Re: Fuel pumps in the gas tank
When the manufacturers switched to modern fuel injection in the late 70’s, early 80’s, they put the fuel pump either in the tank or next to the tank, at the tank’s outlet. The reason is fuel injection requires higher fuel pressures, and it easier to push the fuel rather than pull it. An engine mounted tank has to pull the fuel. Works ok for carbs as carbs don’t need high fuel pressure, but for fuel injection, not so much.
Why does it cost so much to replace the fuel pump? Well, part of it is just the cost of the replacement pump. You could surf to rockauto’s web site and see what replacement fuel pumps cost for your vehicle. There will probably be aftermarket and oem versions available. I expect the shop is quoting the oem version. Then the rest of the cost is labor, which varies greatly depending on how much time is needed to get to the pump.
My old late 70’s VW Rabbit had the pump next to the tank, in the rear wheel well area, so it was easy to access. No fuel tank involvement at all. I think most Toyota sedans have the pump in the tank, but on many of them it is fairly easy to access and remove just by removing the rear seat. i.e. You don’t have to remove the tank to replace the fuel pump. GMC’s, not sure, but it sounds from what you say the tank has to be removed, and would in part explain the high cost to replace the pump.
Removing the tank, that’s not something the typical “change the oil and spark plugs” DIY’er would usually do themselves. I’ve done a variety of DIY repairs to my vehicles, but I’ve never removed a gas tank. Gas tank removal and installation can be very dangerous if the proper procedures and safety aren’t followed. I’d leave that to an expert. It isn’t necessary to use a dealer shop though, any good inde shop can do it.
I concur w/your shop, I wouldn’t be inclined to replace the fuel pump unless there was clear evidence it is the cause of the problem. When I’ve wanted to rule out a fuel pump as a possible problem cause in my vehicles, I’ve rigged up a fuel pressure gauge so that I can watch it while I drive the car. If the fuel pressure drops unexpectedly when it shouldn’t, that’s a big clue there may be something wrong with the fuel pump. It would at least narrow it down to a fuel problem of some sort. Best of luck.