Found a Civic VX; Great Mileage Starts Now!

[NachtRitter]

Filled up today... This time I got 44.96 mpg.

I'm a bit frustrated with the comparatively poor FE that I've been getting after the conversion to the Fed ECU. Generally, my FE has been worse since the conversion than before, when using the Cali ECU. I averaged ~47 for the 3 tanks prior to the conversion, and now only ~44 for the 2 tanks since. Route, driving style, and temp ranges have not been that much different.

One of the main things I've noticed (as mentioned in the previous post) is that the idle is really high when stopped and when coasting out of gear. Last weekend, I took apart things, re-re-checked my newly built conversion harness, checked vacuum connections, checked the IACV (Idle Air Control Valve), etc, etc. I also plugged in my original Cali ECU with the new harness and the 5-wire LAF sensor, and it idled just fine (though it did throw a CEL (check engine light)). Mainly I think that verified for me that there is no problem with the IACV, vacuum, or intake in general, and that it's probably related to either the ECU or one of the sensors the ECU uses to set the IACV opening.

During this past week, I was actually able to find another Fed ECU locally (I only note this because I am, of course, in Cali, and finding a Fed ECU locally was a bit surprising). I picked it up today, swapped it for the current Fed ECU in the Maus, and ... it seems to work quite a bit better! I dunno, I guess on the one hand I was hoping for improvement, while on the other hand, I am surprised that there was any difference at all. Can an ECU degrade over time?? I looked at the innards of the ECU that was giving me trouble, and they looked just fine... so very strange, overall.

For the OBD1-to-OBD1 extension harness, I found a guy that says he'd be willing to sell them for $50 each if I buy 5 or more... I obviously don't need more than one, but if there are others on this board interested, I'll set up a group buy thread.

[Clev]

High idle all the time? Check the connection to the coolant temp. sensor.

[NachtRitter]

Thanks Clev, I'll check into that. It's not high idle *all* the time, but it kinda bounces while I'm coasting with engine on (I typically do that at night time or when the weather's bad) between ~900 and 1200 rpm (occasionally as high as 1500), and is a bit higher than normal when I'm stopped (~1100 rpm). Sometimes, if I'm stopped long enough, the idle gradually works its way down to ~900.

What throws me though is only one of the 3 ECUs I have seems to have a problem with the idle. The original Cali ECU works fine (even with my conversion harness installed) and the new Fed ECU I found this past weekend also works fine (though I haven't put more than 40 miles on the car with the new Fed ECU). Only the first Fed ECU (which I put in a few weekends ago) behaves differently. The model numbers on the two Fed ECUs are the same, so it is a mystery to me right now.

[NachtRitter]

Well I was wrong... the 2nd Fed ECU also behaves the same as the 1st one WRT the bouncy / high idle. Still futzing with it.

FYI... I wrote up a "How To" on converting the Cali VX to a Fed VX here: Converting Cali Civic VX to Fed (lean burn) VX. Actually I didn't really write everything, but rather combined information from a few sites.

[MetroMPG]

That's a bummer. Hope you get it sorted out. It would be frustrating to have a VX and not get its full potential.

[NachtRitter]

Quick update...

Still haven't fixed the bouncy idle. Was able to get a surprisingly consistent 47.x mpg with the Fed ECU over 3 tanks (roughly 4 weeks worth). I'd gotten a better 48.9 mpg with the Cali ECU, and since I didn't have time to further investigate the idle issue, I decided one morning to quickly swap back over to the Cali ECU. Now I get the bouncy idle with that ECU... AUUGH! Ah well, will live with it until I have time to dig into things. The first tank with the Cali ECU I apparently forgot to capture a trip with the gps, as my odo miles were higher than gps miles (normally the odo miles are 2.6% or more below indicated gps miles), so I probably show lower FE than I actually achieved. But last tank I managed my best ever at 49.8 mpg... using the Cali ECU!!

Have ordered a bunch of tune up consumables which I hope to receive during this week so that I can spend this next weekend doing a fairly thorough going over... hope to resolve the bouncy idle with that effort. Also hope to get the MPGuino installed at the same time.

[NachtRitter]

Yay!! Finally hit the 50mpg average mark over a full tank!!

I'd attribute hitting that target to more aggressive EOC (starting to do EOC for shorter distances now; normally I've been doing it on longer downslopes, but now I do it on shorter (and gentler) downslopes as well), better (warmer) weather, and some luck (a few great drafting opportunities, for instance).

Had a little trouble toward the end of this tank with engine stalling; turned out I had forgotten to tighten a ground wire when I switched back to the Cali ECU. Once tightened, no more stalling problems.

Went to a wrecking yard this weekend to get an ECU harness along with the ECU connectors from an ECU so that I could build myself an ECU jumper harness. Cheapest I'd found that was $70 pre-built; still a bit pricey for me. Spent 2 hours at a Pick-n-Pull (they don't organize the Japanese makes, so 45 minutes was spent just finding the right year Honda!) and ended up with the parts I needed for $10 (plus tax). I wanted to get the jumper harness before installing the MPGuino so that I had a way to tap into the signals without cutting into the stock harness. So now I'll need to spend time soldering all the wires...

[AJI]

Originally Posted by NachtRitter

The SOHC VTEC-E (as it's called on the VX) works kind of the opposite direction as a typical VTEC... (again, explaining this as I understand it so apologies if I explain it poorly) The VTEC-E minimally opens the 2nd intake valve at low engine speeds to better help mix the air & fuel (and therefore allow leaner burning at those speeds) and then gradually goes to normal 4-valve operation at higher engine speeds (the ECU definitely can still allow lean burn even at the higher engine speeds). On the other hand, the standard (SOHC) VTEC opened the intake valves normally at low engine speeds and then opened them even more at higher engine speeds.

Apparently, there is also a 3-stage VTEC which combines both the economy of the VTEC-E as well as the performance of a SOHC VTEC... but that one was never made available in the US market.

Yep, all that sounds good to me. I've been looking into the VTEC-E engines a lot recently as one of the cars I'm considering replacing mine with is the UK market EK Civic 1.5 LS, which uses the D15Z6 engine and achieves very impressive economy despite the heavier and larger body than the VX that you have. I test drove one recently and it was an interesting drive - the way I naturally drive seemed to result in the "Eco" light being illuminated fairly frequently, so I reckon I could get some impressive figures out of it should I decide to settle on a Civic.

The 3-stage VTEC you mentioned was used in a few of the JDM/Far Eastern market models (D15Z7 engine). It must be an interesting car to drive, assuming the VTEC-E switchover point is at around 2500rpm like the others, and the performance VTEC switchover point is around 5500rpm like it normally is in the high-performance models. Must be a real Jekyll and Hyde car. Unfortunately, I think that engine was only available with a CVT transmission which must take some of the fun and some of the efficiency out of it

Congrats on hitting 50mpg

[NachtRitter]

Recently changed my oil, going from 10W-40 to a slightly lighter 5W-30 (both recommended specs for the engine). Standard dino oil, nothing special. Also replaced cap, rotor, wires, and plugs. The electrodes (?) on the old cap and rotor were pretty nasty looking... plugs looked pretty OK though. Those two actions had a pretty significant effect on my last tank tho' ... 53.5 mpg!! That is my best ever by a good 7%!!

Weather was good throughout the tank, with highs generally in the high 80's, low 90's. I'm sure the weather helped as well, but I'm guessing the lighter weight oil had a lot to do with the improvement. Will have I can reproduce these kinds of numbers consistently. If so, this does make it seem that my goal of hitting 55mpg this year without any aero mods (as captured in the 2009 EcoModding Resolutions? thread) is actually realistic.