Disconnect MAF Can I force aLean burn

[SmellyCat]

My Volvo runs better with the MAF disconnected. Its probably bad.

The air intake is angled so that the incoming air is not forced into it. I'm thinking that if I add a scoop to the air intake ,I can force more air into the engine and get a lean burn since the MAF is not metering the air and the engine computer is running in limp home mode. Any logic in this? SC

[slownugly]

Usually a limo mode adds more fuel to be safe. I wouldnt mess with it. You will never achieve a true lean burn mode by doing this.

[HydroJim]

in lean burn you want to cut fuel not add air. You might be able to achieve lean burn with your method (I doubt it) but you wouldn't increase your MPG because the fuel amount would be the same.

or as slownugly say, your MPG would probably go down due to the car running in open loop.

[SmellyCat]

I am still messing around with this

When the car is in open loop (Limp home mode) is the o2 sensor still working?

What if I make the EGR stay on? that is like Lean burn , right? SC

[slownugly]

You would have to have a scan tool hooked up to answer the o2 question. Not all vehicle parameters are written the same.

If you make the egr stay on it will run like garbage at idle. Again most manufacturer parameters are different but egr generally only activates a. When revved up at idle b. when you are down the road at a constant speed and throttle position or c. When you are decelerating after a cruise or high load condition. It will not be a lean burn mode.

Only way to make a true lean burn condition is to custom tune the ecu so it runs high afrs

[modproductions]

Any modification will be counter by the ECM and the air-fuel sensor on the exaust manifold

If you lean it out, the ECU will bring the Air/fuel ratio up.

If you want to lean your engine, either you reflash your ECM/ECU or you mess with the Air/Fuel sensor.

It's my suggestion.

[Occasionally6]

If you take the likely forward velocity range of the car as the air flow velocity into a ram air intake, and convert that to a static pressure, there's not a very big increase in air pressure available.

To alter the air:fuel ratio while running n-alpha (rpm vs throttle position) you want to change the relationship between the throttle position sensor voltage/resistance and the true throttle position. One way to do that might be to add some resistance in parallel or series with the TPS.

In most cases the TPS signal on each engine start is learned by the ECU as the idle value, but if it is outside the expected range there will be a fault code set. Not sure how to work around that and still get the change. Maybe an op-amp circuit? You could map it using an Arduino; true TPS V in, emulated TPS V out. It will probably do some strange things with rapid changes in throttle position too.

The O2 sensor is ignored if the TPS is being used in place of the MAF with a fault code set. The air:fuel mixtures do indeed default to rich as a safety measure.

If you find Autospeed, there are articles there on amplifying an EGR valve position signal so as to increase the quantity of EGR. That may be of value for doing that but also might be used similarly as a method of altering the TPS signal.

It's really easy to monitor O2 sensor voltage with a digital multimeter (volt meter). That will tell you if you're running in open loop. Not so good for tuning though.

Altering the TPS signal will also affect ignition timing.

At low engine speed there is a throttle position beyond which opening the throttle further doesn't increase airflow into the engine. You might want to consider that if altering the TPS signal.

[HydroJim]

If you're looking to run lean burn, you need an EFIE.

EFIE is a dirty way to make a simple ECU run in lean burn mode. I don't recommend it. In fact, I recommend not even trying to mess with your ECU unless you do a lot of research first. Best thing would be a megasquirt ECU set-up but that takes a lot of time and dedication.

I know all about this so if you want more info let me know.

Open loop will never get you good MPG. it's the mode used to keep your car running when sensors fail.

[SmellyCat]

Great info, This is a 94 Volvo. so it is pre mega squirt technology, Just has the count blinky light box. the TPS does one thing and that is tell the engine its time to idle.

My kid's car had 12 quarts of oil in it and I had to trade him out the volvo for the over oiled saab. Seems the saab had too much oil , which triggered the oil light so he poured another 5 qrts in. Right now the valves are super rattling, lifters? other than that the Saab seems ok.

.
This has put my VOlvo playing on hold for a day or two..SC

[Occasionally6]

Are you sure the only thing it does is indicate idle? With the MAF disconnected there has to be some other way of determining the fueling, either MAP and rpm or TPS and rpm. With a MAF, it's unlikely to be the MAP.

There are systems that do have a TP switch (or switches) but they won't run without the MAF.