A bit counterintuitive.... when the HVAC setting is for air to be drawn in from the exterior, all is good. But, if I click the recirculate button, I get what must be exhaust gas coming in.

It's odorless, but I would get sleepy, and my wife with the bloodhound nose would bark out the alert... so I bought a Carbon Monoxide measuring device, and I'll be darned, the moment the recirculate button is activated, the CO starts rising until the device sounds the alarm.

So, I can't see any place it could be entering, nor any exhaust escaping. I tried with a flashlight to see if there are holes in the firewall, and I tried clogging the exhaust temporarily to see if I could spot the leak at the manifold gasket - nope.

Any advice would be appreciate, thanks.

BTW, heater doesn't work and isn't required.

 

If enough exhaust was entering to excite the detector immediately after pressing recalculate you would smell it too. And the only way to get this to happen would be with an exhaust leak, so clearly you must have one. The exhaust manifolds are a bit of a known leak point so are you certain they are not? When I looked at mine I found several of the rearward bolts were loose. The EGR interface can also loosen up which is at the back driver side area of the engine. The thing is with recirculate on there is not a lot of cabin vacuum so its odd fumes would be pulled in. And normally I would say to check the hood gasket, but again that would be more of a concern with HVAC intake when not on recirculate. I would also recommend you try a second alarm and not a home wall mount unit as those are horribly inaccurate. You need a proper one with a readout.

 

Thanks - I'll check all that you mentioned. EGR is a good one, I hadn't thought of that. Yes, recirculate is supposed to not let air in from outside, which is why I'm so puzzled.

 

I am pretty sure there is some outside air as one needs oxygen to live. I know my BMW was setup for 5% fresh air when on recirculate.

 

....aren't you also the dude who bypassed your heater core recently???

 

And deleted his thermostat

 

Yes, that's me

The exhaust issue pre-dates the heater bypass, so there shouldn't be a connection. Also, I left the firewall hoses alone, and removed the 2 that run alongside the engine. However, since the heater wasn't working since purchase, I guess it's possible that the PO had tried some sort of repair that resulted in a hole in the firewall, but I can't see one. I'll give them another look just in case, thanks.

 

​​​​​​​Well, different story. You know that the thermostat has no connection to exhaust gases, so I'm not sure what you're suggesting, if not recklessness on my part. However, it isn't the case, as I'm very methodical, although occasionally also clueless LOL. It was removed while trying to find the cause of overheating, which it was not - it was the water pump.

​​​​​​

 

Well running no t-stat causes the engine to run cool and results in a higher fuel burn, more obnoxious exhaust. Also it can cause increased carbon build up and thus burn valves.

Anyway... You need to find your exhaust leak before find holes in the cabin.

 

Yes, exactly. And it's got to be pretty much upstream, like you said: manifold should be the main suspect. EGR was a very good suggestion, BTW.

There's no sound that indicates a manifold leak, but maybe EGR... I'll see what I can find.