Volvo 850 misfiring #2 cylinder

[precopster]

What jblackburn is trying to tell you is that a GOOD REV over 2,500 rpm and using Seafoam MAY FIX IT.

[jblackburn]

They don't like being driven consistently at low RPM - it's actually bad for most OHC engines to do that. The valves need to get going and spin every now and then, and that happens over 3200 RPM on these motors.

If no luck there, then you will probably have to resort to yanking the head. A lot of people around here have had to do that, and hopefully one of them can point you in the right direction of any write-ups, etc they used.

[erikv11]

That is amazing bad luck, burning a valve on the way home after buying a car. But I don't see any way it could have been already burned but hidden by the seller.

I can think of two ways to confirm a burnt valve: (1) pull the head and look at the valves yourself (2) get a boroscope into the exhaust manifold to get a visual that way. (1) will be pricey at home and (2) will be costly at a shop. Oh if you want to know if it is an exhaust valve or an intake valve, do a leakdown test.

Something similar to this happened to my 850, it wasn't a burnt valve it was a broken valve spring. In that case I was able to see the broken spring by just removing the cam cover. Still, while I didn't need to completely pull the head to diagnose, I did pull it to fix it. But broken valve springs are rare, burnt valves are common.

[iancam33]

Ya Im going to remove the cam shaft/ cover tomorrow, I dont want to take it to a shop so Im doing it at home, Before you removed the cam cover did you look up how to? do you know of any forums that show pictures or step by steps?
thanks

[erikv11]

There is a great head gasket tutorial, use that for pulling the cam cover. There is a copy on this site or the original is located at Volvo 5-cylinder: How to Replace the Head Gasket

It is a fair bit of work even to pull and replace the cam cover, so even though driving around at high revs for five minutes or Seafaom in the intake are not likely to fix it, they are worth a try.

[iancam33]

I used seafoam and it didnt do anything, so i took the cam cover off and the shafts, nothing looks wrong with the valves so far no carbon build up on cylinder number two, so now going to remove the head and go from there not really too sure what im looking for now.

[erikv11]

You are into it for head removal anyway. Even if you could see a valve spring problem (you have to peer into the head and eyeball the springs with a flashlight), the head would likely come off to fix it. Is the top end sludgy or are the metal surfaces shiny and visible? Gives you an idea of how well the engine was maintained (oil changes).

A burned exhaust valve will be easy to spot. Turn over the head, look at the valve surfaces, there will be a little chip or hole burned into one of them. Expect it on the exhaust side.

At this point you will be spending money to get this thing back together, minimum head gasket and head resurfacing, plus misc gaskets. And it really doesn't make sense to put the head back on without replacing the valve stem seals. Buy original Volvo or Victor Reinz (cheaper cost, same quality) brand gaskets only for valve stem seals and HG. Now is the time to do the timing components and cam seals too. Ignition parts are your call. So at this point another $700 or so in parts to do it up right.

It's all in the tutorials but: be very careful with the top surface of the block, on the first head I swapped I screwed it up and had to go back in. The other place it is easy to mess up is removing and reinstalling the cam cover - make sure the cams sit flat and don't get cockeyed, in which case you can crack the little groove in the head thatholds the cam journal.

[iancam33]

the engine is very clean. so if it is a burnt valve would you just have to replace that valve or would you have to replace all of them ?

[iancam33]

UPDATE:
So the head is off and we flipped it over and looked at cylinder two and one of the exhaust valves had a huge hole in it so that was the problem now gonna get a new one and a valve job and replace the gaskets !
thanks everyone!!

[erikv11]

Cool, kind of nice when the problem is right there and can be fixed.

You would be advised to replace the valve stem seals, they are a problem area on these heads when they get old, and are the most likely reason why the valve burned. And like posted above, Victor Reinz brand is highly recommended. The machine shop that does the valve job should recommend new seals, but unless they do Volvos a lot they will probably just buy a generic brand - source your own and bring them in, the reconditioned head will last much much longer. Or buy a Victor Reinz head gasket set, you are going top need several other gaskets anyway.