1999 Bravada fixed or?

[PaintedStallions]

I finally got the po codes to quit lighting up. The truck runs like new again. But I can't get more than 14mpg! Now listen all! Everything is new! The fuel pump, filter, the spider system complete with a new regulator, gaskets, all of it new! The fuel system is all new! Now the cap, rotor, plugs and wires are all new! The MAF and the IAC are new now. No cheapies here! It runs great, no stalls, no hesitation or anything of a kind. Does anyone have an idea why the mpg's are so poopy! Before any problems occurred, I was getting 20 to 22mpg on this thing now only 14 hwy and around 12 in town.

[Chris Stewart]

Prior to '96, the OBD I systems used to use "fuel counts" to see the relation between the O2 sensors and computer fueling commands. A sooted up sensor was not reporting true values although they were not out of range enough to set a code.
I'm not sure how this crosses over to OBDII.

[Leeann94astro]

I had trouble with low mpgs due to a dead or dying intake air temperature sensor and coolant temperature sensor (the one for the ECM, not the gauge). Might want to test those.

[PaintedStallions]

Where are these sensors?

[Leeann94astro]

I'd have to go out and look on my '99 Safari, but the IAT is in the intake hose before the throttle body and the coolant temp sensor is on the front of the block, near the thermostat housing on my '93 Bravada.

[PaintedStallions]

I can understand the IAC maybe having something to do with mpg! But how would the temp sensor affect mpg?
You know, this all started a couple of months ago due to a faulty fuel pump. I just seems hiddeous to me that everything in the engine all of a sudden turns to Sh!t! It has to be something simple! Every filter, gas, air, everything is new! No leaks in fuel system or hoses anywhere! Oh well, I guess it takes being ripped off by a dealership to find out huh!

[blazee]

The computer runs two different fuel programs. Open loop and closed loop. Open loop ignores the o2 sensors and controls fuel based on a default program. Open loop generally supplies much more fuel than closed loop operation. The vehicle runs in open loop until it reaches a preset temperature (usually the 160 degree range). After the engine warms up properly it switches to closed loop. Closed loop operation monitors the o2 sensors and adjusts the fuel delivery to provide maximum efficiency. If the engine doesn't reach the proper temperature because of a faulty thermostat, or if it thinks it isn't reaching the proper temperature due to a faulty sensor... the engine will remain in open loop operation.

[PaintedStallions]

That makes sense now! Way cool Blazee! I did notice that the dummy needle on the instrument panel doesn't go much past the cool line during normal driving. Where is that particular sensor on the engine? I have a new tstat, 195 degree. I just haven't put it in yet. But I might as well go ahead and change the sensor too to make sure. Is there more than one temp sensor? If so, where are the other ones? Thanx!

[old_master]

I'd do the thermostat first and make sure engine operating temperature is ~200F. The dash gauge should indicate accordingly. Post your results.

[PaintedStallions]

I replaced the t-stat. No change worth writing about! What kills me is, is that the truck runs excellent. Its just running dangerously rich! I have replaced everything! I mean everything! The one thing that weighs on my mind is the gas tank itself. There is a hose that connects to the tank that is at the opposite end of the filler end. You can't see this unless the tank is out. the hose is that short. The tank hangs until you disconnect it. Well I broke that nozzle when I replaced the pump. I mentioned this in prior posts. And was apparently no big deal, that it is just an air-vent hose. I didn't snap the nozzle off. But it is noticeabbly broke! I know on some vehicles the tank is kind of pressurized. You can hear this when you remove the tank cap. And on some vehicles, if the cap isn't on right, left off, or just loose, it will set off an SES code. But I get nothing. Even a dealer mechanic told me that this was no big deal! Maybe he just has never come across this problem. And I am beginning to wonder now! Even before, the tank never held pressure. But maybe the hose has something to do with something fuel wise. Any inputs on this?