KV6 misfire & cutting out.

Robbybb · 22nd July 2015, 18:33

My previous post was a week or so ago regarding a random misfire and associated annoyances.
After replacing a suspect coil pack, fitting new plugs and having a long run, my local garage has identified a leaking exhaust valve and estimated at least £1k to fix it.....

It's not a job I would attempt myself so is there anyone within a reasonable distance of Dorset who might want to have a go? I have seen a guy on here who says he can do a V6 head gasket replacement for under £500 but can't find him now but i'll keep looking.

Has anyone any ideas or can point me in the right direction?

Thanks

Rob.

SD1too · 22nd July 2015, 19:02

Quote:

Originally Posted by Robbybb

... my local garage has identified a leaking exhaust valve and estimated at least £1k to fix it.....

Rob; I would thank them for their diagnosis and file it, then continue the search for the cause of the misfire.

Do you have a lot of oil ingress into your throttle body and inlet manifold chamber?

Simon

murphyv310 · 22nd July 2015, 19:04

Do a compression check in the first instance to either confirm or dispel that diagnosis.

Robbybb · 22nd July 2015, 19:25

Thanks guys.

The garage have done a compression test and Cyl 6 came up with about 40psi against around 160 on the others. Other symptoms being sooty tailpipes, 24mpg, occasional pops and crackles on the over-run, lumpy running at low revs but a surprising amount of smooth power over about 1500rpm.

Do you reckon this bears out their diagnosis? I used to decoke my 1275GT on a Sunday morning in the 70's and be driving it in the afternoon but today's cars are beyond me...

SD1too · 22nd July 2015, 20:09

As Trevor says, do your own compression check (as £1,000 is at stake). Cylinder no. 6 will be fun.

Simon

Phil-T4 · 22nd July 2015, 20:20

If it's an exhaust valve leaking then a leak down test will pick it up easily.

murphyv310 · 22nd July 2015, 20:27

If number 6 is down as you say and there is popping in the exhaust I'd be inclined to agree with the diagnosis. One other thing is the possibility of a stuck hydraulic lifter keeping the valve open slightly. Snag is that seat and valve burning will have occurred so the head needs to come off I'm afraid.

Your symptoms are classic of a burned exhaust valve. Been there a good few times over the years with mine and friends cars.

Salad-Dodger · 22nd July 2015, 20:30

Do that compression test. If number six is low, give it some oil and re test it. If it goes up, its rings. If it stays about the same, its probably a valve. Steve

22nd July 2015, 18:33	#1
Robbybb Regular poster MG ZTT+ Join Date: Apr 2013 Location: Isle of Wight Posts: 37 Thanks: 12 Thanked 0 Times in 0 Posts	KV6 misfire & cutting out. My previous post was a week or so ago regarding a random misfire and associated annoyances. After replacing a suspect coil pack, fitting new plugs and having a long run, my local garage has identified a leaking exhaust valve and estimated at least £1k to fix it..... It's not a job I would attempt myself so is there anyone within a reasonable distance of Dorset who might want to have a go? I have seen a guy on here who says he can do a V6 head gasket replacement for under £500 but can't find him now but i'll keep looking. Has anyone any ideas or can point me in the right direction? Thanks Rob.

22nd July 2015, 19:04	#3
murphyv310 This is my second home Hyundai i10 998cc Join Date: Mar 2012 Location: Kilmarnock Posts: 6,602 Thanks: 2,088 Thanked 2,298 Times in 1,349 Posts	Do a compression check in the first instance to either confirm or dispel that diagnosis. __________________ Cheers from Trevor MM0KJJ

22nd July 2015, 20:09	#5
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,624 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	As Trevor says, do your own compression check (as £1,000 is at stake). Cylinder no. 6 will be fun. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

22nd July 2015, 20:27	#7
murphyv310 This is my second home Hyundai i10 998cc Join Date: Mar 2012 Location: Kilmarnock Posts: 6,602 Thanks: 2,088 Thanked 2,298 Times in 1,349 Posts	If number 6 is down as you say and there is popping in the exhaust I'd be inclined to agree with the diagnosis. One other thing is the possibility of a stuck hydraulic lifter keeping the valve open slightly. Snag is that seat and valve burning will have occurred so the head needs to come off I'm afraid. Your symptoms are classic of a burned exhaust valve. Been there a good few times over the years with mine and friends cars. __________________ Cheers from Trevor MM0KJJ Last edited by murphyv310; 22nd July 2015 at 20:30..

22nd July 2015, 19:25	#4
Robbybb Regular poster MG ZTT+ Join Date: Apr 2013 Location: Isle of Wight Posts: 37 Thanks: 12 Thanked 0 Times in 0 Posts	Thanks guys. The garage have done a compression test and Cyl 6 came up with about 40psi against around 160 on the others. Other symptoms being sooty tailpipes, 24mpg, occasional pops and crackles on the over-run, lumpy running at low revs but a surprising amount of smooth power over about 1500rpm. Do you reckon this bears out their diagnosis? I used to decoke my 1275GT on a Sunday morning in the 70's and be driving it in the afternoon but today's cars are beyond me...

22nd July 2015, 20:20	#6
Phil-T4 I really should get out more....... MG ZT-T, Rover 75 Tourer Join Date: Mar 2011 Location: Olney Posts: 2,969 Thanks: 245 Thanked 1,088 Times in 657 Posts	If it's an exhaust valve leaking then a leak down test will pick it up easily.

22nd July 2015, 20:30	#8
Salad-Dodger Gets stuck in MG ZT-T 190 Join Date: Feb 2015 Location: Chatham Posts: 592 Thanks: 34 Thanked 66 Times in 62 Posts	Do that compression test. If number six is low, give it some oil and re test it. If it goes up, its rings. If it stays about the same, its probably a valve. Steve