Strange Misfire Problem - VR6

[VR-Sixy 0]

What looked to be a simple misfire problem is turning out to be a bit of a mystery.

The guys at the garage have replaced the plugs, checked the HT leads and compression tested

all cylinders - everything coming back perfectly, so it's not loking like an electrical thing. The coil was

replaced less than two months ago so it's not that.

 

They've had the top off and checked the cam-shaft and that's fine as well.

 

What IS happening though is that after about 5 minutes with the engine idling, there is a great deal of pressure

(an inordinate amount in fact) building up in the water/cooling system, so much that the top radiator pipe is almost impossible to squeeze after this time.

 

The guys at the garage are stumped so i'm wondering if there's anyopne here who might be able to shed a little light on the problem before they take the plunge and take half the engine out. :gag:

 

Any input would be most welcome.

 

Cheers Guys

[dr_mat 0]

Excessive pressure in the coolant system means there's an airlock somewhere. I doubt it's related to the misfire, however, unless the head gasket has gone and you're getting cylinder gases bleed into the coolant system. Any garage should be able to check that though.

[fla 9]

as the doc says, sounds like an airlock. do some basics and let it run for a while with the expansion cap off, whilst massaging the main coolant pipes to get rid of any airlocks. Just make sure you dont let it boil over! Otherwise your head gasket could be on its way out. Is the lower pipe also warming up?

[quicky1980 0]

faulty coil pack? did they check this? can you get a hold of a known working one and swap round?

[VR-Sixy 0]

The entire engine was out 40k miles ago and rebuilt, so i'm not sure it would be the CHG. The coil was replaced less than two months ago and this problem is nothing like the problems that was causing. WIll put that idea forward though as it was the main coil that was replaced and not any of the packs.

 

Any other ideas?

 

Thanks

[quicky1980 0]

I've heard that some cheap after market coil packs can

play up after only a few months. Was yours an original replacement part from be?

[dr_mat 0]

It's not unheard of for rebuilt engines to blow gaskets - no matter how professional the shop that does it, the blocks and heads are ~10 years old and rebuilt engines are usually rebuilt for a reason .. So I would chase the coolant system problem first, then figure out if you still have a misfire afterwards. Unless it's an obvious one like plugs/leads/CP I suppose..

[VR6matty 0]

Does sound like a suspect coilpack.for the misfire had a similar issue with mine since the cold which took out one of my plugs, if you want to try my coil pack I think I am pretty local to you and would save u buying one to find out!

[VR-Sixy 0]

Hi all, found out what the culprit was - looks like the timing chain has jumped a cog somehow. Had the tensioners and chain replaced when the engine was whipped out at about 60k ago, so i guess it's feasible. Hopefully going to get it back from the garage today.

 

Thanks to all who chipped in with suggestions as to what it could have been, and a nod to Matty for the offer of trying his coil pack.

 

Cheers.

[VR-Sixy 0]

Finally got the old bus back on Friday and the engine sounds much better than it was!! But there's still a problem...... it's started spluttering before picking up at lower revs in 2nd or 3rd. I've noticed that the HT leads have been replaced and i know the coil was replaced in November of last year and i presume i have new plugs in for the last visit to the garage as well.

 

Anyone have any ideas as to why it might be running a bit lumpy? Also, is the coil (the cylindical silver thingey near the wipers) the same thing as a 'coil pack'

 

Yours Hopelessly,

 

Nick

[Kevin Bacon 5]

Has it been fault coded? Is it a dizzy model?

 

You say things have been replaced, but replaced with what? Dealer parts, or of equal quality? In my experience, replacement isn't necessarily an end of it. It needs more thorough diagnosis. Has the engine been run at night to see if there are any stray sparks down the head holes or around the dizzy / cap coilpack area? Have the plugs been taken out and inspected for fouling?

[VR-Sixy 0]

I've been taking my Rado to the same guy since i first got it, and as far i am aware he has always used Dealer parts or parts that are of equal quality. As far as i am aware it is not a dizzy model, and I have no idea whether it's been run at night to check for stray sparks. I was just trying to get a general pointer as to what the problem might possibly be. Thanks.

[Roger Blassberg 0]

Sounds like a distributor engine. Have you checked the distributor cap, innards, ignition timing?

 

Best wishes

 

RB

[andy 0]

How has repositioning the timing chain affected the excessive pressure in the cooling system? Does it still do that.

Did they do the compression test hot or cold?

[VR-Sixy 0]

Has it been fault coded? Is it a dizzy model?

 

You say things have been replaced, but replaced with what? Dealer parts, or of equal quality? In my experience, replacement isn't necessarily an end of it. It needs more thorough diagnosis. Has the engine been run at night to see if there are any stray sparks down the head holes or around the dizzy / cap coilpack area? Have the plugs been taken out and inspected for fouling?

Had a good look around in the engine bay last night - no sign of a distributor in there anywhere. I also turned the engine over and no sign of arcing or stray sparks down the head holes in the dark either. One of the HT leads wasn't quite pushed all the way home when i checked them, but even with this done, it's still sluggish as lower revs in gears2/3/4. It kind of splutters before picking up.

 

The timing chain and tensionsers were replaced within the last couple of weeks so i don't think it's a timing issue. More than that, i cannot say.

[VR-Sixy 0]

Hi again.

 

Well, still have the misbehaving problem at lower revs - similar to the problem in this thread

 

http://the-corrado.net/showthread.php?53088-VR6-misfiring-rough-running-till-warm..

 

but not quite so extreme. It's fine up at 60/70mph but there is a definite flat spot when poodling around between 1/2k rpm in 2nd and 3rd.

 

I think the water pressure problem has been resolved with a new hose (probably the last original one to be replaced) and a new thermostat, which just leaves this little flat spot problem. The coil pack was replaced in November 2010and was fine until i had the misfire problem resulting in the tensioners/timing chain replacement in February 2011. It's not really been right since these two items have been replaced. Also have new plugs and HT leads as well.

 

Could the coil pack be on the fritz or intermittent already?

 

Any further input would be greatly appreciated. Just a thought, does anyone know of a Corrado specialist in Surrey (i'm in Walton On Thames) who i could pop it over to as i think my usual garage might have missed something.

 

Cheers Guys

[fleety 10]

1995 corrado vr6. At times sitting in traffic ect the idle appears to be fine then at times the engine without warning would cut off. When driving today she stalled couple of times so I tried keeping the reves up but power came in and out, then had a slight miss fire, in come the power with wheel spin in middle of town. Where do I start to source problem?

[Roger Chatfield 0]

VAGCOM, get it scanned and see what pops up, if you are in the Devon Cornwall area I'll happily scan it for you.

 

Rog.

[fleety 10]

Co Armagh northern Ireland, cheers for reply tho.