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Old 07-18-2007, 03:14 PM   #1
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Civic VX Lean Burn Questions

I recently purchased a 1995 Civic VX with 120K miles on it. The car is a diamond in the rough and is 100% stock. So far I really like it and the FE has been respectable.

My first tank driving roughly 65mph on the freeway resulted in 43mpg with the correction for 175/70/13 tire size. From what I gather my FE could be better.

The previous owner had 175 size tires on the car at roughly 30psi and used 10-40W conventional oil. The tires were recently replaced with Sumitumo HTR T4 LRR tires at 50PSI at the OEM size. The ride and traction aren't too bad despite the high tire pressure. The spark plugs were replaced with the proper NGK V-power. Additionally, I'm planning to change the engine oil to synthetic 5-20W. Overall, the engine runs very well.

The clutch is getting replaced in the near future and the gearbox will be synthetic as well. I realize that the tires still need to break in, but I suspect this tank will be better than the last tank despite more city driving. I'm still getting used to the tall gear ratios as well.

I'm hoping to break 50MPG on a regular basis with mixed driving. The catch is that I have a California VX and from what I gather I'm losing roughly 4MPG. I suspect the CA VX does not run as lean in order to produce less NOx. I currently have a four-wire O2 sensor and would need to chase down a five-wire O2 as well as a 49-state ECU.

Is that all that I would need to change? If anyone has personal experience converting to the 49-state version I'd love to hear from you.

Have people had good success with monitoring their lean burn mode? I know it is easy to set something up with a multimeter, but I'm wondering how much it actually helps MPG-wise if you can watch when the car steps out of learn burn mode. Watching the number changed is one thing, but can you get results?

I'd to be interested to hear any other means of obtaining better mileage without significant effort and/or mods. At this point a boat-tail, pulse and glide, driving at a max of 40MPH, etc. would be difficult. I do glide down longer hills in neutral.

I look forward to hearing everyone's replies. I know there are a number of experienced VX owners on the forum!

Thanks!!
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Old 07-18-2007, 05:39 PM   #2
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Welcome to GasSavers.

The Honda VX is a winner, even the California Version. I don't have a VX, but I have considered adapting my Civic. The conversion to a 49 state version involves the items you identified. I know in the HF's that they had a different transmission for the 49 state vs. California, as well as a high altitude version. I don't know if the VX also has different gearing or not.

The 5 wire oxygen sensor, using a voltmeter or something to monitor, does seem to enable people to better know when and how the car is going into it's lean burn mode. You could accomplish pretty much the same thing with a scan gauge or similar type tool, since your fuel use would drop significantly.

The down sides are: First the 5 wire sensors are a fairly rare item and probably as a consequence fairly pricey. The prices vary anywhere from $150-$350, leaning more towards the $350.

Second, the ecu, 5 wire sensor and lean burn modes seem to be pretty sensitive to a lot more issues with engine sensors and so forth, compared to the 4 wire sensor ecu.

You could, or should, in principal at least be able to pick up the 2-4 mpg difference, or at least some of it, if the transmissions gearing is different, if you were to change those things. I don't know if their are other items the 5 wire ecu might need, as well. Against that you have to trade off the cost of the 5 wire sensor, the ecu and the challenges of getting it to all run right.

In my perspective, unless your driving a phenomenal amount of miles, or unless you just want to do it, to prove to yourself it can be done, or you get some personal satisfaction from it, I don't think the mileage improvement can be justified, from a fuel savings standpoint. From what I've read on here about the 5 wire VX's, when they work they are great, when they don't it can get pricey and very exasperating.
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Old 07-19-2007, 07:59 PM   #3
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Recently Installed LLR Tires Improve MPG

I'm still learning all the details that are involved with the 49-state swap. I would like to understand as much as possible before making a decision.

I did a little research and found a 5-wire O2 for $190 including shipping. Not too bad.

http://www.oxygensensor.net/l1h1.html

Additionally with the new LLR tires I averaged 49MPG across my most recent tank with a significant amount of city driving. A drastic improvement when compared to my 43MPG for the previous tank with lots of freeway driving. It turns out that tires do matter!

Does anyone have an idea of what an 49-state ECU costs and where one can easily be obtained? Does it matter if the car did or did not have air conditioning? My car has AC. I've heard they are fairly cheap given that turners pull so many of the engines.
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Old 07-19-2007, 09:02 PM   #4
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I have a 49 states VX ECU for sale HERE

You can also check out the VX info thread in my signature below for more info.
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Old 07-19-2007, 11:01 PM   #5
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Thanks! I had read a couple of the links, but missed a few good ones as well. I'll take a look at the ECU. Will any 49-state ECU work or are there details that I needed to be concerned with? I'm wondering how difficult it is work out the wiring for the five-wire O2 where it meets the ECU. Perhaps this addressed in your mentioned thread on the subject. The additional wire on the O2 side should not be too difficult.

I may have found a very good deal on a used five-wire O2 sensor. I'm wondering if O2 sensors tend to degrade with time or is it binary in the sense that it either works or it doesn't?
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Old 07-20-2007, 05:58 AM   #6
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O2s degrade over time. When you see a sudden, 2-3MPG drop in mileage, it's time to change even though the O2 isn't setting a code yet. Called a lazy O2.
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Old 07-20-2007, 08:13 AM   #7
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LRR tires are even more important once you get lean burn going. You can spend a lot more time in lean burn with the LRRs.
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Old 07-21-2007, 01:26 PM   #8
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I responded in the VX ECU thread on the different versions. Basically that one I'm selling is from a 92-93 year VX and will work great for a 5 wire O2 change out.
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Old 08-25-2007, 08:57 AM   #9
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Quote:
Originally Posted by Wandering Albatross View Post
[snip]

I?m hoping to break 50MPG on a regular basis with mixed driving. The catch is that I have a California VX and from what I gather I?m losing roughly 4MPG. I suspect the CA VX does not run as lean in order to produce less NOx. I currently have a four-wire O2 sensor and would need to chase down a five-wire O2 as well as a 49-state ECU.

[snip]
Here is a 5 wire sensor. $371 tho. 5 wire oxygen sensor search on that page "5 wire" to locate it from the list.
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Old 08-25-2007, 02:47 PM   #10
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>>If anyone has personal experience converting to the
>>49-state version I’d love to hear from you.

I converted mine. You need the 49-state ECU and and L1H1 off of ebay. Get the o2 wiring swap right though... check the other appends and you'l see the wiring connections. I promised a DIY but that never happended....

Check my gas log to see the difference it made.
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