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Originally Posted by Tractionless
(Post 4667110)
I've been working on this for over the past year with scans etc. Upon the advice of another member today I pulled the vac. line to the fuel pressure regulator while the 1k rpm surging was taking place and it immediately stopped the surging. Even though fuel pressure reads good with the vac line attached at all times, including during surging I may be leaning toward replacing the FPR. I will update the thread with my findings.
Keith I think you are on the right track. |
Originally Posted by Gimme Fuel
(Post 4667154)
I was having some hard start/surging idle issues on my 502 MPI although it is a Mefi3/cool fuel model. Chased TPS and IAC first. Checked Fuel Pressure and found to be only 30 psi, regulator was bypassing and pump wasn't building any static pressure and bleeding off quickly. Replaced regulator and instantly idled and started cold with touch of the key. Didn't miss another beat all season.
I think you are on the right track. Keith |
Replaced the fuel pressure regulator with a new Mercruiser unit and the issue persists.
Keith |
The VST plenum flooding comes into play after a warm engine has sat for a period of time allowing fuel to percolate out of the aged VST internal diaphragm thru the yellow hose and into the plenum. My prior build used the VST and I removed it with current build. The VST is prone to vapor lock, and mine did VL at times, but no time was fuel present in the line Your pressure is 37 psi, and when black smoke comes there is no fuel in the over flow line? |
Originally Posted by AllDodge
(Post 4673151)
Don't agree, at no time should fuel be in the yellow hose.
My prior build used the VST and I removed it with current build. The VST is prone to vapor lock, and mine did VL at times, but no time was fuel present in the line Your pressure is 37 psi, and when black smoke comes there is no fuel in the over flow line? |
Not sure how the VST came back into play but it was fully rebuilt less than 60 hrs. ago which is about 2 years. I also use non-ethanol fuel and the issue will happen prior to shutting the engine off. I have new yellow hose and zero liquid in it.
Keith |
Only reason to ask about the VST is because I don't remember ever seeing what the pressure is, only that it was rebuilt and pressure is ok
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Originally Posted by AllDodge
(Post 4673970)
Only reason to ask about the VST is because I don't remember ever seeing what the pressure is, only that it was rebuilt and pressure is ok
Keith |
With it subsiding when vac is pulled from FPR, keeps me wondering about the fuel pressure. Pressure increases when line is removed and a small increase in air due to leak
VST should be at 37 psi |
Originally Posted by AllDodge
(Post 4674753)
With it subsiding when vac is pulled from FPR, keeps me wondering about the fuel pressure. Pressure increases when line is removed and a small increase in air due to leak
VST should be at 37 psi I see in the manual where the VST equipped engines are to be between 34-36 and cool fuel 28-32. For what it's worth the other engine is at 30 psi and runs fine. So I'm guessing the thinking now is both VST electric fuel pumps are on their way out? |
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