So I have a stock 1994 z28, a4, with ~100k mi. and am experiencing pretty low gas mileage. When I filled up the other day I got a little less than 10mpg with a mix of town/highway driving. I was on it a little as well, but not to where I should get that low. For starters, I'll name off everything that I know is good and everything else that might be in question.

GOOD: -Just replaced opti-spark with new delphi unit. (works beautifully)
-2 new O2 sensors. (exhaust O2's)<-----Any O2's I missed??
-New front wheel bearings
-Tire pressure @ 38psi
-Cold air intake with aluminum 90* elbow

Questionable: -Still need to replace the plugs and wires. I have ngk platinum plugs and 7mm wires. (not yet installed)
*My car still misses slightly on low RPM, so naturally plugs/wires are next.
-I Don't know the fuel pressure.

With that said;
-Where is an access to check the fuel pressure? Also are LT1 F-body's known to have fuel line leaks?
-I know new plugs/wires will help, but could this be the source of the problem?

I know I have a few questions, but any input would be appreciated.

 

To check the fuel pressure, you take the plastic cap off the Schrader valve, and attach a fuel pressure test gauge with a -4AN connector:

Courtesy of Shoebox:

http://shbox.com/1/fp_reg.jpg

Pressure should be in the range of 41-47psi at idle (43.5 preferred), with the vacuum line off the fuel pressure regulator. Reattach the vacuum line and the pressure should drop by about 6 to 8psi. Make sure there is no wet fuel in the vacuum line, or dripping out of the regulator, which would indicate a leaking regulator.

Poor fuel mileage can be caused by misfires, or exhaust system leaks before the O2 sensors (yes, your car only has the 2 you found). The air that enters the exhaust causes the O2 sensors to tell the PCM the engine is running lean, and the PCM adds fuel that is not needed. It may also be a problem with leaking injectors, that need to be cleaned. When you have the fuel pressure gauge on it, turn the key to "run", but don't start the engine. Fuel pressure should jump above 40psi while the pump runs for about 2 seconds. The pump will shut off. If the fuel pressure drops rapidly, you will need to check the injectors.

It is not common for the fuel lines to leak.

 

Thanks, very useful info. I'll try and get a fuel pressure tester this weekend to check. N hopefully I'll have enough motivation to do the plugs/wires (though i'm not looking forward to it).

 

your pcm temp sensor in the front of the water pump maybe bad and cause it to dump excesive fuel into the engine, also if the egr valve is sticking slightly open will also cause a miss or to run bad at idle, i would definatly put in the plugs and wires asap ,

 

take your time with the plugs and wires. Read as many write ups as you can, it will take 3-6hrs to get done depending on your exp with F bodies.

 

i had a blocked fuel filter it was so simple dont know how that works but gave another 350 kms per tank