As late model F430 fall out of the authorised dealer network more and more people are taking the preventative step of removing the small catalytic converters in the exhaust manifold. Despite there being no apparent change in the engine ECU software during the production run, it has become apparent that the catalytic converter monitoring was tightened up for later cars. This means that if you have an early F430 it is possible to remove the pre-cats without causing any issues with the ECU. However, if you have a late car then it is likely that pre-cat removal will cause error codes to be flagged. Essentially, the later the car the more chance of a code like P0420, P0422, P0432, P1423 or P1424.
Before covering remedial actions, it is worth taking a moment to understand how the ECU, catalytic converter and lambda sensors work in managing the engine and emissions. For the purposes of this explanation I will talk about one bank only – the exact same is happening on the other side. This also applies to other modern Ferrari and Maserati tipos with Bosch Motronic engine management.
The F430 has a small catalytic converter in the manifold (red), a main catalytic converter (yellow), upstream lambda sensor (green) and downstream lambda (blue).
A lambda sensor is an incredibly sophisticated piece of kit that produces a signal in relation to the amount of oxygen present in the exhaust gas. The ECU uses this signal from the upstream sensor, together with other data from the engine, to determine the Air-Fuel ratio (AFR) of the mixture being burnt in the cylinders. If a lean condition is detected then the ECU adds more fuel (and vice versa) in an attempt to keep the AFR as close to stoichiometric as possible. The AFR is constantly being tweaked from rich to lean back to rich and so on. The signal from the upstream lambda reflects this and is commonly referred to as “switching”. In fact one can test the operation of the lambda by viewing the output on an oscilloscope.
Both the pre-cat and main cats work in a similar way to each other, their purpose being to convert harmful gasses into less harmful ones. This is achieved by the exhaust gas passing over a structure coated with precious metals and other exotic materials. One of the features of a catalytic converter is the ability to store oxygen. When the AFR is lean, excess oxygen is present in the exhaust gas which the cat stores up. When the AFR is rich this stored oxygen is released, allowing the cat to work as efficiently as possible. This means that the signal from the downstream lambda sensor is relatively steady since the cat is smoothing out the presence of oxygen in the gas it expels.
This difference in lambda output between the upstream and downstream sensors allows the ECU to estimate the efficiency of the cat. As the cat gets less efficient, the signal from the downstream sensor starts to behave more like the upstream (if the cat was removed then the signals would be equal bar the time delay). The ECU can also estimate the performance of the upstream sensor which is more susceptible to degradation due to the higher operating temperatures.
When the pre-cat is removed, the oxygen storage ability of the system is diminished which in turn can cause the ECU to log an error. Assuming that the aftermarket manifolds have been installed correctly and that there are no air leaks, there are a few options open to owners who are experiencing such codes…
- Do nothing and live with the CEL. I wouldn’t advise this as the CEL may be triggered for another problem – if the warning is ignored then damage may occur.
- Replace the lambda sensors. Poorly performing lambda sensors can cause efficiency codes and sometimes it is enough to fit new sensors. This is less likely to be the case for late model cars.
- Remap the ECU. The cat efficiency monitoring can be programmed out of the ECU by companies like DMS.
- Fit an additional cat to smooth out the oxygen in the gas supplied to the downstream lambda so that the warning is not generated.
I prefer to go for the last option. For relatively little money, miniature catalytic converters can be bought that screw into the hole that the downstream lambda occupies. The sensor is then screwed into the tiny cat.
The catalytic converter is housed in the threaded fitting that screws into the exhaust. The lambda screws into the other end. The miniature cat changes the composition of the exhaust gas such that the ECU thinks that the pre-cat is still installed.
The right angled fitting is essential in order to fit under the airbox and to retain the original wiring mounts.
I like this solution because it is cheap, easy to install and easy to reverse should the need arise.
Other posts in this category: Engine and Drivetrain
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Aldous Voice 