Is my fuel pump Bad?

[DC20]

1999 Johnson, Model J150PXEES
Last time out it started hard cold (it ran fine once I got it going and would restart hot just bumping the key), so I replaced the fuel primer bulb and line from the bulk head to the motor and replaced the filter at the motor. Even with it idling on the trailer for a few minutes I can go squeeze the bulb 5 or 6 times.

Does that indicate a bad fuel pump?

 

[schematic]

Re: Is my fuel pump Bad?

It may point towards the pump, but more testing is required to confirm. Do a pressure test on the pump while running. (easy to tap in at the primer valve inlet). Also have a segment of clear hose installed between the engine and squeeze ball to observe the chance of sucking air. A vacuum gauge teed in the clear hose will also indicate fuel supply restrictions (anti-syphon valve, kinked hose, plugged vent etc.)

 

[DC20]

Re: Is my fuel pump Bad?

Thanks for the reply schematic. I need to get a vacuum gauge then. Whats weird is that under throttle, even full throttle it was fine. I did notice that the fuel lines below deck had been replaced with cheap Sierra fuel lines that have an inner plastic lining that seems to be collapsing in, at least on the ends of the hose. I will be replacing that first.

 

[hidef]

Re: Is my fuel pump Bad?

Hard starting cold does not mean a bad fuel pump and based on your other info starts fine when hot and started with a bump of a key I highly doubt that you have an issue with the fuel pump.

Hard starting when cold can be caused by old spark plugs, low compression a fault in the ignition system. There could be an issue with the Quikstart circuit. It can also be caused by not following the proper starting procedure.

 

[daselbee]

Re: Is my fuel pump Bad?

No, after starting, the primer bulb naturally goes soft. It is flowing fuel straight thru as the pump pulls the fuel from the tank. It will not stay hard. It is not unusual to be able to "pump it up" more after it starts.

I don't understand some of the responses above. If you tee into the fuel line anywhere BEFORE the fuel pump, you will always be reading vacuum, if the engine is running.

If you tee into after the fuel pump, you will be reading pressure. A VRO2, OMS, etc pump, will put out 3-4 psi at idle on the output side, and should draw no more than 7 in-hg at WOT on the inlet side. If it pulls more that 7 in-hg of vacuum, the fuel restiction alarm should sound.

Double check those numbers is your particular OMC factory service manual.....

 

[schematic]

Re: Is my fuel pump Bad?

I don't understand some of the responses above. If you tee into the fuel line anywhere BEFORE the fuel pump, you will always be reading vacuum, if the engine is running.

It is possible to have a weak fuel pump or air leak at idle or cranking speeds. High engine RPM can mask this.
These are 2 different tests which can tell a story:

- Installing a pressure gauge at the primer inlet is the easiest place to tap in to measure pressure.

-Teeing in between engine and squeeze ball will definitely give a negative reading and should not exceed 2"HG at Idle or cranking. That's what we're verifying. Its easy to do if you already have a segment of clear hose installed to check for air leaks.

 

[daselbee]

Re: Is my fuel pump Bad?

- Installing a pressure gauge at the primer inlet is the easiest place to tap in to measure pressure.

Sorry, disagree. To me the primer bulb inlet (your words) is the tank side of the primer bulb. This would NEVER show positive pressure, and would barely show a suction vacuum at idle.

Even when priming before start, the positive pressure is generated at the OUTPUT of the primer bulb....between the bulb and fuel pump.

The only place you will see positive pressure when the engine is running is at the output of the fuel pump.

 

[daselbee]

Re: Is my fuel pump Bad?

-Teeing in between engine and squeeze ball will definitely give a negative reading and should not exceed 2"HG at Idle or cranking. That's what we're verifying. Its easy to do if you already have a segment of clear hose installed to check for air leaks.

Again...only when running...you will have a suction or "vacuum" when running at this location. When stopped, and pumping the primer bulb, that tee location will build a positive pressure when the bulb is firm.

 

[schematic]

Re: Is my fuel pump Bad?

daselbee
To clarify......please read complete post to understand context. Squeeze ball is NOT the same as Primer. That's where your misconception lye's. I never stated "primer ball inlet" as you pointed out. Please reread! I said primer inlet. The primer I refer to is a enrichment solenoid often misconceived as the "choke" It has an inlet and 2 outlets. The inlet is an ideal place to tap into for measuring fuel pressure. Often the fuel manifold is too hidden to get at.

Does that help?

 

[daselbee]

Re: Is my fuel pump Bad?

Whatever.

So you mean the output of the fuel pump. Same place. Why didn't you say so?

Squeeze ball...which I have NEVER heard as a term, is to me, the primer bulb. But squeeze ball is for sure a term that defines the primer bulb......

So we must be speaking the same language, yet not communicating.


EDIT: Oh, and I do know what the primer SOLENOID is, and exactly how it works.
Thanks for the tutorial.

 

[schematic]

Re: Is my fuel pump Bad?

Why so angry?

 

[daselbee]

Re: Is my fuel pump Bad?

Don't tutor me on how this stuff works. I will tutor you.

 

[schematic]

Re: Is my fuel pump Bad?

How about if we just concentrate on trying to help DC20. I think he's the one that asked for tutoring....

 

[daselbee]

Re: Is my fuel pump Bad?

Fix him up. We will see how you do. I will bow out.

 

[schematic]

Re: Is my fuel pump Bad?

Thank you

 

[hidef]

Re: Is my fuel pump Bad?

Unless DC20 has an issue with the priming circuit / primer solenoid / primer manifold assembly highly doubt he has an issue with the fuel pump. Also is he running a VRO pump with the oil side hooked up a VRO pump with oil side disconnected or has someone retrofitted an old style pump. DC20 you should checkout the link below if you think you have a fuel issue. Don't start throwing money at a problem until you know where the problem lies. Daselbee offered some good advice and he knows what he is talking about.

http://www.maxrules.com/fixomcvro.html