Engine: TDI: C70 coupe exhaust valve burn out

[andygoldsmth]

Help please. I have a 2.0L 20v LPT turbo C70 coupe with B5204T engine and auto transmission. It is professionally converted to run on LPG (Liquid Propane Gas) - the system is multipoint injection. The car has done about 115,000 miles and has been very well looked after by previous owners. The LPG system was fitted about 50,000miles ago.

My problem is that on two recent occasions an exhaust valve has burnt out

The first was in No2 cylinder - had the head off checked all the other valves and all the seats carefully and no problems found. The valve was quite badly burnt. Replaced the defective valve with a Volvo spare part then lapped all exhaust valves before refitting head. Checked compression before firing up for first time it was bang on on all cylinders and the engine was running sweetly.

About 200 miles later (using 50% time on petrol and 50% on LPG) another valve failed, this time in No3 cylinder. Head off again, just the one valve burnt with less burn damage this time (because I was on to the missfire earlier).

I thought that Volvo 5 cylinder cars dont burn out valves? The spares man certianly expressed suprise that I needed to replace one.

Not really used the car since because I dont understand the problem and taking the head off is doing my back in! Have taken the car to a garage to have the engine management codes read and the mechanic thinks that it could be valve seat recession- he thinks that the valves might not be fully closing on the cam backstroke due to this recession. One of the reasons why he thinks this is happening is that the car is running rich at tick over, with the mixture control device working overtime in an effort to reduce the fuel, yet the system clears itself when the revs are increased and the mixture returns to normal. Otherwise the engine appears to be running fine and there are no standing fault codes other than that associated with high mixture at tick over.

He has asked me to get a second opinion on this but there are no independent Volvo specialists in my area and I dont want to take it to a main dealer just yet - I want to keep the lid on costs!

Has anyone got any ideas? Is there a way of measuring for valve seat recession? Do Volvo 5 cylinder enginers suffer from valve seat recession when run on LPG, particularly if fitted with a turbo? There is some evidence that LPG does cause valve burn out on some engines but all the LPG specialists I have spoken to have not experienced it on a Volvo.

Or am I missing the point and is it something other than the LPG?

Any thoughts on this would be appreciated

[Chris_Rogers]

What year is the car?

What codes were read from the engine management system?

Running rich at idle is not good, does it do this on both petrol and LPG?

Have read of this thread see if it helps:
http://www.volvoforums.org.uk/showth...term+fuel+trim

Independent Volvo specialist near you:

http://www.swautos.co.uk/default.aspx

[r800v6]

Hi,

That was the VERY long thread regarding my car faults LOL
It certainly helped me to learn a bit more about these engines.

Anyway just to clarify for you the fault with the engine not wanting to rev over 3,000 rpm turned out to be a faulty wastegate but more inportantly for you-
The rich running was caused by a sticky injector when the engine was cold, this was causing the engine to run super rich at tickover when cold as the injectors were sticking open when cold, it started not long after I fitted my LPG kit so it seems that the injectors were gummed up but keeping themselves working okay due to the regular fuel passing through them,as soon as I converted to LPG the injectors were only being used when the engine was cold so it seems the gummed up injectors were no longer being cleaned enough by the petrol passing through them so started to gum up and stick open, this sooted up all the plugs and caused loads of smoke at cold tickover and the fuel trims were dropping straight down to -25 on petrol.
I put a full bottle of injector cleaner into half a tank of fuel to give me a stronger concentration of cleaner and then warmed the engine and drove it on petrol giving it plenty of revs to get a good amount of fuel flowing throguh, this instantly solved the problem.
I haven't had any valve problems and am surprised to hear of the problems you are having.
I must say that the help I received was invaluable and without it I would probably still be scratching my head every morning as I watch plumes of grey smoke pouring out of the exhaust and listen to the engine coughing at tickover LOL

Hope this helps,
Paul.

[andygoldsmth]

The car is a 2000 W registration. Cant exactly remember what the fault code message was but it only comes up on tick over when the LPG system is running. Those in the LPG trade that I have spoken to say that Volvo engine menagement systems dont like LPG systems piggy-backed onto them and often throw up fault codes, so the fault light may be a red herring. I managed to make contact with the previous owner (I didn't buy it directly from him) and he said that the car was prone to throwing up fault codes once the LPG was fitted.

I will try the injector cleaner, can't do any harm and may well be the reason why the car is running rich. The car was running richer when on gas than on petrol.

Andy

[adamsky01]

Here I go I run a 940 2 litre on gas and I have had the same problem as u
basically the valves that come as standard on the car are not strong enough to cope with the heat that running on gas causes a lot more heat than running on petrol don’t tell me but I guess u top the water up at least once a week ? . ok to fix this problem u will have to hunt down titanium carbon fiber valves they are special order mind and will set u back £90 each but this will fix the problem big time

hence why ur guy was thinking it was running rich on idle

[r800v6]

Hi Andy,

When I initially fitted my kit I had to get to grips with the new software as I was previously running my other car using the old venturi system.
So at first I did get a fault code after a short while of driving, this was purely because as I was driving the lean/rich LPG setup wasn't tuned precisely so the fuel trims were slowly going off the scale, over time and with a number of motorway crusies and blasts with the laptop plugged in I have now got the LPG 100% in tune with the petrol so now I can watch my fuel trims on LPG and they shift by 3-4 at maximum but always keeping the long term fuel trim at 0 or maybe -2 and upto +2 at most (I have been told by a good friend who does LPG conversions for a living that you should aim to have the long term fuel trims at no more than +10 or -10 and anything within these figures is sometimes quite hard to achieve on LPG)
Since finishing tuning my LPG I do not get a fault code from it at all after thousands of miles, honestly if the LPG is tuned correctly then you shouldn't be getting any codes.
Obviously I do not know your car and I am no expert but I have been fitting kits myself to my cars since 2002, this includes tuning them and I honestly see no reason why with a sequential injection set-up someone cannot tune your car to get it running fine on gas, certainly anyone who knows what they are doing should be able to stop your car from running rich at idle.

Hope this helps,
Paul.

[andygoldsmth]

Paul - Thanks for the tips on setting up the LPG system. I am lacking a laptop at the moment so cannot really do interrogation/experimentation on the LPG set up. I ahevfound an LPG installer who might be able to help me with this but first I have got to get to the bottom of why the exhaust valves are failing.

Adamsky - you are the first person who I have made contact with who has mentioned that there is a problem with exhaust valves. I take it that you have had them fail after fitting up your Volvo with LPG? How many miles before a valve failed? Yours is a different engine but whats the odds on the valves being same material? And did your valve seats suffer any damage?

Strategy for further investigation

Get some injector cleaner and stick it in the fuel tank.

Run car on petrol only and see how many miles I can do without breaking a valve.

Get LPG system trimmed up so that fault codes do not come up regularly.

Think hard about cost benefit of new hardened exhaust valves 10 times £90 plus the cost of removing/replacing the head again!

Anybody got any further ideas?

Andy

[shimon340]

hi there,

how was the problem with the exhaust valves solved in the end? it sounds like the ignition timing was too retarded when on lpg meaning the exhaust valves began to over heat.

interesting that you say it affected one valve at a time, you'd expect all exhuast valves to be affected.

maybe that one cylinder was running excessively lean causing the exhaust valve to overheat?

how were things resolved??