I know there are a lot of threads on all these topics, but I want to see if I have issues relating to one another. I have several codes P0205 and related pending codes for # 5 ignition coil. It was replaced 1 month ago when I bought the car, and now its at it again. Restricted Performance, poor idle, misfires, etc. Also my Cats are hot as heck in the tranny tunnel and you can feel it getting hot in the car.


I ordered Magnaflow # 55975 replacements and the shop I go to told me that they are not a fit because of an O2 sensor that is in the center of the cat itself and the magnaflows won't work. What can I do to get around this? I do not want to pay 1800 per cat from the "Cat" dealers...


Kind of stressed about all the issues since the car runs awesome aside from that. Fast car, rides like a dream!!! Just hoping someone can reach out to me to help me so I can stay a happy Jag owner.


I will update my signature later, but here is my cars info


2003 STR 4.2 Supercharged with 115k miles. No mods no swaps no nonsense.

 

You may need to read some more...

My info about the STR is that Magnaflows 99675 HM are best, plus a Magnaflow 11385 x-pipe. The Denso O2 sensors are installed just ahead of and just after the cats, and the after-cat sensor should be mounted in an extender to minimize error messages.

 

You don't need the extenders with the 99675HM cats. I ran them for over 2 years without the extenders as they are OBDII compliant. The 59975s are designed for OBDI use and would require the extenders.

 

I remember seeing posts from some member(s) who had to use extenders, but don't recall what Magnaflow cats they were using.

Anyway, my STR now has 75k miles and I have been assembling the bits and pieces so as to be ready for the day the cats begin to go. Magnaflow 99675 HM and a pair of (dirt cheap) extenders, just in case.

I recall a discussion about how an extender could, in effect, trick the ECU into believing these hi-flow cats to be (nearly) as good as the OEM's and not sensing an error. Final theory was that the flow of gases was greater than OEM, but the extender moved the sensor away from the mainstream, and located it where there was less oxygen flowing past in unit time.

 

There's not meant to be any oxygen to flow past! It's all supposed to be used up by fuel.

 

Well, it's not MY theory, just A theory, from someone tying to explain an observed fact. As I recall, you were one of the people who had NO idea as to why extenders seemed to work.

Other than in a perfect world, oxygen is bound to be present from time to time, as the catalyst degenerates.

 

I think it must be connected with something like that which would mean either running lean or incomplete combustion. Neither is good.

 

As I understand it, the Magnaflow hi-flow cats are way less expensive than OEM, but are less efficient and permit a higher flow-rate (and hence more power).

So, the exhaust gas passing by the after-cat sensor is moving faster than OEM and contains more oxygen. Not illegal O2 levels, but definitely higher than OEM. Net result - the ECU may decide that there is a problem.

An extender positions the sensor away from mainstream flow, where less gas passes by the sensor and less oxygen is detected in the sampling interval. It's cheating, really, but nothing too serious.

My STR came from California, so my ECU may be used to better days than it's going to see when the Magnaflows are installed. So, I'm taking no chances, especially as extenders are inexpensive and not illegal.

 

It's never going to be illegal to have extra O2 (there's about 20% in air!) but it would imply something's wrong and the only scenarios with extra O2 I could think of I already posted about. (Lean running would be the real nightmare.)

 

If the reason for the extra O2 is incomplete combustion or an inefficient catalyst then it IS illegal, because you are deemed to be polluting the environment, and your car will fail the air-care test.

 

Any exhaust shop competent enough to install high flow cats, should be able to weld on additional oxygen sensor bungs to thread in your existing o2 sensors.

You can use 'extenders' or modified 'spark plug defoulers' on the secondary o2 sensors, to prevent cataylst efficiency codes from popping up when running high flow cats, or no cats at all.

 

If you don't want to mess with the high flow carts, I would be happy to sell you my 49k oem cats to you at a very reasonable price. Pm me for details.