carb - fuel pressure question

Tetanus

Tetanus

Member
Joined
Apr 22, 2005
Location
Kansas
I've been having poor idling with my '75 K10 350 w/ a 4bbl. quadrajet. Someone recommended installing a fuel pressure gauge inline to see if there was a problem with the mechanical fuel pump (which is only a year or so old). The book spec says the fuel pressure should be 5 - 9 psi. My gauge cycles back & forth from about 2 - 7 psi. very quickly (approx. 10 times a second). Is this normal? I understand that the pump has to cycle because the pushrod pushes in and out making the pump function...but I'm not sure if it should be that noticable? I've never seen a gauge on anyone's carbed engine before so I don't know what to compare this to.

Anyone else have a similar setup?
 
My BRAND NEW pump from NAPA for the TBI went bad after about a week! It was cycling like yours sounds like, needle fluctuating and weak. Replaced the pump fixed everything.
 
CYJKrawler, I'm assuming w/ TBI that you were using an Electric fuel pump...is this correct?

Also, how was your engine running with the fluctuating pressure?

I would think that it would definitely affect a TBI engine as the pressure would directly affect the injectors. W/ a carb, the pressure might not be as big of a problem as it fills the fuel bowl in the carb. I'm still trying to figure out if this could be the problem for me.


CYJKrawler said:
My BRAND NEW pump from NAPA for the TBI went bad after about a week! It was cycling like yours sounds like, needle fluctuating and weak. Replaced the pump fixed everything.
Click to expand...
 
Yes, an external, electric pump. Engine went from running fine to wouldn't idle to wouldn't start as the pump went bad and the pressure it was putting out got to be less and less. As long as the bowl is kept full you should be OK I would think.
 
Fuel Pressure

I've got a weber carb on the stock 4.2L CJ motor. My carb is set at 3.5 psi and it stays right there. Upon start up it is about 5 psi and then after the engine warms up it is at 3.5. I purchased a fuel pressure regulator and gauge from summit to track.

Although your pump cycles as the engine runs I would think that the fuel in the fuel filter would keep the fuel going into the carb at a staeady rate assuming the fuel filter is between the pump and carb like mine is on a cj.

Karl
 
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