93 Honda Civic VX horrible fuel economy - Fuelly Forums

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Old 02-19-2010, 02:30 PM   #1
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93 Honda Civic VX horrible fuel economy

So, here's the deal. 93' honda civic vx. 189k. 5 spd. Got it with studded snows mounted on 14" steel rims. Preliminary fuel economy with back seats removed and drum kit in the back during backroad highway driving was 43 mpg. At that time, the 02 sensor was in need of replacement. I replaced it with a new one (non- cali 5 wire). I replaced the filters, plugs, and some other maintenance parts. I'm waiting on wires, cap, rotor button, etc.

Car is bone stock. Intake draws from within the engine bay. Runs good, no more check engine light. Goes into closed loop. I can feel the lean burn happening. New MPG- 28 in town, 32 highway. I don't get it. As the fuel economy went down, I put the original 13" steelies on. 175's because it's what I got with the car. The previous owner removed the air conditioner components completely.

After the fuel economy went down, I retimed it. The car was about 3 degrees retarded, if I'm reading it right. There are three marks to the left on the harmonic balancer, and one on the right. I put the middle mark of the three marks lined up with the mark on the timing cover. This change did nothing for fuel econ that I can tell, only raised the idle. The idle is now at about 1000 rpms and will go no lower even when fully warmed up. I'm wondering if I have the wrong reference marks.

I'm also wondering if the large gaping whole created by the lack of AC is killing my fuel econ because of Aerodynamics. I'm going to block that tomorrow and see what happens.

Also- No brakes dragging. No slipping clutch. Checked speedo with a GPS. Seems dead on. Cleaned the EGR ports, intake manifold, and IAC.

Any help would be greatly appreciated!
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Old 02-19-2010, 05:46 PM   #2
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maybe u didn't put the right plugs

ZFR4F-11
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Old 02-19-2010, 07:03 PM   #3
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put the old o2 back in and see what happens, can't other things trigger a bad o2 sensor signal such as a clogged cat or lean mix?, it's been a while since ive thought about that.. but what air filter did you use? dont use fram, only use purolator, try putting the old air filter back in...

fram is so badly designed I could see an air filter lowering mpg by 5mpg in the worst case scenario

also fram oil filters do not use unless you like sludge bursting into your engine at high rpms, pure one is a good filter

whatever caused your rpms to raise is causing extra fuel to be consumed sure, but how much, probably not alot
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Old 02-19-2010, 08:00 PM   #4
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Winter?
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Old 02-19-2010, 09:15 PM   #5
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Hey all, thanks for the replies-
I'll triple check the plugs tonight when I look at compression in all cylenders. Any idea what they should be? #1 was 130psi, or more, I think.

Air is a new purolator. Old 02 came out very hard; had to cut it with an angle grinder to get a real socket on it as the 02 socket was threatening stripping/snapping.

The rpm raise is directly related to ignition timing. I'm going to make sure my cover isn't on improperly and check it again. I'm using the inside of the V notch on the plastic cover, and the middle mark on the harmonic balancer. Is this right?

As for winter, yes. This car is not driven in snow. I have a 740 turbo 89' that's my truck/snow car.
I'm using winter fuel, which I'm sure is losing a good 5mpg.

Any other ideas?
Thanks everyone.
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Old 02-19-2010, 10:46 PM   #6
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First you can adjust the ignition timing but then you can also adjust the idle speed.. So what you may need to do is adjust the timing so it's within spec then turn down the idle. It's possible somebody adjusted up the idle and retarded the timing because the car wasn't running right for whatever reason. You should get the helms service manual (OEM) for this vehicle so that you can fix every little thing here and there without issue.
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Old 02-20-2010, 12:35 AM   #7
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New plugs are OEM. Wires (waiting on UPS to give me my new ones) are a little tired. I pulled them all and checked compression, compression is about 120 on all 4. When pulling plugs, the metal clip that is attached to the end of the wire stayed in the block for two out of four wires. Maybe that's my smoking gun; won't know until the new wires show up.

Yeah, I need the OEM manual. So far all I have is the Haynes one. It gets you by, but lacks some critical info such as detailed ignition timing reference marks. Any idea besides the dealer where to find that book?


Oh yeah, the cover has a V and a notch. You eyeball down the two (the V is above the notch) and then look over to the harmonic balancer. I was a little advanced, so I put it where it had oughta be. I recleaned the throttle body, taking care to free up all IAC passageways. (they weren't blocked entirely, but showed some junk I missed the first time)
Idle is lower and seems more stable under varying loads, so I'm guessing the IAC is doing it's thing now.

I've got some highway driving to do tomorrow. I'll give an update then.
Thanks for the input.
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Old 02-20-2010, 02:02 AM   #8
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I have the PDF of the 92-95 civic manual, so just PM me if you want it. I made the PDF searchable. I can also give you a copy of the owner's manual as well which too is searchable.
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Old 03-02-2010, 07:29 PM   #9
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I'm having similar issues in Portland, OR:

I have recently bought a 2nd vx, hoping it, looking cleaner and having fewer miles, might replace my 1st. Both are 1992 and have the same size tires. With the first, red one, I consistently get mileage in the mid 40s, never under 42 even with all city driving.

I've only had this second one a few months, and not driving it too much, but its mileage seems to only be in the mid/high 30s. "Lil Blue" seems to run at higher revs in the same gear and at the same speed than "Red Wagon"...I would probably chalk that up to the tach being off if the mileage weren't low, but the two seem to correlate. Anyone have any ideas why this would be?? Seems to imply different transmission gear ratios, no? I guess it's possible the transmission's been changed out--someone had put silly big wheels/tires on it at some point (luckily they'd kept the vx wheels with smaller tires).

The only other possibility I can think of would be low compression or a bad cylinder. Am I right in thinking that might have the same result, requiring higher revs for the same speed? Aside from the clutches feeling different, though, I really don't feel much difference in the driving. I will say that Red Wagon does coast/glide noticeably better than Lil Blue--could that account for the same problem? Why would that be anyhow?

Ooh, I don't think this could have anything to do with it, but the throwout bearing in the blue one is bad/making noise.

Thanks to anyone for any ideas/answers. The forums here have been a great help in everything from troubleshooting problems to routine maintenance tips to buying tires (which I just did today)!
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Old 03-02-2010, 10:13 PM   #10
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Quote:
Originally Posted by PDXChrisVX View Post
I'm having similar issues in Portland, OR:

I have recently bought a 2nd vx, hoping it, looking cleaner and having fewer miles, might replace my 1st. Both are 1992 and have the same size tires. With the first, red one, I consistently get mileage in the mid 40s, never under 42 even with all city driving.

I've only had this second one a few months, and not driving it too much, but its mileage seems to only be in the mid/high 30s. "Lil Blue" seems to run at higher revs in the same gear and at the same speed than "Red Wagon"...I would probably chalk that up to the tach being off if the mileage weren't low, but the two seem to correlate. Anyone have any ideas why this would be?? Seems to imply different transmission gear ratios, no? I guess it's possible the transmission's been changed out--someone had put silly big wheels/tires on it at some point (luckily they'd kept the vx wheels with smaller tires).

The only other possibility I can think of would be low compression or a bad cylinder. Am I right in thinking that might have the same result, requiring higher revs for the same speed? Aside from the clutches feeling different, though, I really don't feel much difference in the driving. I will say that Red Wagon does coast/glide noticeably better than Lil Blue--could that account for the same problem? Why would that be anyhow?

Ooh, I don't think this could have anything to do with it, but the throwout bearing in the blue one is bad/making noise.

Thanks to anyone for any ideas/answers. The forums here have been a great help in everything from troubleshooting problems to routine maintenance tips to buying tires (which I just did today)!
Drive the car in 5th gear at 55-65mph and report back the RPM the car is at a given speed. This is the only way to know if you've had the transmission swapped out or not. If you've had the transmission swapped out, then that is the reason why you're getting worse mileage. It REALLY wouldn't surprise me if the transmission were swapped out, I know that I'm going to swap IN a VX transmission into my car. I might even go as far as to rebuild my existing transmission to have the same final drive.
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