CBU and Plumbing - The Unofficial BMW M5 Messageboard (m5board.com)

everycredit · 27th January 2009, 15:24

So, I was in the shower and started thinking... What if you rerouted the secondary air pump hose and connected them directly to the exhaust (pre-cat)? Install a check valve to prevent water/air backflow. Does the air need to go through the engine block (other than to heat the cats)? If it does, a simple heater element might do the trick.

This is probably over-engineering the solution (powerchip seems like an easier work-around), but this would technically "solve" the problem and make you compliant with state and federal environmental regulations, if you care for that sort of thing.

everycredit · 27th January 2009, 15:35

Thinking a little further (and not toward practicality, as it probably isn't), it wouldn't be as efficient as direct port injection of fresh air, but will still heat up the exhaust gas. I'm curious if it would cause a detonation of unburned hydrocarbons, which could be harmful for your car?

2strokecoldsmoke · 27th January 2009, 22:02

I remember a lot of engines of early 80's vintage used air pumps to burn off excess hydrocarbons in the exhaust pipe.

BTW, why were you thinking of plumbing and pipes while in the shower?
was the missus in there with you?

everycredit · 27th January 2009, 22:53

Aye--is that so wrong?

DouglasABaker · 27th January 2009, 23:40

If you just want to heat the exhaust up, you don't need a small heater, you need DEI.

At a high level, I agree with you - your thoughts are on target and would resolve the issue. My personal opinion is that the only issue with the existing systems are that a) the pump doesn't provide enough pressure, and b) there is no check valve / the pump shuts off. These 2 combine to allow exhaust byproducts into the air channel.

But, I would also question whether or not your proposals would really be that inexpensive to implement and would be effective. Specifically I'd be concerned about the length of time that the newly introduced air has to complete the combustion before reaching the pre-cat O2 sensor. In order to port the air in at a location that is convenient you'd need to be close to them and it may not provide enough time. Moving it upstream far enough to be effective would obviously work better, but would also increase the price tag significantly and likely would make it more expensive than the presently available software upgrade.

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Ledfoot · 28th January 2009, 02:04

When I'm in the shower, I'm usually thinking about a different kind of 'plumbing.'

Sorry, cuoldn't resist.

EM5PWR · 28th January 2009, 03:41

I try not to think in the shower, I just want to relax and wash my plumbing..

2strokecoldsmoke · 28th January 2009, 08:58

oh boy, I was afraid my earlier comment would get this thread off topic.

Douglas brings up a good point concerning the lack of check valve in the existing system. Perhaps the easy/cheap answer is installation of a check valve?

thoughts on that?

everycredit · 28th January 2009, 09:26

Is there enough pressure from the pump to open the valve?

DouglasABaker · 28th January 2009, 16:21

Quote:

Originally Posted by 2strokecoldsmoke

oh boy, I was afraid my earlier comment would get this thread off topic.

Douglas brings up a good point concerning the lack of check valve in the existing system. Perhaps the easy/cheap answer is installation of a check valve?

thoughts on that?

You can't since the check valve would need to be located in the engine block itself and thus would require a new / different block.

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