1997 Volvo 850 - CO2 buildup - pulled over to safety

[xHeart]

yes, check for any cracks in manifold, check all flanges. Was the downpipe w/flex joint changed? joint could be a major candidate, hidden under braided sheath.

The manifold replacement was one piece, from exhaust to cat. I will look at the accordion like joint where it meets cat. Here is more on manif repair https://www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=60494

[jblackburn]

Most cars intentionally leak 10-15% fresh air into the car past the recirculate flap. They are required to do this by some US law.

[kahl]

I think this may work, slightly restrict your exhaust pipe to create back pressure. Shoot some SeaFoam through the intake pipe. SeaFoam will create mucho smoke and with exhaust slightly restricted any exhaust leak will have smoke coming out.

[xHeart]

Starting to undo exhaust manifold.
Prep note: do I use high temp lubricant (same as spark plug one) or thread locker?

[FLXC90]

Does that mean it failed "sea-foam smoke test"? where did you find cracks or leaks?

[xHeart]

...
Shoot some SeaFoam through the intake pipe. SeaFoam will create mucho smoke and with exhaust slightly restricted any exhaust leak will have smoke coming out.

Making it an MLK Day project -- an early morning task.
Is there a step by step for this procedure, kahl.
would it be like seafoam sucked-in at the intake vac tree under the throttle cover -- 1/3 bottle?
would putting a paper cup over the tail pipe opening adequate restriction?

[kahl]

Anyway to get the SeaFoam into the intake manifold. I would just partially block the exhaust, maybe a damp rag. Just enough blockage so exhaust can leak. The spray can SeaFoam comes with that funky "U" shaped pipe.

[FLXC90]

This isn't to clean the valves, so all you have to do is get the seafoam in there. yes siphon into intake at vac tree works well. You won't need much, maybe a few ounces, shut off and let sit, prep your exhaust obstruction, and start back up. Will you have a helper available? just a ignition switch operator would help a lot, since you can't be in two places at once. (in and under car) I guess a remote start if you have it would suffice. And also, you could probably rubber band a damp rag across the tailpipe, it would still run, but add enough backpressure to make leaks evident. This would be a fun video to watch!!

[jimmy57]

If you are getting CO in the vehicle then you have an exhaust leak up front or exhaust leak further back AND a leak in the body. Recirculate being on increases the likelihood of external gases coming in as it reduces cabin pressurization from fresh air inlet in high pressure area from being pushed in through HVAC system and out through the vents in lower rear quarter panels behind bumper.

Air mix is not a direct path to fresh air. Air Mix on 850's is air from evaporator that is sourced either fresh or recirc but is directed through a passage where it can't pass down to go through heater core.
Airflow is: recirc/fresh air housing -> blower motor -> evaporator -> heater core -> air distribution housing -> passenger compartment. The heater ore path can be metered from zero air flow to 100% airflow