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post #2 of Old 08-25-2010
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Evaluation of 'fuel starvation" symptoms:

Apply a vacuum gage somewhere between the lift pump and the 'racor' filter(s). Most racor filters already have a gage port to do this.

Start the engine and watch the gage during constant rpm normal operation. Trial 'should' be at 80% of maximum engine rpm, with normal LOAD (prop turning) on the engine.

If the engine then stalls and the vacuum reading *increases* there IS a fuel restriction such as collapsed filter, undersized filters, totally 'completed' /clogged filter, obstruction on the 'diptube' (blocked screen on the dip tube), kinked fuel delivery tube, blocked tank vent, etc. etc.
If the engine stalls and there is *no increase of vacuum* (gage stays steady) then look for blocked water injection nozzle, in the exhaust system, blocked exhaust system, etc.
If the engine stalls and there is a *DROP of vacuum* ... you have an air leak in the fuel delivery system: pin hole in the lift pump diaphragm, loose compression fitting, etc. (Note: compression fittings 'should' be trimmed back each and every time you open one ... that 'ferrule' in a compression fitting compresses/deforms the copper tube permanently).

To correctly monitor the RACOR filter(s) via use of a vacuum gage, go to Parker - DIESEL FUEL FILTRATION, choose the appropriate filter type .... and find the proper technical FLOW vs. ∆P CURVE for your specific filter.
You are looking for a graph that lists Gallon Per Minute/hour VERSUS 'differential pressure (vacuum)' psid.
You change the racor when the indicated vacuum, with the engine running at 80% of wide open throttle (WOT), is at 80% or rated maximum flow demand of YOUR ENGINE ... so you have to look up the specific engine data for the expected flow, etc.
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