Air intake on a volvo 240 (big lesson learned)

[FuzzyD]

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

[DonR]

You may consider making a shield for the ricer filter and compare the two. This would prevent the splashing you are seeing. Since you have most of the parts to make the comparison already, you would only be out a few bucks and a small amount of time.

Don

[FuzzyD]

Putting 6" of pipe in between the airfilter and MAF would also help it run better than it did with the cone filter on, however my finding was even on days where it had been low humidity and had not rained in days, it still ran like a spastic pre-schooler flailing the fuel mix controls.


Either way, it runs with lots of low end power now, better than it ever has for me, will know in 2 days just what a difference.

[tjts1]

I agree that a cone filter is a useless upgrade on this car but I think you have another problem.
Your 87 240 has LH2.2 engine management which is notorious for problems like this. My guess without touching the car is your AMM is either dirty or damanged. Try this experiment. Turn on the engine and unplug the AMM. If there is no change in the way the engine runs or it smooths out, your AMM is fried. The fact that it runs better between 40-50c intake temp is a sign that something is wrong with the AMM. Also having the intake stuck on the HOT side for a long time (the intake thermostat usually fails after 10 years) will damage the AMM. The thermostatic intake is designed to maintain a MINIMUM 20C intake temperature, not 40-50c. When the intake thermostat fails, it always fails in the HOT only side. Most people simply block off the hot side for improved FE and power.

Originally Posted by FuzzyD

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

From personal experience on half a dozen 80s and early 90s volvos, I think this is a recipe for disaster long term. The system is very aggressive about retarding timing and enriching the mixture as intake temperature goes up. You're not going to trick the system into running lean with hot air. Check your mixture and check your AMM. I think there is a good chance its damaged.
http://www.brickboard.com/FAQ/700-90...ettingBaseIdle

http://www.brickboard.com/FAQ/700-90...AMMCalibration

good luck
Justin

[Thymeclock]

Originally Posted by tjts1

My guess without touching the car is your AMM is either dirty or damanged. Try this experiment. Turn on the engine and unplug the AMM. If there is no change in the way the engine runs or it smooths out, your AMM is fried. The fact that it runs better between 40-50c intake temp is a sign that something is wrong with the AMM.

I looked in the glossary but couldn't find what AMM means.

Please enlighten us.

[tjts1]

Originally Posted by Thymeclock

I looked in the glossary but couldn't find what AMM means.

Please enlighten us.

Air Mass Meter same as Mass Air Flow meter. Its a hot wire intake air sensor.

[FuzzyD]

I had already done tests in the past month or so with the car running with or without it plugged in, it is helping things over all, After this tank of gas Ill pop off my cool intake block, check for further difference.

My understanding was that the fuel system leaned out for higher temperatures, or was this only for the coolant temperature, rather than the intake air sensor? This is good to know.

The first thing I did yesterday (and when I put the cone filter on of the car,*) was to clean the MAF / AMM, Careful of the inside components. Do have a spare one from a 92 240, but its not the adjustable type, so am dubious as to weather or not its compatible. The proper Bosh 02 sensor was replaced two months ago as well.

If the airbox thermostat was supposed to be working at 20 Celsius, minde had definitely failed, as it was operating only at 50! Ill see about getting a replacement thermostat and re-installing the flap, Only removed it, still working.

Thankyou! Any help is appreciated... I can honestly say this is the most mysterious EFI system Ive encountered, as it gives little feedback to the person diagnosing it.

Edit: removing the cool air cap right away, and finding a thermostat.

[Thymeclock]

Originally Posted by tjts1

Air Mass Meter same as Mass Air Flow meter. Its a hot wire intake air sensor.

Ah - MAF becomes AMM... that's alphabet soup.

I remember Campbells: "Mmm, mmm good!" (Decades ago, it encouraged us to learn how to spell.)

Nice photo. It looks like a hair dryer from Star Wars. Apparently such a sophisticated car can't run well without it.

[bgd73]

I mastered a hot air maf, a 93 subaru. singular point injection...(they stayed the same for 9 years- 85-93)

The CAI (went to outsiude air source, real piping- nothing in engine bay) pegged the fuel mileage to 38mpg all year round. I have never had anyhting before or after like it...

the 240 is inline and has no coolant in the intake. This could be the anomoly for you. whatever works.

the subaru also has one long runner, across two heads, also single port. It even roasted in the winter..(all the crazy FI hertz). I went as far as blocking coolant from entering the base of the spfi unit, that is when the 38mpg pegged (reset ecu first)

maybe find a heat rise for external of the engine intake, and continue to get air from outside (wrap it?) as the engine with cool air is gonna be a winner for alot longer with it. hot air is thin, it reduces power, press throttle more, more heat.. the cycle sucks until engine fail prematurely.

be good to those 240 cylinder walls.. cool air in is a part of it.

not to sound confusing... in short, let the heat rise happen last second. find a way for the actual intake on the engine to stay warm, (tere should be a sensor there), and all is good. you described the wild flailing gas metering of an inlines dangling hanging in the willywags intake manifold perfectly.

[tiresmokindad]

Thanks for the information about air intake. I think I learned from the big lesson. I hope that I can fix also my "HOT WIRE" style MAF sensor in my car. I will not do what you did.