Questions and Answers

Jeep Cherokee Laredo Returns Q. Mr. Ciulla, Attached I also have my first letter in case you needed to remember what I had previously asked. My question now is: Someone here with a Jeep also had told me recently that their O2 Sensor was causing the problem to their catalytic converter. I don't know what the purpose of the O2 sensor is or how it would relate to that problem.

Does it bear any weight? Also, I neglected to mention something VERY important in my first letter. I don't know what the part where all the relays are is called, but the last time that I got my car to turn on, I rattled that area a bit (because it is kind of loose).

An electrician buddy of mine thinks it might be that there is a false contact somewhere within that compartment. I really don't know. I just know that if we take off the Power Latch Relay, the car does not start. What that has to do with this? I do not know, but my mechanic had told me that he fussed with that one day. (I just think he got lucky). The ICM is good because we tested it with a new one and got the same results.

I was also warned about the muffler place that I went to about making sure everything was good in the car before fixing the catalytic converter because Jeeps are notorious for melting them. Since my last e-mail the car has been fine. I think it's learning to behave. But I really don't want to be left hanging. What should I do?

Also, are those Tornado Fuel Systems good for gas saving? And would putting a flowmaster muffler on the jeep help it with even more gas efficiency?

A. The Oxygen Sensor (HO2S) is used to determine the oxygen content of the exhaust gases. The HO2S is basically a galvanic battery consisting of a cylindrical electrolyte element of zirconium dioxide which is coated inside and out with platinum. The outer platinum electrode is exposed to atmosphere, while the inner is exposed to the hot exhaust gases. A porous ceramic coating protects the platinum against damage by the exhaust gases.

The air from the atmosphere acts as one conductor of the battery, the exhaust gases act as the other, and the zirconium dioxide acts as the electrolyte. The higher the oxygen content in the exhaust, the less dissimilarity, thus yielding a low voltage output. When the oxygen content is low (rich mixture), the greater the dissimilarity between the outside air and the exhaust gases, this dissimilarity causes a higher voltage output.

Now if the HO2S is telling the computer that the mixture is too lean when it is actually too rich, the computer will richen the mixture until the HO2S says the mixture is good. All of this excess fuel will burn in the catalytic converter, causing it to melt.

The Power Latch Relay has voltage applied to it from the battery through the ignition switch. The ECU controls this relay by applying or taking away the ground from its circuit. When the ground is applied, the relay is energized, and current is allowed to flow to the fuel pump through the fuel pump ballast resistor.

During start up battery voltage is supplied via the starter relay, whereas at wide open throttle battery voltage is supplied via oxygen sensor heater relay.

The ECU controls this relay for safety purposes also. In the event that the vehicle stalls, if no tach signal is sent to the ECU it will not apply the ground to this relay, which will prevent voltage from getting to the fuel pump

So if you remove it, the engine will not run.

Installing a flowmaster muffler certainly won't hurt. So there won't be any problems if you put one on.

As for the Tornado®, read TORNADO Air Management Systems