While troubleshooting this weeks problem, I disconnected my maf to see if the motor would run better. (it did) My question is, could someone explain to me how the engine runs without it? I'm assuming that the ecm subs in a value? Just curious, you would think that it would not run at all.

 

My guess is that it throws the ecm back into "open loop" and the cars runs on open loop mapping.

 

hmmm, so in open loop theres a set of values that the ecm works off,of? Or does it say, run off of one or two other sensor inputs only, i.e. tps signal.

 

There was a "discussion" on this forum a few years back that just about banned everyone....
Seems this guy pulled off his MAF and claimed he had broken the generals code.
SO the discussion ensued for weeks and the mods had a hay day...

So as a MAF user I'll say this once, if it runs better without the MAF, something is wrong.

 

I unplugged mine once and it ran Sh%$y, then died!

 

With the MAF unplugged the PCM uses speed density mode. Speed Density mode uses input from the MAP (Manifold Absolute Pressure) sensor, rpm, and inlet temp. From there the computer uses a set of pre-programmed VE tables and of course the timing tables.

It's no different than the '90 - '93 (IIRC) cars which are Speed Density (no MAF) from the factory.

 

This is the way you check for a bad MAF, if you unplug it and the car runs better something is wrong with the MAF or one of the Burn off modules.Another check is to tap the MAF with a screw driver or similar item and if the motor stumbles you have a bad/broken filiment inside..In open loop the car runs off a set of perameters set in the ECM , in closed loop (around 150/160 degrees) it switches over to running off the sensors...WW

 

ECM/PCM are programed (chipped on early models without MAP backup) with an extra "limp home" mode that gives the computer backup default data in case of failure. The car will run like crap with the MAF disconnected on earlier models unless it is a newer model that has both a MAP & MAF combined setup.

 

With the MAF unplugged the PCM uses speed density mode. Speed Density mode uses input from the MAP (Manifold Absolute Pressure) sensor, rpm, and inlet temp

so if i unplug my maf, and the car dies i have a problem with map, rpm or inlet temp?
thanks
matt

 

Am I being led to believe that there's a rogue group of l98's out there not using their maf's? Hmmm, I'd like to see that thread. Thanks for all of the input guys.

 

There are also guys that run their cars in "open" loop all the time but they are tuned/programed for that kind of stuff.

 

For the most part, Electronic Fuel Injection uses voltage drop as a means of measuring what's being sent by information sensors. To do so, there has to be a source or potential (full voltage), the drop itself, and then 0 or no volts if the full potential has reached ground. Full voltage and/or a complete ground (no volts) are then used to signal a problem - generally an open or a short. There is nothing diagnostic in between; ie, a voltage drop that signals something other than what it really should be is nothing more than garbage in creating garbage out. A MAF, which essentially has to increase voltage to maintain a constant temperature across a thin strand of wire cooled by the volume of air flowing across it, is a little different, but the garbage in/garbage out principle is the same. And when you disable any sensor by disconnecting it from it's source, you're essentially indicating a problem (the ECM only sees the full voltage potential) and the ECM uses a fixed value as a work around, setting a trouble code which illuminates the Check Engine Light. In short, once the fixed value is being used, you've eliminated the garbage and the engine, if the sensor is the cause of the driveability problem, runs better.

It would be nice to know the Year, as until '90, only a MAF was used for Air Flow and Load. The balance of the L98's then switched to a MAP or speed density system, eliminating the MAF. Later, the LT1's adopted a MAF (for air flow) and a MAP (for load). Today, most vehicles use only a MAF. But the principles for using voltage drop to determine what's going on remains the same. And realistically, the best way to determine if the info is accurate is with a scanner, so go get one or find some means of determining what's really going on so that you don't end up with a lot of spare parts that you'll probably never need.

 

Rogue Leader here (or at least enabler).

As an answer to your original question, when the MAF is unplugged or faulted with a code 33 or code 34 present, the ecm replaces the normal MAF airflow signal that is provided by the sensor and internal calibration tables with a calculated default airflow signal.

The default airflow calculation is comprised of 3 basic inputs (throttle position, rpm and IAC position) and some calibratable elements including:

A base offset which is equivalent to the airflow through the closed throttle, an IAC position dependent component, and a 3d look up based on tps% vs rpm.

The end result is then limited by the normal max airflow vs rpm table in the usual manner.

Using these simple inputs, the resulting default airflow signal can be calibrated to behave much like an actual MAF. It's not perfect, but can work very well under most operating conditions when tuned properly.

Closed loop fueling will still function and tune the fuel trims around any calibration errors.

I don't advocate relying upon this method for primary fueling as some have done in the past (with my assistance), since there are better options available, but it can certainly offer a nice backup when the MAF does fail.

 

Oh Oh..Here we go again..Rogue leader

Prepare for some mass "Banning"

 

But, We're just learning and sharing....

 

All you guys have to do is remain civil to each other. No personal attacks, no profanity! If you disagree, simply AGREE to DISAGREE.

Site your sources so we'll all know stuff isn't just being made up. Lots of guys make stuff up and try to pass it off as science. When challenged, be prepared to site your source(s).

Keep it on topic and NOT engage in personal attacks. Take control of your testosterone.

If you don't, you can bet the Moderator(s) will step in to restore civility; and he/they should. Otherwise things get out of control quickly.

Jake

 

That's real good advice Jake,If everyone did it that way there would never be any problems. I really don't think we will have any problems though, I was just kidding around because I remember hearing about the last time this topic was discussed in a very unreasonable fashion, and that some guys did get banned..WW

 

Who would've thought such uglyness could insue over a maf. Next time I'll stick to politics and religion. The car is currently running great with the maf unplugged, new tps set correctly. If it's ok with everyone, I'm just gonna drive it that way for a while. I've had the car a month and only driven it a couple of days. I'm going to enjoy it for a while.

 

Gotta say with that one

 

Brent,
Just let me say one thing about this decision. Even though the car may be running better without the MAF hooked up, it is not running right. If you have a lean or rich condition ( which is very likely without MAF input) this can damage your engine over a fairly short time. Personally I would find out what is really wrong before just letting it go and driving the car as it is..Your call...WW