Exhaust Valve and other repair question

MagnificentSin · Post by **MagnificentSin** » 10 Oct 2021, 17:38

Hey all,
I recently discovered that my car has a misfire on Cyl #4 (yay) and have been trying to diagnose the issue, so far I've checked just the plug (plug looks perfectly fine), and assuming from the strong gas smell I think gas is getting through the injector. After a lot of internet searching and I found the exhaust valves seem to be a weak point in these cars so for now I am assuming the worst and assuming that will be my issue.
Now my question is about what other things should be replaced if I get that done? I'm looking to have it done at a shop, normally I would do that but I am away from home for college so pulling the head with my harbor freight socket set probably wont be in my best interest. Like I said it's not confirmed to be the valve, I would just rather assume the worst so I don't go expecting a bad plug and have them quote me $2k for a head job. I'm just curious what you guys would recommend also requesting to get done while they have everything apart. I'm thinking at least the timing belt as it was repaired almost 60k ago according to the sticker in the engine bay.
Thanks in advance, Nate

Post by **abscate** » 10 Oct 2021, 17:50

Nate, take some time to figure out what’s wrong with your car.

You can’t inspect plugs by looking at them. Move two plugs and two coils,in two different tests, and see if your misfire moves

A compression test on four will tell you if the valves are faulty

Post by **erikv11** » 10 Oct 2021, 17:59

What abscate said, with a few caveats:

- switch plugs between cylinders yes, however you don't need to switch coils since your 850 does not have coil packs
- you're probably right about the diagnosis, however
- if you have head work done, it is worth replacing the valve stem seals. Only use Volvo seals for this, perhaps you can buy them (about $80 for the set) and provide them to the shop.
- you can drive it a very long time on 4 cylinders, like even for a year if you want to, just make sure to unplug the electrical lead to the #4 injector
- are you in the twin cities area? You could send a PM to user SuperHerman and ask for a shop recommendation.

MagnificentSin · Post by **MagnificentSin** » 11 Oct 2021, 02:02

thanks, like I said not completely done with diagnosing so ill try those, and ill send him a message I'm about 40 minutes from the twin cities actually

Post by **misha** » 11 Oct 2021, 13:32

Bad cap,rotor and spark plug wires can give you misfires.

Are they still original?

MagnificentSin · Post by **MagnificentSin** » 11 Oct 2021, 13:53

The wires are Volvo branded, not sure about the cap and rotor, although new issue seems to be here, I unplugged the #4 injector lead (4th from the left right?) and that cylinder was definitely firing before the car stuttered like crazy when I did that, could I have a false misfire code or something like that?

Post by **erikv11** » 11 Oct 2021, 14:21

That's good news, try each injector one at a time.

Yes, it is common for the misfire codes to call the wrong cylinder.

MagnificentSin · Post by **MagnificentSin** » 11 Oct 2021, 14:39

what do you mean try each injector? just unplug and start the car until I don't feel a difference to figure out which cylinder its actually on?

Post by **misha** » 11 Oct 2021, 15:50

MagnificentSin wrote: ↑11 Oct 2021, 13:53 The wires are Volvo branded,

Ok...Volvo branded...but how old they are?
Probably still original.

Remove the spark plug cable from #4 cyl and inspect boot and sleeve for tiny hairline crack(s).

In fact...remove all of them,one at a time and closely inspect them for cracks.

MagnificentSin · Post by **MagnificentSin** » 11 Oct 2021, 17:38

i believe the owner before the last had replaced the cap and wires, although can't really believe that too much, they're all in great shape and look pretty new, I didn't see any cracks when I looked just now though, tomorrow I'll play around with different injectors and see if i can figure out exactly which one is misfiring for sure