850 feels like it it's missing

Post by **Sveedy** » 18 May 2025, 14:39

My guess is that my 850 got jealous over all of the time that I've been spending with the V70.

Driving just fine on the highway, and I notice a sudden lack of power. I don't think the turbo was kicking in either. At the off ramp idle was rough. Just felt like it wasn't firing on all 5. Sounds like it has a performance cam the way it lopes.
Got home and checked all hoses, pulled the plugs ( they looked fine ), and checked and cleaned the cap/rotor ( it has apx 50k on it so due to be replaced ). No difference. Unplugged the MAF - no difference. I thought cam position sensor, but it only has apx 30k on it.

Any thoughts ? I'm thinking of doing a compression test tomorrow, but nothing sounds off internally, and the engine only has apx 30k on it.
Additionally, this happened over 15 miles from home, so I was able to see if there was any difference in its vitals. There were none.
Temperature stayed nice and cool. Mpg was as always. AFR was also normal.

Post by **Sveedy** » 18 May 2025, 15:33

Pulled each plug wire one at a time to see if it was any one cylinder. Still no difference whether 4 or 5 plugged in.

Post by **BlackBart** » 18 May 2025, 16:15

I just went outside to check, and mine is missing too!

Did the red chairs take them?

454cid · Post by **454cid** » 18 May 2025, 19:02

Scan for codes? Look at fuel trims?

Post by **Sveedy** » 18 May 2025, 20:01

I scanned for codes and had none.
I'm planning on doing a real time download with my laptop tomorrow, so that should cover the basics. My first thought was a hose, but nothing I can see is bad. Might be time to buy a evap smoke machine.

Post by **abscate** » 18 May 2025, 20:15

Sveedy wrote: ↑18 May 2025, 15:33 Pulled each plug wire one at a time to see if it was any one cylinder. Still no difference whether 4 or 5 plugged in.

Do two cylinders aren’t firing ??

Post by **Sveedy** » 21 May 2025, 16:10

I'm going out on a limb here and guessing it's missing because it's got 0 compression on cylinder #2. FML.

I can't believe the timing ( bad pun ). The day after I finish putting the head etc back on the V70, I'm pulling the head etc off the 850.
The only good thing is that the 850 is a bit easier to do this on, and I won't have to buy anything more than some gaskets. But still....
Oh well. Got to keep that stoic attitude

. I should be back on it this weekend, so we can see exactly how big a hole I blew in the valve.

Post by **abscate** » 21 May 2025, 20:23

Well there is one thing worse. Three weeks after finishing a head job my 1999 Shagg took out a Tesla on the road and left me with a scrap engine

fredt2 · Post by **fredt2** » 28 May 2025, 17:06

Well, mine had the same issue, i wrongly diagnosed it as a burn valve, but it actually was the head gasket blown between #3 and #4, so if you're getting no difference unplugging 2 cylinders, i bet my dimes on the head gasket

Post by **Sveedy** » 30 May 2025, 14:38

Took a week off from head work. Don't want to have too much of a good thing

This is pretty much what I expected ( a hole in #2 cyl exhaust valve ), but I am wondering about the amount of carbon or burnt oil present.
It seems excessive for only 30k on the rebuild. So I'm going out on a limb, again, and guessing that it was caused by bad valve stem seals.
When I dropped the engine off at the machine shop, I also gave them a engine gasket set, which came with the aftermarket valve stem seals. I went back a week or so later to give them the blue box seals when I got them, but I didn't think to ask for the ones that came in the set back. So there was a 50-50 chance that the wrong seals were installed. Guess I'll never know.

So it looks like two new exhaust valves will need to be sourced. With some aftermarket seals of course