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Discussion in 'A3/S3/Sportback (8P Chassis)' started by -Ju-, Aug 26, 2009.
Just posted a sort of review mate
read the review mate, very interesting. so it hasnt fixed the problem at all then?
you say it pulls away cleaner? thats where mine is a little hesitant and lunging at times.
Been out in the car this morning and the fault is most definitely still there!
There is a stretch of road which is uphill for a few hundred yards at 40mph and it always used to do it there, well it still does. But also after the hill crests you come up to a set of lights and when I stopped, the car ticked over really roughly. At the next set it was fine but intermittently it either idles roughly or at 1100rpm.
I'll check it for fault codes later as it was definitely clear the other day.
The hunt goes on but it's certainly good news for all those that were thinking a chain change was on the cards!!
Mine was at its worse so far yesterday morning, thats the first time i have had the needle actually flicking up and down when you try to hold 2k rpm...You could here one pot popping in the exhaust pipe almost like you have 5 injectors spraying and one dribbleing..That said it was 80% better at lunch time. I knew a guy that had a Nissan Serena a while back that had a similar problem to this...Nissan said his head gasket had gone so he got it fixed and it was no better (£900)....eventually he after a lot of hassle pulled the fuel pump connections of and stuck them back on....problem cured.
interesting....i changed the plugs last night, fired the car up, sounded exactly the same...so i started messing about with the 2 spare coils i have. replaced coil one, fired it up, didnt seem any different. Replaced coil 2, woah, all of a sudden is holding revs lovely!
i could still hear the odd pop every now and then so i took it out for a test drive, it was perfect in all ways.
still was this morning when i drove it. I am assuming the plugs made no difference as a lot of people have changed those, so it could be the coils starting to break down under certain conditions.
Now I have thought i have sorted it before so i am not saying definitively its the answer, but its definately fixed it in the short term.
i will stick a few miles on it and see how it progresses.
good news though eh?
makes me laugh that potentially 1 faulty coil had me with the engine out on the floor on my new car lol
will report back tomorrow to see if there is any change
Fingers crossed again coxy..
I'm surprised you haven't checked the coilpacks already... the first thing we did when mine was playing up was fit a new set of plugs and coilpacks.
i was always told that when the coilpacks fail, they go down completely.
anyways i did about 50 miles last night, and its running rough again. wtf?
i guess the clean plugs made a difference initially.
I am not prepared to fork out for 6 new coils on the off chance that they are at fault. so i guess i will be waiting for someone else to try it first, unless i can find a working car without the fault to swap coils with.
only coils and fuel pump left now.
this is getting right up my nose now. its stupid.
Well as Pete says, he's done coils so i think we can cross that off the list.
Have any of you guys who have done major top end work here had injectors tested for spray pattern and so on ?
Thinking that this is a mileage related problem and not an obscure problem because its to common. So trying to think of the bloody obvious that we haven't looked at. I have popping in the exhaust pipe which is more noticeable now i have a noisier back box, this points to unburnt fuel. some of us were getting **** mpg as well.............just thinking out loud....
i think petes problem is different to ours. correct me if i am wrong but his revs bounce up and down on idle, which i had when i first fired the car up, until i messed about with the vvt solonoids.
i have that popping in the exhaust pipe too. my thinking was on coils, one of them was borderline not producing enough power to ignite a partial cylinder fill, which is the part throttle situation. The plugs them selves look ok when you take them out becuase the misfire is so relatively infrequent.
how much are coils?
i doubt it can be injectors to be honest, i have not had a car that ever had problems with injectors?
this is my thoughts as I couldnt sleep
The thing we have in common is the 2k bit. So what happens on our cars at 2k ??? Well I think that could well be the start of the advance curve. I no nothing about cars but I do know about bike engines. The advance curve would run from about 5 ° before top dead centre ( BTDC) to approx 35° (BTDC)..
We know that at tick over (off the advance curve) things are ok, we know on cold mornings when the engine advances its self to a higher rpm tick over ( above the std 5° BTDC) things are ok. We know that once the advance curve is started we are ok.
So what if the sensor/sender unit that triggers the advance is fluffy and the advance is jumping. Fore instance you could have a point where the plugs are firing at different advance levels each 6 cyl rev. this would in affect throw everything out from your spark to valve timing to injector spray in relation to the pistons position/spark but by maybe only a few degrees
If the advance curve started to early or late the knock sensor might be cutting in and trying to retard the ignition just as the ECU is trying to advance it
.Suppose by 40-50k miles the compression has risen due to coke because the oil fume recycling is throwing oil into the bores
This would not show up on a remap because although the remap basically adjusts the advance curve, remaps start to adjust over 2krpm
The reason we dont get this when we are on Choke could be that the engine is already advanced to a point above the normal 2krpm start of the advance curve.
Now if it was a bike I would simply put a strobe lamp on it and set the tick over at 2krpm and check the timing marks and position with a degree disc
.but its a bloody car !!!
i think the problem exists not just at 2000rpm rpm but from idle up to then.
sit the car and gentle touch the accelerator so it just starts to raise the revs, sounds quite rough to me.
Yes but my thinking still aplies because at tick over my car is perfect......off the advance curve....maybe the advance curve starts well below 2k and 2k is the point at whick it stops getting a fluffy signal and starts to advance properly..?
yeah, mine is perfect on tickover too. the engine does start advancing the ignition straight from idle, i have checked on vagcom.
the ecu gets signals from everywhere, i should check the readings from them, although i dont really know what the baseline norm is so i am on a loser from the kick off lol
just had a mess about in the garage, vagcom'd the car and there were zero faults on it.
only thing that i found unusual was the voltage.
it sits at 11.8 when the engine is off, which is fairly normal i think. but when i fire it up it only lifts up to 13.5 volts. Is that right? every other car i have test sits around 14.5 volts.
That start making me think that maybe there is not enough current to provide a proper spark?
so i performed a little experiment, I have a mega battery charger with a boost facility that can provide enough starting power to turn a truck engine over. I put it in boost mode, fired the car up and rev'd it to just under 2k, or the best i could hold it. it was doing it bouncing about thing, then hit boost button, the volts went up to 15, the revs picked up straight away, without me moving my foot at all.
it did everytime on from idle to 2k.
voltage problem? i could have sworn you are supposed to have 14.5 volts on them engines ?
interesting because when we tried to remap my engine we had to attach a booster pack too it because the remap thingy said "not enough voltage to communicate" without the engine running and yet that battery will start the car on a frosty morning.
I can understand a voltage drop with the battery in the boot because of the Resistance of the very long leads. let me check the manual for running voltages...
Nothing in the manual.....
you need to be a bit more scientific i think. a 12v battery should put out 12v under no load at all. It may have an input of 14.V at the battery but measured at the fuse box i would expect it to be 12-13v as the battery acts as a sort of voltage regulator..By putting 15v across the thing after the battery you are running the risk of blowing your electrics up. I suspect what you did was take all the load off the alternator and so the engine speeded up. However it is most likly if it solved the problem there is a low voltage somewhere in the system thats messing us up. but finding it could be very tricky if it doesn't show as a fault code.
Whats the running voltage at tick over at the +terminal under the bonnet and what is it at 2k rpm..
once the car is fired up the battery is effectively out of the equation. I am in no danger of blowing my electrics up, as the thing was designed to go onto car electrics. This is my point, all the cars I have had show a voltage of 14.5v with the engine running. a battery standalone will normally show 12.5 volt.
wasnt just a load thing, as the engine seemed to clean itself up a bit. not so much popping.
Could all be down to a bad earth. I will have a dig about at work tomorrow,
It could be nothing, but hearing that with your voltage too low when you tried to map it seems to be a canny coincidence doesnt it?
just got at the boot, checked the battery terminals - all tight, decided to loosen off the main battery earth point to the body in the boot and possibly clean it up if necessary, it snapped clean off!
Now i know i have been known to snap a few bolt heads in my time but that snapped way too easily - and i was trying to loosen it not tighten it!
car is now completely dead. need to weld it back up.
The battery is not out of the equation. The charge goes from the alternator to the voltage reg then too the battery. its smoothed by the battery and then goes to the fuse box. boosters are designed to be put across the battery. the reason your lights dont glow really bright when you rev your engine is because the battery has regulated the voltage.
correct me if i am wrong but the regulator on the alternator 'regulates' the voltage
I just noticed this same problem (or at least I think its the same thing) in my 2.0 TDI... I was about to post a thread about it when I saw this one right up at the top of the page. It only just started today though (I've had the car about 2 weeks now) and when it gets to around 2.5 K RPM it seems to drop the revs quite noticeably and then suddenly picks back up again after a second or two - basically it sounds as if I just put my foot on the clutch for a second. Is that the same thing that you guys are experiencing?
The regulator, regulates the votage to the battery which will be about 14.5v.- 15.5v the battaery then smooths that voltage to a constant voltage and feeds that to the fuse box.
If you just ran a feed from the voltage reg to the fuse box and cut out the battery the voltage to the fuse box would go up and down with the revs. your lights would glow dim at tickover and probably blow the bulbs at 70mph
A 12v battery will give off 12v under load. It has 6 x 2v cells. you could put 20v into it and it could still only give off 12v under load.The reason you have a voltage reg is to stop the alternator putting more than 15v in to the battery because any more would buckle the plates and short the cells.
well i am not doubting your experience paddy, but thats not my experience. I have ran a car with no battery before, and the voltage did not rise with the revs, other than the obvious from tickover. Batteries are not clever enough nor accurate enough to cap voltage. Smoothing the voltage sounds feasible though. Definately worth a bit more investigation IMO.
I had a play around on the way to work this morning to see if my issue was exactly the same as you guys and I'm not sure it is. Mine does not seem to be tied to a specific rev range, although it does only seem to happen below 3.5K RPM (not that I really go above that very often but I was just testing it out today). Basically it is just whenever I floor it, it goes for a bit and then just stays at the same revs for a couple of seconds, then suddenly picks up. The odd thing is that I dont feel this in the cabin, I mean its not as if the car lurches or slows down noticeably - its only the rev counter and the sound that makes me realise it is happening. Sound like a totally separate issue to you guys? I took a video of my rev counter which I'll upload later so you can see exactly what I mean
doesnt sound like the same issue to me mate.
do all a3's have theirn batteries in the boot?
Checked my voltage on vagcom last night and on block 4 it shows the same voltage as your Ian, 13.5V ish. I'll dig out my voltmeter later on and check it on the positive terminal under the bonnet, but tbh I don't think thats the problem. Also all 3.2's have the battery in the boot as there is no room under the bonnet for it!
Hopefully one night this week, my mate is bringing his 3.2 up and I'll try some logging and comparing. I logged blocks 90 and 91 last night which are for the camshaft adjustment and the specified and actual seemed miles away.
Any ideas on what else I could log as tbh it's all going over my head now.
I think we could also do with a recap regarding what people have changed so far, then we can work out what's left.
Hi Chris, Not sure it can be related to our problem tbh, especially with yours being diesel. Our problem could be generic to the A3 , but I would think it would have to be common to the petrol variants.
Get yourself a vagcom scan done in the first instance and good luck with getting to the bottom of it.
Where did you connect the boost cables too?
Its not going to be a current shortage if you have 120 amps to turn the starter. and given its a 12v system its dificult to see why the problem is solved at 15v and not 13.5...Plot thickens....
I would expect the revs to pick up when you hit boost because you are taking all the load of the alternator. the test would be , can you hold it at 2k revs on boost and see what happens ?
Actually when I turn all the auto lights etc off, it does show over 14V.
Turning everything off tells you nothing. You need to turn something on like the lights and then measure the voltage under load.
OK cheers, hope you guys get yours sorted too - seems like you have almost run out of things to replace!
Right I did some logging last night with a know good 3.2. I logged blocks 4, 90 and 91 (votage, exhaust cam, inlet cam). It showed that the voltage was the same as mine so I think we can forget that as being a cause, but as I suspected the specified and actual camshaft adjustment on mine looks out of tolerance.
I have the logs on an excel spredsheet, but I have no idea how to post it up as when I do it comes out as a mess of figures!
Does anybody know what actually controls the operation of the VVT actuators, are they electrical or do the work off oil pressure?
I think its a solinoid, didnt coxy say they stick but you can free them by flashing 12v across them a few times
Ju, when you measure blocks do you do this with the car stopped or do you take it for a run ?
its basically a solonoid for each cam, operated by th ecu, which reroute the oil pressure from one set of chambers in the sprocket to the other, forcing the cam one way or the other. But you have changed the full VVT unit haven't you?!
or are they filling you full of sh**?
if your vvt unit is new, and the sprockets are new, then thats the entire system changed over, so then i suppose it could only be either a weak signal from the ecu thats not operating the solonoid properly, or poor oil pressure?
good work mate.
Coxylaad, 3.2Ju and Myself are fairly local to each other I think.
How about a meet and look at the figures!
that sounds like a plan. but we need someone with a known good car for comparison.
Mine is good I think.....