collinhawks

1993 Z28, I average a little under 200 miles to a tank, only use premium gas. There have only been 4 owners, the previous guy said he had the top part of the engine rebuilt, bone stock car, stock tire size and rims, 241,000 miles, still runs well. I don't feel like all of the power is there either. I've read on all these forums that we should be able to smoke an R/T challenger, but I raced my dad who drives one and he won by half a car length. New optispark and spark plugs less than 10k miles ago.

Also, whenever I press the gas there's a loud an obnoxious ticking noise coming from under he valve cover, it's only under load and gets louder the higher the RPM's and goes away after driving for about 5 min and then comes back if I let it idle for too long.

shoebox

Ticking could be an exhaust leak (might be at the head/manifold, if it sounds like it is in the valve cover area). That could also throw off your O2 readings and cause poor mileage. Leaks are usually louder under load.

collinhawks

What can I do to check if it is an exhaust leaks and how can I repair it? My dad thought it was a lifter.
I get about 13-14mpg mixed highway and city, 15 highway, and about 12 city.
Idk when the o2 sensors were replaced last and can an exhaust leak really cause that big of a gas mileage drop?

Injuneer

Manual or auto trans? Ever done a cylinder compression test? Any significant oil consumption? Still running the original cat at 241K miles? What is the elevation where you live? Did the old plugs show any signs of running rich? Do the new ones? Checked the air filter lately?

Rule out or verify its a lifter with a stethoscope.

Long time exhaust leaks, possibly suffering from high back pressure due to a partially plugged cat, should shows signs of carbon at the leaks. An exhaust leak before the O2 sensor cause a "false" lean, and the ECM reacts by adding fuel the engine doesn't need. Add that to any one or more of the potential problems mentioned above and it could account for the poor mileage.

collinhawks

Automatic transmission.

Never done a cylinder compression test, how can I do that?

There is a good amount of oil consumption but I'm also leaking some towards the front on the passenger side I believe.

I believe it's still the original cat, if it is how can I unplug it if it is plugged?

I live in Florida.

I didn't change the spark plugs, so I couldn't tell ya

And the air filter is new and I just checked it last week and it's pretty clean.

Sorry for all the noobish questions and thank you all for your help! I really appreciate it, I love the forum! And it's a pleasure to be talking with two of the most respected people on the forum!!

collinhawks

Ticking noise ended up being the exhaust manifold as mentioned. Thanks guys!

Injuneer

See if the mileage improves. Look for 17-18 MPG in town, and upwards of 24-25 on the highway. If not, replace the O2 sensors. They are 1-wire on a 93, so not real expensive. Buy only AC Delco.

An exhaust shop can measure the backpressure in the exhaust system, to identify a plugged cat. If it's plugged, needs to be replaced. Plugged cat will reduce fuel mileage.