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Old 09-14-2018, 03:12 AM   #1 (permalink)
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Civic VX poor mpgs help

Hello, I picked up a 92 civic VX to replace a 94 DX that got totaled. I'm not getting the mileage that I should be. I'm only getting about 44mpg. I was getting 47-48 on the DX, so I think I should be getting even better than that with the VX. I've replaced the plugs, wires, air filter, fuel filter, engine oil, tranny oil, O2 sensor, checked the timing, adjusted the valves, good compression, alignment (the rear has some negative camber due to worn springs). Brakes aren't dragging, tire pressure is a few psi above stock. I can't figure out what I'm missing. Any thoughts?


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Old 09-14-2018, 11:35 AM   #2 (permalink)
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What kind and size of tires does it have?
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Old 09-14-2018, 01:43 PM   #3 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
What kind and size of tires does it have?
It has 175/70/13 on the front, and 155/80/13 on the back with the factory 9lb rims.
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Old 09-14-2018, 02:23 PM   #4 (permalink)
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I ask this first question not to be obnoxious but because I don't know you and the car is very old but new to you and your previous car was not a VX: are you sure you have the complete VX engine, with the VX cams (not EX) and the VX transmission? Dudes swap these parts on VXs sometimes. Intake manifold?

What driving conditions are you in? The VX shines in freeway crusing, but its super tall grearing is not necessarily better than your fifth gen DX in the city.

How did you check the timing? And did you jump the ECU first?

Have felt Lean Burn kick in? I have never felt it, but guys who own the lean burn civics sometimes say they can feel it.

Is a check engine light on for any reason? (It would block lean burn.)
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Old 09-14-2018, 02:29 PM   #5 (permalink)
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Having the "wrong" tires on my Insight can easily be worth 15+ mpg in some circumstances.
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Old 09-14-2018, 02:37 PM   #6 (permalink)
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Quote:
Originally Posted by California98Civic View Post
I ask this first question not to be obnoxious but because I don't know you and the car is very old but new to you and your previous car was not a VX: are you sure you have the complete VX engine, with the VX cams (not EX) and the VX transmission? Dudes swap these parts on VXs sometimes. Intake manifold?

What driving conditions are you in? The VX shines in freeway crusing, but its super tall grearing is not necessarily better than your fifth gen DX in the city.

How did you check the timing? And did you jump the ECU first?

Have felt Lean Burn kick in? I have never felt it, but guys who own the lean burn civics sometimes say they can feel it.

Is a check engine light on for any reason? (It would block lean burn.)
Yes, it definitely has the Z1 engine, and taller gearing. I can feel the lean burn kicking in and out, and I def notice the taller gearing as well.

Most of the driving I do, is on hilly back roads maybe averaging 50mph. Not a whole lot of stop and go.

I checked the (ignition) timing with a timing light, and the timing was dead on, so no need to jump the connector. I'm pretty sure I checked the (valve timing) belt too, but I'll check it again, just to be sure.

There is a very noticeable step down in power when the lean burn kicks in. When I'm on the highway cruising at 60-75mph, it's probably in lean burn for about 80% the time.

No engine light.
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Old 09-14-2018, 02:39 PM   #7 (permalink)
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Quote:
Originally Posted by Ecky View Post
Having the "wrong" tires on my Insight can easily be worth 15+ mpg in some circumstances.
I've run the 175's all around before, which is what the DX has from the factory, and I've also run the 155's all around, but not really any difference in mpgs.
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Old 09-14-2018, 02:59 PM   #8 (permalink)
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It isn't the width or aspect ratio, it's the tread compound and pattern. Two different 165/65r14 tires can deliver more than 15mpg difference at the same tire pressure in my car. In some cases the difference can be as large as 40mpg. Make sure you have tires which have a low rolling resistance compound and tread pattern.
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Old 09-14-2018, 03:32 PM   #9 (permalink)
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Ecky has good points. There are no objectively reliable stats available to us little people on LRR, either. So it is a crap-shoot wat you get when you choose.

Have you checked for brake drag or wheel bearig wear? Lift each wheel off the groud and spin it?
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Old 09-14-2018, 03:51 PM   #10 (permalink)
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Quote:
Originally Posted by Ecky View Post
It isn't the width or aspect ratio, it's the tread compound and pattern. Two different 165/65r14 tires can deliver more than 15mpg difference at the same tire pressure in my car. In some cases the difference can be as large as 40mpg. Make sure you have tires which have a low rolling resistance compound and tread pattern.
I was using the same (Sumic GT) tires (175 -13's) on the DX, so I doubt it's a tire issue. I am running a summer tread pattern, but I'm not even sure they make low rolling resistance tires in 13 inch. Maybe in the future, i'll get some fancy tires, but for the moment I'm just trying to figure out why I can just barely get the EPA MPG rating, when I smashed the EPA rating by 15mpg in my DX. I feel like I should be getting 10 more MPGs with the way I drive.

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