looseconnection

I performed a no load test on my fuel rail. Pressure maxed at 20 psi and as soon as the pump quit running pressure fell to 5 psi. I have been chasing a lack of rpm on my port motor and have gone thru all ignition components now checking fuel psi. My adapter started leaking once I connected it to other good running motor so I have nothing to compare to. Merc manual only states 30 psi for this engine but does not indicate if pressure should drop once fuel pump turns off. Any pointers?

Thanks, LC

looseconnection

will testing under no load tell me anything?

Expensive Date

If these are like the 6.2s and you have the cool fuel set up, rectangular box that has both pumps in it that sounds low. I believe that injector needs 44 psi to cycle. You may have two pumps if they are like the 6.2s a high pressure and a low pressure,, if so there is a regulator that has a vacuum line connected to it, if I remember correctly there s also a screen under the regulator that gets clogged. There was somebody on here that had a pick up in the tank break on a 292, but not sure if that would cause low pressure would think it would cause no pressure.Load shopuld not matter much as long as you can run the RPMs up

Let me know if you have the pumps that I described, bad news is I don't think you can get them (pumps) anymore and you have to retro to the new style.

looseconnection

i have cool fuel but its mounted in a black box on the lower port side of the motor. not down by the water pump.

LC

looseconnection

just one pump.

Expensive Date

Maybe someone will chime in that knows for sure, but like I said pretty sure the injectors need more than 20psi to cycle. You could always switch the fuel pump boxes side to side and see if problem follows, just don't take them apart the rubber that the pumps sit in will be swollen from the ethanol in the fuel, you may nor be able to get it back together without new seals.

spectras only

You have a returnless fuel system, so it should keep fuel pressure up for a little while it bleeds back through the fuel cooler system.The pressure regulator is sitting atop the round copper cooler and the excess fuel returns to the water separator via a small s/s screen under the pressure regulator.The high pressure pump is in the rectangular black box and the low pressure [ sucking] pump is before the water separator.You should have between 38-42 psi at the Schrader valve at idle.Either the pressure pump is weak or doesn't get enough fuel from the low pressure pump.Check the water separator for water contamination [ just empty it for now and reinstall it] and maybe check the screen for debris [ mesh] on the inlet side of the high pressure pump.

looseconnection

SO,

There is no low pressure pump. Fuel tank to fuel water sep, then on to pump intake, fuel cooler, then either to fuel rail or return from regulator to fuel water sep.

I am gonna check at idle today, yesterday was no load/no run just the 2 second period of run time allowed by the ecm.

looseconnection

Needle in fuel psi gauge is bouncing. Like pump is getting air. Turn off engine gauge goes to zero. Otger motor is rock solid at 28/30 psi and holds 21 when off. I think my problem is on suction side of pump..

spectras only

I'd get a low pressure fuel pump.If the Bosch unit is too expensive for you, get a cheaper Carter electric [6-7 lbs ] from any auto accessory shop to find out if it fixes the propblem.i used Carter electric pumps as a primer for all my engines with mechanical diaphram type fuel pumps.It was setup as a bypass with switch on the dash. Never had to pump the throttle to start them and it served as a backup, in case the diaghram ruptures.I rather have redundancy than get stuck in the middle of nowhere.