My 98 blazer is burning through gas like crazy. Now i did have a bad cat which i know causes bad gas milage but i replaced it and its still burning gas just as bad. Im planing on doing a full tune up, plugs, wires, cap and rotor and im also gonna replace the o2 sensor. Is there anything else that could cause this bad milage?

 

Dirty fuel injectors or stuck poppet valves, clogged fuel filter, bad fuel pressure regulator, dirty MAF sensor.

Also, if you do a full tune up make sure you go with ACDelco.

 

There is a good chance that your cat went bad because of rich fuel mixture (possibly caused by items mentioned by 01xtreme). This would also mean poor gas mileage. Is there any DTC's set?

 

Take the plenum off. The entire thing should look dirty as hell. If you have shiny gold spots there is a leak.


If you don't want to do that search leak down test on this site.


Your dumping fuel someplace and that's what killed your cat.

 

The reason im posting this is because its giving me no DTC's and the cat was bad because there was a hole rusted through it. it drives fine
But at idle it feels like there is a missfire in one of the cylinders and durring hard acceleration its hesitant which is leading me more twords a miss fire.

 

My 1999 was getting horible gas mileage also.

I found out the fuel line was rusted through and leaking above the fuel tank.

I replaced the line and alll is fine now.

 

Have you checked your distributor cap/rotor, plugs and wires?

 

I'm not dead positive, but I believe if your engine is misfiring a DTC will be recorded. A lot of times its P0300 which can be tough to diagnose exactly where or what is causing the misfire. With your latest statement concerning the hesitation and misfire like feeling...before you start throwing money at the problem, conduct a fuel pressure and leakdown test (it's free).

If you don't have one, get a loaner fuel test gauge from the auto parts store. Hook it up to the test port on the fuel feed line behind the throttle body. With your key ON engine OFF you must see a reading of 60-66psi in the first ~2 seconds when the fuel pump is running. After that, the pressure should not drop below 55psi for at least 10 minutes. Post both numbers.

Just in general, and I have not tried this on a 4.3L Vortec yet, there are a couple other ways to check if you think one cylinder may not be firing. One way is to use one of those laser thermometers and measure the temp on each cylinder exhaust manifold pipe (right where it exits the head). If one of the temps is significantly lower than the others, that cylinder in not firing. Another way is to squirt water at the same location...if one of the pipes do not steam off the water immediately like the rest, that cylinder is not firing. With how short the pipes are, I don't know if these tests will work...basically because I haven't tried it on Blazers yet. But it's another FREE step and only takes a couple minutes.

 

Well i do have a hole in my fuel filler neck so im gonna replace that before i check them cause with the hole the fuel could just be evaporating.

 

If you want easy and cheap there is a two part kit for muffler repair that will work. Its white tape with a tube of goop you soak it then wrap it around. Ad some epoxy hardener to the goop and it will set off faster without the heat of the exhaust.