93 Civic VX -What should my mileage be?
 

So I just put about 2300 miles on my VX. All Freeway miles. The best tank was about 38MPG. This was while driving 65 the entire time.
The worst tank was 33 MPG. This was while driving 75-80 MPG. I know it's winter so mileage is going to be low regardless. I have a warm air intake installed, but that didn't seem to effect anything.

Should I be getting better MPG? Everything is stock. Recently had a tune up so plugs, wires, etc are new.

Overall average was 36MPG.

I don't have any check engine lights on so I'm not sure what's causing the mileage to be this low. I was expecting mid 40s.

Any ideas? The car has over 320k miles on it, but the engine has 190 psig when i did a compression test.

Tires were at 40 PSI. -Kumho power star 758 13in 175

Re: 93 Civic VX -What should my mileage be?
 

Your engine compression may be high due to carbon buildup and at 320K miles, I wouldn't be surprised if you needed a major overhaul of your car. Yes your car operates but probably not very efficiently. Do you have your smog reports for this car? 36mpg for a VX is pretty low but considering the age, I guess it's not a surprise. Check to see if you have any check engine codes by looking into the service manual and see how you can prompt the ECU for any check engine codes which may or may not be hidden. Make sure the battery is fully charged, clean out the egr, adjust valve lash, tell us how the car idles and at what speed, and best of all, replace ALL FLUIDS!

To give you an idea, I have a Civic LX with 175K miles on the clock and I can get about 45-50mpg cruising at 55mph despite the "short" gearing transmission the car has relative to yours.

Re: 93 Civic VX -What should my mileage be?
 

It would be a lot easier to see what really the car is doing by slowing down to at least 60mph. At 75-80mph your really not giving the car a chance to do whats its designed for. Your working outside of the lean burn parameters.

Re: 93 Civic VX -What should my mileage be?
 

Are you using low rolling resistance tires?


What would I need to do to give the car a major overhaul?

Re: 93 Civic VX -What should my mileage be?
 

48 MPG has been my best so far. I was going at 55 MPH for about 150 miles.

Re: 93 Civic VX -What should my mileage be?
 

Yeah it should be doing better then that. Thats not very good at all.

Do you access to a W/B?

Re: 93 Civic VX -What should my mileage be?
 

An important question is, do you really have the transmission that came with the car? At 55mph how many RPM is your engine spinning at? Can you make sure your check engine light is working and hasn't been disabled? That you have the original ECU and not something else? A picture of the ECU's Serial/Model number would be useful.

Re: 93 Civic VX -What should my mileage be?
 

I assume you've been watching the other thread about my 93' vx. There is a data collection thread I posted a few days ago looking for data on what rpms/speed you get in your car. It's listed under the general fuel economy section. Please post that info there as well if you can.

Most of what was causing my car to get less than stellar MPG's has been covered in the 93 civic horrible FE thread. I recommend reading it start to finish if you haven't already.

Thanks!
B

Re: 93 Civic VX -What should my mileage be?
 

CEL is working I've unplugged several different sensors and each time the light comes on.

While I don't have the exact numbers, I know that my transmission is a VX. I used a similar chart a few months ago to determine that. At 60 MPH I'm just under 2000 RPM. During my long road trip to SC the RPMs didn't go over 3000k unless I was 80-85 MPH. I'll get the exact numbers and post them in a few days.

I don't know where the ECU is located, but there is a chance that it's not the original. Where can I find this?

I think the problem could be the timing, the O2, and now I'm suspicious about the ECU.

Re: 93 Civic VX -What should my mileage be?
 

it's in the passenger kick panel. Passenger side of the car, in front of the seat on the floor, under the carpet. You do have an EGR, VTEC and all that going on, right? I guess if you have absolutely no check engine codes and you have the correct ECU, then you should have the correct engine. I'm just thinking it's possible an engine swap was done on this vehicle. Can you take a high resolution picture of the engine bay?