BLUF:
Engine starts, runs and then begins to stumble, I troubleshoot and see 0 psi on the fuel pressure gage. Once I check the lines, etc. and start the engine, the pressure is 5+ psi and then slowly drops to 0 psi again in about 4-6 minutes of idle time. The engine stumbles, runs lean (I have an AFR meter in the car), and it idles rough, etc.
Background:
New engine I built, <500-ish miles on it, mechanical fuel pump (High Volume Mechanical Fuel Pump - Black). New gas tank, new tank pickup and sending unit, new fuel lines, new filters. Simple fuel system, no return. Car has run great for several months now (other than the transmission giving me fits... it's been great)
Troubleshooting: (after each step, put everything back together. Ran fine, good PSI, then slowly drops off to zero psi)
* - Confirmed, full fuel tank. Brand new gas... filled up just the other day.
* - Removed and cleaned fuel filter. Was fine. Cleaned anyway.
* - Used compressed air to blow back (from pump to tank) the fuel line. No obstructions.
* - Removed pump to check it and the push rod. Push rod looked great. Checked the cam lobe with a bore scope, looked great. Pump seemed to operate ok, but at first it was "sticky", but seemed ok.
* - Tested gage, worked fine.
* - Confirmed all fuel lines were ok and not leaking.
* - I checked engine oil, several times, level consistent, no gas in oil.
Conclusion... I think it's the pump. Perhaps there's a pinhole in it that is slowly filling the other side of the diaphragm?.. but I also think I'm wrong. Something doesn't seem right about it having good pressure and then dropping off slowly to zero. And it's brand new.
I very much welcome your insights!
Here's some pics... always nice to see what you're working on
Engine starts, runs and then begins to stumble, I troubleshoot and see 0 psi on the fuel pressure gage. Once I check the lines, etc. and start the engine, the pressure is 5+ psi and then slowly drops to 0 psi again in about 4-6 minutes of idle time. The engine stumbles, runs lean (I have an AFR meter in the car), and it idles rough, etc.
Background:
New engine I built, <500-ish miles on it, mechanical fuel pump (High Volume Mechanical Fuel Pump - Black). New gas tank, new tank pickup and sending unit, new fuel lines, new filters. Simple fuel system, no return. Car has run great for several months now (other than the transmission giving me fits... it's been great)
Troubleshooting: (after each step, put everything back together. Ran fine, good PSI, then slowly drops off to zero psi)
* - Confirmed, full fuel tank. Brand new gas... filled up just the other day.
* - Removed and cleaned fuel filter. Was fine. Cleaned anyway.
* - Used compressed air to blow back (from pump to tank) the fuel line. No obstructions.
* - Removed pump to check it and the push rod. Push rod looked great. Checked the cam lobe with a bore scope, looked great. Pump seemed to operate ok, but at first it was "sticky", but seemed ok.
* - Tested gage, worked fine.
* - Confirmed all fuel lines were ok and not leaking.
* - I checked engine oil, several times, level consistent, no gas in oil.
Conclusion... I think it's the pump. Perhaps there's a pinhole in it that is slowly filling the other side of the diaphragm?.. but I also think I'm wrong. Something doesn't seem right about it having good pressure and then dropping off slowly to zero. And it's brand new.
I very much welcome your insights!
Here's some pics... always nice to see what you're working on
