Fuel pump check valve

Phil Rose pjrose at frontiernet.net
Fri Sep 13 20:12:22 EDT 2002

At 5:20 PM -0400 9/13/02, DasWolfen at aol.com wrote:
>  A failing fuel pump checkvalve can cause hard warm starting for a very
>simple reason........HEAT. The fuel must be under a certain amount of
>pressure to prevent it from boiling in the rail, ie: vapor lock. Not as much
>a problem for injected engines as it was for carbs because the pump is able
>to shove enough fuel at pressure to raise the pressure and cool the rail given
>enough time. During cold starting the checkvalve isnt nearly as important in
>an EFI engine. There isnt any vapor pressure in the rail to overcome and the
>rail doesnt need cooling thereby masking the defective checkvalve.
>  Phil, your idea will cause the ECU to switch into cold start/run strategy.
>The problem is the only real effect is to increase the duty cycle of the
>injectors during the start attempt, not cool the rail or eliminate the vapor

Well, at cooler temps  the vapor bubble(s) will diminish although not
necessarily vanish-- but in any case (when still hot) if the injector
duty cycle is increased by fooling the ECU, then fuel flow will be
faster and the vapor will be purged faster--although I don't know if
it would be enough to make a significant difference in cranking

As to the resistance value that Eyvind asked about: if it's taken
from G62 (coolant temp sensor), then a "hot" temp (around 90 deg C)
corresponds to a resistance of about 200 to 300 ohms; a cold temp
(below 25 deg C) is on the order of 2000-3000 ohms.

Phil Rose
Rochester, NY
mailto:pjrose at frontiernet.net

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