DeTomaso Mailing List: June 2001, Message #180

I found a few articles on the net last night about diagnosing engine problems 
using a simple vacuum gauge.

I connected a gauge to the PCV hose, which is connected to the large plenum in 
my EFI intake and should therefore have good engine vacuum.

I started the engine and let it idle at around 900rpm and I saw that the vacuum 
was around 0.4bar, or 12in Hg, which is a bit low. The needle fluctuated 
slightly.

I raised the rpms to around 2000 and the needle then began fluctuating more and 
more.

When I let it drop down to idle the needle was fluctuating quite a bit, but that 
evened out in a short while.

Low vacuum at idle indicates late ignition or valve timing, low compression, 
stuck throttle or a vacuum leak.

Fluctuating needle as rpm increase indicates weak valve springs, worn valve 
guides or leaking head gasket.

Intermittent fluctuation at idle: ignition miss, lifter bleeding off or a BIG 
camshaft.

Personally I believe it to be bleeding lifters and perhaps worn valve guides.

One thing that I believe speaks against the guides is that the engine doesn't 
seem to consume oil and I haven't seen any blue smoke when I step of the gas and 
hit it again.

Comments?

Thomas