Please Help Civic VX MPG
 

Hello,I'm new here and I have a 94 vx. It's 100% stock except vacuum gauge, proper size tires, runs great,clean egr ports,new 02,no check engine light. I am a mechanic & have rebuilt many many honda motors including this one.It is timed perfectly,proper compression,valve lash ect. I got 55mpg 3 times.Once i was going about 55 on a long trip feathering gas.The other 2 times was hwy/city mix shutting engine off and coasting alot,also watching vacuum gauge to keep in lean burn.Nnder normal conditions without shutting engine off, city/hwy is averaging about 43mpg

My question is for all vx owners who get more then 55mpg. What am i doing wrong to not get more then 55mpg?

welcome,

I'm not a VX driver but have a DX and am knocking on the door of 55mpg with it.
have you read the 100+ hypermiling tips?

City driving I suspect makes it very hard to keep the thing in lean burn. Breaking early and coasting to give the light time to turn green may help in your city driving.

Have you checked your odometer/speedometer against a GPS (distance) or distance of a known route? If not you may already be much closer.

instantaneous fuel consumption readouts are nice MPGuino is not hard to install.

I think you answered your own question there.

43 mpg sounds like what you should expect to see from a car like the VX driven "conservatively" (minus lots of driving without brakes, or engine-off stuff). After all, in mixed use, its ace in the hole - lean burn - isn't contributing much.

Highway driving at moderate speeds in continuous lean burn is where these cars really shine.

Yeah, you're definitely getting above average mileage. Excellent work! You've got a great light weight chassis to work with.

From there you might work on some aerodynamic mods and weight reduction.

Worst mileage for me recently due to local temps exceeding 100 on many days.

AC kills mileage.

VX is superb at DFCO use it to anticipate any unwanted stops. 5th,4th,3rd downshifts to maintain DFCO when slowing down.

Pulse & glide the AC, in particular whenever you are cruising and especially in DFCO, you want to go max air, recirculate, and max fan. It will raise your DFCO threshold RPM but you can compensate by downshifting to keep engine speed above 1300 RPM.

Accelerate briskly (about the traffic flow rate normally) and get it into lean burn cruise fairly quickly. Do not use AC on acceleration.

In some cases it may be better to just bite the bullet and get on the limited access higher speed roads, if you have to use AC. This strategy minimises the time you are using AC, while slower stop a go situations increase the total AC power consumption.

You live fairly close to me and probably have already experienced the extreme heat this summer. At 90-93 degrees I can tolerate no AC, but when it hits 106 here I either use AC in the car or just ride my motorcycle, which gets close to 90 MPG.

regards
Mech

Forgot some things. VX lean burn threshold is 6 inches of vacuum, if you can't feel lean burn engage.

Without AC lean burn acceleration is practical. Remember to accelerate in lean burn in 3rd gear is about the same fuel consumption as no lean burn in 5th.

The VX has very tall gears, 3rd will get you to about 110 MPH at max revs. A balance of under 2500 RPM operational limit and using 3rd 4th and 5th gears for acceleration may keep you in lean burn more, but dragging out the acceleration phase of operation may not be your best tactic.

My VX is a rebuilt salvage vehicle that I bought in March 2008. It had sat in an insurance training facility (controlled environment) for close to 13 years and had only 27,492 miles on the odometer. It now has 58k miles.

Tires can be a huge factor, with rolling resistance and significant part of any mileage penalty. Run the tires at sidewall max to minimise rolling resistance.

When you are cruising keep engine RPM as low as possible, but above 1000 RPM. Even in 5th at 1k RPM you can still stay in 5th gear. This is where the mileage gets really high, probably close to 70 MPG steady at 35 MPH in 5th with no AC. With AC increase your average engine speed by about 25% while still trying to stay below 2500 RPM.

regards
Mech

The gasoline you are putting it can also play a role, pure gasoline is the only way to go, no alcohol.

That's easy for you to say! Here in the Northeast, I can't recall when I last saw an alcohol-free pump. At least I guess we can say we're doing our part to keep the corn belt farmers happy.

thank you bestclimb,metro,redline,bruce,ryland & old mechanic for responding with great tips and ideas.Sorry it took a while to get back.For fun, because is has been +90F this past week,i tried something different.with a slightly heavy foot and the A/C on full time, i went 200 miles and only got 33mpg.this proved that we hypermilers have to work for high mpg figures.
few questions for old mechanic-my idle is about 22" vacuum, my lean burn kicks in a 6" and kicks out at 3". Does this sound about right? Have you ever got above 55mpg? looks like my dfco rpm is the same as yours because with a/c off, injectors stay off below 1000rpm,and 1300rpm with a/c on.
I'm glad to hear that my vx is getting the milage it should but i still want to get better then 55mpg.i am little disappointed they rated this car 55mpg from the fctory and have yet to get better then 55. one problem is i carry about 150lb of tools around with me because im a mobile mechanic.Also where i live is in the mountains so its hard if not impossible to stay in lean burn up hills(the car really slows down).

few other things,my speedo is right on,tires are correct 165/70/13 summitomos @45psi,gas is mainly enmark 87octane sometimes i put premium,currently i have no aero mods,oil is 5w30,timing 16 degreesbtc @ 600rpm.

thank you all for resonding.please keep it coming.are there any other tricks for this car in particular? one idea i might add is a hobbs vac switch to turn on and off a/c above so many inches.

lets get more ideas and tips up for the honda civic vx.thanks

Putting premium gas in anything but a high compression engine is just a waste of gas and money. I does absolutely no good, since it needs the higher compression to ignite the higher octane fuel. Stick to regular gas and save your money.

It's not about the higher octane, it's the lack of alcohol as alcohol burning engines have different needs then gasoline burning engines, yes it will "work" but it will also work to dump a small amount of diesel in to a gasoline engine, not the best idea but it will work, veggie oil would almost be a better idea then alcohol.

You've got a lot of factors working against you Robertsvx, the fact you are getting 55mpg is impressive. How long have you been driving it? More than just those 3 tanks right? Look at any of our mpg charts and it took a long time to crank out the big mpgs, mine actually improved quite a bit as I learned to DWL. Don't just keep the vac. over 6", hold it at a constant spot (9, 8, whatever it takes to hold your preferred -average- speed). Yeah you'll slow down on the hills but if you speed up going down the other side it all evens out. My DX w/VX motor is lowered 2", has a 3/4 grill block, no mudflaps, .030 shaved head, VX 13s, vac gauge and MPGuino, and my best ever is 63.8mpg, so you are doing great for no mods. My tires are at 48psi (shhh:D) and its pretty flat around here, mostly 60mph commute. I noticed a small boost running a block heater on a timer back in the spring, although I haven't used it since it got warm out. Speeding hurts mpg, and you won't really get there faster if you are in city/traffic lights anyways. Timing the green lights will help (watch the X-walk flashers for side road, or when the side road traffic stops). As others have said coast in gear with no gas pedal as much as possible. Where you can try to do a lazy "pulse & glide", get up to say 50 or so and DFCO down to 45, then accelerate at around 6" vac til you are back up, coast down again. That last few mpg's you want is going to take an MPGuino and some patience. Good luck :thumbup:

tim3058
I would like to know a bit more about getting and installing a MPGuino for my 92 VX .
What can you tell me about cost, installing and setting it up in the VX .
I really appreciate any help or insight you may have .
Thanks in advance, Dennis

Good stuff tim3058!! Keep it coming people!!

The alcohol in your fuel is a major disadvantage, in trying to match the original EPA figures.

My best tank ever was in the spring of 08 on a 300 miles trip from Williamsburg to Chantilly and back, exactly 300 miles on 4.627 gallons of regular for 68 MPG.

The problem was that was on the original, made in March, 1993 tires!

I would not use premium unless you have it set up where you have to. I run the cheapest regular I can buy in mine, and tried premium with not benefit.

Idle speed should be as low as you can get it. I have no instrumentation above OE, but the idle on mine is very low, almost to low. Lowest idle speed car I ever owned was a 37 Ford flat head at 350 RPM/ My VX is probably around 500, but I have never checked it.

At 58k miles mine still has the original brake pads, still over 50% left, the ORIGINAL fan belts, that are yet to show and cracking. I am taking the same 300 mile trip today, but I will probably not try to get the same mileage I did 2 years ago, going 64 in the right lane of I95 with 3 stripes separation between me and a big rig in the same lane.

The VX has always been a difficult car to get much over original EPA mileage.
It proves the point that when the manufacturers really pay attention to high mileage in their designs, it will really require drastic driving techniques to significantly improve mileage over estimates.

And I am not talking about averaging 22 MPH, more like 64 MPH.

regards
Mech

Another thing Robert, is the original EPA mpg was way overestimated - the corrected new values for that car are 39/50, avg of 43- your 55 is well over EPA in that case. The old values were pretty unrealistic for any vehicle as we all know.

thats very interesting to have a high mpg machine that does not do much better with hypermile techniques.I am very happy with it even though 55mpg is the best i can get this summer. I will continue with a light foot,coasting and watching the vacuum gauge to save gas.this car has a super low idle too.with fan and lights off idle is around 300rpm.with fan or lights on,rpm goes to about 500,a/c on goes to about 900.i am not putting anymore premium in the tank since i havent notice any advantage either.also the only 100% gas station near me is about 45 minutes away(according to internt).I have put 8k on this car since i purchased it.

Why would you coast with the clutch engaged? Makes more sense to disengage the clutch so the engine can drop to idle RPMs.

When coasting with the clutch engaged the car's momentum is pushing the motor to continue turning. The Civic computer senses this and cuts all fuel to the injectors, creating a "dead" engine until you touch the gas or put the clutch in, idle rpm or not (called deceleration fuel cut-off, or DFCO). Not all stick shift cars cut the fuel on decel, but Civics do. If you were to put the car in neutral or push the clutch in the computer would continue to pump fuel to keep the engine at idle. DFCO can really bump up your mpgs going down a long hill or where you can decel slowly without ticking off other drivers.

Got it. I didn't know it cut the fuel.

Im trying to hook up a vacuum gauge its a 2 5/8 autometer. I am unsure where to hook it up. i have a 92 hb civic with a 1.5L bone stock I have everything setup but not pulling any vacuum. Anyone know where i can plug it into?

I used a cone shaped fitting and just punched a hole in the brake booster hose and forced the cone shaped fitting in the hole until it was very snug. The hose to the vac gauge was plugged into the cone shaped (tapered) fitting. If you ever removed the gauge, you could fill the hole with some silicone or wrap it with tape.

regards
Mech

thanks for the quick response. Is that the best place to tap into on a civic? just verifying before i splice into the line. Just want the most accurate reading i can get.

I would recommend going to an auto parts store, gett a "tee" connector for vacuum hoses and "tee-ing" into the vacuum line that runs to the fuel pressure regulator or the vacuum line feeding the Purge Solenoid (little black cylinder on the backside of the intake manifold).

The car has an aftermarket cruise control that was tapped into the booster line. it doesnt work so i plugged in there. I also tried else where but for some reason needle doesnt move. im guessing gauge is faulty weird because its new.