I tried but fell short of my goals...

[Mpgian]

As some of you may know, I bought a 1990 Honda CRX dx with a fuel gulping b18 motor and super short geared b16 gsr tranny. After getting a 25-30mpg for a month, I finnaly had enough. I bought a D15z1 (from a 95 civic VX) and a CRX HF tranny. It took me about a month to install the motor/tranny/ECU and get everything working good enough to drive my commute (650+ miles a week). After all this work, Im still haveing a little trouble finding the sweet spot for FE.

So far I have installed:
d15z1 motor (<45k mi)
HF tranny (48k mi)
taller 195/60-15 tires
New CV axles
New Wheel hubs/bearings
New Plugs / Wires
New Hoses and vac lines
New clutch/flywheel/bearings
New timing belt
New Ball joints upper/lower
New HID headlights/Projector housing (low power 35w)
P07-a00 ECU

I had a few bad tanks, a good tank, and a few ok tanks, Im averaging about 40ish MPG. I havent kept up with my sig mpg log, but I have the data on a note book, havent had time to type it in...

I drive 55-60mpg depending if there are hills or not, (i go very slow up hills) Ive monitored leanburn on my way to and from work (staying in LB for 50%+ of the time) Drafting semi-trucks, Keeping it in the highest gear/lowest RPM as I can. After all the mods, and all the driving like a GD slug, I cant break 50mpg average! I drove it going the speedlimit 70mph today and still got 40mpg.

I Just bought a 4x8' sheet of Coroplast and plan on blocking my grill, fog holes, building a cover for my wipers and some under belly panels. Maybe a front air dam too. I also have a MPGuino and Vac gauge comming and am tring to figure out how to wire an AEM A/F wideband monitor to let me know how to drive better.

Any Ideas??? I just want to get 50-60mpg average like the others out there with CRX-VX conversions

[hondaguy72]

Tires, tire pressure is important. 60 series does not help you, go narrower if you can. Is the alignment good? Just those two things will help greatly.

[jakobnev]

Lean burn (AFAIK) isn't the most efficient condition for you engine, high load is. Trying to stay in LB even in situations where high load was actually called for is working against you.

LB is only a crutch intended to compensate for the fact that the engine is mostly run with low load, it is not a reason to avoid high load.

[Mpgian]

Originally Posted by hondaguy72

Tires, tire pressure is important. 60 series does not help you, go narrower if you can. Is the alignment good? Just those two things will help greatly.

The Tires are Brand new, Parelli 195/60-15 I have them at 2-3lbs below sidewall max pressure...

The alignment on the CRX is only adjustable for the toe... I think?... and It dosent pull, even when turning... I may get an alignment this summer but I dont have any issues with it that i notice

Im kindof concerned about a couple of things that could be robbing me of MPG's

1) Oxygenated Fuel (Im going to switch over to non ethanol fuel this week and see if it helps)

2) EGR valve, Its hooked up right, and wired correctly (even the control solenoid is wired up correctly) Im not sure if the actual valve is working correctly

3) I have the charcoal canister set up correctly, but Ive disconnected because I dont have a purge valve... I may try and use the one off of a CRX HF that I have laying around.

[Mpgian]

Originally Posted by jakobnev

Lean burn (AFAIK) isn't the most efficient condition for you engine, high load is. Trying to stay in LB even in situations where high load was actually called for is working against you.

LB is only a crutch intended to compensate for the fact that the engine is mostly run with low load, it is not a reason to avoid high load.

wha wha what??? You mean Vtec-E? are you saying going into vtec is more FE then Lean burn? I hope your right, this would help me understand why I got 62mpg when I neglected lean burn to draft a semi truck (I used alot of vtech and high load) This whole time I was trying to stay in LOW RPM's like 1700 at 60mph...

I cant wait till I get my MPGuino, I think this will teach me alot about my car...

[hondaguy72]

Plugs. Have the right ones?

[Mpgian]

4 brand new NKG ZFR4F-11 plugs
new 10mm tripple strand plug wires
new 193* thermostat
new belts
new hoses


one thing to note, the idle surges when its cold and when moving at high speeds out of gear when idling. but when it comes to a stop it calms down to 650rpm's

I cleaned the IACV with brake cleaner, it helped with the surging after it was warm and moving at freeway speeds.

I need to clean the FITV and rebuild it. every morning the car goes to 1500-2k and surges until it warms up. then its fine...

Im wondering if one of these is causing a VAC leak when on the freeway...

[hamsterpower]

Originally Posted by Mpgian

one thing to note, the idle surges when its cold and when moving at high speeds out of gear when idling. but when it comes to a stop it calms down to 650rpm's

I cleaned the IACV with brake cleaner, it helped with the surging after it was warm and moving at freeway speeds.

I need to clean the FITV and rebuild it. every morning the car goes to 1500-2k and surges until it warms up. then its fine...

Im wondering if one of these is causing a VAC leak when on the freeway...

What you just described is the symptoms of a vacuum leak. That will certainly cause bad MPGs. Clean and tighten your FITV and look for any other leaks. While idling spray the all around the intake manifold with carb cleaner. If the idle changes you just found your leak.

I once had a CRX DX. I loved that car. Would get 55mpg highway easy.

[Mpgian]

I will try spraying it down when its warm and idling low, I tried this when it was not fully warmed up and it would not change even if it removed a hose and sprayed it in.

I have yet to remove the IACV and am dreding it! Im away from my tools and home for 2 weeks. All I have is a set of metric wrenches and a couple of screw drivers. Ive heard you must remove the Throttle body to get to it... Im also nervous that I might not get the internal piece screwed back down exactly where it was, and my idle will be wrong...

I guess I will just have to go for it!

[War_Wagon]

If you have access to a set of 13 inch Honda wheels/tires, I would try those out. 175/70/13s inflated to sidewall max psi would probably make a noticeable difference. Less rotational mass and a smaller contact patch along with maximum inflation pressure should give you a bump in mpg's.