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Old 03-26-2014, 06:43 PM   #1
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At my wits with poor mileage

So I'm at my wits with my 92 Civic VX. I purchased this car for $2700 from San Francisco about a month ago and took the drive back home with a check engine light but otherwise ran fine. As soon as I got it home, I got to work. The following work was done to it:

Replaced NTK 24300 o2 sensor
OEM exhaust manifold heat shield
New Brakes
New Rotors
Alignment
Replaced Water Pump
Replaced radiator cap
Replaced Radiator
Replaced Thermostat
Replaced radiator hoses
Replaced air filter
Replaced main relay
Replaced coolant hoses
Refilled a/c freon
Added Koni Yellow/Ground control coilovers with top hats since shock/struts were shot and had these laying around in like new condition
Added Engine block heater
Added mpguino
Replaced PCV valve
Set tire PSI at 50. Purchased the car with new tires.
Added Tire pressure monitor valve caps
Replaced fuel filter
Cleaned egr valve
Replaced spark plugs with ngk zfr4f-11
Replaced ignition wires with ngk he76
Replaced ecu with 37820-p07-a00 (No more check engine light and now federal)
Replaced timing belt
Added fuel injection cleaner additive

A few things to consider, the b pipe from the exhaust looks like it was replaced and welded on at some point. It doesn't effect the performance though and looks original in any case. The car does have a tow hook which I'm thinking I should remove but only weighs a few pounds anyways. The main shaft bearing will need to be replaced at some point but tranny still shifts fine, just noisy.

Other then that my commute is about 70 miles a day mostly highway but LOTS of uphill and downhill. To give you an idea, I drive from Canyon Country (a few minutes from six flags) to culver city everyday for work and it consists of not only uphill/downhills but lots of stop and go traffic on the 405. I'm averaging about 40mpg a tank. That's about average for the 3 tanks I've kept track of with mpguino so far. I shift between 1500-2000rpm and drive between 60-70mph. Never over.

Should I be happy with these numbers considering my commute? I was really looking forward to averaging around 45-50 with the work I've put into it. I will be taking it to a local honda dealership in the next few days to have the engine oil replaced as well as the transmission.
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Old 03-27-2014, 01:01 AM   #2
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You should be getting close to optimum economy given the work you've put in. I would say the rest is down to your driving, keep as many things turned off as you can, air con, radio, lights, fan etc. Shifting early is good, but do you skip gears too? Try pulling away in 2nd and then shift to 5th once you reach 30 to 40 MPH that way you're only changing gear once. Also, downhill, dip the clutch, or take the car out of gear and you will go faster for longer without the need to accelerate. Change your tyres for a hard compound tyre and use the best fuel you can!

I get over 50 MPG in my little Abarth driving this way.
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Old 03-27-2014, 01:55 AM   #3
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Thanks for the advice. I'll give your shifting technique a shot. One question though, as far as the a/c goes, should I keep the vent open to let the air from the engine in open or closed? I only ask because I'm not sure if letting the hot air in from the engine and keeping the temperature low is better for fuel economy or just keeping the vent closed and higher temperature is better. Huge Abarth fan btw. Amazing car!
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Old 03-27-2014, 06:06 AM   #4
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43mpg combined is the new, adjusted rating for the VX, but there were two versions of the VX, the federal and California, and no way of knowing which one the current entry is for. The federal had lean burn, which was disabled for CARB. The lean burn is what returned the big numbers for the car.

That said, what is your tire pressure at? The recommended on the sticker is too low for optimum economy. It really only applies to OEM tires also.
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Old 03-27-2014, 10:08 AM   #5
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Originally Posted by trollbait View Post
43mpg combined is the new, adjusted rating for the VX, but there were two versions of the VX, the federal and California, and no way of knowing which one the current entry is for. The federal had lean burn, which was disabled for CARB. The lean burn is what returned the big numbers for the car.

That said, what is your tire pressure at? The recommended on the sticker is too low for optimum economy. It really only applies to OEM tires also.
Even though my VX is a California model, given that it's a 92 I converted it to a federal simply by purchasing a 5 wire o2 sensor and the federal ecu. So you might say it's a federal edition VX now.

My tire pressure is at 50 psi for each tire.
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Old 03-27-2014, 11:20 AM   #6
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In that case, do you have a way of determining when it goes into lean burn? Comments from other VX owners gave the impression that it can be finicky, requiring a light foot. Lean burn might not be possible depending on how steep your hills are. Your average speed might also be too high. Hopefully some VX owners will chime in.

Only having it a month, it could very well be that you are still getting familiar with the car, and winter blend could still be at the stations.
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Old 03-28-2014, 04:01 AM   #7
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Avoid downshifting when climbing hills whenever possible. Up to ~80% throttle in high gear is better than downshifting with less throttle in most cases.
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Old 03-28-2014, 07:54 AM   #8
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Most of the work you did is routine maintenance and will have no effect at all on your fuel consumption. Personally, I'd be afraid to inflate the tires to 50PSI, since their sidewall rating is probably 35 or so. I also feel the advice to either declutch or shift to Neutral and coast downhill is bad. Aside from possibly being illegal, it will cause more brake wear controlling speed on steep downhills. Your biggest improvement in gas mileage will come from the simplest and likely most unacceptable thing - slow down. There was a reason for the old 55 mph speed limit, and that reason was fuel conservation.
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Old 03-28-2014, 08:37 AM   #9
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Quote:
Originally Posted by Draigflag View Post
You should be getting close to optimum economy given the work you've put in. I would say the rest is down to your driving, keep as many things turned off as you can, air con, radio, lights, fan etc. Shifting early is good, but do you skip gears too? Try pulling away in 2nd and then shift to 5th once you reach 30 to 40 MPH that way you're only changing gear once. Also, downhill, dip the clutch, or take the car out of gear and you will go faster for longer without the need to accelerate. Change your tyres for a hard compound tyre and use the best fuel you can!

I get over 50 MPG in my little Abarth driving this way.
Following your advice, I had a 130 mile trip yesterday mostly freeway and I'm happy to say I got 46mpg I think the most help was shifting from 1st, 2nd, to 5th as soon as I reach that 40mph sweet spot. Also, when cruising on a downhill slope, I take the car out of gear and and leave it on neutral until I reach close to the bottom of the hill then pop it back into 5th.
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Old 03-28-2014, 08:41 AM   #10
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Quote:
Originally Posted by Charon View Post
Most of the work you did is routine maintenance and will have no effect at all on your fuel consumption. Personally, I'd be afraid to inflate the tires to 50PSI, since their sidewall rating is probably 35 or so. I also feel the advice to either declutch or shift to Neutral and coast downhill is bad. Aside from possibly being illegal, it will cause more brake wear controlling speed on steep downhills. Your biggest improvement in gas mileage will come from the simplest and likely most unacceptable thing - slow down. There was a reason for the old 55 mph speed limit, and that reason was fuel conservation.
My tires are rated at 42 psi which I thought were a bit high for these size of tires. This 122 mile trip I recently made I drop between 60-65mph which I thought was a good speed. I would've gladly driven around 55mph but the speed limit was 65mph and I thought driving at 55mph I would start impeding traffic which is a big no no in this area.
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