7.4 MPI Stalling wont idle.

[Al D Perkins]

1999 Mercruiser 7.4 MPI. Engine will start after a few attempts when increasing throttle then die. Finally will run with throttle (giving extra gas) while idling but revs and calms and revs and calms, got a little miss or mild backfire after running for a while. All of this is out of gear. Had the sea pump replaced las year, bearing seized up. Got the boat back and it took a few tries to start but started and idled. Took the boat out and it ran fine, but started to notice a slight change in sound and speed at high speed. Had the boat winterized and now this problem.

 

[alldodge]

Remove the fuel filter and dump contents into a clear jar. Should only see clear gas

Check fuel pressure, should be 43 psi
Pull some plugs and see what they look like

 

[1990dtgl98]

I had a surging at idle an backfiring above 1600rpms issue as well. Check your rail pressure. I only had 28psi. Was most likely the pressure regulator but I wound up replacing the pump while I was down there as.well.

 

[Al D Perkins]

Ok all, just now able to get to it. Pressure goes to 80 initially them drops to 42. Try to start the engine and pressure goes up to 80 then drips back to 40 when it dies. I'm attaching a pic. Glass jar on the right is from the pressure relief of the gauge. The jar on the left is non ethanol gas I use for my mower. A lot darker. Bad fuel issue?

 

[alldodge]

Bad fuel and bad fuel pressure regulator.

 

[Al D Perkins]

Bad fuel and bad fuel pressure regulator.

Damn, put $70 worth of new gas in 2 weeks ago. Just my luck.

 

[alldodge]

You might be able to burn thru the gas, probably won't run very well. The regulator is way to high and can damage things

 

[Al D Perkins]

Thanks. Ordered the regulator from Merc and will see how it runs after installing. Many thanks for the help!!!!