92 civic vx 29mpg ??help? - Gas Savers

amaterasu71 · 02-04-2012, 07:27 PM

Hi everyone, I bought a 93 civic hatch dx for my kids this fall it had 60k original and it has the 4 sp auto. I was so impressed with it as it got 43mpg on the freeway that I kept my eyes open for my dream mpg car the VX model. Just bought this vx here is the stats.. 199,000 miles, new tires, new exhaust, im the 3rd owner, and the car appears to be in great shape as there is just the start of bubbleing of rust spots. the engine light is on and the previous owner told me it was the o2 sensoer, he siad it was really exspensive to replace so he never did. So on my initial trip it only pulled 29 mpg. very dissapointed so im going to change everything oil, filter, air filter and such my question is would the o2 sensor be the cause of such low mpg? what other things should i be looking at? I was hoping for atleast 40 on the open rode i only was driving 55 mph and im really easy on it. looking forward to any help thanks, shawn

Fetch · 02-05-2012, 05:35 AM

Quote:

Originally Posted by amaterasu71

Hi everyone, I bought a 93 civic hatch dx for my kids this fall it had 60k original and it has the 4 sp auto. I was so impressed with it as it got 43mpg on the freeway that I kept my eyes open for my dream mpg car the VX model. Just bought this vx here is the stats.. 199,000 miles, new tires, new exhaust, im the 3rd owner, and the car appears to be in great shape as there is just the start of bubbleing of rust spots. the engine light is on and the previous owner told me it was the o2 sensoer, he siad it was really exspensive to replace so he never did. So on my initial trip it only pulled 29 mpg. very dissapointed so im going to change everything oil, filter, air filter and such my question is would the o2 sensor be the cause of such low mpg? what other things should i be looking at? I was hoping for atleast 40 on the open rode i only was driving 55 mph and im really easy on it. looking forward to any help thanks, shawn

The O2 sensor is a wideband 5-wire sensor, and is expensive. I know some of the guys on this site have links to cheap ones online. Others have bought them and they work just fine.

A bad O2 sensor in a VX is usually responsible for dropping the mileage from 55-ish to 40-ish. 29 is terrible for that car. What kind of tires are on it? Air them up all the way to the max sidewall pressure. What viscosity oil (run 5W30 or thinner). Check the plugs, wires, cap, and rotor, and replace if necessary. Check for a dragging brake by jacking the car up and attempting to turn the wheel. Have the alignment checked. The toe should be 0 degrees front and rear for a VX.

That will get you started. Note that the VX does not go into lean burn unless speeds are 75 and below. The engine RPM should be at 2400 RPM at 75 mph. If your RPM is higher, than you have a DX/LX or an Si/EX transmission, and that will hurt mileage.

As always, keep your speed down and keep momentum going as much as possible. If you were getting 43 mpg out of a DX auto, I think you know how to drive one just fine.

**theholycow** · 02-05-2012, 06:12 AM

Is there any evidence that the car was modified?

Any driveability symptoms?

amaterasu71 · 02-05-2012, 03:42 PM

Quote:

Originally Posted by Fetch

The O2 sensor is a wideband 5-wire sensor, and is expensive. I know some of the guys on this site have links to cheap ones online. Others have bought them and they work just fine.

A bad O2 sensor in a VX is usually responsible for dropping the mileage from 55-ish to 40-ish. 29 is terrible for that car. What kind of tires are on it? Air them up all the way to the max sidewall pressure. What viscosity oil (run 5W30 or thinner). Check the plugs, wires, cap, and rotor, and replace if necessary. Check for a dragging brake by jacking the car up and attempting to turn the wheel. Have the alignment checked. The toe should be 0 degrees front and rear for a VX.

That will get you started. Note that the VX does not go into lean burn unless speeds are 75 and below. The engine RPM should be at 2400 RPM at 75 mph. If your RPM is higher, than you have a DX/LX or an Si/EX transmission, and that will hurt mileage.

As always, keep your speed down and keep momentum going as much as possible. If you were getting 43 mpg out of a DX auto, I think you know how to drive one just fine.

thanks fetch, well today I changed the oil, air filter, and found the tires to be inflated to 26 pounds, so I put them to 40psi (44 max)and i checked for dragging brakes didnt seem so be a problem the front tires didnt exactly free wheel but i fugured that was normal as it didnt seem that brakes were causing a prob.. I found the o2 sensor unit was unplugged so i cleaned it outand plugged it in but the shifter light was telling me to shift in fifth and after the car warmed up it started to choke and loss of power so I think it needs replacing. So i hope what i did today will reap some benifits.. Ill let you know... thanks, shawn

add|ct · 02-05-2012, 04:32 PM

Is the CEL still on after re-plugging in the 02 sensor?

The way to test for this is to drive the car in 3rd gear and 1,500 RPMs for as long as possible(like 30-35 MPH, I cant recall) and hold at 1,500 RPMS...the light will come on if the 02 is bad. Do that at full temp, of course.

VX can feel choked w/ a loss of power when lean-burn is engaged, by the way.

On the other hand, a replacement 02...go for the NGK or Denso on a site like RockAuto or Amazon. $175-$200 are their price range for the correct wide-band/5-wire 02/LAF sensor on the VX. Compare that to $300+ at an autoparts place for a Bosch(now the OE/dealer outsourced part ironically) or $500+ at the dealer itself!

My dealer wanted $630 for it...

I've bought the SG355 model by Standard Motor Products, hard to find. It pops up as 'available' every few months on Amazon, I keep that page bookmarked. It was only $55 or so. Another user with a VX on this site, ben, uses the same SG335 SMP part. Hard to find, but might save you $150.

Fetch · 02-05-2012, 08:49 PM

Another thing...

The VX will only go into lean-burn mode once the catalyst warms up, so short trips are not going to get you good mpg. Winter mileage always dropped to the high 40s at best in mine.

If the car feels extra sluggish and the previous owner unplugged the O2 sensor, I wonder if the catalytic converter could be partially clogged.

add|ct · 02-05-2012, 11:34 PM

^Heh, I actually suspect as much is the case more my car sometimes.

add|ct · 02-07-2012, 01:58 PM

Driving on the freeway with headlights on the other night, my RPMs were at 2,500 @ 75 MPH.

amaterasu71 · 02-07-2012, 03:15 PM

Quote:

Originally Posted by add|ct

Driving on the freeway with headlights on the other night, my RPMs were at 2,500 @ 75 MPH.

well guys I really think that everything on this car is stock but I can tell you that my rpms at 65 are 2500 or 2600 rpms, what should the car idle at becasue its idling over 1000. I know this cars get switched around alot but id be suprised if the tranny was switched ive ordered the o2 unit should be here on saturday so we shall see... where could I look to verify the tranny? thanks

Fetch · 02-07-2012, 03:37 PM

It should idle at 650-700 rpm. The highway revs are too high. That transmission is not correct for the car. I think you have a DX/LX transmission.

add|ct · 02-07-2012, 03:40 PM

^This.

Try adjusting the idle speed with the IACV disconnected, then verifying its around 650-700 with it connected. The manual goes over several steps of fine-tuning the idle.

The more north you are, you'll want a slightly higher idle to help with cold starts, but anything over 1,000 after full temp is awkward. Sometimes my idle gets hung slightly with IACV issues and it doesn't settle to 650 until I rev the engine.

Fetch · 02-07-2012, 04:48 PM

Quote:

Originally Posted by add|ct

^This.

Try adjusting the idle speed with the IACV disconnected, then verifying its around 650-700 with it connected. The manual goes over several steps of fine-tuning the idle.

The more north you are, you'll want a slightly higher idle to help with cold starts, but anything over 1,000 after full temp is awkward. Sometimes my idle gets hung slightly with IACV issues and it doesn't settle to 650 until I rev the engine.

Correct me if I'm wrong, but I think you can clean out the IACV with brake parts cleaner. Remove it and clean it out, and then re-install using the existing gasket, if applicable.

Is this correct?

bowtieguy · 02-07-2012, 05:55 PM

cleaned mine w/ carb cleaner and did re-install the same gasket.

add|ct · 02-08-2012, 03:54 AM

^Yes, and by disconnected I meant the wiring harness only(not removal for cleansing as far as setting the idle, you do that with it attached of course).

Just to clarify what I was saying, anyway.

I should pull it and give cleaning a whirl. I might replace the gasket this time. A mechanic did the servicing for me 2 years ago before I started getting more experience doing mechanic related work myself.

amaterasu71 · 02-09-2012, 04:22 PM

Update... Well I got an o2 sensor and installed it.. here is what i have, the car does fine up to cruising speed, at 55 or 65 the motor starts to choke up losing power and feeling very doggy. the idle is where it should be but the rpms at 65 are 2600 and the shift light is on the whole time i have it in 5th gear? So im going to email the guy I bought it from and see if he changed the tranny but he told me averything else he replaced i would have thought he would have mentioned the tranny(ah optimism). ive changed iol, air filters next im going to check the plugs anything else? appreciate you guys opinions... ive looked over the postings about the tranny is there a way to look under neath and identify the tranny or do i have to look at timing and gears and such? thanks..

add|ct · 02-09-2012, 08:35 PM

I mean, what else would cause the RPMs to be that high? Wrong computer or transmission, aside from huge vacuum leak but you say the idle is fine. You should have an EGR system on the VX, that's for sure. Probably a new transmission, unless something else is keeping idle higher.

**theholycow** · 02-09-2012, 08:55 PM

With a manual transmission the only thing that can make cruising RPM higher is the wrong transmission, way wrong size tires, a slipping clutch, or a miscalibrated tachometer. Vacuum leak or wrong computer can't do that (unless the computer reports the wrong RPM to the tachometer, of course).

add|ct · 02-10-2012, 12:45 AM

^Okay, that's what I needed to hear. That's why my RPMs read higher(2,500 RPM @ 75 MPH instead of 2,400) is because my tires are larger than stock size(by 2.5%) and the speedometer reads slightly faster as well?

**theholycow** · 02-10-2012, 04:22 AM

No. Larger tires would make RPM lower at the same real speed and the speedometer would read slower. RPM would be the same at the miscalibrated speedometer's "same" speed.

Example:
10% oversized tires

Speedometer reads: 65mph
Actual speed: 71.5mph
RPM: Whatever RPM you would have seen when your speedometer read 65mph before the oversized tires.

Actual speed: 65mph
Speedometer reads: 59mph
RPM: Whatever RPM you would have seen when your speedometer read 59mph before the oversized tires.

Have you been calculating your 2.5% into your gaslog? Before you enter miles, multiply by 1.025.

Kendaddy126 · 02-20-2012, 01:13 PM

I have a vx with a bad o2. I replaced the o2 and the thing started to choke out in lean burn. I need to clean the EGR ports... not easy... I can say that with my 02 disconnected I still get like 38.5 MPG... so I don't think it's only the 02. Sounds like you got the wrong gears or something going on. good luck... If the shift light works... bty... you don't have a CEL on... but why would it tell you to shift in 5th? Unless you have the world's first 6speed VX... Ha.. sorry, I amuse myself. If it studders under load at low RPM there is a good chance your egr valve or ports need to be cleaned/ replaced. Good luck!

bowtieguy · 02-20-2012, 03:09 PM

Quote:

Originally Posted by Kendaddy126

I need to clean the EGR ports... not easy...

have you seen this?...How to clean your EGR Ports on 88-91 Crx HF

amaterasu71 · 02-20-2012, 03:09 PM

well everyone here is the latest... I installed the new o2 sensor , all the fluids and put the tires up from 26psi to 42(max 44) and wamo milage went from 29 to 47mpg the last fill up (all highway). Im thrilled, I just replaced the fuel filter (which when i drained the gas was filthy) so hopefully it gets better. My rpms still seem high as they are running 3000 strong at 70 2600 at 65 but i could feel the lean burn going into effect at 65 so as long as im getting over 45 i guess i wont question the mpg gods. the speedo needs a sensor as its all over the board sometimes but the tach seems to register idle correctly so who knows .. Ill keep you informed as to my next fill up mpgs , thanks guys...

amaterasu71 · 02-20-2012, 03:11 PM

Quote:

Originally Posted by amaterasu71

well everyone here is the latest... I installed the new o2 sensor , all the fluids and put the tires up from 26psi to 42(max 44) and wamo milage went from 29 to 47mpg the last fill up (all highway). Im thrilled, I just replaced the fuel filter (which when i drained the gas was filthy) so hopefully it gets better. My rpms still seem high as they are running 3000 strong at 70 2600 at 65 but i could feel the lean burn going into effect at 65 so as long as im getting over 45 i guess i wont question the mpg gods. the speedo needs a sensor as its all over the board sometimes but the tach seems to register idle correctly so who knows .. Ill keep you informed as to my next fill up mpgs , thanks guys...

oh yea the shift light still tells me to shift in 5th gear ??? strange?

add|ct · 02-20-2012, 06:15 PM

^You have a non-VX/CX transmission.

The 'feel' at 65mph with your stated 2600 RPM is the vtec engaging for more power/more fuel consumption.

The VX transmission has lean burn primarily from 1,500 rpm - 2,200/2,300 RPM or so.

This means, you would probably be getting another 5-10 mpg 'potentially' out of this car on the highway with the original transmission.