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Old 05-11-2010, 03:03 PM   #1 (permalink)
FuzzyD
Pro Driver, Will Attempt
 
Join Date: Apr 2010
Location: halifax
Posts: 9

Brick Samson (sweedish murder machine) - '87 Volvo 244 DL
90 day: 24.38 mpg (US)

Brick Second - '87 Volvo 244 DL
90 day: 25.68 mpg (US)
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Air intake on a volvo 240 (big lesson learned)

Well, when I first got the car I removed the factory airbox, and the manifold warm air intake pipe was missing, but the stove was on the manifold.

Put a "ricer" performance filter right onto the MAF sensor, short, simple, much less stuff under the hood, $5 more than a stock filter that was honestly plugged solid. Weight reduction and simplicity!

The wiring harness is getting bad and needs work, so I was blaming my runnability issues on that. Engine would randomly get bad fuel economy, from 20 city to 14 mpg city.... in a blink of a eye, and after a few months, started noticing that premium gas reduced the issue, and it was WAY WORSE in the rain.

Symptoms included, increased idle, (with the automatic in gear, it would fight to increase the idle from the load, and be having to hold the brake harder. Would unplug the idle control valve and use the thumb screw to hit a "driveable" balance to save that problem some. On damp days it was dumping so much fuel in the engine I could see black smoke in my rear view mirror, much to the displeasure of cars behind me.

Read up on HOW most of the ECU works in a Bosh LH-Jetronic fuel system, and learned that the MAF (mass air flow sensor) uses a "hot wire" module, so blowing colder, more turbulant intake air across it is bad mojo. Further checking and testing the factory airbox, the valve for bringing air in from the exhaust stove would try to maintain approx 40-50 degrees celcius, not just for startup.

In the MAF, the hot wire actually will glow red, and the air being pulled across it changes its temperature and resistance, sending a signal back to the computer indicating the MASS of air, accounting for density too, so when a puddle splashed my fancy looking air filter, it would WET DOWN the MAF and make it think a cold hurricane is blowing into the intake, and the computer would DUMP FUEL accordingly, also explaining the high idle that it couldnt work out, as the MAF was giving one reading and the O2 sensor was saying the opposite.

Put back in the factory airbox with it ONLY pulling air through the exhaust stove, giving it a nice warm flow at all times, and right away, it idles perfect. no confused ECU for 15-60 seconds on startup either.

Cant wait to see what new heights I get on my next tank of gas. will forgo my last two partial tanks in my log, because I know its well below average due to serious malfunction in heavy rain. Going to fill it tonight and should have a new city reading after 2-3 days of urban pizza delivery, and see just now much my other little mods (including timing advance, electric fan etc) have really helped.

So if you have a "HOT WIRE" style MAF sensor in your car, Warm air intake is your friend! Also, clean the MAF every few months, dirty one is less accurate as well

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