no compression 96 850 NA

[rspi]

This is how the common occurrence on the 850/x70 relates to that list: The oil dripping on the back of the exhaust valve burns and causes carbon buildup.

Is there a sign that you have bad valve seals? I have seen several 960 motors with burnt valves. Do you think the injector cleaner will help? It is said to clean the valves as well as the injectors.

[erikv11]

Yes, there is a tell-tale sign, starts with certain puffs of blue smoke.

(1) Puff of blue smoke at startup (because oil leaked down through the seals after the car was shut off)
(2) and then as it gets worse, smoke upon throttle after prolonged idling, like when you take off from a stop light (same thing, oil leaks down, then burns).
(3) Past that point, in the cylinder(s) with the leaky valve stems, the spark plug(s) accumulate chunky black deposits, if the engine makes it that far then a burned valve is close behind.

I would (do!) speculate that most 850s that are at or past 180k miles, have at least that puff of blue smoke at startup.

I don't really know if injector cleaner would help but I kind of doubt it, only because the problem is the seals get hard and non-pliable, so lose their sealing capabilities. Like any high-mileage seal. If you pull the valve stem seals out of a well-used 850 head it is clear, they are rock hard. The injector cleaner I would guess can work on the face of the valve (towards the combustion chamber) but I don't know, maybe it can also help on the backside.

[waynej]

Yes it has been acting like bad valve seals just recently.
Injector cleaner in the fuel will not help the carbon on the exhaust valves.
Here's the trick for removing carbon.
You need to be sure the car is parked on the level and put a hose and funnel on the largest port on the vacuum tree. Have someone start the car and you pour about 40% of a can of Sea Foam onto the funnel and quickly turn off the engine. Wait 20 minutes for the Sea Foam to dissolve the carbon.
There is an art to this, if you pour too slowly all the Sea Foam will be burned in the cylinders and not get to the exhaust valves. If you pour too fast of if the car is not level, you can get a hydraulic lock in one cylinder and do great damage.
After the 20 minutes start the car and hold RPM at about 2000. You will fill the neighborhood with white smoke as the carbon is burned off.

[byeboy]

Wayne, my 97 850R got badly crippled when I decided (like a teenager) to "show that guy tailgating me", and pulled away from a stop sign Full Bore, and wound it up just a little, like to 70 MPH,,,next stop sign (3 miles later) I get a CEL, and the engine is really chuffin' hard...I head mostly downhill to the small town I was heading to, and the car gradually get to running better, but still with a noticeable miss.

In my mind, i convince myself it is all a one cylinder ignition miss, and go about replacing first the plugs, then the wires, then the distributor cap and rotor...all told over $150.00 wasted on crappy O'Reilly's and NAPA stuff (weekend, out in the country)...

Then I did a compression test, and got mild, but decent , except #2, which was a roaring 10. Puled the head, burnt exhaust valve, sent to machine shop for valve job (only needed that one), seals, cleaning, pressure test, and surface planing. ($225.00). I bought the Fel Pro gasket set from Rock Auto, and the Headbolts (you need new ones) from FCP Groton (I think??). the job really wasn't bad, because the forum guys were right there with me all the way. A camshaft holding tool is invaluable when doing this or a belt change (which you might as well consider now, as well as Water Pump).
My car runs fine (176,000 miles), and I saved $1,500.00 in labor by doing it myself...plus I believe I bonded with the car a bit y'know!!?