fuel pump problem

[shelikesit]

i put this in the wrong forum, sorry........

when a fuel pump has power, should it run constantly? this one is triggering and not running fully. here goes

a freind of mine just bought a 94 I/O Mercrusier 4.3 with an electric fuel pump. since i had a problem with mine, i took him through the steps to see where power made it to.

his made it all the way to the pump. we took it off and jumped the oil pressure switch and when the pump was held in my hand, on a key turn it felt like it engaged but would not run.

should this electric fuel pump hummmmmm or run completely when power is straight to it? you can trigger the key and it would feel like something moved but stopped. kind of like an impeller turning for a split second.

even when we propped it up against the thermostat housing, it would move just a titch on the key turn but not run.

make sense?

 

[Don S]

Re: fuel pump problem

Here is the info from the Merc Service Bulletin 2004-01
Hope it helps and makes sense.

[colour=navy]Electric Fuel Pump Troubleshooting
Models Affected
All MerCruiser V6 and V8 carburetor, EFI and MPI gas engines.
Situation
Mercury MerCruiser receives electric fuel pumps returned for warranty that function
properly when tested (No Trouble Found).
Engines that are not run for extended periods of time or are placed in storage with
untreated fuel are at risk of forming fuel gum. The accumulation of fuel gum can seize
electric fuel pumps, which typically results in the replacement of a mechanically sound
fuel pump.
NOTE: Boost pumps used on EFI or MPI models are the same low pressure pump used
on carbureted models. The pumps used to pressurize the EFI or MPI system is a high
pressure pump.
IMPORTANT: Electric fuel pump can be run dry for 10 seconds. Do not run the pump dry
repeatedly or internal damage may occur.
A lot can be learned by putting your hand on the fuel pump when voltage is applied to the
pump.
1. If the pump does not run but feels like a solenoid closing when battery voltage is
applied, it is locked up. In most cases, the pump is locked up because of fuel gum and
can be freed by doing the following.
a. Leave the pump full of a mixture of fresh gasoline and Fuel System Treatment
and Stabilizer overnight.
b. Use mixture as outlined in the fogging procedure in MerCruiser Service Bulletin
2001-15.
IMPORTANT: Do not use the FSTS concentrate when doing this. Other fuel system
components that may be gummed up should be treated with this same mixture.
c. Use 29 ml (1 fl. oz. ) of the FSTS per 3.7 L (1 US gal) of fuel for the next 75.7 L
(20 US gal) of fuel used in the engine.
NOTE: On low pressure boost or carburetor fuel pumps, plugging the outlet, and then
running the pump against this blockage for a short time can loosen the stuck internal
check valve.
2. If the pump runs but feels like a rough ball bearing when battery voltage is applied, it
more than likely has an internal problem and needs to be replaced. A normal pump
running will not feel "rough". The low pressure pump has less vibration to it than the
high pressure pump.
3. If the pump does not run at all when battery voltage is applied, check for battery
voltage at the pump. Check the following.
NOTE: Use the wiring diagrams, pressure gauge connections and observe all Warnings
and Cautions as outlined in the Service Manual for the engine being worked on. Items
listed below may not apply to the engine that you are working on.
• Ignition key, cannon plug connector corrosion, loose connection at 50A circuit
breaker, blown fuse, etc.
• Check fuel pump electric harness connector. The pump needs good positive and
ground connection.
• Fuel pump relay (EFI or MPI models).
• Oil pressure switch (carb models).
4. If the pump runs when battery voltage is applied, check fuel pump pressure. Connect a
service test fuel gauge to the location outlined in the Service Manual. On MPI engine, a
Schrader valve is provided for this purpose. On EFI (TBI) models and carbureted
models, a test Tee-fitting is required to connect the test gauge. Compare pressure
reading to the specifications listed in the Service Manual.
If the pressure is higher than specifications:
• The pump’s internal check valve may be stuck from fuel gum.
• A defective fuel pressure regulator (EFI or MPI models).
• Check for a pinched or plugged hose going to fuel pressure regulator (EFI or MPI
models).
If the pressure is lower than specifications:
• Low battery voltage to the pump.
• Fuel tank pickup, fuel tank vent hose, fuel filter or fuel line restriction.
• Faulty anti-siphon valve.
• Air leak somewhere in boat’s fuel line.
• Vapor locking.
• Faulty fuel pressure regulator (EFI or MPI models).
NOTE: Refer to MerCruiser Service Bulletins 1998-04, 1998-05, 1999-07, 1999-08 and
2001-04 for additional information concerning electric fuel pumps.[/colour]

 

[Don S]

Re: fuel pump problem

You can get the information from the oither service bulletins mentioned above at this link.

http://www.boatfix.com/merc/Bullet/sbcover.pdf

 

[johnbo]

Re: fuel pump problem

Hi,

I had a similar problem last year. My '96 Volvo likely has the identical pump on it. I was running into non-starts last year on an occasional basis. The engine would run at idle for a couple of minutes and then starve for fuel.

I believe that the pump should run continuously, the power to it is certainly there all the time (that the starter is running or the oil pressure is present).

When this happened, I could jumper the pump (pulling the relay mounted in the bracket that holds the fuel pump -- this might be a Volvo thing), and it would run briefly and then stop. Like it was pressurizing the fuel line to the carb. Might take 1 or 2 seconds. Kind of a HMMMmmmmm...

There are a series of tests to check for proper fuel delivery, but the simplest, my opinion, is to hook up everything back up, let the problem happen if intermittent, then with the pump jumpered, check the current going to the pump, and/or just crack open the fuel line fitting from the fuel pump to the steel line to the carb.

What I found, is that the pump would stall and draw about 8-9 Amps, and yet there was no fuel pressure in the hard line. I believe that there is an internal check valve (in the pump) that is supposed to pop open at a certain pressure to relieve the pump pressure at the desired couple of PSI. I think that this gets jammed and seals the output of the pump. So the pump motor stalls (and takes a lot more current), and the there is no fuel going to the motor, because the valve is jammed.

Because my pump failed only occasionally I had the chance to look at both the running and non-running cases.

Running: Pump current about 1-2 Amps (no matter how much, if any, fuel is being pumped). Fuel oozes quickly out of the slightly opened fuel line connection.

Not Working: Pump current about 8-9 Amps (when the pump is not running), and no fuel other than seepage from the slightly opened fuel line connection.

WARNING - DISCLAIMER - WARNING

Measuring current on a motor means playing with the wiring and enough current to create sparks. And, you are opening, occasionally, fuel lines which will drip fuel.... These things need to be done carefully, it at all. I'm an electrical engineer, so I'm pretty comfortable doing this. If the description above sounds confusing, this might not be the best problem to learn on.

In the end, I replaced my pump, about $150 (shipped) from Ebay. Solved all of the problems, except for the one in the wallet.

Later,

johnbo

 

[shelikesit]

Re: fuel pump problem

this is it...........

1. If the pump does not run but feels like a solenoid closing when battery voltage is
applied, it is locked up. In most cases, the pump is locked up because of fuel gum and
can be freed by doing the following.
a. Leave the pump full of a mixture of fresh gasoline and Fuel System Treatment
and Stabilizer overnight.

when i left him, he had PB blaster in the bottom of the pump hoping it would seep down in. I'll call him now and tell him to use gas.

he has the pump on his bench upside down. is this the correct way of letting the gas/stabalizer mixture to sit?

is that PB blaster going to ruin the pump, i guess its been like that for a few hours. i know the pump may be gummed up beyond repair, but if there's a chance, im sure he needs to get that oil out of it and get gas in

my next question would be how do you get the gas inside the pump, it seems closed, we can't blow into either end of it if that makes sense

thanks DonS. your very much appreciated.

 

[Don S]

Re: fuel pump problem

Do like the instructions say. Don't use PB Blaster because you don't know if it will hurt the pump or not.
Not even sure it will cure the gum problem.
The real cleaner will mix with the gas on it's own. Trust me, I have used it and it works. Fix several that way every year.

 

[shelikesit]

Re: fuel pump problem

ok, thanks again.

do we just submerge the entire pump in this mixture, or try and let it seep in from the bottom/

the unit is a closed unit, so we're thinking we can drop it right into this mixture without hurtung anything.

 

[Don S]

Re: fuel pump problem

No, don't submerge it, it's not designed to work inside a tank.
Put a fitting in the top and fill it up with the cleaner and let it set overnight. This is usually done without removing the pump from the engine.

 

[shelikesit]

Re: fuel pump problem

ok, sounds good, i'd imagine that this mixture is going to seep right through the pump while it sits.

is it correct to assume this? picturing it in my head, if the pumps are not removed during the procedure, it would have to seep into the pump......... right........... if it seeps in, there's a chance it will free it.

or am i confused over something that sounds quite simple?

 

[shelikesit]

Re: fuel pump problem

this is an awesome thread with that bulletin. thank you.

i slept on this thought last night and am going over there today after work. my thoughts are to setup something like an IV drip with this mixture and put the fuel pump back on. we're going to add a fitting and have a hose connected to the top of the pump and let this mixture work it's way down.

i'm hoping this is what i got from the post.

 

[shelikesit]

Re: fuel pump problem

ok, we did this, now the fuel pump has a slight hummmm / vibration when held. keep this mixture in or is the pump dead, or just not fred up yet. we left it overnight.

it went from the solenoid click / stop to a very slight vibration, kind of like holding a real low voltage live wire