Missfire/lack of power

[Chrisdut 0]

Hi all, ive had an intermittant misfire with my vr6 for a while, it will start first time no worries but if i rev it to say about 4k and let the throttle off it will just cut out dead, now most of the time it will restart after 5 or seconds but will idle with a miss fire for a while and then clear off to noraml running on 6, now today was another matter, it cut out as i approched a set of lights after i rev'd it to see if it would happen today(silly me lol) but when trying to restart it it felt completely like it had no compression, i even had to put my hazards on because it wouldn't start but eventually it started to try and start and then started but missed for 10 secs or so then cleared and was fine for the rest of the way home, i've changed the coil pack last weekend so i know this new one is ok

anyone got any ideas

cheers

[dellert 0]

Checked the leads and plugs?

[clarkie 1]

is this only when cold? i was told this is because of the auto choke as you rev it when cold it over fuels it and once the fuel had burt off it will run as normal. to be honest you shouldnt highly rev a car when still cold (if this is when cold) has 1 else heard of that?

[Chrisdut 0]

did it again today and didnt rev it too 4k this time, which isnt that highly rev'd anyway lol, it happened again and again.

Luckly there is a bloke now working in our garage that used to work for an engine rebuild company so he came out and had a look at it with me, as soon as i described my fault and he saw it happen he said "hydraulic tappets sticking to far open"

Sounds right to me and with the amount of them he has done in his time at his previous job it makes perfect sense, it totally lose's all its compression after cutting out, tappets stuck open to much so valves open slightly which cause no compression, after cranking for a few seconds it starts to try and start(tappets returning to correct length) and away you go.

So new tappets it is, going to cost me £70 which isnt going to be to bad woohoo lol

cheers

[jaysVR6 2]

did it again today and didnt rev it too 4k this time' date=' which isnt that highly rev'd anyway lol, it happened again and again.

Luckly there is a bloke now working in our garage that used to work for an engine rebuild company so he came out and had a look at it with me, as soon as i described my fault and he saw it happen he said "hydraulic tappets sticking to far open"

Sounds right to me and with the amount of them he has done in his time at his previous job it makes perfect sense, it totally lose's all its compression after cutting out, tappets stuck open to much so valves open slightly which cause no compression, after cranking for a few seconds it starts to try and start(tappets returning to correct length) and away you go.

So new tappets it is, going to cost me £70 which isnt going to be to bad woohoo lol

cheers

[/quote']

I don't think so somehow :S

[Chrisdut 0]

why not?? at least give a reason lol

plus being a mechanic myself the cause would give the exact symptoms i have, starts fine, rev then cuts out and then no compression for 5-6 secs then starts with misfire

so what do you think is the cause, oh and if i dont rev it to about 3 k it will run fine so it aint plugs or leads or a coil pack, it aint head gasket or rings or valves

[jaysVR6 2]

I'm no mechanic mate, but I've never heard of this problem with a VR engine before.

It just sounds like a bit of a stab in the dark tbh, I may be wrong though mate. Be interested to know the results.

[mannie 0]

i'm no mechanic too,"hydraulic tappets" works on oil pressure does it not ?very interested to know the real results all the same.

[Chrisdut 0]

yeah they do work on oil pressure but they stay open and can stick to far open when knackered, well im getting then tomoz and hopefully sort it out soon

[dellert 0]

Me thinks you still gonna have a problem after new tappets..........

[Chrisdut 0]

at least give us a reason what else you think could be the fault lol

[dellert 0]

Why would all your tappets fail at the same time? Surely if they all started sticking open you would have hit them with the pistons? Never say never, but every time a VR fails, itfails for something that is a common problem. Tappets although they get noisy are not something that generallt fail. Why do you think there is no compresssion? Its not something you can just tell by listening to it. It is more likely that you are missing one of the primary components of running- such as Fuel or Spark or one of these is not being delivered correctly. IMO, which is by no means an expert opinion. My first port of call would always be to see what the ECU has logged.

[Chrisdut 0]

its very easy to tell if you don't have compression, when you turn the key the engine turns over but it doesnt even attempt to start, then it builds up and eventually it starts, dont think its a fuel or spark issue but a compression issue, the valves only have to be open slightly for it to loss compression and i mean only ever so slightly, as working in a vw garage i put it on the diagnostic machine today and the only fault was voltage low and throttle valve basic settings fault so its a mechanical fault somewhere, cleared these so we'll see what happens, got the new tappets today, cleaned them out and will try to get them fitted next weekend.

[Chrisdut 0]

well tappets going in today so ill let you know the results

[Chrisdut 0]

started the job, went really wrong and i ended up breaking the top timing chain tensioner by accident lol, so in the end i removed the gearbox, end engine cover and am replacing the timing chains and guides aswell, might aswell replace the clutch while ive got the gearbox off

[dellert 0]

Had a good day then! You gonna have a proper stropo on if its still playing up when it all goes back together!

[Chrisdut 0]

lol i know lol, oh well at least ill have all new tappets timing chains rails and guides plus new rear main and clutch lol

[Chrisdut 0]

oh and the fact i went this far the head is now off and stripped ready for a slight skim, the seats recut and valves relapped, new valve stem seals aswell, at least it will save me have to strip it again lol

[Chrisdut 0]

well finally its back together after a long wait and only being able to do a bit at a time after work, well the list of work is quite long, while the head was off i put some coolant mix into the cylinders to make sure they were holding, and to my horror cylinders 1 and 5 let fluid through while 2, 3, 4 and 6 held, so i eneded completely stripping the engine down

Sump gasket, new oil and oil filter, mains and big ends, set of rings, front and rear crank seal, oil cooler seals, clutch kit, full set of chains tensioners and rails, head gasket, headbolt set, valves reground, valve stem seals, tappets split down and cleaned out, rocker cover gasket, exhaust and inlet manifold gaskets, cooling system flushed and new G12+ coolant used, y piece for the long coolant pipe from the group buy on this forum, had to replace the driverside inner cv joint gaiter as it split while pushing the car in and out of the workshop lol, all in all i've spent around £550 for all the parts and if i add all the time spent to do the job id say its taken me about 3 days work in total

one thing tho dont use the VW special tool to refit the piston and ring, i had to buy a new set for 1 cylinder as it broke 2 rings while i tried to refit them, i ended up fitting the pistons back in using just my fingers

[purple highline monster 0]

does it run though?

[Chrisdut 0]

does it run, yeah it runs, i turned it over for 30 secs with no plugs in and coil disconnected to build up the oil pressure then put the plugs in but still coil unplugged, then plugged the coil in connected leads and it started it up, it started first turn of the key and ran on all 6 with no misfires, was chuffed