Have 4 Gas, Now , what are the settings?

I'm no technician - but here are some shadetree mechanic suggestions......just know that my "disclaimer" is in full force here....

With the O2 sensors disconnected:
CO about 1.25%
HC a bit below 200ppm

After reconnecting O2 sensors:
CO about 1% - 2%
HC 150ppm or lower
CO2 12% - 15%

Prior to adjusting the fuel mixtures, it's a good idea to install new spark plugs, and verify everything like plug wires, vacuum hoses...etc......are in good shape. Be sure that the throttle linkage at both throttle bodies is adjusted, there should be just a tad of play - maybe .004" but no more - before throttle plate movement when the gas peddle is pressed.

Adjust the throttle plate bypass screws to balance the vacuum, in very small increments. Sometimes it's a good idea, with the engine off of course, to run them in until they bottom out (finger tight only) - while making note of how many turns it takes, so you will know where your at. Some technicians screw them in, and then back them both out 1.5 turns or so I think...as a base starting point.

For the the mixture screws, try to always adjust from lean to rich (clockwise), if you go too far rich, back up and do it again. You have to sneek up on the optimum values. Once you make a change to the mixture - blip the throttle and then let things settle down for a few seconds before taking note of the readings.

Be sure the plug up the mixture screw holes after each adjustment - you dont want a vacuum leak to drastically throw things off. Also remember that the left side exhaust is actually the right side cylinder bank, and visa versa. When adjusting the mixture screws - do so in VERY small increments, it takes very little change to really affect things.

It's a delicate dancing act to get everything into harmony, so you will probably go through this process a couple of times. But once right, the car will run VERY smoooth with no rpm surges...etc.

This information is from memory...so I could be wrong on a few points. Hopefully one of our resident experts will post about this topic, because I don't ever remember these numbers being posted here on fchat.

 

Note that the various values Jeff is talking about are as measured upstream of the cats -- i.e, as leaving the cylinder without treatment (so don't measure at the tailpipe looking for these values if you still have precats or cats in place -- they'll be much lower at the tailpipes if the cats are really working).

 

Good point Steve.....I was reciting numbers and thinking of the Borla exhaust sytem I had....which does away with precats and cats. If Kerry's precats and cats are hollowed out - then he can use the numbers I posted. Otherwise he will have to access the sampling ports located at the precats.

 

Okay......I'm bumping this thread up. If anyone has any more specific information add, please do so. I do recall a thread that went into details about performing this procedure, but I searched and can't find it.

 

Disconnect O2's and close off the idle air bleeds all the way and balance the motor at 700-800 rpm on the throttle stop screws. Unwind the air bleeds to 1050-1100 rpm and balanced. If the CO is set at 1.25% and HC below 200 with the O2's disconnected the CO should drop to about .6% and HC should drop some too when O2's are reconnected. If both do not go down there is a serious issue.

If everything is good it will be below 2% O2 and over 14% CO2

Reconnect the O2's and reset idle to 1100 and balanced.

Final numbers should be .6% CO, If the car is great it will have under 100 ppm HC but up to about 170 is OK. O2 needs to be under 2%. CO2 14% +

If those numbers are not attainable something is wrong with the car.

Idle should be balanced and at 1000-1100 the entire time. Dropping the idle will affect it considerably.

Also you should be able to snap the throttle wide open and closed again very rapidly with the idle dropping straight to 1000. If it dips down then back up something is not correct.

 

Thank You Brian! I'm printing this thread out and sticking it in my book for future reference!

Your method of closing off the air bypass and using the throttle stops right at the start is new to me - but it makes a lot of sense and leaves no room for doubt - I like it. I've always heard that you are supposed to run the bypass screws in till bottom - then back them both out about 1.25 to 1.50 turns and go from there.

Thank You for taking the time to post this information.