All you had to say was 'I wouldn't leave it disconnected too long, it may damage the CAT' :tongue:
Yeah sorry mate, no offence intended  :embarassed:
We got so obsessed with the argument, that we were basically the same thing anyway.
It wasn't until i read it all again i realised  :grin:
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cool,now u got that out the way,anymore advice please people! :wink:
As i already said, trace the wiring, looking for obvious damage. The most likely place is where the loom runs under the floor by the doors.
If all is ok, replace the fuel pump.
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Yeah sorry mate, no offence intended  :embarassed:
We got so obsessed with the argument, that we were basically the same thing anyway.
It wasn't until i read it all again i realised  :grin:
Hurt my feelings you know, I cried myself to sleep that night :cry: :laugh:
Yeah complete waste of time really, at least the thread got lots of free bumps :grin:
The fact its so random leads me to belive its a wiring fault somewhere as well, gotta be rubbing on the chassis somewhere, check all the rubber grommets where the wires pop thru the bodywork, and the metal flap under the boot carpet where the wires run down to the pump/level sender. Worth taking out the driver side dash under tray out and dropping the fusebox down as well.
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I still think its the pump itself.
A while back my brother had a Rover which kept blowing the wiper blade motor circuit fuse, you would think again wiring fault, but it was the motor the whole time.
If you can't find any problems with the wiring as Jon suggests, try a new pump.
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Good point, MK3s are 'at that age' when bits like this can start to fail. I still think of the MK3 as quite a 'young' car, but it isn't really!
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cheerz people you've been a great help.gonna get a new fuel filter,checked and re-checked all wires and lamda sensor,which also made me fit a de-cat.a few people have suggested a blockage in the fuel filter so i will try that while working my way back to the pump if neccessary.trying all easy options before i attemp the pump! :huh:
hopefully my v-rarrrrr will be back to normal by the weekend! i hope :smiley:
any hints or tips on the above would be greatfully recieved! cheerz :wink:
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ah so you've got rid of the cat? If so you can safely unplug the lambda sensor for a bit to see if its a wiring problem to the lambda heater :)
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ok,so what will happen if i do that? im gonna try the fuel filter,how much difference will it make to my car now ive de-catted it? thanks again for all the advice! :wink:
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all it will do is confirm if the fuse blowing is anything to do with the lambda or not, since you say its protected by the same fuse? The car wont run as well with the lambda unplugged and there is a possibility of CAT damage, but since you don't have one we don't care ;)