I think my cats are plugged. Sluggish performance, failed smog, and I had this kind of issue with my Range Rover. Should I replace them with used units at $400+labor? New they are $800+labor, I had my car past smogged (good for 2 years) and was considering just taking cats out and hollowing them out. Any problems with this?
I also am afraid of blowback to my heads causing a head gasket failure.The car (1997 XK8 Coupe) is not mixing and it does not leak at all. The engine was replaced at 87k miles updated, ect. It has never run hot.

The car sat for 10 days while on vacation and upon starting had white smoke. Very worrying. Pulled all plugs and they were clean. Car has not had any smoking issues since. The car actually runs very well, covering 709 miles last week.
I am getting a noise, exhaust leak sounding or valve, gets more noisy with acceleration, but sounds like an exhaust issue...idk. Short on Ca$h and need to keep it running. Any suggestion?
What should I pay for an indie shop to Diagnose? In San Diego, CA? I could possibly squeeze about $150 to do so.

 

Your first thought should NOT be throw new cats on. It may turn out to need them but it could just as easily be a sensor in the engine management system has failed.

The starting point is a systematic check. The sensors are shown in the diagram on page 2:

XK8 1999 - Electronic Engine Controls.pdf

Having the codes read will give you better information on the electronic engine controls, fuel trim and emissions.

The noise could be another indicator. Describing it as valve or exhaust suggests possible head gasket problems. A compression test will confirm or eliminate this.

I know you have much greater freedom to modify exhaust systems in the US than we do in the UK and won't begin to speculate on removing the cats.

Graham

 

Try to describe the noise better, if it is a rattle on the overun it could be "cat brick"...

This is the term we use when the internals of the cat break away and rattle inside the casing, this might explain your other issue

 

White smoke episode might only have been a valve seal/seat letting oil drip by while the car sat. If it doesn't become persistant, you don't need to worry about it. If you hollow out the CATS you certainly won't pass SMOG anymore. Seeing you are in CA would make that an issue. Try to diagnose the problem then develop a plan of action from your findings. MC

 

If your cats are indeed bad you need to find out why they went bad. I have never seen cats fail without an underlying cause. Throwing on a new pair without first diagnosing the real problem will just cause more expense when the second set also fails.

There are several ways to test the cats - using a fuel pressure gauge tapped into the pipe ahead of the cat, for example. While that may be difficult on an XK8, measuring backpressure is definitive. Anything over three psi while blipping the throttle is suspect. Then, there is the use of a non-contact thermometer, measuring temps before and after the cat(s).

 

Hey Beav,

Just curious...what are the typical underlying causes that can destroy a catalytic converter? I failed Exhaust Sciences in college.

 

I lost the cats in one car when ignition failure dumped raw fuel into the exhaust. Even a rich condition could cause failure.
RJ

 

If I had to guess at the stat's I would attribute over-fueling as the #1 cause. At its low end it can slightly overheat a cat and cause the shell to expand enough that the substrate becomes loose and rattles. Once that occurs the substrate can begin breaking up and flow downstream, plugging pipes and/or mufflers. At the high end over-fueling can cause the substrate to melt, collapsing the cells and blocking flow. Then there is excessive oil consumption which basically results in either coking and plugging or or overheating and melting.

I should correct myself, I mispoke. I should have written that I have never seen a cat plug up without an underlying concern. I have seen cats just die. In other words they quit doing the job they were designed to do. Whether it is due to the continued use of crap gas or just the erosion of the precious metals used inside, some just become ineffectual with old age. My experience has been that rarely occurs below 100,000 miles.

Speaking of precious metals, cats contain rhodium, palladium and platinum. Rhodium was at a high of $10,000USD/oz. in July, '08. Palladium has reached up to $1100/oz. at one time and platinum $2300/oz. It makes you wonder how thin can a coating be and remain effectual, especially when consideration is given to the environment in which it functions. I've seen universal replacement cats sell for $69 retail for a number of years, just how thick can those metals be applied at that price?

 

Wow Beav, It sure sounds like you have done some research on Cats. I live in Wash st. I once had a motorhome and I simply removed the cat and put in a straight pipe. Funny thing is, it still passed the state emissions test. Why is that sir?

 

Yes, this is what I think it is, a semi-rattle/ exhaust sound that cannot be heard outside of the car at all, only in the driver's seat while actually driving under acceleration, if I am light on throttle, not to be heard. ECU, computer, mass air, all replaced in last year by previous owner. The sound seems to come from driver's side cat.

 

yes, this seems to have happened in the past with a throttle body/mass air failure. both were replaced with new parts within last year, by previous owner. i spoke with their mechanic and he did think i should replace the cats.

 

Some states are very lenient on their specs, especially with trucks. I don't know of any that enforce Federal standards, but I'm no expert on the subject. The fact that they allowed you to pass with missing parts is indicative of either lazy personnel or a program that exists merely for the revenue.

Then again I've seen many cars that would pass state level requirements without cats and/or other emission equipment.

 

XK8Paul, If you have to replace your cats, consider replacing them with a set of Nameless Performance Cats. They flow significantly better and will not affect your emissions tests. Not to mention you will get more power out of them.

Nameless Performance Inc.

 

If it is indeed your catalytic converters, I'd highly suggest a set of our high flow cats as a replacement. They are T304 Stainless Steel throughout with 3/8" thick flanges, mandrel bent tubing and high flow conical formed 200 cell catalytic converters which are 49 state legal and are each rated to clean the exhaust of a 6.3l V8 engine. Depending on the model they're around $869, which is less than half the cost of a single factory replacement (which is cast iron, has a hard 90 degree bend in the outlet and features four 600 cell catalytic elements).

Power gains on our cats are between 10-15 wheel horsepower depending on other exhaust modifications (higher power without any other mods due to exhaust gains being asymptotic on these cars).

Any questions, feel free to email me for further information: jason.g@namelessperformance.com. We sell our products through a variety of independent shops and OEM dealerships.

Jason Griffith
Engineering Director
Nameless Performance, Inc
360.263.5001

 

Wow awesome sound!!!

 

My 1997 XK8 Coupe passed smog the second time around, I had to replace some of the ignition coils and all the plugs. It had some exhaust leaks too that were addressed. I had a full stainless exhaust from a 2000 XKR I bought for only $100 retro fitted to my Jag. Cats still remain an issue.

 

Good to know you're at least legal, but those cats aren't going to get any better with time. Best to put it on your list of 'to dos' and try to budget the replacement before something worse happens (i've heard of clogged cats melting)

 

Do the manifolds have issue, tech says this is where leak is...