Friday, August 28, 2015

Mechanic's corner

The Rolling Steel Tent has a little over 170,000 miles on it and it's mechanically sound. But the past few week the performance and gas milage have dropped off. It doesn't accelerate like it used to and I have to downshift for even moderate hills. It felt like it was running out of breath.

Running out of breath...


Essential part of the combustion process...


I knew the air filter was good because I'd had it had replaced at the last oil change. When I popped the hood and started poking around the intake system, I saw the problem.

This is part of the intake system of a 2007 Chevy Express van. Air comes in through the mail slot, to the filter inside that drum shaped thing, through the mass air flow sensor (henceforth, MAF), then down a snorkel to the throttle body (way back where it's hard to reach). The setup of other vehicles will look different, but it's the same principle: Air through the filter, into the MAF and onward to the engine.

The air filter is a cylinder, closed at one end and open at the other.  To service it, you pop off the dome on the end of the housing. Putting the filter back in can be a bit of a wrestling match. The open end squeezes over the end of the mass air flow sensor, which sticks into the end of the filter housing.

The "trained service technician" who replaced the filter last time managed to shove the MAF out of the filter housing. Because somewhere along the line, someone had removed the bolts that attach the MAF to the housing. This created a gap between the two. Air—and junk—was bypassing the filter. Not good.

Here are the air filter housing and MAF removed from the Rolling Steel Tent

Here's a view down the filter housing with the filter removed. Besides the bugs, seeds and bits of vegetable matter trapped in the MAF's screen, plain old dust and dirt had clogged the MAF's sensors.

The MAF measures the amount of incoming air so that the engine computer can tell how much gasoline the fuel injectors should supply for a proper mixture. The MAF can't do its job right when it's dirty. Symptoms of a dirty MAF include sluggish power and lower fuel milage—my symptoms.

So I blasted the inside of the MAF with MAF cleaner. Don't use carb cleaner or any other fluid. They can destroy the MAF.

With everything (except the bolts) back in place, you can see how the MAF is supposed to snug up against the housing. Until I can get the correct size bolts, the squeeze fit of the filter should hold it in place, like it had before the knucklehead got his hands on it.

So, you might want to double-check that your air filter is properly positioned. And it's a good thing to clean the MAF once in a while, like annually. After all, you'll have all that left over cleaner to use up.

Oh, and if a mechanic tells you he needs to replace your MAF instead of just cleaning it, it's because the profit on a new MAF is greater. Ask if he has actually tested the MAF.


  1. Sure glad you knew what to do; I wouldn't have a clue. Hope you are able to get the right bolts soon.

  2. In case anyone needs to know, the bolts were metric—M6. GM uses a mixture of metric and SAE fasteners, because America.