fuel questions

[gmcturbo]

when i energize my fuel pump through the test lead (engine off) i get 42PSI. when i turn on the engine the feul pressure gauge starts ticking like crazy. im trying to track down a rough idle problem im having. how do i do a leakdown test? im doing a compression test today. it also seems to get worse in closed loop. thansk

mike

 

[jwaller]

the fp gauge ticking or moving around under eng load is normal. it is just the pressure reacting to the opening and closing of the injectors. unlees by ticking you mean dropping very sharply then coming way back and droping sharply..

 

[Sy769]

Well people are different in their perception of rough. Me... a 12.5:1 compression big block with as much cam duration as the day is long sounds good. So my Sy's idle doesn't bother me.
Seriously how rough is it? Stock truck tend to idle rough according to some peoples definition.

42 is about right for the fuel pressure. Energizing the pump is the best way to check the pressure. With the vac line connected to the regulator fuel pressure will vary with vacuum and boost. The more vacuum you have the lower the fuel pressure, the higher the boost the higher the fuel pressure.

Can't remember the specifics on the leadown test. Most testers will come with instructions though.