Hi, I've got an 00 z28. its got about 83000 miles on it. For some time its been getting bad gas mileage (it dropped from almost 20 around town to near 14 or 15). I've changed the fuel filter, 02s, and now the spark plugs. When I did the spark plugs, they were pretty well worn out, but it also appeared that many of them had a brown, wet substance on them (gas or oil?). The electrodes were a light gray to a white color. Also changed the air check valves, they were setting a code. the air filter is in good shape and the plug wires look ok. Also, ever since I've bought it, its had a very slightly rough idle. if I watch the oil dipstick, the printed " ENGINE OIL" on the top of the handle rocks back and forth and i cant read it, although the odd thing is about every 2 seconds it quits vibrating for a split second, to where I can read it. Another odd thing is it seems if I leave it over night, my gas gauge will drop a bit (around an 1/8th tank, sometimes). I know f body gas gauges arent too great, but still. I pulled the fuel injectors to check for leaks, but they all seemed ok. anyone have any ideas? thanks

Edit: Two other things. If I watch the oil dipstick when the engine is first started, it doesnt vibrate like normal. Also, it backfires through the exhaust quite a bit when the weather is cold, although I dont know if thats normal or not.

 

I am studying to take my ASE tests in may and I remeber reading something about oil on the spark plugs. Can't exactly remember and my book is packed since I am moveing. It tells you another test to do but I can't recall if its a compresion test and it was something about your piston rings being worn but not exactly sure. I am moveing on wednesday so I will check the book when I get it out if noone esle answers by then.

 

the black stuff wasnt so much on the electrode as it was on the threading

 

My car had a vaccuum leak in the intake manifold that was causing it to run rich. Horrible mileage resulted, and it tended to 'tick' when you goosed it. Turned out to be a 1" long rubber tube with a hole in it.

 

I tried checking for a vacuum leak, but i dont really know where theyre all at. does anyone have a diagram so i can look around? Also while I was messing around, I cleaned the throttle blade and also took a q t ip to the maf. Didnt really seem to effect anything. I should note that as Id noticed the oil dipstick shaking, it only does that once its warmed up, so that would be something with closed loop right? There is a little bit of a tick I can hear, Thats why I checked out the vacuum line. Thanks!

 

So the fuel gauges on ls1 cars are messed up?! i thought i just got like 12 mpg in town! + when it drops to empty, filling it up full is only 12 gallons! I didnt know if convertibles had smaller tanks for some reason or if my gauge is completely wrong. any fixes for this? or do you think i am also getting really crappy gas milage and may have a vacuum leak like bigz here?

 

As far as I know convertables have the same tanks. The gauges are pretty unreliable, you can go much longer on the first "quarter"(as the gauge reads) then the last quarter. As far as only being able to fill up 12 gallons, you really can only get 12 or 13 in there because theres extra room in the tank for vapors. And also, even if you could run to where itd take the full 15 gallons to fill up, you dont want to run it all the way down anyway, that could damage the fuel pump. To measure your gas mileage, fill it all the way till pump stops, then reset your trip odometer. Then next time you fill, fill it till the pump stops again. Then take the mileage from your trip odometer, then divide by how many gallons you filled up. I usually only get 200-210 miles per tank in town, which with 13 gallons to fill up is only about 15 mpg.

 

Another thing I forgot to mention. If I let the gas get down below the quarter mark, and then fill it up, i notice a HUGE improvement in power. Could something be wrong with my fuel system?

 

i think we have the same problems, i get a real "seat of hte pants" increase when i fill up..