Can't Get Good Fuel Economy - 2008 Civic Manual

[whatjigg]

Good to know, I will order one up (although I'm hoping to find the cd/dvd version).

Found some interesting info over on automotiveforums.com, there was an explanation regarding VTEC's operation, now it wasn't about the R18A which is a reversal of the typical VTEC concept. It says...

"To make VTEC happen, the ECU has to realize the following parameters from the sensors on the motor:
1 Your MAP (Manifold Absolute Pressure) sensor must read 0hg (aka 0 inches of vacuum). When it reads this it will send a 3volt signal to the ECU.
2. Your throttle has to be open at least 50% because your TPS sensor has to send a 4.5-volt signal to the ECU.
3. Your coolant temp has to be at running temp.
4. Vehicle speed has to be above 20mph.
5. You have to have 65-80 oil psi.
6. The engine must be running at a minimum of 4500 RPM."

This is EXACTLY the kind of info I'm hoping to find for the R18A. So far, a few things that may be on the R18A's VTEC activation list may be...
- must be between 1000-3500RPM
- must not be accelerating or idle (i'm inferring this from the article about iVTEC on the R18A --> Technical Overview of Honda's new R18 i-VTEC Implementation)
- maybe a positive MAP reading?? (just guessing almost randomly)
- throttle % would need to be extremely low as well
- engine warmed up

Any chance the service manual has such an explanation?

[Christ]

AF.com is another forum I frequent, specifically the '88-'91 Honda Civic/CRX sub-forum.

Post under Dr0pZ0n3.

As far as the helm manual, it differs slightly, in my experience, from the Honda FSM, in that the helm manual tends to provide more walkthrough type information, versus the FSM which normally just provides the actual data one would need to diagnose or service the vehicle without the actual step-by-step direction one may need.

I personally prefer the Helm for most procedures, but use the FSM as well.

IMO, without further information, I'm guessing the iVtec setup the R18 uses is exactly the opposite of the normal Vtec system, in that it is designed to make less power. The normal Vtec system was designed to have a second profile that would aid in making power above the standard RPM range of a standard cam design.

[fanamingo]

Originally Posted by whatjigg

This is EXACTLY the kind of info I'm hoping to find for the R18A. So far, a few things that may be on the R18A's VTEC activation list may be...
- must be between 1000-3500RPM
- must not be accelerating or idle (i'm inferring this from the article about iVTEC on the R18A --> Technical Overview of Honda's new R18 i-VTEC Implementation)
- maybe a positive MAP reading?? (just guessing almost randomly)
- throttle % would need to be extremely low as well
- engine warmed up

Any chance the service manual has such an explanation?

Unfortunately it doesn't have much to go on. When trouble shooting i-VTEC, the oil pressure sensor is the only one checked for faulty operation. When testing i-VTEC (with Honda's proprietary computer system), it recommends testing with the coolant temp > 167F (75C) and rpm 1,100 - 3,300.

I'm going to see if I can tap into some of the other sensors with my multimeter to monitor when i-VTEC is active over the next few days. I'll try to correlate it with sensors viewable on the ScanGauge.

Edit: For anyone interested, the Helm service manual has lots of detail on trouble shooting various problems, but it assumes you have access to the Honda Diagnostic Service (HDS) Software. It also has the expected stuff like how to replace various parts. If you don't need the finer detail you might do better to wait until a Chilton or Haynes manual is available at a much cheaper price.

[Christ]

I'd chance a guess to say the i-Vtec engagement was designed to be seamless.. You could try a standard vacuum gauge (or tapping the MAP sensor's signal) to check for difference in vacuum that is controllable by modulating the throttle.

Wait for a defined change while you're not moving the throttle, then move it ever so slightly, see if you notice another more defined change in the signal/readout.

I don't know a whole lot about the R18 engine, other than they have a ~0.95 R/S ratio, by standard measurement, but the crank is offset from the bore centerline, helping the combustion stroke's efficiency.

They have an integrated header, plastic intake manifold... that's pretty much what I know about them so far. Until the local dealers get me more information, I'm afraid I can't contribute much more than that.

[whatjigg]

thanks fanamingo, it'd be awesome to figure out how to keep iVtec active as much as possible as there seems to be a few tricks to it!

[dichotomous]

sorry but it sounds like there is just a ton of bad information going on here. Hondas i-VTEC system does that, people think its voodoo but its really simple.

there are two types of i-VTEC I know of, and the first is designed for power. its a lot like standard VTEC, whick is a second, more aggressive higher lift and duration cam profile that engages above a certain RPM/load/throttle%. This is good, and is typically applied to both the intake and exhaust valves and you can really have a very smooth gas sipper untill you get on the gas enough to trip it on the big cam lobes. my 95ex civic had the non "i" version of this, and it would get 45mpg if you were nice to it, but I got down to 23mpg one time at full speed all the way to college one morning(found top speed too).

the other version of VTEC is only applied to the intake valves, and it has one valve always running on the "big cam lobe" and the other valve rides on a VERY mild cam, almost round, below 2200rpms. not sure if it's load dependant after that or not. so the engine effectively acts as a 12valve engine below 2200rpms (the other valves open enough to create a nice swirl for completer combustion) and then as a single cam profile engine after that.

the "i" in i-VTEC means that the cam gears are auto adjustable by angle, they can adjust to create the best power or economy for that load/rpm/throttle%/etc.

I belive all of these things can be adjusted via the programmable computer mofication (kpro) and/or the fully adjustable ECU (AEM makes one of these for about 2x the cost of kpro).

its common for the civics to have a 5500rpm vtec crossover (switches to big cam lobes) for full vtec

[Christ]

adding to that -
Vtec isn't actually a separate cam profile... the cam has an extra lobe between the standard lobes, that is always riding on a rocker arm.

When Vtec engages, the solenoid fires up and it moves a lever in the head which engages the rocker that is riding on the larger cam lobe.

The cam doesnt shift positions, nothing of the sort happens.

[dichotomous]

Originally Posted by Christ

adding to that -
Vtec isn't actually a separate cam profile... the cam has an extra lobe between the standard lobes, that is always riding on a rocker arm.

When Vtec engages, the solenoid fires up and it moves a lever in the head which engages the rocker that is riding on the larger cam lobe.

The cam doesnt shift positions, nothing of the sort happens.

well it IS a seperate cam profile, or there would be no point, its a different cam profile on a lobe between the two standard lobes, which as you say rides on a trailing arm that is seperate from the trailing arms which acuate the valves (which the standard cam lobes ride on). the vtec solinoid allows oil pressure to push a pin through the trailing arms to connect them all as one, riding on the big lobe.

the economy version does similar stuff but with only 2 cams per cyl, one arm and valve rides on the big lobe, one on the small lobe, then the vtec solinoid allows oil pressure to push a pin out and lock them together so they ride on the big cam. is that how I wrote it before? sorry if it got confusing.

though, this is for the Kseries, so the fits and Si's and all 4cyl acuras do this, as well as 4cyl accords and crv's and the element. the accords, base RSX, crv, element, 2002-2005 Si and I belive the fit all run off the "2lobe vtec" whereas the 06+Si, TSX, RSX-s, and some of the sportier accords run the "3lobe vtec" ("true vtec")

after reading about the "lean burn" civics this 2 lobe system looks to do the same thing, only I dont think we are seeing af ratios over 14:1 come stock. again, out comes the laptop and hook into your programmable ECU and lean that baby out a little, run a test and check for detonation, try a little more..... anyone wanna give me one of these units to test out the eco benefits of a fully tunable 2.0 engine?

[Christ]

LOL I'll get right on investing in that Kpro for someone else's benefit :P

When I said it's not a separate cam profile, I meant that in a way that wouldn't confuse people who have no idea. Obviously, it is (technically) another profile, but it's on the same cam, is what I meant to say.

The cam, as stated, does not move, rather a pin/arm/blah locks the rockers together so they may all actuate on the larger lobe, thus effectively making one rocker arm actuate two valves.

We're basically in agreement, just using different words to explain the same thing.

[whatjigg]

now that we've got a decent understanding on how vtec works, what are the best driving techniques to use to maximize fuel efficiency, because I don't think all of the typical hypermiling are entirely applicable? (please include details & examples) I'm doubtful that early shifts does much, as long as its before 3500 rpm, no worries.