a/f ratio

[jhaggadone]

how do i get my a/f ratio right?

Topic

[djdevon3]

I suggest reading the sticky topic in this forum category… it’s labled as “A Primer, for those wanting to fix their car with internet advice”

[dreamer2355]

If you want to see your exact a/f ratio, you would need to use a wide band o2 sensor.

Generally speaking, your stoichiometric ratio should be 14.7:1 at cruising speed and idle. That will drop down to around 12.5:1 or lower at WOT seeing as the PCM would be out of closed loop and not using the o2 sensor to maintain that desired stoichiometirc ratio of 14:7.1

[Matt]

Quoted From college man:

your air/ fuel mixture starts with your mass air flow sensor and ends with the o2 sensor. there are other sensors that contribute feed back to the computer.
what do you feel is wrong with the a/f ratio? C8-)

This is what I’m wondering as well. Check engine light? Just generally curious?

[Brucifer79]

The best way to check it is hooking up a scan tool and going through the list of systems running with the car on. Any shop could help with that or Auto Zone, O’Reilly’s, pretty much anywhere.
Second, if it seems to be running rough, rich, lean, bogs down, misfires. Check with the MAF sensor, couldnt hurt to give it a nice cleaning. Just make sure its outta the car and use a properly made cleaner for it. Oops skipped a step, look at the air filter. If it looks like you should replace it then go for it. Basically what Im getting at is check everything you can and depending on mileage and service history perform a tuneup.

Good Luck and Happy Wrenching

[Trcustoms719]

Is there a reason why your asking about your A/F ratio?

[TheArete]

Pick up a Haynes, Chiltons or Factory Service manual. Type in “Chiltons” in the search function and you can have access to their online library.

Depending on the Car (fuel injected vs. Carb) it will be mech controlled or controlled by the PCM/ECU/ECM. What you’re looking for isn’t that, but a part of the system thats not doing its job, such as a clogged air filter, malfunctioning IAC valve.

choose a system and work forward on it, double check everything and then move onto the next one.

1. First go ahead and do a fuel pressure test between the fuel rail and after the filter. Do it at idle and WOT, as well as snap tests and after the car has been of for a 10 or so minutes. It should stay consistently w/in your cars specs (once again snag a manual or that).

2. I’d run a compression test and once again look to see if it’s somewhere in the factory specs.

3. As for spark, lets check your battery first key on, engine off and then at idle and WOT. It should be reading somewhere near 12.5 volts without engine running. With the car on it should jump up into the 13 to 14.5 volt range (depends on the car) as the alt. Charges the battery.

Anyways thats a start, some more experienced peeps can chime in here. Start here and lets work forward.

[college man]

what year, make , model and engine size are we working on?

[jhaggadone]

1997 cougar 3.8L

[college man]

your air/ fuel mixture starts with your mass air flow sensor and ends with the o2 sensor. there are other sensors that contribute feed back to the computer.
what do you feel is wrong with the a/f ratio? C8-)

[EricTheCarGuy]

The simple answer is ‘don’t mess with it’. The A/F ratio is NOT meant to be ‘adjusted’ it’s either on or it’s not.

Anyway you can shed some light on why you’re asking the question.

[jhaggadone]

sorry guys i have other post i just bought this car a lil while ago its popping codes 1)running lean 2)misefire #2 and 3)bad catalyst just trying to figure everything out has new air n fuel filter plugs wires swapped coil pack and iac valve from wrecked mustang trying to save from replacing unneeded stuff runs the same as ever. and it drives great nice and smooth cant feel no misfire but at an idle in D its def misfiring and idling rough shift into N and smooths out so i am at a loss uugggghhhhh

[dreamer2355]

Can you post the exact codes?

Lean conditions usually indicate a vacuum leak. A can scan tool showing PID data would be a big help here.

Here is a video from Eric on finding vacuum leaks without a smoke machine –

http://www.youtube.com/watch?v=9CPqbaSg … t3EVppbf88

You may also want to try cleaning your MAF sensor with the correct chemical also.

For the misfire code, i would recommend stress testing the ignition system. Single cylinder misfire’s can be due to faulty plug, faulty injector, faulty coil, faulty ignition wire, broken valve spring or burnt valve.

I would start with a power balance test as shown in this video by Eric –

http://www.youtube.com/watch?v=bAOmUjAj … t3EVppbf88

And another video on voltage leaks –

http://www.youtube.com/watch?v=x-U9WqJf … yyMYSZRIOn

For the catalyst efficiency code, that may be present due to the ignition misfire. However, there are several ways to test catalytic converters but you will need the correct equipment. If you have a scan tool, you would need to look at post-cat o2 sensor readings. They should have a nice flat line of around 0.5v. If they are fluctuating between 0.1 and 0.9v, that is a sign usually of a failing catalytic converter. You can also use a exhaust gas analyzer machine as well as a temperature gun where you measure the temperature before and after the catalytic converter. There should be an increase of 100f after the cat.

Good luck and keep us posted.

[EricTheCarGuy]

+1 on Dreamers post (I should get a stamp that says that). It sounds to me like a possible ignition problem as ignition systems often fail under load and when you put it in drive a load is created on the engine by the transmission so it’s worth doin

[jhaggadone]

ok thanks dreamer and eric ill dig a lil deeper on it

[Author]

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