Engine cutting out under load

[LakeErieFishing]

Descant, fuel tank was replaced when I rebuilt the stringers and flooring. After we drained the gas this spring I looked into it with light and nothing unusual in regards to particles at the bottom of the tank. Fuel pickup tube was clear that goes into tank. It's also about 1/4" off the bottom. I can easily blow into the line that goes from the tank to the fuel filter and hear it bubble. I'll double checking the air vent line but it appears clear.

The fuel pump is mechanical and new this year. It's not the fuel pump.

The engine stutters then dies after it gets warm, and especially when rpm's get above 2,000. It can be running great for 5 minutes up on plane, then it losers power and quits if you don't back off the throttle. Even then it will quit if you don't shut it down and let it cool. It will restart but you usually have to let it cool for awhile to restart it. The more it runs, the longer you have to let it cool before it will restart. This all appears to be electrical to me, not fuel system.

[LakeErieFishing]

We can try an alternate fuel source but the engine is acting wacky only after it gets warm. We've been told by a few folks that electrical issues can cause this to happen. Maybe it is fuel delivery but there is a definite correlation between the engine and electrical system getting warm and the issues popping up.

The coil is good, the electronic ignition module is good. The spark plug wires and primary coil wire from the distributor are older wires, at least 20 years old so that might be part of the issue (arcing when they warm up). The ignition switch and wiring could also be causing the issue when those wires get hot - so others have advised.

At this juncture we will triple check the fuel system to make sure the vent hose is clear and the fuel line isn't collapsing. Also, might go ahead and change plug and distributor to coil wires. I can hot wire the engine to by pass the ignition switch. I don't like doing that but if the switch or wiring is the cause that will show it.

Suggestions beyond how I intend to trouble shoot?

[SIKSUKR]

Sounds like a fuel delivery issue. As was posted earlier, run it till it happens again and open the fuel cap to see if it has a vacuum. If you're not sure, then try to loosen the cap to let air in without letting water in to at least prove/disprove this.

[LakeErieFishing]

I'll give it a try (taking gas cap off) and let everyone know.

[Orion]

Originally Posted by LakeErieFishing

.......
The fuel pump is mechanical and new this year. It's not the fuel pump.
.......

Never rule out new parts as being the problem. One time I spent 4 days trying to diagnose an issue after having recently replaced ignition components, swearing that they were new and couldn't be the problem......they were (bad condenser).

It does sound like fuel to me as well.

[Rich]

Originally Posted by LakeErieFishing

The fuel pump is mechanical and new this year. It's not the fuel pump.

Here's a mildly related story... which happened to me.

I had a car that did the same sort of thing. When cold, it would run fine. But when warmed up, it would lose power and sometimes I couldn't start it again if I shut it off until it was stone cold.

We checked everything that you can think of. It seemed like it wasn't getting any fuel, so we replaced the mechanical fuel pump.

The problem continued, so I ended up solving the problem at the time with an electric fuel pump. This seemed to solve the issue, and we couldn't find out why the mechanical fuel pump would stop pumping fuel when the engine was hot.

One day when I had nothing to do, I decided to try to find out why the replacement brand new mechanical fuel pump did not solve the issue.

I removed it and analyzed it very closely to fully understand how it worked. It was a very simple device, so I couldn't understand how it wasn't working when the engine was warm. As long as the pushrod that was activating the mechanical fuel pump was pushing in on the pump's lever, then it had to work. There was no way that it couldn't function when warm if the lever was being depressed.

That was the clue! This car had well over 170,000 miles on it (closer to 200,000). I removed the pushrod and found a replacement, mostly as a comparison as the end of the original one seemed to have a bit of wear on it. It turned out that the old one was just a bit shorter than the new one due to wear (it probably wasn't getting enough oil, or was a bit softer than it should have been, perhaps due to a manufacturing defect).

Evidentially, over the many miles, the push rod had some wear on it. And as the engine warmed up, some tolerance would change due to the heat, which would cause the mechanical fuel pump to not pump the fuel because the push rod that activated wasn't pushing fully enough on it's lever.

At the time, the replacement pushrod cost me about $5 to replace.

I replaced the old pushrod with the new one, and was able to remove the electric fuel pump.

So don't just think that because you replaced the mechanical fuel pump that the problem is solved. You still need to verify that the engine is getting enough fuel when it's warmed up and under load.

I can't tell you how many hours we spent trying to find the source of this issue.

[LakeErieFishing]

Where could I find the pushrod, or even know the part needed for my engine? It's a merc 888 Ford 302 early mid70s vintage.

[TiltonBB]

Not sure if I read it here.

I had a fuel line with an inner liner that looked good on the outside but the inner liner was collapsing and restricting the fuel flow. I had similar problems to the OP and after replacing the fuel line they disappeared.

[Rich]

Originally Posted by LakeErieFishing

Where could I find the pushrod, or even know the part needed for my engine? It's a merc 888 Ford 302 early mid70s vintage.

I don't know. This particular engine may have the fuel pump driven directly from a cam lobe, instead of a push rod that rides on the lobe of a cam.

My example wasn't to say that a push rod was worn, but to say, just because you replaced the fuel pump itself, unless you measured the fuel pressure output from the pump, don't discount that there would be still be issues with a part that you replaced. Of course it's very rare, but a new part could somehow also been faulty.

Good luck with your problem, I hope you let us know what the final fix is when you find it.