By on July 11, 2011


TTAC Commentator Mazder3 writes:

Hey Sajeev,

I have an auto parts question that I’ve been meaning to ask for a while but I keep forgetting about it. Back in February, going to my car after doing some shopping, I spotted a cute college woman acting strangely around her Volvo 850 sedan. She’d walk around it a couple feet then would look underneath it.  I angled myself to take a peek and I saw her problem; there was a large black box being dragged next to the left front wheel. After exchanging pleasantries and a failed attempt to get the hood open (the car was an obvious salvage, the whole front end was visibly skewed to the right), I finally just reached under the car and popped the box out, muddy and snowy parking lot be damned. At the time I thought it was a windshield washer reservoir, as the hose that was holding it on was a similar size and had a similar fitting to a windshield washer line, but when I got home I realized it couldn’t be. There was no way of filling it or checking its level.

So what was it? My memory has faded on it a bit but it was made of jet black plastic, was roughly the size of a 124 count tissue box, had a hose at the top and two fittings at the base, there was a sponge inside of it and the whole thing came down from in front of the driver’s side axle line. It had some major road rash so all of the parts might not have been there. The thing that I really remember, though, that it was branded with the GM “Mark of Excellence”!

Sajeev answers:

No matter who you are, everyone goes out of their way to spend a moment with a pretty face. Insert “dreamy sigh” here. I am not a Volvo-savvy individual, so let’s do a step-by-step analysis of how to solve an automotive mystery.

  1. Find said component using aftermarket (NAPA, AutoZone, etc) vendors’ websites, provided you got a good look at the part. A big plus for those of us working in a cubicle, but OEM Dealership systems are a far smarter way to find it. Those dealer parts guys often find the part just by pinpointing it’s location on the vehicle.
  2. Hit up the forums for that make or model.  They failed me, as I used the wrong search terms. The next step is to post a “Sorry for being a n00b, but I have a stupid question” with as much modesty and humility as possible.

Running out of time before my deadline for publishing, I cheated: an internal discussion with TTAC’s Volvo guru and all around righteous dude Mr. Alex Dykes.  Our man is said, “it’s probably the evaporative emissions canister or a part of the vacuum pump system.”

Is he right?  I’m betting on him, and I think it’s the charcoal canister in the EVAP system, as this wicked video shows far better than I can explain. Plus, the location sounds right: they are bulky and better off destroyed in a frontal collision compared to something like an ABS metering block. More to the point, parts with the GM Mark of Excellence will be cheap to certify with the EPA, and cheap to replace in said frontal collision. Because, at the end of the day, automotive real estate is just as precious as a corner lot in Manhattan.

Best and Brightest: your collective knowledge will prove me right or wrong…right?

Bonus!  A Piston Slap Nugget of Wisdom:

Did I just say automotive real estate is precious?  In this age of minuscule overhangs and excessive (but necessary) accessories for our environment, our well being and our need for ever more perfect automotive transports…no really, I have a point here…we need more space for all this stuff.  Maybe one day we’ll give our automotive technicians, shadetree wrenchers and our insurance premiums a little more “room” for error, but for now, deal with the stubby noses and the blocky faces that come with our current crop of front clips.

Repeat after me: not everything needs the snout of a BMW, a little overhang is actually good thing.

Send your queries to [email protected]. Spare no details and ask for a speedy resolution if you’re in a hurry.

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19 Comments on “Piston Slap: Solving the Black Box Mystery...”

  • avatar

    If you say “automotive real estate is precious”, you must not have checked under the hood of an 850 recently. I think that model would be prime for a v8 conversion with the acreage up front — and not much difference in price than for the older volvox these days. Lots of high-miles 850s that spew oil are out there…

  • avatar

    Sounds like some kinda EVAP canister to me…

  • avatar
    bumpy ii

    Evap canister is the most likely answer, though I’ll venture afield and guess the resonator box for the air intake (if the intake is on that side of the car).

  • avatar

    Why exactly are we doing this? Did Mazder3 get the woman’s phone number, and now he needs to know what the black box is so he has an excuse to call her back? Or is this just to satisfy his curiosity?

  • avatar

    i want to get Jack Baruth’s version of this…

  • avatar

    Yup it sounds like part of the EVAP system. The fact that it has the GM mark of excellence is not surprising and supports that it is part of the emissions system. Since the first real emissions controls were introduced GM’s Rochester Products division has led the way in the production of those parts. Carbon Cannisters, which at the time comprised the entirety of the EVAP system was one of their biggest sellers. However virtually all Malaise era US born and many Euro vehicles hit the road with at least some RP emissions controls, as they were the leaders in TVS valves (temp vacuum sw), EGR valves, Air pumps and related air injection hardware.

  • avatar

    I didn’t notice a car in that photo……..

  • avatar

    Sir, the FBI will be knocking on your door soon for their GPS Tracker. Just leave it on your front porch and shut the door. If you didn’t take it …. huhhh …Thank You.

  • avatar

    The old black box under the Volvo trick. That’s the second time I feel for that this week…

  • avatar

    Hey Sajeev,

    Thank you for running this! Before writing you, I went through some online schematics but didn’t see the evap canister. I’ll look harder next time. Oh, and the girl looked sorta like the brunette on the left only with fair skin and Bs.

  • avatar

    I don’t understand something. When Volvo was building the 850, wasn’t GM sticking their Mark of Excellence to a different Swedish model (not the one on the right above)?

    Just curious.

  • avatar

    front driver’s side, black plastic box? Almost definitely the charcoal canister for the evap system. My family has owned ~6 of these cars and I am 99% sure that’s what it is. I’ve never had one out of the car so I don’t know if they tend to have GM labels or not. Volvo did use a lot of GM’s supplier’s parts in those days.

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