mpg sudden drop

Dirtautoguy · March 12, 2015

Over the last couple weeks I have been trying to figure out why my MPG has dropped on my 1996 chevy k1500 with 230,000 miles with 3.42 gears. At first I pawned it off as a bad tank of gas but 2 tanks later it didnt get better. I went from getting my usual 17-20 MPG to only getting 10-13mpg. It seemed to have happened more of suddenly. I have also noticed that my truck has had to turn over more than usual to start.

I have been watching my O2 sensors. the front ones seem to change pretty good from what I can tell, however I don't know how many miles are on them or if they have been replaced ever. the rear ones that measure the catalytic converter efficiency seem to be all over the place especially on bank 1. They will stay at a fairly constant high 65-70 for a little bit and then switch to a low number 9-18 and change back and forth between those numbers at a constant 2000 rpm.

I have also been watching my fuel trims. at idle it will reach -10 even after the truck has warmed up. as I start going down the road the trims get better but still stay around -5. the truck was idling at 800-1000 so i checked my coolant temperature and it was saying that my truck was only running at 179 degrees when it has a 195 thermostat. so I replaced the thermostat and it now runs at 193 degrees and idles around 650. but it still is running rich.

I did a compression check and got 140-145 on 4 cylinders I have not had the time quite yet to get to the other 4 but I will ASAP.
I havent noticed a real loss of power if I get on it, but I have noticed that where it used to go 65mph at 1700-1900 rpm it now takes 2100 rpm.

At Idle it does have a slight shake and as the rpms come back down from being reved its almost like it gets choked for a second.

I was questioning maybe my catalytic converters were the cause so I crawled under the truck and examined the o2 sensor wires. I also unbolted the exhaust and I could see one cat and it looked kind of a yellowish color and in a healthy honey come shape. I couldnt see the other cat but when I give it a good whack it sounds like something is loose inside almost like a powder nothing big or heavy sounding but there is something loose in there. I isolated the heat sheild the best that I could but I'm pretty positive its coming from inside the cat. I know that for more than 3/4 of the trucks life it was ran on 85 octane gas and didnt get a tune up untill it couldnt hardly run. After I did a tune up it was a beast.

I did get new tires recently however this issue did not start untill about 3 weeks after. I have also double checked the tire pressure.

the truck has:
new distributor shaft, cap, rotor, wires, platinum plugs.
clean k&n air filter.
new fuel filter
new fuel pump
new thermostat

I'm not really sure what direction to go from here. I want to replace the o2 sensors and cats but not if they arent bad.

Dirtautoguy · March 14, 2015

A friend of mine mentioned that it sounded like I had a leaky injector. So I took all the black stuff off the throttle body and looked down in there with a flashlight. The lines that I could see looked wet and it smelt faintly of gas. There was also a couple wet spots on the bottom of the intake. I'm guessing that this is most of my problem.

The only thing that confuses me is that my truck doesn't miss or miss real bad and usually when I read about these spider injectors it usually talks about how the truck will miss and have other issues other than just running rich. Any thoughts? Iv never dealt wth the spider injectors but I know they have issues from what I understand. And that there is a new version that is much better.