Engine runs great, until it doesn't.

[laseron]

I've been trying to sort out a problem with my 89 FJ. The engine runs well on startup, and for several miles runs great. Then it loses power, won't accelerate, and eventually stumbles until it cuts off. What I've tried so far: replaced battery, spark plugs, fuel pump and fuel filter, as well as replacing the fuel. Rebuilt carbs (discovered a fuel leak-fixed it). Cleared the fuel petcock and all vent and fuel hoses with compressed air. Checked to see if opening the fuel filler cap restored power (no change).I think I've pretty well eliminated the fuel system as the culprit, but who knows? So, could it be the computer? It's the original unit, and the bike has over 91,000 miles on it. Since it's an aftermarket fuel pump, I guess it could be defective, since at times I don't hear it ticking. Maybe the fuel pump relay is going, but that seems like a part that either works or doesn't work. I truly hate intermittent problems.

[FJmonkey]

Some have reported cracks that in the ignition module that allow moisture/corrosion and then intermittent problems. So it could be the fuel pump cutting out after being in demand for a short time. Relays tend to just fail and not be intermittent, but that is not a rule, just common failure mode.

[laseron]

Thanks, I'll check the coils. They're Dyna coils - about 8 years old. I'm considering just putting the whole Dynatek 2000 computer kit in. Expensive, but couldn't hurt. (Just not sure a bike with 91,000 miles on it is worth it).

[Pat Conlon]

The engine runs well on startup, and for several miles runs great. Then it loses power, won't accelerate, and eventually stumbles until it cuts off.......Since it's an aftermarket fuel pump, I guess it could be defective, since at times I don't hear it ticking......

My money's on a defective fuel pump. My symptoms sure match what you have gone thru..
I put a new eBay Chinese (lifetime warranty) fuel pump on a '92 and learned my lesson....never again.

When this happens, connect the fuel lines together (with a coupling) to bypass the fuel pump.
It will get you home.

Get a quality fuel pump. No more Chinese shit for me. Lifetime Warranty my ass.

 Cheers   Pat