Nissan Primera P11 2.0l CAT CONVERTER REPLACEMENT

 

Replacing the Cat seems to be a bit of an expensive job and the prices seem to vary - a lot!!

 

Be wary when looking for a cheap replacement. bear in mind it's likely to be ceramic.

 

What is the difference between a ceramic and steel monolith ?
Steel monoliths are more durable than ceramic. A steel monolith will last longer than a ceramic one.
In addition as ceramic materials are more brittle than steel, the steel monolith is more likely to survive impact damage from grounding than ceramic. However impact damage can destroy either type.

What is the best choice?
Diesel cats are fitted with a steel monolith as standard. For petrol engined vehicles the choice is largely a financial one. A steel monolith may survive impact damage that would most likely destroy a more brittle ceramic monolith. To make your choice you should compare the price of the part and fitting cost against the improved warranty/durability and perhaps factor in how long you are likely to retain the car. Where your original cat has required replacing prematurely because of a loose, rattling cat, replacement with the superior steel monolith is recommended.

Here are some tips on what can cause issues with the unit (useful when considering an engine mod!) and how to best avoid damaging this costly unit in the first place!

 

Road/Impact Damage
Impact damage is caused to the catalyst when it hits, or is struck by hard objects. This can cause the monolith to fracture and the pieces to rattle around inside the unit. Possible causes are a hard object striking the converter, hitting speed bumps and off-road driving. Impact damage can usually be seen with the naked eye on the housing of the unit.

Plugged or Contaminated Monolith
This is when the monolith becomes coated and blocked with soot, preventing it from converting the gases that pass through it. This can be caused by the car running rich, using the incorrect fuel or unsuitable fuel additives, and oil or antifreeze entering the exhaust. Excessive levels of hydrocarbons (neat fuel) entering the exhaust can also contaminate the monolith and prevent it working. Always ensure that the vehicle is running nicely before fitting a new catalyst.

Melted or Broken Monolith
Monoliths can be broken in a variety of ways, the most common being impact damage (see section above). It can also be broken when it suffers a sudden drop in temperature (e.g. driving through a ford) as the steel shell contracts faster than the ceramic monolith as it cools and crushes it (another advantage of steel monolith!!). The monolith can be melted when unburned fuel is injected into the catalyst. Causes of this are tow or bump starting, or the car’s engine not firing properly on starting. More information on the causes of melting monoliths can be found below.

Overheating
There are many problems that can cause a catalyst to overheat or fail. The most common of these is when unburned fuel enters the catalyst. This fuel ignites when it reaches the catalyst because of the high operating temperatures, causing the catalyst to superheat and melt down. Some causes of this are faulty spark plugs and leads, which cause the engine to misfire, and a badly timed distributor.

Oxygen/Lambda Sensor
The oxygen (lambda) sensor collects and sends information to the ECU (Electronic Control Unit). This is used to control the air/fuel mix. If the oxygen sensor is faulty, the air/fuel mixture will not be corrected. In the case of it running rich excess fuel will enter the catalyst, causing it to superheat and melt down. It is advised that oxygen sensors are checked to be functioning correctly every time a catalyst is replaced.

Fuel Injection Systems
A catalyst can be damaged if a fuel injector is leaking internally or dribbling fuel into the engine. The excess fuel will then enter the exhaust system and superheat the catalyst, causing the monolith to melt down.

Map Sensors
Map sensors inform the ECU of the load on the engine and the amount of air entering it. If this sensor fails it causes a rich condition in the engine, which can superheat the catalyst and cause it to fail.

Carburettor Systems
A worn or defective carburettor can cause a catalyst to overheat. Problems such as improper float or air/fuel mix adjustments and worn metering rods can damage the catalyst. The choke system also needs to be operating properly so the right level of fuel enters the system. If too much fuel enters the system the catalyst will overheat and eventually fail.

Canister Purge Valve Control
This vacuum operated valve vents fuel vapour from the carburettor bowl to the charcoal canister. If the vacuum is breached, the charcoal canister will flood and the air/fuel mixture will become very rich. This excess fuel will enter the catalyst and the monolith will melt down.

Noisy
A catalyst should not be considered to be a silencer although it does have some silencing qualities. Noise can be caused by excessive amounts of fuel getting into the converter.

 

Type approval (EU Cat standards certified quality of fitting and fitness for purpose approval)

 

One final bit of advice from me is to make sure your new non OEM cat is a "Type approved". Its the best way of ensuring that you don't end up with a dud that has a lack of precious metal ingredient that most likely means a short and inefficient lifespan for the part, which could cause you an MOT failure as soon as your next scheduled, and further unnecessary hassle, engine efficiency checks based on the assumption that you already have a decent (nearly new) cat installed!! A "type approved" certificate denotes a standard of cat on par with a genuine dealer supplied part for your specific car make and model. In other words, it will not disrupt your BHP, exhaust flow or be the most likely cause of an emissions MOT failure!

 

In short, it means you will guarantee the Cat meeting current legislation, a type approved catalyst brings complete reassurance that the catalyst will fit the vehicle it is intended for and it is compatible with the ECU and other fitted equipment. The personal benefit to you is that there is no loss of performance or fuel consumption after the approved part is fitted.

 

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I am currently trying to locate the parts I will need for the best quality and least cash I can on a tight budget (off to Brazil for 2weeks on monday, so spent all my cash!!).

 

If anyone has any pointers, let me know; I will do the same.

 

By the way, my Cat has not failed emissions (original cat on 130,000miles) , its just rusted to hell at the joints. The large support bracket holding the middle section of my exhaust to the chassis has also rusted - and snapped off! This has caused my downpipe to take on some considerable load, which has caused the flexible (braided wire on downpipe section) part to collapse resulting in a huge hole! I suggest you go outside and have a quick look at your bracket and make sure its in good order - if not get it replaced now - could save you a few quid later on!!

 

The upside - it sounds like a carnivorous beast and performance is up!

Downside - its completely damn illegal

 

 

 

We also discussed the robbery that is going down with the cat support bracket! The cheapest I can find this part for is on ebay for over £40 (incl 4-5 day del which sucks!).

 

Rob says this part cannot possibly be being sold at a fair price and has got onto his contacts who are now looking into the patent on this part and hoping to produce it at a much reduced cost to retail. Rob said that at his meeting with the manufacurers they forcast a consumer price of between £15-20 tops - I wish him luck and asked him to let me know if it comes to fruition so that I could let you guys know. Seems for my purposes this will come a little too late in either case so I am going to have to fork out a stupid amount of cash for a cheap-arse small piece of metal - gutted.

 

NOTE TO ADMIN: I hope I have not overstepped the mark by mentioning Rob, but as you can see above, he seems friendly, cheap and eager to help. He also likes a good chin-wag (he is an older guy) and so is very forthcoming and honest about the industry and what he can/can't do for you. Service like this is rare these days and worth noting for the benefit of us all in my opinion. I hope the other members would do the same for me!

Glad you had a good holiday