AF readings without cats??

[Jim Vaccaro]

Do cars run richer without cats or is it just that a catted pipe shows leaner reading?????

 

[DTMach1]

If I had to guess...i'd say a tad richer

 

[bdcardinal]

usually there are more HC readings on a sniffer test without cats. i think its mostly the same, engine wise, its just that the cats arent cleaning up the emissions.

 

[twogts4us]

In theory, anything more free flowing than stock will cause a lean condition, not rich.

 

[JohnnyLangton]

In theory, anything more free flowing than stock will cause a lean condition, not rich.

Care to explain how air/fuel is altered when all of the airflow that enters the engine is drawn through the MAF(Mass Airflow Meter)?
JL

 

[twogts4us]

Care to explain how air/fuel is altered when all of the airflow that enters the engine is drawn through the MAF(Mass Airflow Meter)?
JL

Sure Johnny - Less backpressure, which causes more air to be drawn into each cylinder. Though a set amount of air may flow through the MAF, whether or not it makes it into the cylinders is affected by the amount of backpressure through the exhaust system.

 

[JohnnyLangton]

Sure Johnny - Less backpressure, which causes more air to be drawn into each cylinder. Though a set amount of air may flow through the MAF, whether or not it makes it into the cylinders is affected by the amount of backpressure through the exhaust system.

So the engine is magically producing air?
JL

 

[jstreet0204]

So the engine is magically producing air?
JL

engines don't produce air they pump air. A free flowing exhaust will scavenge exhaust out of the ports more efficiently. Creating this 'extra room' in the exhaust port while the engine is running means that the otherwise unchanged engine will flow more air. Forutnately the EEC is capable of compensating for this and will add the needed fuel to keep the A/F in check.

 

[JohnnyLangton]

engines don't produce air they pump air. A free flowing exhaust will scavenge exhaust out of the ports more efficiently. Creating this 'extra room' in the exhaust port while the engine is running means that the otherwise unchanged engine will flow more air. Forutnately the EEC is capable of compensating for this and will add the needed fuel to keep the A/F in check.

Well,No ****...
The more free-flowing exhaust will scavenge a bit more air,and that air has to come from somewhere...the air inlet tube..and what's connected to that tube?
That's right,the MAF.
Therefore stating that headers,etc will make a car run leaner is simply BS,and is the typical answer of somebody that knows nothing about the engine management system on an EEC controlled Ford.
JL

 

[jstreet0204]

Well,No ****...
The more free-flowing exhaust will scavenge a bit more air,and that air has to come from somewhere...the air inlet tube..and what's connected to that tube?
That's right,the MAF.
Therefore stating that headers,etc will make a car run leaner is simply BS,and is the typical answer of somebody that knows nothing about the engine management system on an EEC controlled Ford.
JL

You asked I answered. No need to be an ass...

 

[twogts4us]

So the engine is magically producing air?

Where did you come up with this?

Well,No ****...
The more free-flowing exhaust will scavenge a bit more air,and that air has to come from somewhere...the air inlet tube..and what's connected to that tube?
That's right,the MAF.
Therefore stating that headers,etc will make a car run leaner is simply BS,and is the typical answer of somebody that knows nothing about the engine management system on an EEC controlled Ford.
JL

So are you are saying that regardless of the exhaust mods, every bit of air metered makes it to the cylinders, and the EEC will automatically compensate and adjust the A/F? Please share with us your wealth of knowledge on the EEC. Nonetheless, technical info and a healthy debate are welcome, but no need for your attitude.

 

[Saleen201]

What he is saying, is that all the air entering the engine must go though the MAF. The MAF tells the computer how much air is going into the engine, and therefore, can determine how much fuel to add. Yes you will have a less restrictive exhaust allowing air to flow easier, meaning the more air can enter/exit the car. The computer will also compinsate for this (because, remember, all air going into the engine goes though the MAF) by adding more fuel.... keeping your air/fuel mixture the same.

If you dont have cats, it shouldnt have an effect on your air/fuel mixture, just emissions. LTs will effect it because it puts the O2 sensors further away from the exhaust ports, allowing the air to cool causing a slight missreading. or so i have heard, i hope somebody else can clarify this.

 

[GT2000JAY]

What he is saying, is that all the air entering the engine must go though the MAF. The MAF tells the computer how much air is going into the engine, and therefore, can determine how much fuel to add. Yes you will have a less restrictive exhaust allowing air to flow easier, meaning the more air can enter/exit the car. The computer will also compinsate for this (because, remember, all air going into the engine goes though the MAF) by adding more fuel.... keeping your air/fuel mixture the same.

If you dont have cats, it shouldnt have an effect on your air/fuel mixture, just emissions. LTs will effect it because it puts the O2 sensors further away from the exhaust ports, allowing the air to cool causing a slight missreading. or so i have heard, i hope somebody else can clarify this.

I don't believe your a/f readings will change that much as a result of moving the O2's. Otherwise widebands that use a sniffer in the tailpipes would be completely ineffective (with a catted midpipe they will read off - usually lean). However, moving the O2's further down stream will change the delay between the O2 sending it's reading to the PCM and the computer making small adjustments to the mix - this delay can be corrected/adjusted with a tune.

Regardless of what changes you make between the MAF and O2 sensors, as long as you're MAF xfer function is correct, your O2's are functioning properly, you don't have any vacuum leaks (unmetered air), or exhaust leaks (especially before the O2's) your car will run as it's tuned. A/F will be close to 14.64:1 at idle/part throttle (closed loop) and will be what is commanded at WOT (open loop). There is really no way around this.

Sorry for jumping in so late in the thread - just had a couple thoughts on the subject.

Jay

 

[Red35th]

JL, I agree with you in theory, but...

After plenum/TB combo my car leaned out a little. I don't know why. I fixed it using the maf curve, but it shouldn't have happened because the EEC should have corrected. I think the EEC is only adaptive to a point. I don't know why it happened, but it did.

 

[Saleen201]

I don't believe your a/f readings will change that much as a result of moving the O2's. Otherwise widebands that use a sniffer in the tailpipes would be completely ineffective (with a catted midpipe they will read off - usually lean).

The back o2 sensors are only used to read the efficiency of the cats. If you dont have cats (and dont have MILs, it will trip your SES light. Your front 02 sensors read the rich/lean condition before the cats. If they read it before the cats... and the cats are removed, how does that effect the air/fuel condition?

However, moving the O2's further down stream will change the delay between the O2 sending it's reading to the PCM and the computer making small adjustments to the mix - this delay can be corrected/adjusted with a tune.

Thats what i said... just in a different way

A/F will be close to 14.64:1 at idle/part throttle (closed loop) and will be what is commanded at WOT (open loop). There is really no way around this.

Closed loop is when your car is still not at operating temperature, your computer keeps emissions functions cut off untill the car warms up. Open loop is after the car has reach operating temperature and emissions fuctions resume.

I didnt know closed loop was at idle and open loop was WOT I could be wrong.

-Mike

 

[jstreet0204]

Closed loop is when your car is still not at operating temperature, your computer keeps emissions functions cut off untill the car warms up. Open loop is after the car has reach operating temperature and emissions fuctions resume.

I didnt know closed loop was at idle and open loop was WOT I could be wrong.

-Mike

Closed loop is when the EEC depends on sensors to adjust timing fuel etc. Open loop depends on defined tables, and slightly on some adaptive variables defined during closed loop operation. Open loop occurs during warm up and WOT.

 

[jstreet0204]

I don't believe your a/f readings will change that much as a result of moving the O2's. Otherwise widebands that use a sniffer in the tailpipes would be completely ineffective (with a catted midpipe they will read off - usually lean). However, moving the O2's further down stream will change the delay between the O2 sending it's reading to the PCM and the computer making small adjustments to the mix - this delay can be corrected/adjusted with a tune.

This is true on self heated o2's like ours, but putting a wideband further down stream in the tailpipe does read slightly leaner. I can tell a slight difference with my PLX by putting it in the front bung and the back bung, (I don't have any cats) but there is a greater difference by putting it in the tailpipe. I beleive this has more to do with initial exposure the outside air though.

 

[rpburnette]

Lets assume that you measured the O2 content throughout the entire exhaust system at the same time. The O2 content will vary according to the location. The reason for this is oxidation of the unspent fuel will continue throughout the exhaust. However, this should not affect the ratio very much, but it will change the %O2, or a/f reading. The O2 reading using a/f meters such as LM-1 is not meant to be a reading for how much emissions are released into the atmosphere, if it were than it would only be taken at the end of the tailpipe, like they do for inspections. The O2 reading by a/f meters are for tuning, so if you keep the sample port at the same place than you can properly tune your vehicle. My car might give slightly different readings at the same location in the exhaust than someone elses. Don't start measuring at different places in your exhaust and re-tune your car b/c you think your a/f ratio has changed.

Point to this:

Keep your a/f reading port in the same location
Tune your car according to that reading

This is true on self heated o2's like ours, but putting a wideband further down stream in the tailpipe does read slightly leaner. I can tell a slight difference with my PLX by putting it in the front bung and the back bung, (I don't have any cats) but there is a greater difference by putting it in the tailpipe. I beleive this has more to do with initial exposure the outside air though.