30 MPG Hwy - 13 MPG City on 90 S13

[Peabody]

How can this be? I have a mainly stock manual 90 s13 with 180,000 miles on it. Mods are just a header, no cat, performance chip, air intake. Did a tune up in June, set timing to 20, cleaned intake & everything else to keep the car running fine. Have new Michelin tires, engine idles fine but stays around 800 RPM's. Cleaned ICV, does not have Iaa and runes fine and pulls hard. I can drive at 75 all day and will get between 28 and 32 MPG all the time. But if I drive in the city my mileage is bad. Will get around 12-14 MPG if I drive it a little hard and sometimes about 15 or 16 if I am lucky when I baby it & drive like a old lady. Could it just be the high miles starting to decrease the mileage? I am the original owner and always got great mileage on the Hwy and usually around 18 in the ciry but this 12-14 is really bad. Hell, I get between 10 & 12 on my 67 GTO with a 6.5 litre 370 hp stock engine. I do not understand how the Hwy can be so great and the city sucks!Any suggestions to help?

[nelson8708]

if it is an actual eprom performance chip they could of leaned it out on the top end and left the bottom end stock. The ka24e runs rich fromt the factory. With as many miles that are on it, it could have blow by which would effect the car more often when taking off because of the load on the engine where it might not be as appearent at the top end because there is much less of a load when just maintaining speed on the highway.

My 2cents

[180fan]

yeah I suspect something's up with the way your ecu was tuned.

[nuts510]

I have seen several of the aftermarket chips destroy the your gas mileage in the pursuit of more horsepower I bet if you go back to the stock chip your gas mileage will improve plus you may have damage the O2 sender by running such a rich mixture. You can also make sure the fuel pressure is correct I have seen leaky feel pressure regulators only affect the car at light throttle. Also check the ECU for trouble codes

[Peabody]

I got the ECU back in 1993 and back then I had to send them my factory one as a core to get $100 back. It cost $850 back then and stated that it raised the stock HP from 140 to 157 and I had to use high octane gas all the time. It make a big difference in power and response. At the time I got it I did not have my header, air intake, and the car was BONE STOCK. My friend had a 91 stock manual hatch and I would take him from a stop or a roll at any speeds. Over 4000 RPM's I would pull away from him at least 3 or more car lenghts so I know it was working. The bad thing is that it does not have any lights on the ECU so I cannot pull codes off it. I guess I could buy a stock ECU and see if any codes are there. Also how do I check the feul pressure? I just replaced all injectors because 2 were leaking. The bad mileage was even worse before I changed themTHANKS

[redtop91]

My SR20 gets better gas mileage

[ricebike]

what instructions came w/ that "performance chip"????

stock timing is ~15 not 20 unless u got the DOHC engine in thurr... or you're running premium octane to warrant such extra advance timing setting?

stock highway mileage is ~26 mpg

stock tire sizes: 195/60R15 or 205/60R15