Mercruiser- Fuel or Electrical?

[garyplotner]

Hello All
Engine is a 1986-7 MCM 4 cylinder 224 cu in. 190hp.

Had the boat out a few days ago after several false starts earlier a few week ago. Thanks to everyone's help.
Full tank of fuel 27 gal. After a half hour of warm up time, we headed out the Oakland estuary into SF bay, flat water, very rare, at 42 MPH at 4500 rpm.

Stayed at this speed for around 15 minutes. Idled back to around 3000 rpm for a short time and and then accelerated back up to around 35 mph. On acceleration noticed a slight hesitation. Then it came up to around 3500 rpm. Stayed there for a few more minutes and then reduced speed to around 20 mph.

The it happened. The engine started to hesitate and run very erratic. Would not clear up even when trying to increase or reduce rpm's. Made it back to the dock and shut the engine down. Started it again and it ran very smoothly. Tried to run up rpm but the erratic running was still there

I thinking it's not electrical but contaminated fuel. When I thought i had removed all the fuel, I had not. the bow of the boat was probably higher and all of the fuel was out of reach of my suction hose.

A week before this exercise i added 14 gal of new fuel. It there a screen installed where the fuel line connects to the tank? Could that be restricting fuel flow. I had changed the filters and water separator a few weeks ago.
I just keep coming back to watered down fuel.

Cheers Gary

 

[wellcraft-classic210]

Re: Mercruiser- Fuel or Electrical?

Sounds like fuel flow is restricted (possibly).

Did you by any chance inspect the check valve in the barb fitting on the fuel pickup in your tank? Thats a notorious trouble area for certain sizes of debris.

Also if you can monitor fuel pressure at the carb while this problem is occurring that would verify if supply and the resulting pressure is the issue. ( Be sure its done with absolutely no leaks for safety.) You should also be able to see fuel coming out of the venturis in the carb when the engine is over 1500 rpm.

Could be debris in the carb or an electrical component that acts up when its warm or maybe even bad fuel but I would look at the fuel supply / pressue situation first.

Good luck.. The experts here may also have some ideas on this...

 

[garyplotner]

Re: Mercruiser- Fuel or Electrical?

Thanks for the lead. I was totally unaware that the fuel supply line fro the tank had any type of check valve. Is this to prevent back flow? I had cleaned and rebuilt the 4 barrel carb. and at that time is was surprisingly clean. Though I still need to fine tune it while loaded. The pressure gauge and checking for fuel flow at the venturis is an excellent idea.
Thanks Gary

 

[wellcraft-classic210]

Re: Mercruiser- Fuel or Electrical?

Yes prevent sback flow-- the inline filter and lines would siphon back otherwise.

By the way-- typically thier is no screen on the bottom of the fuel tank pickup-- just a tube.

 

[Bondo]

Re: Mercruiser- Fuel or Electrical?

Thanks for the lead. I was totally unaware that the fuel supply line fro the tank had any type of check valve. Is this to prevent back flow? I had cleaned and rebuilt the 4 barrel carb. and at that time is was surprisingly clean. Though I still need to fine tune it while loaded. The pressure gauge and checking for fuel flow at the venturis is an excellent idea.
Thanks Gary

Nope,... Nothin' to do with Back-flow,...

It's called the Anti-siphon valve, it's to prevent the fuel tank from emptying itself in any case of fuel system failure, resulting in the possibility of the fuel tank siphoning itself empty, into the bilge...

 

[wellcraft-classic210]

Re: Mercruiser- Fuel or Electrical?

Learn something every day--- Thanks bondo !!! Nothing beats experience.

 

[a1nowell]

Re: Mercruiser- Fuel or Electrical?

Gary,
Go ahead and check out all fuel supply issues because it certainly could be a fuel problem. If the fuel checks out OK the take a look at this previous thread of mine and see if it helps. Its a thread within a thread,


http://forums.iboats.com/mercruiser...quent-sputtering-4-oclock-charlie-576098.html
Thanks,
Larry

 

[garyplotner]

Re: Mercruiser- Fuel or Electrical?

Thanks for the assistance. The other threads were very helpful.
Okay, just returned for the boat and here is what i have to report.

Fuel; checked vent line and it was clear. also checked the connection to the fuel tank supply to the engine. All components when disassembled appeared to be in working order and reconnected them. Looked for any loose connections and found none.

Electrical; First checked for any loose connections for plugs, ignition wires, etc. And guess what. I was preparing to check the components in side the distributor and the cap was loose, maybe a thirty second of an inch on one side. I'm thinking can this be the cause? Continued to remove the cap and all components within were secure. Checked the coil (new merc coil) and on the side of the coil was printed "use external resistor" Is this a special wire or is there a resistor located somewhere in the wiring harness?

Back to the loose cap. All this stuff is new and its quite possible that I did not tighten is as tight as it should be. I guess it's possible that running at 4600 rpm for a period of time might further loose the cap screw and continue to loosen as time went by.

In hind sight, when I was subjected to bad fuel in the past, (my daughters car) the engine would hunt or vary in rpm. In this case the rpm did not vary it just ran erratic. I'll have a chance to check this in a few weeks.
Cheers Gary

 

[Fishermark]

Re: Mercruiser- Fuel or Electrical?

Easiest way to isolate the fuel from the equation is to run it from a portable fuel tank and see if the problem goes away. If it does, you search for the fuel restriction or bad fuel. If it doesn't go away, then the problem is probably ignition related.

 

[EddiePetty]

Re: Mercruiser- Fuel or Electrical?

Remove your currently installed water separator filter and pour the contents into a clear container. Allow the liquid to settle and separate (an hour ought to do it). Anymore than a few teaspoons of water in the fuel would be cause to clean the fuel system.

 

[garyplotner]

Re: Mercruiser- Fuel or Electrical?

Hello All
Taking a suggestion from the last post, I was able to remove the fuel filter a few days ago and just let it set around. about a half pint of fuel. Well, the good news is that their does not appear to be any water in this sample.. Replaced the fuel in the filter with new fuel and now I'll just wait until I can get the boat back on the water. I hope it was that loose distributor cap.

Cheers Gary