1998 V70 CO coming in through air vents

[SonicAdventure]

Hello,

When I start my car, there is usually a short blast of exhaust-like odor from the dash vents. It goes away in 20-30 seconds or so, and doesn't usually come back again until the car is shut down and restarted.

Using my Fieldpiece CO sensor, I tried starting the car with the sensor close to the vents. It registers between 10-20 PPM of CO for a few seconds then it dissipates to nothing. If I drive with the windows completely up and the vents blowing, the CO PPM drops to 0 within a minute or so.

It seems to be a higher concentration if the fresh air wheel is turned towards the ceiling; slightly less concentration if it's turned towards the floor.

Since the PPMs drop to 0 even with all the windows shut, I feel the car is safe to drive, but I'm trying to figure out why I'm getting this burst of exhaust through the airvents when the car is started. If the PPM went up and stayed up as I drove with the windows up, I would figure there must be some hole in the exhaust or a bad exhaust manifold gasket. But, the fact that it 0's out consistently after starting makes me think it has something to do with start-up, and I can't figure out what.

Any ideas? Then sensor I am testing with is a Fieldpiece SMC3 its a good meter not a Harbour Freight special

[Ozark Lee]

Fieldpiece is indeed the real deal, I have a couple of their tools in my HVAC kit. Their digital wet bulb thermometer is aces.

The source would logically be an exhaust leak, in fact that is about all it could be, but the behavior is strange since it quits after the car runs for 30 seconds. Does it sound like you have an exhaust leak?

I suppose some slightly loose nuts on the exhaust manifold could leak but then it seals itself back up after the manifold gets hot but you should be able to hear that.

...Lee

[oragex]

I also smell exhaust gases after a cold start-up, for a few moments - less than a minute. I know it's my flexible exhaust section that has a leak, but as the pipe heats up it expands and closes the gap. This can go up near the bottom of the windshield where the cabin fan is sucking the outside air in. You may have a leaking exhaust manifold gasket that expands and seals as the temperature rises. May worth a check with a mirror to see if it gets fogged.

[kahl]

another way to check exhaust amid old and pipes is to take a piece of tissue tapes to a coat hanger. Any place where there is a leak the tissue will flutter.

[abscate]

It might be worth checking all of your exhaust manifold and gaskets for holes leaks etc. if you have EGR that's another place to look.

There are a number of reagents that will give false positives with CO electrodes, coolants. cleaning agents, etc.

A brief exposure to 20ppm CO isn't worrisome, but I would get rid of it as I doubt this will get better if its real.

[jreed]

I realize you're sensing exhaust gas and not fuel, so this may not be of use to you, but on my '97 855 I used to get a strong smell of fuel at start-up inside the car. I tracked it down to a split in the PCV vacuum line that connects to the intake manifold on the passenger's side near the power steering pump. That might be a good place to check for a leak or damage if you haven't already checked it. Other places to check would be the rest of the lines and connections in the PCV system to see if blow by or unburned fuel + exhaust is escaping somewhere. I would also check the oil fill gasket on top of the engine to see if it is present and supple. Once I replaced the PCV elbow that had split, the smell was gone and hasn't come back.

[RussB]

Run some Seafoam directly. Into the intake. You'll see where the leak is when the smoke comes billowing out. It worked for me.