MPG down 20%

Yes, there is a better one from $50 and up. I bet the one you pointed out at the website could be just as confusing as a $50 model. Confusing part is the code and text,

Fuel Trim Adaptation Additive Bank 1 Malfunction is another phrase for "a vacuum leak. Quick, go find and fix it!"

They are too general and don't explain it in human language. Unless it's just an O2 sensor. And have a *factory* service manual handy. And no, it's not cost effective to get an expensive OBD scanner unless you own a lemon or about to be lemon. The codes shows up once every three years (guessing).

A nearby AutoZone will read the codes for you at no charge. If you don't have a Check Engine glaring at you there may be no codes, tho. It seems that parts stores and O2 sensor makers want you to replace them regularly. My suspicion is that, if they are bad, the ODB will tell you. Were there any changes made (even gas brands) at about the time as the mileage died?

Paul in Dayton

Assuming it's not the tires or tire pressure or a sticking brake caliper, etc. I'd be checking the following:

Coolant Temperature Sensor circuit. Mass Air Flow Sensor (they need to be cleaned periodically anyway). Vacuum or air leaks. O2 sensor

Most of the above mentioned items won't affect your gas mileage much except the Coolant Temperature Sensor which can easily lower your gas mileage by 20% or more. On my car I had corroded electrical contacts on my coolant temperature sensor which when cleaned (several times) restored my gas mileage.

I'll check out AutoZone. The engine light did come on once for a day a while after the mileage dropped, but went back out (first and only time it's ever come on). And nothing has really changed; I fill up at the same few stations regularly. I've also added several bottles of injector cleaner with no effect.

This web page talks about various gauge installations in a 97 4runner. When he installed the FP gauge he noticed the regulator had been clogged by some pieces of rubber hose. Hope this helps,

Dan

The AutoEnginuity tool is by far the most comprehensive of the scan tool lot. It is bi-directional and supports the COMPLETE OBDII specification; all that with ONE connector. In your case, it even dedicates a screen to o2 sensors. It not only shows you what a switchcount is supposed to look like, it shows you the values wher the switch should take place. Generically, the answer that was given is correct (that they are not too consumer friendly); however, this scan tool (which I think your previous answer looked at it) is better than most. Remember spending more doesn't always equate to a better product. Look at all of them then decide. Look around, the marketplace is full a REALLY bad scan tools. This is a professional tool that was written to the SAE specifications. That connector is used in half the emissions houses in this country. The software is finally written by engineers and not hobbiests. Enough lambasting.

Scan tools are simply tools; you must still have some understanding on how to use them. This one does teach you about how o2 sensors influence the fuel trim. But what to do is a matter of learning your vehicle.

I would never recommend turning a wrench on any car without a Chilton (or such) if you are unfamaliar with working on cars. This area your trying to get into requires a little more engine management then you might be ready for.

I will tell you how to look at this though. Short Term and Long Term Fuel trim and O2 sensors switchcounts would definitely be a great place to start. The o2 sensor is one of the most important feedback components in all the engine management systems since emissions. The core OBDII implementation might not give you all the data you need for this though. The statement is not correct that it will have to be a lemon for these tools to work. Generally, you would start with a Check Engine Light and debug from there; however, in your case even your ECU hasn't decided that you have a flaw. This could mean a lot of things. These sensors wil be available on most tools today. Any tool you buy should be able to work on all three electrical interfaces and it should support what the SAE considers as the core functionality. Don't buy a simply code reader nor do you want one that can't show you data in a format that can be used effectively (example being graphs). If you get a check engine light, the sensors that are used to elevate that code to a trouble code are then available to you to service your vehicle. No tool out there is really that simple to use; their wouldn't be an automotive repair industry if their was.