I have had to replace the fuel pumps in both tanks numerous times. My mechanic who is very knowledgable doesn't seem to know what makes them go. It is expensive to have done each time. He has been getting them at Auto Zone ($150) and dropping the tank to get them replaced ($100), each time. Is there anything wrong here? Is there some better aftermarket replacement? Has anyone else experienced this problem? I really like the trunck and don't want to replace it, but after 5 pumps, I have to do something.

 

Maybe they are overheating? Do you let either tank get below 1/4 full?

 

never really let tanks get that low.

 

Does your mechanic live in a big house and drive a fancy car?

 

he has worked for the county maintenance department for 20+ years, and has done work at his home(small) for 30 years. Has seen a lot but is stumped. Drives an old Caddy, and I mean old.

 

Never Fails! Them driving those old Caddy's got them huge stock portfolios.


(Sorry devildog, I ain't much help on this one)

 

It sounds like both lifting pumps in the tanks are failing. First thing to determine is if both pumps are running at the same time. When you switch from one tank to another, the pump of the unused tank is supposed to be off. If it doesn't shut off, then it's pumping continuously against a static head and that's not good for a non-centrifugal pump.

Next thing to check, if both pumps are not running at the same time, is to check the valve and the filter. There's a filter at the valve and if it's a bit clogged, it might be causing an increases head pressure that could be causing the pumps to wear out faster.

Finally, check the fuel pressure at the engine. If it's not at spec, then maybe the high pressure pump is not up to par or the filter is clogged. It's a long shot, but it might be enough to cause the pumps in the tanks to overwork.

Raoul asked this question, but I'll ask it again. Are you running the tanks low or dry at all? I know with dual tanks, some people run tend to run their tanks really low or even dry. That's one of the worst things you can do to the pumps in the tanks. It doesn't take many low/dry tanks to cause the failure of those pumps.

BTW, I had an '87 with dual tanks and never had a problem. Never gave the tanks a chance to get below 1/4 tank.

What year and engine? Is it fuel injected?

 

I've also heard of problems with the various selector valves causing excess pressure in some situations. Over the years they had three or four different set ups.


On the subject, had anyone pulled a Fuel Delivery Module in the 4x4s? From what I understand it is more or less a small tank within the tank so the truck doesn't fuel starve when at sharp angles. I just got done siphoning all the gas from my rear tank and putting it in the front, the rear tank is leaking! Anyway, if anyone has experience with the FDMs fill me in on any differences in tank swap procedures. I can live on the front tank until I have time to get to it.

Also, can you siphon gas through the in tank pump? My truck is a '95 with the high pressure pump in the tank (actually the FDM from what I understand)? If not is there a good way to get the tank empty without dropping it. With the setup on the later trucks I have to leave the pump/FDM/in tank valve in place so I can use the front tank. I want to get it bone dry in case I have to order a new tank in, don't want to take a chance since I know the tank is leaking....

 

I have some experience here---It sounds like Dennis knows what he is doing...

You can drain the tank using the FDM, just reroute the fuel line, At work we use a plastic tank/pump and hand crank it or drain it using gravity...

Heres a trick I use on the duals tanks...strap the bed and lift it off the frame...I think there is 6-8 bolts that hold the bed down...this way you dont have to mess with dropping tanks or fuel lines or straps...We use the lift to lift the beds...You dont have to drain...

On the FDM parts, you either have something wrong or the FDM's you are using are a cheap brand..i hope this is not true because I used some autozone ones the other day on the in-laws truck...

dennis has some good ideas on how to determine what is happening....

Dennis are you turning wrenchs or have you in the past???

You need to supply additional info year, tanks, 4x4, long bed????

 

Mach 1,

Sounds like you've played this game a few times.

Do you have any idea if the switching units in the FDM function without the key on? From the explanation in my Haynes book, the dash switch provides voltage to the approprate pump, and the shuttle valve is open only in the "active" tank to ensure that the return fuel goes to the tank being used.

OK, here's the problem. My '95 lines (supply and return) use a "Y" type setup with no fitting. This is before the first disconnect in the supply line which is at the fuel filter. I don't wan to use the fuel pump to pump out the gas, but if I drain from that point I would have to empty both tanks, correct?

Either way, I siphoned out enough to drop the tank, at which point I can drain what's left.

 

Mach1, when you practically grow up on farms and boats, you can't help but turn wrenches. I've rebuilt 4 boat engines. 3 of them were small block Chevies and helped rebuild a 6-71N (circa WWII) in a friend's old boat (new sleeves, bearings, oil pump, rings, valves). It had almost 50,000 hours on it. Dirty engine (oil all over the engine room), but rock solid dependable. Parts were cheap too.

Even had to learn how to arc weld. A skill that comes in handy to repair harrows and broken boat trailer axles.

I could never be a professional mechanic for a couple of reasons that you'll find funny. The major reason is that I can't stand working while laying on my back. In other words, I really hate working under the vehicles and I REALLY hate working under the dash which helps to explain why I don't have a Superchip even though I really want one. The second reason is I don't care for the smell of grease.

I've always been mechanically inclined, but never made any money at it, much to the chagrin of my father. My mom, on the other hand was relieved, having lived through my various exploits. Most notable was building an arc furnace when I was around 8 years old, just to see how big an arc I could make (almost 2 inches on 120 volts). I built it out of a clay flower pot, curtain rods, and carbon rods from batteries. I wanted to hook it up to a variac my father had and try it at higher voltages, but the heat my furnace generated was nothing when compared to the fire that was shooting out of my mother's eyes which was, btw, rivaled by the smoke that was coming out of her ears! LOL.