Agree

He has MEFI 3 reporting so clear flood is in the mix. but does the injectors fire at all - like I said simple test is noid lites on the injector connectors and see if you have that signal at least to the injectors. MEFI ecms can suffer from bad injector drivers. I had 2 Mefi ecm s last week alone with bad injector drivers. - one was a MEFI 3 and the other was a 4.

That is what we thought was happening. Fuel pressure was spiking and pegging the pressure gauge when I cranked it.

My engine builder was thinking the fuel pressure regulator was suspect and the computer (MEFI 3) was shutting down the injectors when it saw too much fuel. First he wanted me to check the return line for obstructions and change the separator . My return goes back to the separator not the tank. That was good and still no change. Then he shipped me a new Aeromotive Regulator with all required A N fittings and fuel line, as I needed to re-plum some things.

The adjustable Holley regulator I had they no longer make. Only a fixed pressure one at about 43 lbs. That won't work for me as mine runs at 62 lbs. The Holley regulator fit up into the bottom of the fuel rail similar to the way the injectors fit up into it. I had a machinist friend of mine drill, tap and plug the spot where the old regulator fit into the rail.

I installed the new parts and still no go.

Our season up here is getting short and I don't want to keep figuring this thing out. So next week I am going to pull the boat back to my engine builder and he is going to help me get it up and running. He has been very helpful.

I will update when I am back with the results.

You guys were right. Fuel pressure was the problem.

Took some troubleshooting, but it was a pinhole air leak in the braided fuel line of the return line.

In an effort to avoid future fuel issues we decided to upgrade the entire fuel system which included new pump, regulator and all fuel lines and fittings.

Then tuned on the water, with a laptop, reprogramming the computer's air fuel mixture ratio's through the entire RPM range. Fuel pressure is now at the normal 43 lbs.

It is running about as good as you can get now.

My Holley EFI ( sequential port ) has a pressure gauge on the fuel rail. You might want to install one.

I did add one. Just easier to see what is happening.

Asked about this post for someone so I will post the answer here.. The Merc 555 ecm / pcm DO NOT HAVE CLEAR FLOOD MODE. The MEFI ecms did. So if your 555 controlled engine is hard to start or no start - I would do fuel pressure testing - ignition spark events and take a look at the crank and cam sensor and the IAC before anything else. Also try using a remote gas tank and very fresh gas along with a primer bulb / new fuel line set up to see if the engine will start easier or start ??

How does a pin leak on the return side affect anything beside causing a gas leak?

I am not exactly sure.

Mainly it wouldn't hold fuel pressure. I did not see any fuel leaks.

You had a hole in a fuel line but didn`t see any fuel leaks and it wouldn`t hold fuel pressure because of a hole on the return side.. none of that makes any sense .