mercruiser 7.4

[boatmann]

Hello everyone, I just bought a 1996 Celebrity with a 7.4 EFI Mercruiser...it had 75 hrs on it...it sat a lot and looks brand new...I have had it out 3 times and it runs good at about 3000-3500 rpm but can't get it above that..I ran a whole tank out and replaced with fresh gas...It will run great for 1-2 hrs but throughout it acts like it is missing, sputtering at times and it has backfired a couple of times...then it will run great again...but still cant get it over 3500 rpm...yesterday was the worse when it ran great for 2 hrs, I stopped for and hr and started back up and it would miss out and cutout terribly...especially when trying to plane...I got it back planing but still feel theres power loss...thanks in advance with any insight of this problem.

 

[scutly]

Re: mercruiser 7.4

change plugs, wires, cap and rotor. check timing. replace fuel filter and fuel/water separator filter. maybe run some injector cleaner through it as well. then see if you have any improvement. sitting idle and not being used for great lengths of time is a boats worst enemy. oh and welcome to the forum!

 

[26aftcab454]

Re: mercruiser 7.4

last year i had similar issues with my 1996 7.4/Bravo3
new plugs-wires looked good-- the cap had a discolored lug so put on new distributor cap-( buy mercruiser ) ran great for several weeks-
then started acting up again. --- pull fuel line at carb-put line in empty plastic bottle-turn key a couple seconds-should shoot some gas- -I had nothing- -traced fuel to in side of fuel pump- lifter worn out. wound up replacing the mechanical fuel pump.
Knock on wood but running like a champ still today!

This may not be the correct methods but is what I did.
study the adults only section and read up on the manual.

 

[boatmann]

Re: mercruiser 7.4

Thank you Scutly, I do believe its related to the fuel. I am going to have the jets cleaned and replace the filters and of course check the obvious, plugs, wires, timing etc. I may even put some B 12 cleaner and hopefully that will clear it up.

 

[boatmann]

Re: mercruiser 7.4

Thanks Bubba, I agree I think its the filters and its gunked up a bit.

 

[boatmann]

Re: mercruiser 7.4

Thanks Aftcab, I hope its just the filters but will keep this in mind. It has sat too much and I think just needs filters, injectors cleaned and we'll see.

 

[26aftcab454]

Re: mercruiser 7.4

good luck and let us know how it turns out!

 

[boatmann]

Re: mercruiser 7.4

Ok, need some more help. I did the full tune up. Still same problem, so I took to the marine mechanic. He said I wasn't getting enough PSI in fuel pump. He traced it to the fuel regulator. He installed a new one. I took it out and it ran great for the first 1/2 Hour. It is now bogging down worse than before. (it is great for the first 1/2 hr). It seems when engine gets to operating temp that is when my problems start. I talked to mechanic and he has ordered in an IT? Valve. This controls the air mixture? It does seem like it is flooding out. Now he did ask about the tach acting erratic, which it does. So he said take the wire off the back and tape it, then run to see if it is the tach. Anyway, just checking to see if anyone has any other suggestions. Thanks!

 

[Don S]

Re: mercruiser 7.4

I would guess he ordered an IAT (Intake Air Temperature) sensor. did it have any codes set? A problem with the IAT would have set a #23 code.
Has he done an injector balance test?

 

[boatmann]

Re: mercruiser 7.4

Hey Don, he said it didn't show any codes. You are correct with the IAT sensor. (I will say something to him about the code) He has not done an injector balance test. Do you think the tach would have anything to do with this?

 

[Don S]

Re: mercruiser 7.4

Do you think the tach would have anything to do with this?

No, but if it's on your mind, disconnect the gray wire from the tach and give it a try. It won't hurt anything.

 

[boatmann]

Re: mercruiser 7.4

No, but if it's on your mind, disconnect the gray wire from the tach and give it a try. It won't hurt anything.

With the tach erractic like it is I will probably need to replace anyway so I might as well try. I will talk to mechanic tomorrow and order a new tach. Any suggestions of what brand of tach I should get. I am sure I can replace this on my own.

 

[scutly]

Re: mercruiser 7.4

i just changed out my tach and oil gauge. easy peasy. look close and you should see the make of the gauges maybe somewhere along the bottom of the face or definately on the back. lots of boat manufacturers all use the same parts. mine where simple black face with white numbers backlit with black bezel. they ended up being the Faria Euro gauges. wow as i type this im gettin the link where i got mine and found this.
Faria Celebrity 6000 RPM Inboard / Outboard Tachometer Boat Gauge. maybe we got lucky?

 

[boatmann]

Re: mercruiser 7.4

i just changed out my tach and oil gauge. easy peasy. look close and you should see the make of the gauges maybe somewhere along the bottom of the face or definately on the back. lots of boat manufacturers all use the same parts. mine where simple black face with white numbers backlit with black bezel. they ended up being the Faria Euro gauges. wow as i type this im gettin the link where i got mine and found this.
Faria Celebrity 6000 RPM Inboard / Outboard Tachometer Boat Gauge. maybe we got lucky?

Thanks for the info and I have been told by a couple mechanics that the problems with my boat may be the pickup coil and that may be causing the tach to be jumping as well. The Marine mechanic is putting a IACT sensor in and see if that works but if it doesn't then I may just replace the distributor. Hopefully, I can get this boat figured out before the summer is gone.

 

[scutly]

Re: mercruiser 7.4

Hopefully, I can get this boat figured out before the summer is gone.

summers only 2 days old man.

 

[boatmann]

Re: mercruiser 7.4

ok, $1100.00 later. Full tuneup, fuel pump, fuel regulator, fuel line to tank (replacing pickup line in tank later this week). It is doing the exact same problem. Mechanic thinks it is fuel related because psi goes to 20 when WOT. He thinks it is the VSI fuel pump? now. $650.00 + labor. I feel we are just throwing parts at it. I am just wondering if this is the proper procedure and if we are going to do this where I can find spare parts for this engine. I know risky, but budget is broke. I am just wondering about if its electrical, pickup coil, distributor etc. Anyway, looking for some direction of how to diagnose this problem.

thanks

 

[boatmann]

Re: mercruiser 7.4

Well, took boat out and hooked it up to an external gas tank. Boat ran like it should. Sounded awesome! So the mechanic said it is either pickup tube clogged or anti-syphon valve. I said replace both. He went to unscrew the fitting(he said that it was tough to get off) and the pickup tube is welded on. So there if there is a crack in the tube or clogged we would have to replace the gas tank. Well guess what, he can't get the fitting to screw back on. It is like the threads are off and he can't get it started. So now I am looking at replacing the gas tank to solve all issues. Here are the specs:

Model number FMT-62-CBT
manufactured 11/95
1996 Celebrity 240 CC

I tried the company that originally supplied this tank and they are out until the 19th of July (odd?). What suppliers would you recommend for this?


thanks

 

[captcrankshaft]

Re: mercruiser 7.4

So now I am looking at replacing the gas tank to solve all issues.

I guess I missed something. Why can't the tank be repaired?

Another question, why does it seem this fellow replaced all those parts when the real problem appears to be the clogged pickup tube?

A combination of fuel pump pressure/ dead head test and a volume test would have revealed this situation.

Perhaps its time for a new shop / second opinion.