I have a 2002 Yukon XL 2500 8.1L Its a great truck. The entire time I've owned it I got about 12-13 MPG on the freeway and 9-10 in the city. Recently I had both fuel pumps replaced. One died so I had them both replaced. OEM AC Delco parts. They are located in the gas tanks, so it was an expensive fix, due to labor. Also replaced the fuel filter. Now I am getting about 20% less fuel economy. I've run 3 tanks through it and am getting 10 on the freeway and 7.5 in the city. I always reset my trip odometer and calculate the MPG when I fill the tank. Every time. I did some research and have read that perhaps the fuel regulator needs to be replaced, or something about the return lines? I am taking it back to my mechanic (great guy and I trust him) next week for him to troubleshoot. Over the phone, he did not have any idea what it might be. If anyone here has anything to add, I'd appreciate it and I will add it to the list for the mechanic to check out. Thanks in advance!

The 12-13 is outstanding for a big block chev. Back in the 1990-1996 time frame, I had one of the 454 SS pickups. For most of its life it got 10 mpg no matter what you did. Street/highway, it didn't matter a bit. Then one day leaving work it was sputtering and barely running. I pulled over and got out my milsurp cowhide gloves. I "exercised" the EGR valve. After a few cycles (each of which nearly killed the engine), it began running smoother. So I pulled the vacuum line. Found a gold T in the ditch and plugged the line. It was running good.

Next tank of gas, it was getting 12 for the first time ever. Kept doing that, too. It was just a malfunctioning emissions system. The government doesn't care, they want to to obey. The vehicle costs a few grand more, its not their money being wasted.

Have you looked at your exhaust pipes? Black and dirty? Using that much fuel has got to leave soot. How about the catalytic converters? are they blazing hot when the thing is running. Again, the fuel is going someplace. The applecart has been upset in some way.

The thing is, it happened immediately after putting in the new fuel pumps. So the problem has something to do with that repair? I will ask the mechanic to look at the cats. Thanks!

You need to have the fuel pressure checked at the fuel rail. It could be low due to something being dislodged from a tank or from a fuel filter being partially clogged, or bad regulator.

Either way, get it checked.

quote:

Originally posted by PowerSurge:
You need to have the fuel pressure checked at the fuel rail. It could be low due to something being dislodged from a tank or from a fuel filter being partially clogged, or bad regulator.

Either way, get it checked.

Thanks, I will def ask my mechanic to do that. Would low fuel pressure cause 20% greater fuel consumption?

There is a tap on the engine's fuel injector rail. Hook a pressure gauge to it and see if the fuel pressure is too high (normal is 65 psi, minimum 55) and/or bleeding down rapidly after shutting off. High pressure could be a kinked return line (assuming the parts are not defective). Bleeding down is often a fuel pressure regulator. The regulator should be on the same fuel rail. ASAP after running and then shutting off, pull the vacuum line and see if gas comes out of it.

quote:

Originally posted by FishOn:
The thing is, it happened immediately after putting in the new fuel pumps. So the problem has something to do with that repair? I will ask the mechanic to look at the cats. Thanks!

Gas station switched from summer fuel to winter fuel.

quote:

Originally posted by bubbatime:

quote:

Originally posted by FishOn:
The thing is, it happened immediately after putting in the new fuel pumps. So the problem has something to do with that repair? I will ask the mechanic to look at the cats. Thanks!

Gas station switched from summer fuel to winter fuel.

^^^^^^^^^^^^
That was my first thought exactly. Normally I lose 1mpg. But wouldn't the OP have seen this in past years? Interesting to see what the outcome is.

quote:

Originally posted by bubbatime:

quote:

Originally posted by FishOn:
The thing is, it happened immediately after putting in the new fuel pumps. So the problem has something to do with that repair? I will ask the mechanic to look at the cats. Thanks!

Gas station switched from summer fuel to winter fuel.

I have been driving this truck since I bought it new in late 2001, and over 175,000 miles this has never happened before, even when they do switch to winter gas every year around this time. Something happened related to when they recently installed the new fuel pumps. 20% lower gas mileage is significant.

quote:

Originally posted by egregore:
There is a tap on the engine's fuel injector rail. Hook a pressure gauge to it and see if the fuel pressure is too high (normal is 65 psi, minimum 55) and/or bleeding down rapidly after shutting off. High pressure could be a kinked return line (assuming the parts are not defective). Bleeding down is often a fuel pressure regulator. The regulator should be on the same fuel rail. ASAP after running and then shutting off, pull the vacuum line and see if gas comes out of it.

Thanks, this sounds good. I will have the mechanic check this. Appreciate it.

quote:

Thanks, this sounds good. I will have the mechanic check this.

I should add that this gas mileage drop doesn't make sense to me and sounds like a "correlation does not equal causation" situation, but this is in the interest of being thorough, that all the bases are covered. Also, I was not aware of that generation of Suburban having dual tanks. Is the second tank aftermarket? Could the problem be just on that tank, i.e., the pump for that tank having too much pressure while the OE one is OK?

It has been over two weeks. Did you find anything out yet?

I've had issues with new A/C delco fuel pumps more than once. I now use only delphi fuel pumps on GM cars and trucks.

quote:

Originally posted by Greymann:
I've had issues with new A/C delco fuel pumps more than once. I now use only delphi fuel pumps on GM cars and trucks.

That AC Delco pump may have been made by Delphi since Delphi used to be part of GM.