99 Tahoe bad mileage and jumping fuel gauge

[wade98030]

I just recently purchased a 99 tahoe about three weeks ago. However after recording my mileage for a few weeks I realized that I was getting roughly 8 mpg. Maybe that is around what I should be getting, but it seemed a tad low. When turning the car on some times it will go down to around 100rpms and almost die and then slowly climb up to a stable idle. Other time that this happens it will jump up to normal rpms as if its going to start and then immediately die. The Tahoe is mostly stock, save 33 inch tires and an under mounted winch.

99 tahoe LS 4WD

I also have an issue with my fuel gauge bouncing around all the time. It never goes all the way to E and back up to F or anything like that though some times it will jump from F to 3/4 tank and go back. It is simply always just vibrating up and down very quickly.


I have already done all the basic maintenance such as oil change, new plugs and wires, ran sea foam through it.

I hope that I have posted this into the right subforum, as I am new here. If not I apologize! I know that there is not much information to go off of, but any help is greatly appreciated. Also, I will check in to answer an questions that might help figure out whats going on.


-Wade :emotions33:

 

[willua11]

I was going to suggest Z-Max, but you used sea foam already. My fuel guage jumps as well, but still stays fairly accurate. My suggestion to fix that would be buy a whole new cluster. That is the only thing I have seen that will fix that and I saw that on here. I also think that 8mpg is too low, should be more like 14.

 

[moguy]

umm check the ground wire at the sending unit plug

on my 97 it is grounded to the crossmember to the front of the tank on the front side of that beam. just above the rear axle just to theright side of the truck.

 

[lesterl]

99 NBS or OBS? OBS check the fuel pressure, could have a leaky FPR causing it to use excessive fuel, should be around 15mpg if you are easy on her.....

 

[XLDENALIXL]

99 is GMT 400 which is OBS.... and the dancing fuel gauge is a common problem on all the OBS tahoe yukon Subs.... when i got a new fuel pump it fixed the problem... as far as bad MPG since you did a tune up already id suggest Air filter and fuel filter for now and see what happens

 

[lesterl]

99 could be either, I had a 99 NBS......

 

[XLDENALIXL]

99 nbs was silverado and sierra... Tahoe and yukons werent updated till 2000 for some strange reason

 

[lesterl]

Your right, my bad, I thought I was in my truck forum....... Duh! Yeah, never had a Tahoe before the 95 that I am working on to get on the road now........

 

[XLDENALIXL]

Your right, my bad, I thought I was in my truck forum....... Duh! Yeah, never had a Tahoe before the 95 that I am working on to get on the road now........

Awsome! toss up some pics...... the one in my avatar is a 95 i was suppose to buy it 3 years ago and the guy sold it for under me, i ran into it 2 months ago offered the new owner 3k buy he dident budge,.... when i start my new job im going back to the bar and dropping 3k of hard saved up money for it and see what he does lol... any plans for it?

 

[lesterl]

I have always had pickups (GMC Sierras on the full size), S10's on the mini trucks....... Pix to follow in a new thread before too long...... It is pretty ghetto for now.....

 

[gmantcmn]

Hey wade I have the same issues with my 99 ToeHoe! only dif. 4 me is when my Gas gauge "jumps" it's ALWAYS towards E !
When you tuned it did you clean your MAF(Mass Air Flow)?
Makes a significant change to performance on fuelyinjected's when there dirty!
Bout the only way I get over 8MPG is by TAILGATING the S-IT out of a BIG AsSemi-Trailer!

 

[TrueNorthAK]

My fuel gauge does the same thing, but like another response, it is fairly accurate. If I go from F to E I am putting in about 23/24 gallons. My 99 is stock and I get between 12-13 MPG so sounds like a tune up is needed on yours.

 

[2Kbabyhauler]

2000 OBS I have the dancing needle on mine and it goes to E or F constantly. Had a new fuel pump in it when I bought it. Gauge worked but now does not. Avg Mpg was 10-13 city. Also when gauge worked the tank took 24 gals to fill from E. 30 gal tank. New fuel filter,cap,plugs, wires helped. 142k