Diagnosing bad fuel pump?

[rcsummers]

Hello captains! I'm diagnosing an engine that won't fire. Put in for the season (Michigan), starboard engine ran for a bit to get on plane but then lost power. Won't fire now. Suspecting I have condensation in my fuel. Removed fuel filter and found water, wasn't pretty. Replaced and primed 3/4 full with fresh fuel. Still wont fire. I'm wondering if the cruddy fuel mucked up my pump.

After having the ignition on several times and trying to fire the engine I checked the filter again and it was only still at the 3/4 level I had originally filled it to. Shouldn't it have drawn enough fuel through to fill the filter? I'm considering replacing that as a next step.

Regarding the fuel in the tank, I store indoor in heated storage and I put away with between 1/4 to 1/2 tank. I'm wondering if I fill the tank and treat if that would be sufficient, or at what point would you all do a full flush and re-fill of the fuel?

[mmwjr]

What year is the engine? Fuel injected or carburetor? Fuel injected will have an electric fuel pump while carburetor engines 1997 and older will have a mechanical pump and newer will have an electric. Testing depends on your answers.

[rcsummers]

Sorry, should have had those details. It's a 1998 5.0L, carburated. It has the fuel pump p/n 861155A3.

[mmwjr]

Ok so you have the electric pump for a carburetor. It should put out 6-7 psi. The pump gets power when cranking from the starter solenoid and once started power comes from an oil pressure switch.

To test disconnect the fuel line to the carburetor and divert it into a container. Crank the engine a few times then check to see if there is fuel in the container. To check the pressure install a pressure gauge on the fuel line then crank to see its pressure.

[mmwjr]

Have you tried squirting a little fresh gas into the carburetor to see if the engine will fire?

[rcsummers]

Mike, yes I did put a little gas in the carb, but still didn't get it to fire. I'll check out that test on the fuel pump though when I get back at it Friday afternoon. Thanks for the info.

As far as the condensation goes, at what point would you pump out/replace the fuel vs. treating it and running it through?

[mmwjr]

If you poured a little gas into and it didn’t fire I would verify that there is spark.
This should have tried to make it start if there is spark.

If you poured the fuel from the filter into a glass jar how much water is there on the bottom?

[rcsummers]

From the filter I would say nearly half. It did not look good coming out of there. I have about 1/4 tank in the reservoir remaining.

[mmwjr]

Is this ethanol fuel? If so it sounds like it phase separated and the tank needs to be completely drained and refilled with fresh fuel.

[bjasin1]

Originally Posted by rcsummers

Mike, yes I did put a little gas in the carb, but still didn't get it to fire. I'll check out that test on the fuel pump though when I get back at it Friday afternoon. Thanks for the info.

As far as the condensation goes, at what point would you pump out/replace the fuel vs. treating it and running it through?

My Starboard engine (6.2 mercruiser) was intermittently shutting down..Had all the symptoms of bad fuel pump. I had replaced plugs and cap and rotor recently and it ran good most of the time…but at an idle it would slowly start sputtering and die just like it was running out of fuel…had my local mercruiser dealer come and give his opinion because he could use the laptop..he tried hooking his laptop up but couldn’t get a good reading…he eventually said it’s the fuel pump. I replaced it and it acted the same…tried the idle air sensor and still no luck…out of desperation i took to another mechanic ( i usually do all my own work) He quickly diagnosed as a bad rotor on that motor…I checked the cap and rotor and they both looked good…i even swapped the cap but for whatever reason i ruled out the rotor being bad…Felt like an idiot as i’ve rebuilt a few motors in the past couple of years but this one stumped me.

Whenever i rule something out because im “sure” that couldn’t be the issue …it comes back to bite me.
Always need to start at the beginning and go thru the basics

[BrianC72]

I would pump out the fuel of questionable vintage by rigging something up to the electric fuel pump. Speaker wire and alligator clips come to mind along with a length of low pressure fuel hose. Surely the factory manual or the pump mfr. has a spec that it should pump out so many fluid ounces per unit of time of time.

It is useful to know a couple of simple methods to check for spark. An inductive timing light will tell you if timed voltage from the coil is passing through that spark plug wire. Clip it on to #1 wire, alligator clips to the battery and have a helper crank it whilst you point the light at the front pulley (harmonic balancer). if it doesn't strobe while cranking, then you aren't getting any spark. Or keep a spare sparkplug in the glove box, pull the lead, and ground the hex of the plug to exposed metal, crank and spark. You haven't lived until you get shocked this way. Theoretically you could die this way, but mostly it just tickles in a mistress-of-pleasure-and-pain sort of way. I'm supposed to say it is unpleasant.

There is a logic to this. there has to be, otherwise you will be reloading the parts cannon with blind luck.