My 1991 Sonoma idals low and will not pass emissons

Not sure what dynamometers have to do with this, as they are not necessary for emissions diagnostics or testing, but rather are used for performance tuning. However, sure you can change your 1991 to OBDII. Simply replace the engine, wiring and computer to a 1998 or later system.

Evaporative Emission Vent System Performance. the emissions system on these ventures suck! good luck. It basically means the fumes aren't going where they are supposed to be going and if you live in a county or state that requires emissions testing, it will not pass until you get it fixed. other than that you probably wont see any other problems, you might smell gas but like i said those are just fumes not going to the right place.

REGISTER THE CAR THERE THEN. WHAT IS THE CODE. P0421 OR P0431, P0420 OR P0430 ?? TELL ME.

The check engine light issue could be a faulty dash bulb or consul. It looks like you could do worse than get your car checked out on a diagnostic consul.

Failing that, emissions failure is usually a fault of the engine not running at optimum. Is the air filter clean, air temperature sensors clean. Finally take it out for a good run to burn of any residues before checking emissions.

Did you install new spark plugs? Definitely replace the O2 sensor.

CRC makes the 'guaranteed to pass emissions' which you must follow directions-add to full gas tank, run for certain amount of time, etc.before testing. If you were close to passing emissions, it could help, I used it and my test #;s were close, and I passed, HOWEVER, since you are missing one cat, I don't think the guarantee is valid, nor do I think it would work. In my state they visually check for cats, and if you don't have one, FAIL. You can find generic cats on the internet for a good price, of course then you have the job of installing it. As far as the gas for free, water to gas, stay away, save your money, that scam has been around for a long time. Good luck!

It will not Hurt anything. It is the First thing that I do whenever I buy a New Truck. It Increases Horsepower and Mileage + Sounds Really good with Flowmasters. Nothing to Worry about. I have NEVER had a Problem doing this. Please Rate My Response! Thanks!

Go to http://alldatadiy.com/ and buy a subscription for your vehicle. If you want to repair it yourself you will need this data. It is good for 1 year and has, testing and inspection guides, component locations, wiring digrams and a lot of info the DIY'er needs.  I am looking in all my code manuals and still do not see an e49. AIR is a system that puts fresh air into your exhaust so the emissions at the tailpipe are lower. It's an EPA mandated system. If you have to pass an emissions test in your state or county you will have to get them system woking properly. Check out alldata it is worth the 30.00.

Unfortunately yes.

its possible that the old pump and filter were about shot so the carhad been tuned to work with them, now its got true fuel coming through try changing the mixture setting.
Good Luck Davelee