Guidance needed on determining fuel pump vacuum reading

[jerryny]

I have a 1988 Johnson 88 V4 SPL w/o the VRO option. Could someone guide me on how to determine if the engine is providing enough vacuum to run the fuel pump correctly. I think I have a carb problem as the top 2 plugs are wet and black. The bottom 2 are a nice brown. That is why I am assuming its the top carb. But since I am going to be doing some service I figured I would check out the fuel pump vacuum reading at the same time.

Thank you in advance for any help given. You guys are a blessing a newbie!
Jerry

 

[Watermann]

Re: Guidance needed on determining fuel pump vacuum reading

I'm not sure how you would go about increasing the vacuum if you found it to be low. Most of the time the fuel pump diaphragm is either ruptured or old and stiff causing low or no pressure. Not a huge investment to just grab a repair kit and when the pumps off check the vacuum hole to make sure it's not obstructed.

 

[boobie]

Re: Guidance needed on determining fuel pump vacuum reading

Do a compression test on it and see what you come up with.

 

[schematic]

Re: Guidance needed on determining fuel pump vacuum reading

Simply measure fuel pressure at idle. If its within specs.....the pump is getting what it needs.

 

[jerryny]

Re: Guidance needed on determining fuel pump vacuum reading

The fuel pump is new so I wouldn't think that is the problem. The local repair shop told be to check the engine vacuum that runs the fuel pump. If its low then the engine is shot. I wanted to eliminate that before bringing it in for diagnosing. Not sure why the top 2 plugs are wet and the bottom two are dry. I'm thinking either the top carb is flooding or the bottom carb is not giving gas to the bottom 2 cylinders.
It idles really rough and as soon as you put it in gear it wants to die. Even when I can get the boat moving it really bogs down at WOT.

I checked the spark with the engine running and the little lite appears to be pulsing. Plan to do the spark plug gap test as soon as it stops raining. I'm really bummed. My last Johnson, a 1972 50hp ran for 20 years w/o any problems before it finally died. Thanks all

 

[F_R]

Re: Guidance needed on determining fuel pump vacuum reading

The shop was pretty much on target. What they are saying is that the pressure/vacuum pulses that operate the pump are caused by the piston stroking back and forth in that cylinder. If the pulses are not there, that indicates the piston is shot. Rather than try to test the pulses, it is way easier to simply do a compression check on the cylinder.

 

[Tim Frank]

Re: Guidance needed on determining fuel pump vacuum reading

I have a 1988 Johnson 88 V4 SPL w/o the VRO option. Could someone guide me on how to determine if the engine is providing enough vacuum to run the fuel pump correctly. I think I have a carb problem as the top 2 plugs are wet and black. The bottom 2 are a nice brown. That is why I am assuming its the top carb. But since I am going to be doing some service I figured I would check out the fuel pump vacuum reading at the same time.

Thank you in advance for any help given. You guys are a blessing a newbie!
Jerry

Is this engine new to you...and is this a new problem?
Nothing you have posted makes me think I'd be checking the fuel pump as a first step.
But as suggested, it is much easier to test the output.

 

[Tim Frank]

Re: Guidance needed on determining fuel pump vacuum reading

The fuel pump is new so I wouldn't think that is the problem. The local repair shop told be to check the engine vacuum that runs the fuel pump. If its low then the engine is shot. I wanted to eliminate that before bringing it in for diagnosing. Not sure why the top 2 plugs are wet and the bottom two are dry. I'm thinking either the top carb is flooding or the bottom carb is not giving gas to the bottom 2 cylinders.
It idles really rough and as soon as you put it in gear it wants to die. Even when I can get the boat moving it really bogs down at WOT.

I checked the spark with the engine running and the little lite appears to be pulsing. Plan to do the spark plug gap test as soon as it stops raining. I'm really bummed. My last Johnson, a 1972 50hp ran for 20 years w/o any problems before it finally died. Thanks all

I'd be looking for an ignition problem first...

Not sure why the top 2 plugs are wet and the bottom two are dry. I'm thinking either the top carb is flooding or the bottom carb is not giving gas to the bottom 2 cylinders.

The bottom two plugs show that that carb is working fine....you already said that those plugs are a nice brown colour....the top ones are black and wet.....so they are getting gas....just may not be firing.

If you have already replaced the fuel pump, this is obviously chapter three and we are missing the start of the story....and you are missing a lot of help.

If you post the full details of your problems, we may be able to assist.

 

[jerryny]

Re: Guidance needed on determining fuel pump vacuum reading

Here is the whole story. Last fall my son bought the boat and it wasn't running right so he gave up and gave it to me. The original problem was that the engine would run fine all the time at idle. But once you put it in gear it would lose all power after about 5 minutes and never regain it till the next time you went out and then the same thing would happen. So here is what I did and found:

1) Replaced fuel pump. It was a cheap shot at solving the problem. The problem still existed.
2) Rebuilt carbs. Didn't help
3) Did both a warm and cold compression test. If I remember right all 4 cylinders were about 135lbs.
4) Did a spark plug gap test on all 4 cylinders. All 4 had a nice blue spark that jumped the gap.

By now it was winter so I decided to replace the deck which was soft in a few spots. Its at this time that I found that the vent line for the inboard gas tank was bloated and falling apart. So I replaced the vent line and waited for spring.

This spring I took it out and it ran like a champ. I have had it out at least 4 or 5 times and it always ran great until this last weekend.

So while I was out on the river I did the following:

1) Removed vent line from gas tank but no difference which I kinda already knew.

2) I put a spark plug monitor on each of the two top plugs since they were the ones that were wet.
It was pretty bright out so I put my hat over the tester and I could see that the light was pulsing on both top
cylinders. (didn't check the bottom two cylinders since the plugs were a brownish color and dry)

3) I then took the carb cover off to look at them while the engine was running. I could see gas flowing into the carbs.
Not sure if this is good or bad. I did see some white greasy substance on the bottom of what I think they call air
horns. The choke plates and the rest of what I could see were nice and shiny.

I then brought the boat in. Here are my plans for shooting the problem. Please let me know if I'm doing the right steps in the right order:

- Gonna redo the compression test just for sanity's sake.

- Redo the spark gap test again just to make sure all 4 coils and 2 power paks are still working.

- If all that looks good I was thinking maybe I need to pull the top carb and open it up and check the float and jets and
blow it all out. The white greasy stuff has me puzzled. Never saw that on my last Johnson motor.

Am I missing something or is this the right way to precede? I want to thank all that reply. This is so frustrating.

Jerry