FE not so good for Civic

[maxxgraphix]

I was hoping for 35-40. I get 28.9. I drove it hard for the first tank full and got 28.9. Second round I did 110 miles mostly highway @ 65-75 and refilled and got 28.9. I was being easy on the throttle.

Here's the specs of the HB:
95 VX Shell
CX 5 speed trans (it looks like one)
D15B Vtech performance JDM
P08 ECU stock programing
1 wire O2
17" Rims 205/40/17 tires
Stock suspension
Stock bumpers
Stock air intakes
Stock exhaust
SI doors with power windows / power locks
I do have AC not being used right now.
CX seats

Car shouldn't be much heavier than the VX. I doubt weight is the problem. I check the air filter and plugs and both look clean.

Suggestions? taller tires? O2? P28 / 4 wire O2 and lean it out?

[popimp]

Drive 60 instead of 65-75. Coast more.

[jadziasman]

You will get better mpg with a four wire oxygen sensor since it has a built in heater to speed up its operation and allow the engine to go into closed loop operation quicker. I am surprised that 1 wire sensors are still in use.

And - your tires are too wide. Swap to a narrower size if possible.

[Minger]

Stop using AC if you can. If you need the AC defroster, you can see how well it does with the defroster on with the AC off - I believe you turn it off by pressing the circulate air and AC buttons with the key in the off position, and then in the on...they'll blink at some point. Not sure if applies to your civic though, it works on my 04.

[VetteOwner]

Originally Posted by jadziasman

You will get better mpg with a four wire oxygen sensor since it has a built in heater to speed up its operation and allow the engine to go into closed loop operation quicker. I am surprised that 1 wire sensors are still in use.

And - your tires are too wide. Swap to a narrower size if possible.

i would say most OBD1 cars are single wire.

i would almost suspect somehtign ebign clogged on your car. my truck would routinely get 25mpg no matter what or were i drove or how i drove. i took the blasted egr valve off and mpg instantly shot up.

how well is your engine maintained?

[StorminMatt]

First of all, the P08 (stock DX/LX ECU) uses a FOUR WIRE SENSOR. Using a single wire sensor is going to cause you to get a check engine light and a code 41. And this is going to make your engine run rich and KILL your mileage. Remedy this, and your mileage is sure to increase. Also, are you sure you are using the correct ECU for this motor? The JDM ECU for this motor would probably be best. Or you could use a P28. By the way, I have a Civic 4DR with a B20Z CR-V motor, and a CRX with a B18C5 ITR swap. Neither of these cars are really built for economy. And I drive these cars like jet fighters. Yet both will give me over 30MPG on the freeway. So something isREALLY, REALLY wrong here.

But there is something else to consider. A tall transmission may not be the best way to go with this motor. This motor was never made to pull a CX transmission. So it may not operate very efficiently cruising down the highway at under 2000RPM. Lower revs are not necessarily better. After all, I tried swapping a 2G HF transmission on my 1989 Civic. And I gained NOTHING in terms of fuel economy as a result.

[Danronian]

What are your crusing RPMs at? I think you might not have a CX tranny.

But the other mentioned things are a great start to raising your MPG.

I would also do a complete tune-up on the d15 including plugs/wires.

[maxxgraphix]

It's the right ECU for the engine. The 1 wire O2 is what these use. I know it's not the VX tranny, it doesn't have the LSD stamp, so I doubt it's the D15B tranny. The engine timing belt cover has LSD written on it. I bet the tranny was sold seperate. Should be the CX tranny, since it was the donor car. I don't have a tach right now, but the RPM doesn't seem low to my ear. I'll get a tach soon.

Spark plugs looked good. Doubt that would improve anything. It's not setting any ECU codes. Runs great. Perhaps an O2 change. I'm sure it's the original one.

If tires don't make that much difference then I'd like to keep this set of rims. I have a set of stock steels I can use. But they need new tires.

[broadwayline]

There is no H in VTEC.

Looking for an LSD print is a very inaccurate way to tell if you have LSD, most of the time print is rubbed off. The only way to properly tell is by pulling an axle out of the tranny.

If there is a bar seperating the two sides you do not have LSD, if there is no bar you have LSD.

You have somthing seriously more wrong than a weight issue, or a tranny issue to cause your low MPG.

My B16a gets 33-34 MPG with lots of VTEC and poor fuel economy driving in a VX chassis.

[broadwayline]

Originally Posted by StorminMatt

A tall transmission may not be the best way to go with this motor. This motor was never made to pull a CX transmission. So it may not operate very efficiently cruising down the highway at under 2000RPM. Lower revs are not necessarily better. After all, I tried swapping a 2G HF transmission on my 1989 Civic. And I gained NOTHING in terms of fuel economy as a result.

This is very true, my B16 is very inefficent shifting at low rpms, I get better FE by shifting at 4000 rpm where the motor is more efficent.

[kamesama980]

The easiest way to check for a LSD is to jack both drive wheels off the ground with the tranny in gear and try to turn one wheel. with an open differential, it'll be easy as pie. with a LSD, it'll range from difficult to impossible by hand.

The fun way is to do a burnout...2 tire tracks=LSD. 1 tire track=open diff

+1 keep the engine close to the peak torque when accelerating or fighting wind etc for best FE, lowest rpm without lugging to cruise

[broadwayline]

Originally Posted by kamesama980

The fun way is to do a burnout...2 tire tracks=LSD. 1 tire track=open diff

This is extremly inaccurate with most honda trannys, my open diff will leave 2 marks 98% of the time doing a burnout on pavement.

[maxxgraphix]

I got a tach now. In 5th at 60mph my RPM is about 2600. Sounds about right for this motor to me.

Today I changed the O2 1 wire to a Bosch 4 wire Universal. The heater circuit is wired to be just ON when the key is ON.

Overall it runs better. I'll post back on MPG after a 100 miles (typically 1 day).

Also it's NOT a LSD. The snow and ice this weekend proved that.

[VetteOwner]

maybe the new O2 sensor was the culpret OBD1 cars use it as a primary scource to conrol fuel air mix, when it doesnt work right it goes into default mode which is usually richer than leaner

[kamesama980]

Originally Posted by broadwayline

This is extremly inaccurate with most honda trannys, my open diff will leave 2 marks 98% of the time doing a burnout on pavement.

*shrug* touche. I'm used to RWD.

[Ryland]

the CX and VX tranny are the same so your engine speed at 60mph should be less then 2,000 you shouldn't see 2,600rpm in 5th gear untill you reach about 85mph, also your tires are almost 1.5 inches wider then is recomended, if you look at that in terms of weight, a quick search on tirerack.com shows that "light weight" 17" rims weigh around 20 pounds each and tires are 19-21 pounds each as well, so 40 pounds per wheel/tire combo, lets now compare the stock VX rims, 11pounds each with a 14 pound tire comes to 25 pounds total, 15 pounds less per wheel/tire, 60 pounds less total rotating weight on your vehicle, and people who race anything will tell you that a pound of ratotaing weight saved is like 3 pounds of body weight saved, now add to that the lower rolling resistance that is gained with narrower tires, and sudenly your mileage makes a big jump, when I switched from 175/70-13" tires to 165/70-13" tires, the handling improved, acceleration improved, the car just felt lighter and more nimble, so unless you spend alot of time going a consistant speed around a race track, I don't see a need for such wide tires, I've never had a problem with cornering or traction.
I also wonder what modle of D15B you have, as there were atleast 3 differnt ones sold, one was a non-vtec, one was a single stage vtec, and one was a duel stage vtec, and from what I've read, it can take a little bit of skill to wire them up properly and that it was often left undone.

[maxxgraphix]

At those RPM's I have the VTi trans (original D15B 5speed). The D15B's only came in 2 flavors.
http://asia.vtec.net/article/d15b/

2 stage Vtec - most common (what I have)
and
3 stage Vtec - hard to find and later years. Has 2 Vtec solenoids.

I'm trying to trade the rims and tires for some 15's or 16's. Rides too rough.

I changed the O2 to a 4 wire Bosch and plugs to NGK V-Power. FE jumped to 39.5mpg
I used key on power for the O2 heater since the P08 doesn't support it.

The Vtec is wired right. Works well. I got a schematic and since I have a VX chasis, very simple. Check out http://www.hondahookup.com/manuals/

[civic94]

maxxgraphix, i think you have an ex tranny just like mines, 60mph is at 2600, 70 is at 3100, 80 is at 3500. in other words, if you floor your 1st gear and it hauls *** for a 1.5 liter engine, you pretty much have a ex tranny.

i thought i had a dx tranny, but i found out after i sat in a friends ex that the rpms were that high, which sucks.

[maxxgraphix]

I'm sure that the trans came with the D15B. It sounds like the same as the EX tranny you have. It will smoke the front tires until you let off. That was with 205/40/17's. Reminds me of my Civic CRX Si.

Is that your MPG? 29.33? I only got the 39.5 once. Today, I calculated at 18. But I filled up on unlevel ground. I'll test again. I really want 40mpg. Many others with D16Z's and turbos say they get 36mpg. What engine do you have?

I sold the Motegi MR7 17" rims and tires today. I'm getting a set of Honda Del Sol 15" Fat Fives next week. I'll order a set of new tires from TireRack and might step it up an inch to drop the R's.

Almost all our highways around here are 65-70, but we drive 75-80. Even my back country roads are 55. I'd rather be in 4th at 55-60.

I had a Saleen Mustang with a 355 gear and 90% of the time I had to stay in 3rd and 4th to keep under 60. I ran it up one time and shifted out of 4th to 5th @ 120. Nothing like American V8 muscle.

[maxxgraphix]

Here's a link to Honda gear ratios
http://www.knology.net/~jediklc/gearratiosdseries.htm

It looks like the final drive is 4.25 EX/SI, 4.05 DX, 3.25 VX / CX

Might explain the 7300 rpm red line on the tach.

[maxxgraphix]

MPG is still not improving. Only all highway do I get 40mpg. My last fillup was 26.8 due to 50% city and short highway trips. It's also been 10F outside.

I got a set of acura fat fives 15" x 6 with 195/60/15. The speedo is now right verified with GPS. My planned mods for this weekend are installing a 192F thermostat and maybe bump the timing up. I filled up with premium this time. I don't think the engine is getting hot enough.