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Old June 25th, 2016, 12:27 AM
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Mike & Carrie Wendt
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Odd noise - 2.5NA

Okay all you 2.5NA haters, have your fun.

Recently my '86 90 ExMod started making a -cha-cha-cha- noise when I start. Matches RPM changes and sounded to me like an exhaust leak. As the engine warms up, the sound goes away.

So I opened the bonnet and put a wrench on the 8 manifold nuts expecting to find one or more loose. All were tight, so gave each a small turn.

Still have the noise. With the bonnet open, it sounds like the -cha-cha-cha- noise is coming from the vacuum pump. (I know, it can be difficult locating noise source in noisy environments.)

Can the vacuum pump make a noise that goes away when it warms up? Does this mean the pump is about to fail? What should I do if anything?

Mike
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Old June 25th, 2016, 04:06 AM
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Ed
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Not sure if it's the same problem, but I have, what I think is, the same sound. It's coming from my Cyl #1 that is at 40% compression, so I have blow-by. This blow-by comes out of the line on my valve cover cap and back into the intake manifold. Manifold seems to resonate the cha, cha, cha. Mine seems to quiet down when warm as well -- attribute that, and less smoke, to piston rings expanding and sealing better.
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Old June 25th, 2016, 08:15 AM
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Robert Davis
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Great insight Ed.
Most likely piston rings that expand upon heat up or leaking injector that is puddling fuel in one or more cylinders after shut down.
Hard worn valve guide seals can contribute, but unlikely the sole cause.

I ran a 2.5 in a 109 for a few months.
Pulled out on the highway one time and a car 5 miles back nearly rear-ended me.
Was at a stop light and a guy who had passed me once, gotten off the road, done some shopping or something, gotten back on the road and caught up with me at a light rolled down his window and said Race you jokingly.
It had RHD so was close to his side of the car.
I said sure, let's race across that small ditch and through that field.
He rolled his window back up...
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