Engine dies, bad fuel pump?

[Just for fun]

I have a '99 Chaparral 180 LE 4.3 190 hp 2 barrel, Thunderbolt ignition, Alpha one Gen 2 1.81 outdrive with a 14 1/4 x 21 aluminum prop. When I bought it, I did the normal maintenance so I would know what I had. Oil, filter, battery, engine water pump, outdrive impeller and new fluid, new prop, new thermostat, checked timing and plugs, and a general cleanup. I took the family out for the first time last week, everything was OK but after a couple of hours, I made a high speed run to verify the prop pitch was correct. On the second attempt, the engine quit. I looked it over, no leaks or damage, cranked it back up and it seemed OK. Again for the full throttle run and it quit again. It was about 3/4 tank on fuel. I cruised around for a few more hours below 3500 rpm and all was well. Fuel was down to 1/4 when we finished.
I had not changed the water seperator filter, so I changed it, the carb inlet filter was clean, no trash or water, and cleaned the flame arrestor (air cleaner). Took it out today with the same results, except it would not run above 1500 rpm. By the time I got to the ramp, it would stall every few minutes at idle.
I came home, pulled the fuel pump and tested it from a gas can. It shot fuel 2 to 3 feet and sounded normal, smooth, no weird noises or spurts.
I blew out the fuel line from the tank and all lines. I pulled the fuel tank (what a job...) but found no trash or water in it. I pulled the pickup tube to check for air leaks in the tube, none found.
I haven't pulled the carb because it runs perfectly before it quits.
Here are my questions:

1) Could the pump be weak and can't pull fuel when the tank gets low? (it first did it at 3/4 tank...and the pump is mounted about at the level of the bottom of the tank)
2) Is the current to the pump controlled by an oil pressure sending unit so it shuts off when the engine is not running or oil pressure is lost? I thought only the injected engines had that setup. The SELOC manual shows an oil pressure switch, do you know where it is placed on the engine? That switch is probably cheap so changing it is a possibility if I can locate it.
3) Is there something else that would cause the pump to quit? If it is quitting, it's for long enough for the carb to run out of fuel already in the bowl.
4) Could it be something other than fuel?

Has any of you had this happen? Any help or suggestions are welcome. I can't work on it until next week so I'll do some searching.

Thanks, Fred

 

[Don S]

Re: Engine dies, bad fuel pump?

Engine dies, bad fuel pump?

When it dies, is it lacking fuel or spark?

 

[Just for fun]

Re: Engine dies, bad fuel pump?

Don, thanks for the reply.
I don't know for sure because it starts right back up. Voltage, oil pressure, temperatures are all normal. It feels like it runs out of gas. The distributor cap, rotor, wires and plugs are all fairly new. When it is running it performs great and runs perfectly, then feels like it runs out of gas, it just decelerates and stalls. If I wait a few seconds it starts back up, but any throttle causes it to quit again.

I'm going to check the electrical connections from the oil pressure switch to the fuel pump. I think the switch is below the #5 plug since it is below the #7 plug on v-8's. If there was a bad connection, a broken wire, or a bad oil pressure switch it would explain my symptoms. I may bypass the oil pressure switch just to see if it is bad. I will unplug the fuel pump connector until I am ready to crank up and unplug after my trial run.
BTW, I did open the fuel cap while on the lake to rule out a vacuum, no change.
When I blew on the fuel line from the tank, I blew bubbles in the tank. That tells me the anti-siphon valve is letting fuel pass back into the tank. I'll replace that for safety reasons, but that would not cause my symptoms (open line vs. a restriction)
I know with fuel injection engines, turning on the key bypasses the oil pressure switch so the pump can run a bit to deliver fuel pressure. I wonder if the carbureted engines do this too. That would explain the fuel that allows the engine to start up again.

 

[drrm123]

Re: Engine dies, bad fuel pump?

the fuel pressure on a pump should be 4-7lbs. one other thing you can check is the ignition module there is a di-electric grease that goes on the back of module and sometimes people forget to use it and it causes the module to burn up. i could not tell you how to test module in ignition but you can try putting grease on the back if none is there and take boat out again, also there is a in line plug that goes between the spark plug and plug wire you can use to tell is ignition is cutting out on top end any parts store should have them. if you can take someone out with you have them to watch for spark when you run engine at full throttle. sounds like it may be something else though since you said it cutting out at lower rpm's now. there should be a filter in the carb also.

 

[Gary H NC]

Re: Engine dies, bad fuel pump?

Another thought,
The next time you are out on the water try running it with the fuel fill cap off.
Or double check that the vent line from the tank is clear and under full load its not creating a vacuum...

 

[180shabah]

Re: Engine dies, bad fuel pump?

Also thinking about the vent line, but Gary beat me to it.

 

[Just for fun]

Re: Engine dies, bad fuel pump?

I tried opening the fuel cap while on the lake, no change. I checked the vent line while the tank was out, all clear. Carb filter was perfectly clean, tank was clean, pickup tube intact and without cracks or holes. To me it seems to run out of gas, but it could be ignition.
The ignition module mounts on the port exhaust manifold on three raised pads. The manifold doesn't get too hot and the module attaches by the tabs fore and aft. What does the dialectric paste do? The module was clean on the back side.
I'm leaning toward either a loose wire to the pump, or a bad oil pressure switch. I'll wire a test light on the wires powering the pump to see if I lose power. If so, I'll check the wire and connections, with boats and moisture it could be a bad connection.
It could be ignition, it's hard to tell when it starts right back up. I'll look for the plug wire light to check ignition. Everything I've look at is in great shape, I never thought I would look forward to finding something ugly..... Troubleshooting an intermittent problem is not fun.
Thanks for all your suggestions. I can't get back to it until next week. I'll report back after a few more tests. Fred

 

[Don S]

Re: Engine dies, bad fuel pump?

Do the test in this link.
http://forums.iboats.com/showthread.php?t=167561

Also hook up a fuel PRESSURE gauge between the fuel pump and carb at the same time. Then run it till the problem show up and see what is going on.
That's about all you can do. That or start throwing a lot of money at it with high hopes.

 

[Just for fun]

Re: Engine dies, bad fuel pump?

Bingo... The oil pressure sensor was bad, the pump was good.
I changed the sensor and discovered a cracked brass adapter before the sensor "T". I knew I had a slight oil leak, but had not located it. I would get a small amount of oil in the bilge after a long boat ride. That was my mysterious oil leak I have been looking for. With the new adapter, "T", and sensor, it runs great with no leaks. I made a fuel line with a "T" in it and adapted a fuel pressure gauge as suggested by Don. I ran it on the lake without the engine cover and watched the fuel pressure. It never dropped below 7 psi and ran at full throttle just fine.
I filled the fuel tank after my test run. When I removed the temporary rubber fuel line with the gauge, I discovered the anti-siphon valve was allowing a small amount of fuel to pass. The full tank allowed it to siphon. I'll replace the valve tomorrow. So foe less than $50 the problem is solved. Thanks for everyone's input and suggestions, they taught me about the system and made me think outside the box. By the way, the sensor was easy to get to once I removed the rear port side seat (8 screws). It only takes 10 minutes to remove or replace them and saves a lot of cursing. Now it is time for a beer.