5.7 MP issues

[Mynameisbrandin]

At a total loss here being semi mechanically inclined.. 08 Z1 with MP 5.7L.

Had an issue with fuel pressure not being up to par(10-30psi), changed the high pressure fuel pump cartridge as the low pressure pump was working correctly (verified at the high pressure pump while changing it out). Fuel pressure now reads a steady 55-60psi while running And under throttle on the fake-lake. While I had the tools out I changed the plugs, distributor cap and rotor and the 4 relays by the ECM.

Got it on the water thinking my vapor lock/rough idle was fixed.. sure enough, same problem. Launch the boat and fires right up and runs great at idle and in gear, putt around the no wake zone and wait for the ole lady to get to the dock to get her, mind you, running my bilge blower constantly. Pick her up and get to open water(motor is warmed up by now), give it throttle and it falls on it’s face and starts idling rough and kind of surging. Put it in neutral, starts to run rough and eventually dies out. Try starting again and nothing.. probably try about 10 times before it sounds like it wants to run and still nothing. Operating temps are normal(140-145) the fuel looked good when I got some out of the fuel pump. I’m stumped. Any guesses on what it might be?

edit: was doing the exact same thing before changing the high pressure pump

[boatwakes]

When did it start doing this and what, if anything, was done to the engine prior to this happening? How did the spark plugs look? Were the two center plugs on each side different colors or rusted?

[Mynameisbrandin]

When did it start doing this and what, if anything, was done to the engine prior to this happening? How did the spark plugs look? Were the two center plugs on each side different colors or rusted?

It started beginning of the season this year after about 3-4 successful outings with no problems at all. It happened once but not as severe with some friends with us. Was able to idle around and it randomly cleared up and ran great the rest of the day and the next day also. I did change the horrid looking fuel filter before taking it out again after that and ever since it has given us the problem I described. The plugs I pulled looked great and I’m not sure when the last time they had been replaced. I replaced them with the recommended plugs and made sure they were gapped to spec. This week I planned to pull the injectors and have them checked to make sure any of them are not clogged or stuck closed/open.

[boatwakes]

Before pulling the injectors, run the fuel pressure gauge on it under load. I.e. when it's on the lake and in gear, accelerating. The low pressure pump may be causing a delivery problem under load.

[Mynameisbrandin]

Before pulling the injectors, run the fuel pressure gauge on it under load. I.e. when it's on the lake and in gear, accelerating. The low pressure pump may be causing a delivery problem under load.

I can do that. Thanks for the replies. Will report back with the results

[Mynameisbrandin]

I want to say I have found my issue.. I feel like an idiot not doing this from the beginning.. I definitely got the shaft on some gas recently

[boatwakes]

Good GAWD!!! If that's ethanol gas you gotta drain the whole tank. If not, just pull the water off the bottom. Run some 2 cycle oil through the engine using a remote fuel tank like a dingy 6 gallon tank or something similar. It'll help save the fuel pump and injectors. Run it at 3 oz/gallon (50:1) mix ratio.

[Mynameisbrandin]

Drained the tank, replaced some fuel lines and the filter, got it on the water today and did Put a little 2 cycle in the new fuel. Got it started and it was running a little rough but not stalling like before. Decided to idle around the no wake zone and it was doing good. Got on the throttle a little bit at a time and could tell plugs weren’t firing and it was running a cylinder or 2 down. Sounded like the plugs dried up and started firing correctly and it ran like a bat outta hell the whole day. Motor sounds great and running smoothly now. Thanks for all the help