Ideal speed to change gears for maximum fuel economy

[mekmek 0]

My 450 Cdi has no tach 'eyeball' and I was wondering what is the best speed to gained the most fuel efficiency. I usually wait for the arrow on the dash to come on to change but the car sound like its revving too high. The car does change gear on its own but only when it is revving high. I'm only going by the sound of the car and the speedo to change gears.Eventually I will get a scanguage.

[Huronlad 186]

If you are not already aware the SGII does not make a very good tach. I have a feeling there is a thread with speed and correlating tach values somewhere on the site.

[Alex 21]

Run in auto mode to get a sense of reasonable shift points while accelerating. Auto is not bad at shifting, mileage problem is that when cruising it will often leave you one gear too high. I usually skip gears, 1st to 3700 RPM (35 kph), doubleshift, 3rd to 3900 RPM (65 kph) or traffic speed, then 5th for city cruising or the final acceleration to highway speed. Both those shift points end up at about 2000 RPM, into the torque band. Remap helps with a little extra oomph down at the approx 2000 rpm those shift points land you at. Acceleration shifting is not nearly as important as the correct RPM for cruising, under higher throttle the engine is efficient throughout the power band. The key is to get down to 1700-2200 RPM to cruise. Even as low as 1500, but only on flat ground with low throttle input. Hills, strong headwinds or acceleration need a shift down. Any energy you waste braking and then have to put back accelerating is just that, a waste. Anticipate lights as best you can, avoid braking. This can be impossible in traffic, though.Tachs are great. Get one! Especially considering how gorgeous the pods are.Edit: Confirmed those shift points for the skip-a-gear technique during acceleration, I was a touch off. Above figures are the confirmed ones now.

Edited August 10, 2011 by Alex

[Pingu 0]

For normal startup, try shifting at 25, 35, 50, 70, and 90 km/hr. When you're used to the car, engine sound will tell you when to shift.

[MikeT 744]

Or buy a tach which would not cost all that much, even with the activation fee. I still use my tach after nearly 7 years.

[mekmek 0]

Thank you for the suggestions. I will have to search for a tach. Approximately how much is for one and installed? I've been listening to the car as it revs and have been using the auto mode mostly. Currently I'm working at identifying the low end pick-up issue that I have when in first gear and that might be my main issue to resolve. I'm getting the P0702 code and going through some of the troubleshooting posts that have come up.Also is there a some way of know if the turbo has kicked in. I have lubricated the wastegate rod trying to see what the problem could be for the low end pick-up. I have a feeling that everything is tied into my current issue that is why I asked about the speed.Thank you again for you help.

[Alex 21]

P0702 is a transmission code. Some info here.

P0702 is a vague general code, often resolved by just cleaning and reseating all connections. Good place to start.

Evilution's full listing of codes, both generic and smart-specific. Evilution is a great resource, second only to CsC. Most smarts in Europe, especially the UK are gas engines, so Evilution is a little light on CDI-specific issues, but still a great site.

Edited August 10, 2011 by Alex

[mekmek 0]

P0702 is a transmission code. Some info here.P0702 is a vague general code, often resolved by just cleaning and reseating all connections. Good place to start.Evilution's full listing of codes, both generic and smart-specific. Evilution is a great resource, second only to CsC. Most smarts in Europe, especially the UK are gas engines, so Evilution is a little light on CDI-specific issues, but still a great site.

Thank you Alex for letting me know. I will be doing the cleanout of the connectors tonight. I'm hoping that solves my problems. I'll keep you all posted.

[houseofdiesel 9]

I started off with a scanguage, now I know to shift at 15, 30, 45, 60, 80 km/h. You can shift earlier if your just maintaining speed (like a true automatic would) or light on the throttle/downhill. Letting the car shift for itself is way to much fuel useage, when I test drive some they never see 6th gear even on the highway at 90. Diesels like low rpm and steady state/light loads, that is were they accel at fuel economy.

[smartzuuk 167]

The Scangauge will be cheaper I think then a tach with the turn-on fee... and if you don't have a clock, one POD looks a bit gimpy........5th at 60 kmh and 6th at 80 to 85 kmh on flats will give you fairly decent fuel economy. 6th at 83 kmh (on your speedo, which is 80 with a GPS) is 1800 RPM, which is a sweet spot.

[Francesco 71]

Ideally, you want to be cruising at the "sweet spot," which is 1800-2000 rpm, so the best shifting would be at an engine speed that drops right into the sweet spot the next gear up. This is right around 2500 rpm.

[smart142 605]

I will have to search for a tach.

I can install and activate a tach(brand new) for $95

[gordo.bernard 1]

I can install and activate a tach(brand new) for $95

That's an incredible price.

[Alex 21]

That is a great price! Will look goofy without the matching clock, though.

[mekmek 0]

I can install and activate a tach(brand new) for $95

Hello Glen,that is a great price. I will pm some other things. Chuck

[CANMAN 23]

Mekmek,Posted below is a reply I did to another member about reseating connectors.There are 3 connectors you wan't to do first, the clutch actuator (bottom of engine) and two transmission ones on the left side, the gear change actuator and gear position sensor.I can't remember which one but one is in the intercooler scoop, if you have small hands you may get at it from under the car reaching up into the scoop, otherwise you have to pull the intercooler to get to it.I would clean all the ones I could easily get to first and take it for a drive to see if it's better before tearing the car apart.Don't forget to disconnect the battery.CANMAN

2seat,If you are going to reseat your connectors, go to Canadian Tire or Partsource and get a spray can of electrical contact cleaner and a tube of silicon dielectric grease. ( and a bundle of strap ties)Disconnect the battery carefully disconnect the connections, release the latch and wiggle, don't use force or you will break something.Spray both sides with the contact cleaner, allow it time to evaporate or spray with compressed air to speed up evaporation and lightly coat the pins on the male end and any rubber o-ring with the dielectric grease, it is important that you hold the latch open and connect and disconnect the connector a couple of times before finally latching it.The ECU is on the side of the air box.Make sure the battery is disconnected or you may fry something.You may have to cut some strap ties on the big wire bundle along the top of the air box and around the intercooler.The ECU has two big electrical connectors, one above the other, there is a post somewhere on this site with pictures.Release the latch and keep holding it in the open position with one hand while you wiggle and gently pull on the connector, the latch will open further, keep holding the latch open, wiggling and pulling, don't force anything until you get it off, then do the other connector, they are slightly different so you can't mix them up.Clean, grease, assemble and disassemble a couple of times (important) before making sure connector is seated well and the latch is locked then before you redo all the strap ties carefully check all the cables for chaffing and wear before redoing the strap ties.CANMAN

[mekmek 0]

Mekmek,Posted below is a reply I did to another member about reseating connectors.There are 3 connectors you wan't to do first, the clutch actuator (bottom of engine) and two transmission ones on the left side, the gear change actuator and gear position sensor.I can't remember which one but one is in the intercooler scoop, if you have small hands you may get at it from under the car reaching up into the scoop, otherwise you have to pull the intercooler to get to it.I would clean all the ones I could easily get to first and take it for a drive to see if it's better before tearing the car apart.Don't forget to disconnect the battery.CANMAN

Thanks CANMAN. I followed the contact cleaning recommendations that you listed. Same problem. Today I am taking the shift actuator off to examine it more closely and see if it is the original. The car being almost 190,000 kms. I think it time to change it. I don't know what kind of frequency of change over everyone is getting for this item but looking at the past history on the car at M-B. I don't think it was ever replaced.My plan it to fully clean out the actuator, put it back in then drive again. No change then I'm buying a new one. I'll have to find someone to electronically teach it afterwards.

[CANMAN 23]

Mekmek,

Do not electrically actuate the clutch actuator without it being connected to the car, bad things will happen.

Here's how to clean it.

http://www.evilution.co.uk/index.php?id=533

While you have the actuator off, check the rod end and clutch fork for wear.

http://clubsmartcar.com/index.php?showtopi...867&hl=Fork

CANMAN