“07 5.0 MPI No start without throttle

[Modred33]

2007 Mercruiser 5.0 MPI Bravo III
SN 1A070616
167 hrs Original owner bought new.

Hey all and thank ye ahead of time, for your time!

Let me start by saying I’m trying to get someone with a scanner to troubleshoot the motor. Problem is I didn’t buy a trailer with the boat and the mechanic around the corner is swamped and reluctant to make a house call. Hoping someone can point me in a Direction until I can get a scan done.

Motor won’t start unless full throttle is applied and when it does start runs rough.

Changed spark plugs today. All were dark with soot
Number three and number five plugs had electrodes missing Installing new plugs made no difference in performance. I have also replaced the IAC valve and throttle position sensor.. installed two brand new batteries last month. Replaced cap rotor and wires two years ago. Feel like I should perhaps change them again as they were after market and now I’m doubting their quality. Done working on it today but will be back at it tomorrow to try suggestions .

Thanks!

 

[Fun Times]

All were dark with soot
Number three and number five plugs had electrodes missing

Hi there, welcome to iboats...

Looks like your engine may be running to rich possibly either due to the fuel pressure to high or maybe a bad MAP sensor could do that as well plus be sure your engine temp is running normal in the 160 -175ish range ?.

If the electrodes on the spark plugs were missing then that might be an indication of internal engine damage so you might want to preform an engine cylinder compression test and maybe an leak-down test too. And if you can get your hands on a digital borescope to have a look around inside each cylinder might be warranted too just to be sure.

Motor won’t start unless full throttle is applied and when it does start runs rough.

You might be entering clear flood mode if the fuel pressure is to high. Clear flood mode is the ecm turning off the fuel injectors at a certain throttle percentage usually nearing 100% depending on engine models.

 

[Modred33]

Thanks so much. Engine temp has been good. I think I’ll try the MAP as my last attempt of R and R. Will post back after that is replaced.

everything you said makes sense. Buddy at work has a borescope will try to borrow it next week. Other than that going to have to make arrangements to get it up to the mechanic for the other test.

when it was under warranty it went twice for the spark plug issue never get a straight answer of why.. it has been plagued from the beginning with these kinds of issues. Thanks again for the info will post back when I have something .

 

[alldodge]

I would check that your distributor is installed correctly, then ensure you are using AC 41-932 plugs and gap at .060

 

[Modred33]

Got the plugs from the dealer this morning, NGK ITR4A15 5599 I did check the gap it is .060 As far as I know distrib, has never been taken out, Will check rotor position tomorrow,

 

[Modred33]

Ok have some updates. Fuel pressure at the rail is 40 psi. Replaced MAP sensor. Had code reed done. Code 75 and 94 present.

Engine starts now now and idles decent. Now won’t take any throttle. With hard feathering of the throttle can keep it going. Getting some popping back through the throttle body as it struggles to stay running. When throttle is pulled back to neutral, snaps back to a solid idle.

Guy that did scan thinks one of the gen iii cool fuel pumps could be to blame. Doing a compression test this weekend. Thought I might mention the drive trim on the throttle is inop. I’m sure it’s not related but just in case.

 

[alldodge]

Codes 75 fuel level ckt hi and 94 pitot ckt lo should not be an issue unless you have digital fuel and speed sensors, most don't

Fuel pressure should be good enough (manual 43 psi at 1800 rpm) if its stays there when throttling up

 

[Modred33]

Went back through my notes. Looks like running pressure was low. It’s either 24 or 2.4 psi. Was trying to write everything down as the guy was scanning it and calling it out. My fuel pressure tester gauge holds the highest pressure it see’s. The value the scanner gave was running pressure.