This truck's seen it's share of seafoam. Even tried the intake cleaner from Seafoam

I just ran a can of BG44k through the tank a few weeks ago, ran poorly afterward, turned out it clogged the fuel filter. After a new filter there was noticeable improvement, but still mileage in the 12s.

I will definitely update after I see what these new injectors do.

Thanks

 

Ive been in the same boat for years. I use to get 15-16 in town and about 17 highway with 305/70/16's. Then out of the blue it started dropping. I finally decided to look into it and found that both my rear 02's would drop out to 0. I replaced both (130k miles) rears and saw no improvement. Replaced the front also. Still spitting out 12-13 mpg. I need to do a compression and leak down to check that.

I have a friend with an '01 Z71 ECSB that I replaced the original motor with an '05 unit. He sent me a picture of his trip meter and he was about to hit 500 miles on a tank. Weither he is pulling my leg or not, it pisses me off every time lol.

 

rear 02's only moniter cat efficiency won't effect mileage
how is the power? when the cats fail you will defiantly feel the difference.
- only way cats fail is from raw fuel entering them(mis-fire) you will need to do a pressure test to check them.. take it to a shop

codes?

 

So after 2 weeks with the new injectors I'm now averaging 11.8, dropped further. I'm assuming it's the PCM needing recalibrating. Does run much better though.

No DTCs

Is it possible the fuel pressure regulator is stuck open or closed? Theres no fuel coming out when I pull the vacuum line from it, so I'm sure the diaghram is good.

Any chance fuel is evaporating from somewhere? We have had quite a hot summer here in Houston. I would assume I'd get a CEL if it were. Did notice no hiss when I opened the fuel cap, so I picked up a new cap today.

 

But wouldn't that have thrown an EVAP code?

 

Update: figured out my front diff was stuck, gave it a bit of a workout, and now drives better, got it up to 14mpg. Still not impressive, but I ordered black bear's data logger tune and just put a volant on today (sounds mean!). My cats tested great.

New issue started a few days ago, feels like it's randomly losing fuel pressure. Whether just accelerating from a light to 30, or getting on the freeway, it feels like I'm back and forth on the gas pedal. Really annoying, idles fine, starts fine. Any ideas???

 

I think since yours is a 99 the injectors are actually smaller than 24lbs. I think they are like 18-19. So if you but in 28lbers your dumping in WAY more fuel than what is needed. I bet you fuel trims are going nuts. Either get a tune or put the stockers back in.

 

did the DIC throw a code like "Power Reduction"?

 

When you were getting 17mpg, were you running regular gas? If you were, and are now running E10, it will hurt your mileage too.

 

The injectors dumping too much fuel sounds valid, I ordered the black bear tune last week. Would that answer the up and down with the power?

I've seen no codes at all, not displaying anything.

I'd heard that E10 will drop mileage and thought that was an issue too, as ethanol has less BTUs than gasoline, any idea how much would be loss to that?