should I just change the fuel pump?

[gumbyaz]

2008 4.3 GL-J. Over the last 3 trips on the water, have noticed it start bogging down at progressively lower RPM - it recovers as soon as you back down. First time was only after about 30 seconds at WOT - did it once, near end of day on way back to dock. Second time was at about 3600 RPM, beginning of day, again after about 30 seconds running great at that RPM. Did not have a need to go that fast for rest of day, so I just left well enough alone while on the water. After that, I pulled the anti-siphon valve on the fuel tank and checked it - no signs of blockage, ball moved fine, so I put it back. Also checked that gas cap venting looked OK.

Today was 3rd time, now I can't even get on plane. 2500 RPM max. It would get to 3200 RPM, but same thing...bog after 15-20 seconds of running great. I unplugged and replugged electrical connection to the fuel pump, fuel pump relay, even swapped fuel pump and ignition relays while on the water just to rule out basic electrical.

Fuel filter was new not that long ago, no reason to suspect blockage. I may just change that also.

I haven't gone looking for the inverted flare fittings yet to hook in a fuel pressure gauge. Pretty sure that it is fuel starvation based on symptoms.

But I guess my question is - when these fuel pumps go bad, do they do it gradually like this?

 

[89retta]

Have you checked the cap and rotor ?

 

[Grub54891]

Had a customers boat with similar issues. After checking numerous things, all it needed was spark plugs. Same thing happened to a buddy just last week. Spark plugs were the culprit. Start simple. Although the cap and rotor should be checked also.

 

[Scott Danforth]

Check the contents of your fuel filter

check the fuel pressure

Replace the cap and rotor

 

[gumbyaz]

ok, will have to head to the parts store and try to find fittings to get my fuel pressure gauge in there.

Pulled the cap off. Not experienced enough to know how bad is bad on a distributor, but there is definitely burnt appearance on each contact and the rotor tip. Don't know how old it is from previous owner so worth doing anyway.

I was just thinking it felt more like fuel starvation than ignition since it will run great for way more than a few seconds, but then just suddenly stumble and lose power. I did check the small filter on the carb inlet last weekend also - perfectly clean.

 

[enginesilo]

I was experiencing similar symptoms as you. Last time I took the boat out I was revving around 3000 rpms max, and it would even get worse where I couldnt rev over 2000rpms. It then got to the point where it was hard starting. I took the advice of these awesome members of the forum and changed my cap and rotor. Incredible how well it runs now and the response I get from the throttle. My contacts in the distributor cap were chalkly and corroded and it was obvious after I saw how they looked. Cost around $100 for the cap and rotor OEM. Worth a try and it’s a good tune up item to change regardless. Good luck.

 

[Insomnium]

"Fuel filter was new not that long ago, no reason to suspect blockage. I may just change that also"


It can happen quick sometimes. Its worth dumping into a clear jar and inspecting.

 

[gumbyaz]

I bought new distributor cap/rotor, spark plug wires, and spark plugs. Gapped the plugs, installed all yesterday.

Also, pulled the fuel filter and drained into a jar. Only abnormality was presence of a small amount of rusty looking sediment - I did fuel the boat from a toy tank on a houseboat shortly before this issue started.....so was thinking maybe that was cause of a little bit of rust. Replaced the fuel filter anyway, and also rigged up a fuel pressure gauge.

Took the boat on the water today. Started right up, at idle running just as well as it was before. Fuel pressure of just at or below 8 psi. Got out of no wake zone and revved it up - fuel pressure stayed at 7-8 psi, never dropped below, but boat bogged down again after about 10 seconds of running well. The faster you push it, the sooner it bogs down. It will hold 2500 rpm for minute or more, if you go WOT it runs great but then bogs down within about 5 seconds.

Pulled the carb inlet screen out again while on the water - still looked great. Left it out for one run just to see if it helped - no help. Replaced.

So I am still thinking fuel issue, but now thinking about float needle in the carb? I didn't want to pull the fuel bowl on the water. Will pull it this week. Anything I am looking for? On the right track from a thought process?

Also was thinking of taking the fuel line off and blowing it out - not sure how something would get in there past the filter, but that is the only other possible restriction point. The way I tee'd the fuel gauge in, it is right after the fuel pump, but 2 feet of fuel line shouldn't cause much pressure drop.

Other thing I noticed today - voltmeter hovers about 1 volt low right after engine starts, then gradually climbs back to and stays at normal if left at idle, or quickly climbs to normal if engine is revved. Could a bad alternator output be causing this? Battery seems strong, I keep it topped off in the garage.

 

[Maclin]

If the fuel pressure is staying constant as you described, probably not an alternator problem. Sounds like an internal carb problem. The fuel pressure will read towards the high side of pump capacity if the carb is not letting in the proper amount of fuel. Could be a float setting issue, or clogged jets passages in the carb. I think you will not be able to fix this without a looksee into the carb, a rebuild may be the ticket..

 

[gumbyaz]

Problem found!!!

No fuel hose restriction (didn't think so), but upon opening the fuel bowl tonight, found the black plastic part shown here (this is from a pic when I rebuilt the carb back in March) wedged underneath the float!!! No wonder it wasn't letting gas in - it was wedged up.

What is this little black plastic piece (Metering Body Vent Baffle?), and how can I tell how to mount it correctly to avoid this from happening again? I looked quickly at a Holley diagram, and it looks like it goes under the gasket on the metering block side of the gasket. I think I may have had it on the fuel bowl side of the gasket?

Given that my gasket is only a few months old, can I reuse it and just screw the thing back together? Or should I go get a new one? If so, do auto parts stores keep these in stock usually?

 

[Maclin]

Between gasket and metering plate, otherwise it falls off like you experienced. If you have the blue waxed gaskets, those are reusable for almost the life of the carb. If you have just the cork, go to a speed shop and get the blue ones, man. totally worth it. Even though It looks like not much residue was left by what appears to be cork, the blue ones are an order of magnitude (or two) better.

 

[DouglasW]

Sounds like an internal carb problem. The fuel pressure will read towards the high side of pump capacity if the carb is not letting in the proper amount of fuel. Could be a float setting issue, or clogged jets passages in the carb. I think you will not be able to fix this without a looksee into the carb, a rebuild may be the ticket..

You nailed it.