jon@dakota-truck.net wrote:
> "Jamie Calder" <jcalder3@cfl.rr.com> wrote:
>
>
>>Me too...It would seem to me that a clogged cat would create more pressure
>>(back pressure) and not vacuum. I realize this isn't so...but why? How
>>about Vacuum 101, The Why's and Why Not's.
>
>
>
> A clogged cat would indeed create more backpressure, which
> basically creates more pressure in the engine than would normally be
> there with a free flowing system. Pressure is the opposite of vacuum,
> so when you combine the two, naturally the vacuum will drop. The
> clogged cat isn't creating vacuum, its decreasing vacuum.
>
> Picture a sealed container with a vacuum gauge in it as well as a
> couple of ports. Hook a vacuum cleaner to one of the ports and block
> off the other one, and you will be able to see the level of vacuum
> inside the container on the gauge. Now if you unblock the other port,
> the vacuum level will drop, this is basically a vacuum leak. If the
> vacuum cleaner is strong enough to overcome the leak, the vacuum level
> won't drop down to zero, but it will drop down by some amount,
> depending on the strength of the vacuum cleaner and the size of the
> leak. Now, instead of that second port just being a vacuum leak,
> picture hooking the hose from your air compressor to the second port.
> The vacuum will drop even further, and you may reach zero vacuum or
> even positive pressure, depending on the relative strengths of the
> vaccum cleaner and the air compressor. This is basically what is
> happening when you have a clogged cat or other restriction in the
> exhaust system. Essentially, your engine *is* a big air compressor,
> so when the exhaust becomes restricted, the pressure will go up inside
> it almost like the engine is an air compressor which is treating the
> exhaust tubing as an air tank and is trying to pressurize it.
>
> That's probably as clear as mud, but it was fun to think about so
> I'll hit "send" anyway. :-)
>
Ok - I'm going to get a mechanical vacuum gauge and plug it into the
Ram's engine - and see exactly whats happening. Bernd - back when you
said you noticed the MAP readings on the RAM were going the opposite way
of what you expected? I hooked the scan tool up to my neon and noticed
that the numbers behaved in the same way. I'm not sure what that means.
Might mean that the scan tool operates differently? The Neon is running
just fine.
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