99 cobra.....P0420 code

has the conveter been removed?

No.......the converters are still in tact. All four oxygen sensors are in place

I doubt and would be very suprised if an 02 is causing the converter code. I never say never but I would be REALLY suprised. Is there anything as a power adder that could be causing the car to run too rich or too lean which could be causing the converter failure/code. I would take it to the dealer and see if the converter is still covered under warranty.

the mustang is pretty much stock except for the exhaust. Im running 89 octage gas in the car. Could it be the fuel im using? I also read that a bad coolant temparature sensor could cause a PO420 code. The car seems to run good. Is there a way to test the converters. They are very expensive for this car. Im hoping its something else.

exhaust including conveters? Headers? 89 octane shouldn't effect it but if the car is supposed to be 91 or higher then if it's run on 91 for a couple of tanks does the code return? Has it ever run race gas cause that'll burn a conveter out? I again doubt the coolant sensor is going to fix it. The code means that the rear 02's signal is moving around too much like the front 02's which means the converter isn't buffering the pollutants out of the exhaust fast enough. No warranty left? Is there software update available from the dealer?

The stock headers, cats, 02 sensors are the originals.The only components replaced were from the cats back. The code only shows up about once a month. Probably about every 800 miles or so. I could start running 91 octane and see if solves the problem. The engine seems to run fine on 89 octane, but if thats what causing the code i would switch to 91. Will a lower actane fuel cause a 0420 code? The warranty on the converters expired last summer. I'm not familar with the software update. Ill check with the dealer. What specifically should I request from him? I really appreciate your help.

tell him the code number and that you're curious if they're is a tsb, extended warranty etc for the converters on that car. They may charge you to hook the scanner up or to update the software but they'll probably have seen that code on that car before and have some experience with it. good luck

thanks Jeff.................i appreciate you advice. Ill swing by the dealer toworrow morning

Steve Check out this topic and look for the post by me about some links regarding Catalytic Efficiency Failures. http://www.obd-codes.com/forums/viewtop ... f=1&t=3448 Gary

Gary Thanks .........those are some awesome links. That gave me some hope that it might not have to replace my cats. Im hoping its a defective 02 sensor. Im going to reverse the sensors on the downstream side of the converters. If the problem moves to the other side ill know that its a bad sensor.......i hope. Thanks.......i appreciate the links

I took the cobra into the dealer yesterday. The service manger attempted to do a reflash on the cars system. He commented that the car already had the latest updates loaded. He did a diagnosis on the exhaust system. He scratched his head and said that it appears that the cats are bad. It bothers me that he wasnt sure. I dont want to replace my cats if it isnt necessary. He said that with the low milage on the vehicle (36K) its unusual that both cats appear to be bad. He said if the car were his he would install MIL eliminators and forget about it. It sounds to me like that would just hide the problem. Any input?

Mil eliminators are for cars that have have the converters removed and for people trying to cheat the system. If he suspects that the converters are shot then he may be in fact right. If you don't know the history of the car in terms of how it was driven or raced, what fuels were poured into it etc then it's a good chance that something caused them to fail. As for what I don't know. You get a second opinion or bite the bullet and replace the converters with new ones from the dealer or a really good quality aftermarket set and hope that it fixes it.

The previous owner claimed that he never used racing fuel. He also claimed he never raced it(HAH). Hes an old guy like me but im sure he had his foot in it a few times. Will the MIL eliminators work on a car that still has the converters?

You're asking the wrong guy and the wrong forum. Other forums on the net maybe with Cobra owners would know better then me. Im trained to diagnose and repair, not cheat the systems that are in place within the car. An mil eliminator is not to be sold for a vehicle that is to be used on the highway. Race cars only so Im not sure what the ramifications are legally for using them!

all car manufacturers have an 8 year, 80,000 mile warranty on their catalytic converters and ecm/pcm reguardless of who owns the vehicle (provided they have not been tampered with....) go back to ford and make them replace the cat's under warranty.

United States Air and Radiation EPA420-F-96-020 Environmental Protection March 1996 Agency Office of Mobile Sources --------------------------------------------------------------------- EPA Environmental Fact Sheet --------------------------------------------------------------------- EMISSIONS WARRANTIES FOR 1995 AND NEWER CARS & TRUCKS Federally required emission control warranties protect you, the vehicle owner, from the cost of repairs for certain emission related failures that result from manufacturer defects in materials and workmanship or that cause your vehicle to exceed federal emission standards. Manufacturers have been required by federal law to provide emission control coverage for vehicles since 1972. There are two federal emission control warranties discussed in this fact sheet: (A) "Performance Warranty" and (B) "Design and Defect Warranty". This fact sheet explains each warranty in detail, provides you with a list of some of the parts covered under these warranties, explains the procedures for making an emissions warranty claim, and answers some of the most commonly asked questions about emissions warranties. Finally, we will give you some tips on how to prevent future emission-related failures and maintain the longevity of your vehicle's engine. A. PERFORMANCE WARRANTY The Performance Warranty covers repairs which are required during the first 2 years or 24,000 miles of vehicle use because the vehicle failed an emission test. Specified major emission control components are covered for the first 8 years or 80,000 miles . If you are a resident of an area with an Inspection and Maintenance (I/M) program that meets federal guidelines, you are eligible for this warranty protection provided that: * Your car or light-duty truck fails an approved emissions test; and * Your vehicle is less than 2 years old and has less than 24,000 miles (up to 8 years/80,000 miles for certain components); and * Your state or local government requires that you repair the vehicle; and * The test failure does not result from misuse of the vehicle or a failure to follow the manufacturers' written maintenance instructions; and * You present the vehicle to a warranty-authorized manufacturer representative, along with evidence of the emission test failure, during the warranty period. During the first 2 years/24,000 miles, the Performance Warranty covers any repair or adjustment which is necessary to make your vehicle pass an approved, locally-required emission test and as long as your vehicle has not exceeded the warranty time or mileage limitations and has been properly maintained according to the manufacturer's specifications.