alter ego

I just got through checking my fuel pressure on my motor. I havn't been getting good performance from it this season and I noticed my plugs were way too clean after runs so I figured my regulator is adjustable and the previous owner told me that he had the same symptoms before he got the regulator and he adjusted it up to about 40psi and it ran fine. The place that sold the boat may have adjusted it down because at idle it ran very rich. The motor is not stock. I found 15psi @ idle then 20psi with the vacuum line removed. When I gave it throttle in nuetral it went down by about 5psi with the line still on. I know this isn't right and probably explains my lack of performance and great fuel mileage. Is the pump shot or will adjustments back up to normal levels fix this? Thanks in advance for any advice...

jspeeddemon

I wouldn't even consider starting that motor until you get to the bottom of that issue, pump or regulator. That thing will start spitting aluminum chunks out the exhausts if you run it with low fuel pressure, you're injector flow drops way off at fuel pressures like that. Most GM injectors are rated at 43 psi nad falls or raises 7-8% for every 10 psi one way or the other. Check the pressure with a gauge before the regulator to see if it's the pump or not.

jspeeddemon

[QUOTE=jspeeddemon]I wouldn't even consider starting that motor until you get to the bottom of that issue, pump or regulator. That thing will start spitting aluminum chunks out the exhausts if you run it with low fuel pressure, you're injector flow drops way off at fuel pressures like that. Most GM injectors are rated at 43 psi and falls or raises 7-8% for every 10 psi one way or the other. Check the pressure with a gauge before the regulator to see if it's the pump or not.

Tim G.

Maybe not the right track, but My 502MPIs recently needed the entire injection/fuel system cleaned out. The injectors were pretty clogged up... You'd be suprised how much crap makes it past the merc fuel filter...
Oh, and we put big Raycors ahead of the merc filters now....
These engines have never run as good as they do now.

alter ego

Do you think I could adjust the pressure back up to the 36-40psi level with the adjustment on the regulator and diagnose from there? My thought was that someone at the dealership turned the pressure down or someone took it off and reinstalled without readjusting. I did just have closed cooling installed and it is mounted right there next to the regulator. I just don't know why the pressure drops with throttle....I can't remember if that is normal because i havn't had to play with fuel pressure in a long time.

alter ego

Reset fuel pressure, put in fuel treatment and gained 6.5 mph back. No stalling or pinging anymore. Final pressure was 42psi @ idle. I am going to get a new raycor water seperator too. Thanks for all your advice.