Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

[stingray165ss]

Hey guys I need some opinions on a problem i am having with my Mercruiser 2.5 120 Hp. The problem i am having is, i can take the boat out and run it for 1 hour to 1 1/2 hour and it runs great then it will start sputtering and eventually stall. I have taken the tank out & cleaned it and also checked the pick up tube for cracks or holes. It is an alluminum fuel tank. I have had the Carb rebuilt. I replaced the Vent line and the fill line. I have not replaced the line coming from the tank to the Carb. I also bought a 12 gallon attwood plastic tank and i still have the same problem. I am begining to think it might be the fuel pump but i have been told that the mechanical fuel pump would not work intermitently once it goes out thats it, it will not work at all. I have also been told that it is possible the rubber line coming from the tank to the pump could be collapsing internally. I have fought this battle all last summer and now i am at it again now that spring is around the corner. please help i want a summer without boat problems!! If it is any help the boat is a 1987 Stingray SVB 165ss.

 

[Howard Sterndrive]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

Could be the ignition coil failing. For something to take 90 minutes to act up is tough, I'd lean towards electrical things rather than fuel at a hour-and-a-half to make it start happening.
Monitoring Voltage at the coil + might tell a story.
Done a complete tune-up lately? Is there a ballast resistor on a 87? I'd probably swap that out too.

Pull the plugs when it dies to see if any moisture on them. Compression test the engine hot.

 

[Silly Seville]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

Mechanical fuel pumps CAN go bad slowly...but my first inclination is definitely the coil. It heats up when under load and then the voltage drops to your plugs, causing the missing and finally the engine stalls. Let coil cool off...engine restarts I bet, doesn't it?

 

[thumpar]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

As I was reading I was thinking ignition also. When it fails just push the throttle from neutral and see if you get a squirt of fuel from the accelerator pump. I bet that works and means the bowl has fuel. You could also check for spark. My coil failed a few years ago and I switched everything to pertronix with electronic ignition.

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

Hey guys thanks for the speedy replies, I also thought it was electrical at first, I forgot to mention that I did replace the coil and the same problem keep coming up. What leads me to believe it is fuel is that I have a glass inline fuel filter just before the pump and when it started acting up I pulled the doghouse and saw that the filter had hardly any fuel in it. ( I apologize for not including this information in my original post) I was messing around with. It earlier and replaced the line coming from the tank to the pump. I also noticed a check valve fitting coming out of the tank for the fuel line, the ball in the fitting appears to be sticking so hopefully if I replace that it will fix it. I will def be converting to electronic ign. And check the voltage output on the coil. Any other suggestions would be much appreciated thank you.

 

[Howard Sterndrive]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

I have a glass inline fuel filter just before the pump and when it started acting up I pulled the doghouse and saw that the filter had hardly any fuel in it.

If this glass thing is factory part? that's not a filter, that's a collector. If there's any fuel in the glass, your fuel pump diaphragm has ruptured - you need a new pump.

If you mean one of these:

1) they tend to never have much fuel in them - I don't know why
2) get it out of there - not marine safe or approved for use in bilge

anti-siphon valve is the name for that valve at the fuel pickup- might as well replace that.

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

It's not one of the old fuel pump glass collectors, it is a inline fuel filter I installed. My fuel pump does not have the glass collector it has the line that runs from the bottom of the pump up to the carb in case the diaphragm ruptures. But thank you anyways.

 

[NHGuy]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

You say you did the fuel & vent lines, but you didn't check the vent for obstruction. Try running with the fuel fill cap partly loosened so no tank vacuum can occur as the pump pulls fuel from the tank. If it runs fine with the cap loose, then either clear the vent or change it for one that's not obstructed.
If it stalls, look down the top of the carburetor while someone pumps the throttle to see if there's any fuel there right after a stall. There should be a nice squirt of fuel when you pump the gas.
If there's gas and it still stumbles or quits, go on to check the ignition.
Look through the diagnostics for the ignition system. Is yours a TB IV? Does your engine box get really hot? I have heard of Thunderbolt IV's getting heat soak issues in the controller. Does it have an ignition sensor under the distributor cap? They can get corroded and can partially fail.

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

Thank you for the reply, I actually tried the fuel cap thing last time I was out. I don't think mine is a tb Iv. I have done so much research as to what this could be and everything I try I come up empty handed. I will pump the throttle and look for fuel next time I take it to the lake. I am hoping that replacing the rubber fuel hose and the anti siphon valve might fix it. Could it possibly be vapor lock? I ran the rubber fuel line as far away from the engine as I could just i case it was getting to hot. If none of this works I will have a 87 stingray for sale!!!!

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

Also howardsterndrive I will remove that filter, the guy that rebuilt my carb installed that on there, I wonder why u can't use them on inboard engines. It's nice to be able to the fuel flowing

 

[Howard Sterndrive]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

It's nice to be able to the fuel flowing

however, I think it might be misleading you- those things always look too empty and the fuel sort of "slides" through it in a thin sheet. not a fuel delivery problem when you see that.

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

I just ordered the filter that goes in the pump, so i will definitely be removing the inline filter. Well i guess all thats left to do is go to the lake and see if it acts up after replacing the fuel delivery hose and the anti-siphon valve. If it stalls i will get someone to hit the gas while i check the carb for fuel, if there is fuel i will know to look more at the electrical system.

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

I really do appreciate everyones advice and i will test it this weekend and let you guys know what i come up with.

 

[frantically relaxing]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

Been thru this issue twice recently-- once with the starboard engine in the houseboat (120 merc exactly like yours), and also my father-in-law's old Ford pickup.

You say you haven't changed the fuel line from the tank, and the filter has no gas in it...

I'll bet a buck you're sucking air into that fuel line, and odds are it's at the tank connection.

On our houseboat I had a cracked line right at the port engine fuel pump. The starboard fuel line Tees into the port line about 3' before the port pump. Because the line runs downhill to the port pump, and the crack in the hose -right along the clamp at the pump- was so close to the pump, it was able to get enough fuel. But the starboard engine would suck air from the crack, and it could get enough fuel SOMETIMES to run, sometimes not, but usually enough to idle. And hardly ever did the filter have much fuel in it. I found the crack by accident after 2 new electric fuel pumps wouldn't draw fuel. The crack didn't leak a bit of gas, it wasn't until I tugged on the gas line that it started dripping gas. All I did was snip off 2" of line and reconnected it, and it's been fine ever since. (but yes, new line is going in this spring!)

Pickup truck, my BIL changed the fuel pump on the thing, which helped but it still stalled out after running awhile. Where the hardline from the tank connected to the rubber hose is where it was sucking air, the hose was just old and soft and the clamp wasn't tight enough. Put in a new piece of hose and a new clamp and she's good as new...

change out that line, it's a cheap fix if it works--

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

Thank you, I think taking out the Anti siphon valve is going to fix it, I fired the boat up yesterday and the inline filter was slap full of fuel and it has never been like that. I am just keeping my fingers crossed that i fixed the problem.

 

[72jerry98]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

I had this happen to me on my 3.0 140hp merc. It was the fuel pump. When it got hot, the pump did not create any vacuum to pull fuel, so the pump would not pump any fuel. But when it cooled down it would pull vacuum and pull fuel and pump just fine. I changed the fuel pump and fixed the problem.

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

well guys i went to the lake this weekend and only had time to run about an hour. I had no problems with the engine cutting out. but i did have a problem with a patch i put on the bottom of the boat. If its not one thing its another. The previous owner kept putting the boat on the trailer with a broken keel roller and it put a small hole in the keel. I patched it with marine tex and that obviously did not work. So this today i sanded down the gel coat and put a new fiberglass patch on it. I just posted another post on here about the fiberglass being waterproof or should i paint it or gelcoat. appearance is not that important since it will be below the waterline.

 

[Don S]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

So this today i sanded down the gel coat and put a new fiberglass patch on it. I just posted another post on here about the fiberglass being waterproof or should i paint it or gelcoat. appearance is not that important since it will be below the waterline.

Your best bet would be to post this question over in the Restoration/Hull repair forum That's what they do there, we do engines and drives in this forum.

 

[stingray165ss]

Re: Mercruiser 2.5 120 Hp 153 CI. Fuel delivery issue

Hey Don S. i started a thread over there i wasnt really expecting an answer over here, i was just kinda stating the problem i had. thanks for the reply.