Weak Fuel Pump? Or Circuit Resistance

[Angelo Voltura]

Well, I've been stumped. My beater truck and has served me well for many years now and will be torn down soon, but I've noticed something weird.

The thing has been a nightmare to start lately. 4 or 5 good cranks before it really takes off. This doesn't matter if I prime it or not. This is an EFI truck. Once it runs, it runs ok, but it doesn't like heavy throttle anymore because it will break up (like passing). Sometimes however, that doesn't happen at all and I can go to the floor. Sometimes, it idles great, others it misses and pops and stalls. I changed the filter and pressure regulator. Seemed to help a little. The filter had 400k on it and plugged solid, yikes I know.

So my first thought was well the fuel pumps on it's way out.

Until it lasted like this for almost 100,000 miles, and still refuses to die. It's almost like it's super picky with fuel, because it will act up for a week and then go 2-4 months without a hiccup. When it gets really bad the truck will barely go 30mph full throttle, and I noticed its like only sometimes it cannot maintain pressure, as I'll throw it in neutral at 55mph, wind it up, throw it back in drive and we're off for another few miles. Other times, runs beautifully for a few months, well enough you'd never know there was a problem.

What I noticed yesterday was the prime always sounded a little low in volume, like a weak battery even with a brand new 65 series in it. Well this time the battery was dead, so I threw my roll cart battery charger on it, set it to run. Jumped in the truck, and WOW that fuel pump SCREAMED. I primed it twice, and cranked. VROOM. Fired up like a brand new car in half a crank. It has never ever done that on its own even when I first bought it years ago.

What the hell? Is there some kind of massive resistance in my circuit to the pump somewhere that putting juice to the battery pushed through? I'm just curious, never had a vehicle do that before. I guess I should figure it out being a mechanic, but I'm curious on your guys thoughts.

[old55pete]

Check your battery with a new, modern tester, not the old style carbon pile tester. The newer ones will test to see if it is shorted and how many OMS of resestance is in it. I have seen a shorted battery mess with the electronics on cars, trucks and construction equipment.

[Angelo Voltura]

It's done it with any battery I've ever had in it. Currently has a 34 series battery in it, and swapped between 2 65 series I've had. Everything on the truck works as intended otherwise.