[Naughty Dog]

Hey all, I have 2001 Z275 7.4L GSI Duo Prop. After running it and sitting for a few minutes it doesn't want to start without putting the throttle control to full power. It smells gassy when it does fire up. I have had suggestions for checking the vacuum fuel pressure regulator for fuel leaks into the vacuum line that goes into the intake - it's OK, no leak. MAP sensor was the next suggestion - replaced with no improvement, so I guess I got a $115 spare part that probably will never be needed. This morning I checked a few more things, the way it acts (because it starts perfect when cold) it may be in "choke" mode all the time?? I checked for voltage at the coolant temp sensor and the manifold air temp sensor with ignition switch in run position and I don't appear to have 12v at these. Should these get 12v from the ECU?? I don't see any type of fuse in the system that would prevent power from getting to these two sensors - my fear is the ECU has gone bad (if it is possible to go partially bad??)

Anyone have any suggestions on where to go with this issue next??




Thanks

Tom

[Naughty Dog]

Update - Talked with a boat mechanic that's a friend of a friend and he says that the signal to the two sensors is a milli volt signal so I wouldn't see it with the test light. So that leads me to think I may have a bad sensor?? Hopefully not the ECU as finding it online my best guess I have for cost is $1200 to $1400... He is loaning me his scan tool today hopefully and I am going to try to get back to boat today or tomorrow and see if I have any codes that will lead me in the right direction.


T

[Naughty Dog]

Update - took the scantool to the boat last night, cleared some codes I created while I have been troubleshooting this issue and restarted and ran it some, no current trouble codes. Took it out on lake with the scanner to monitor sensors and such then shut it down after about 10 minutes of 40 MPH cruising. Sat for about 10 min and wouldn't start. Still no codes. Tried to start with part throttle in neutral and wouldn't start, smells gassy out the rear. Put throttle to wide open and won't start still - wind blowing about 20 mph and we blowing towards a boat ramp / shore. So I run up front to grab the anchor and my buddy messes with the throttle - starts cranking and pulling back from full throttle and she fires up at about 60% throttle???

Ran it back to marina - have about a 6-8 minute run at idle in the no wake zone, park it back in slip shut it down and wait a few minute and starts fine???

So the issue is after running fairly hard and shutting down. I don't think it is vapor lock because of the gassy smell when try to crank it after sitting???

TPS, Manifold air temp and MAP sensors seem to be reading fine on scan tool???

Any thought out there???

[DFZ272]

Hey Dog, I don't have much experience with this series of engines but I have a few general suggestions. This may sound redundant, but have you done all the basic checks. Many problems, as I am sure you know, may not set a code. Have you put a fuel pressure gauge on the system when cold and when hot? Have checked that the ignition system has power to it once the engine is hot? Maybe something is getting hot then taking a few minutes to cool off. Sounds like you are getting plenty of fuel, possibly not enough spark? Does the engine have a pressure relief in the fuel system to bleed off excess fuel pressure when the engine is shut down?
Like I said general suggestions, lol. I will do a little reading up on your engine and maybe come up with some better ideas.
Happy Boating
Dan

[Naughty Dog]

Dan - Thanks for the input. I finally gave up on this issue and took into the local experts. We have 6-7 repair places in the area and I went to the guys that are considered by all to be the best (and maybe the most $ but worth it as I found out). I just got it back after almost 4 weeks in the shop due to waiting on machine shop and extent of what all they did.

They started with compression check - 3 cyclinder low 70-80 PSI. went ahead and pulled motor to check out the cause and found the heads to be screwed up pretty bad. Sent them in to machine shop and had bent valves on intake side, seats were screwed up on several exhaust valves as well. In the mean time had them service outdrive joints, bellow, fixed trim sending unit, and several other small items. They also did some research as to the cause of this issue. They found that prop was WAY to steep. Had F7s on it which equal about a 26" pitch. Troy called Volvo and Mercruiser for their recommendations. They agreed on the drive ratio, weight of boat and motor that we should have about a 21 pitch for the props. The overloading of the engine has caused the motor to work way to hard. The machine shop found that one of the heads was also a re-man head - so this isn't the first time it was a problem. Put 21 pitch mercury props on it with the 4 blade front prop - very nice setup!

All said and done we got it back Friday and have been out 3 times over the weekend and it is absolutely a night and day difference - it jumps up on plane with little effort, accelerates fantastic, and to my surprise the top end is exactly the same even with such a drastic pitch change! (49-50 MPH). they found the tach to be off about 350 RPM at WOT so it looked like I was running at 4800-4900 and was actually at 4500, so it was too low for a 5200 RPM motor with the wrong props. Tops out at 4900 corrected RPM now. Needless to say that I am very happy with the outcome and wish the shop that worked on it for one of the other previous owners would have been as thorough and figured out what the root cause of the problems were so I didn't need to spend $5k making it right!

But all in all good outcome but missed almost a month of the warmest weather in central Iowa, but will have much happy boating to finish out the season. Also, fuel mileage has increased dramatically and the motor sounds 'happier' to be working in the range it was meant to originally. Have no idea why we would have such wrong props on the thing, but now we should now have a long lasting power package!

[DFZ272]

Tom, Great Post!. I mean it is very informative. It stinks about having to spend a lot of money, but at least you are lucky enough to have good shop around. Most of the shops around me I wouldn't let them work on a paper boat. You said something in it that we should all realize, especially if we bought a pre-owned boat. Did the owner make any changes to the engine/drive/prop combo. These can like in your case result in a big problem down the road. And it also reminds us of a basic maintenance thing we can easily check, a compression test, before we start guessing at things because we are only seeing a symptom, not the problem.
Again, Great Post!
Happy Boating
Dan