CODFISH or Pulse and Glide?

[SVOboy]

I think darin has a test of codfishing versus coasting in gear on his site, no?

[diamondlarry]

Originally Posted by Peakster

My Geo uses 0.1gph (800rpm) when it's warmed up and idling at a stop. When the car is rolling during a coast with the engine on, the car uses 0.2gph (1250-1300rpm). Is it normal for the ICE to idle higher when the car is in motion?

It seems to be normal. On all of the Saturn's I've had, they generally idle about 500 rpm's higher while coasting than they do from a dead stop. Why it is normal, I'm not sure. I imagine it's got something to do with emissions.

[Peakster]

I've been trying to do some P&G the last couple of days, and I've noticed that my FE goes down every time I do it! So frustrating. My car does about 25mpg during the pulse (20-30mph), kill the engine, and then I glide back down to 20mph and bump start, repeat (pending no one is on my tail). I usually only glide 2X the distance of the pulse.

Does it just make more sense to keep a 0.4-0.5 GPH @ 30mph? I just don't get how other people can get great FE with P&G and I get poor results.

[MetroMPG]

What gear(s) during the pulse? How fast is the acceleration (time spent accelerating relative to the glide length)? How's your tire pressure? Make a video

[diamondlarry]

Hmm, interesting. I probably don't have to ask but, for everyone else's benefit, have you checked tire psi lately, brakes dragging, bad wheel bearing(s), etc.? When I do my P&G it's usually on county/rural roads and, if traffic cooperates, I pulse to 50-60 mph(depends on whether I'm going to or from work) and glide down to 35-40 mph. The roads in the county in my area are pretty much all 1 mile apart and I've found that if I can get to 45-55 mph(depending on temps, wind etc.) within 1/4-1/3 of a mile that I can make it to the next mile. This is with my tires at 60 psi.

[trebuchet03]

Originally Posted by Peakster

How long should the engine be shut off to offset the extra fuel required to bump-start and/or key-start the car?

If you're bump starting... I would think that the fuel necessary is either zero, or very close to zero.... Especially if you bump start into an rpm range where fuel isn't being injected

Here's my bump start process - I don't like doing this in my lower gears due to gear lash though....

Engine Off - Out of Gear:

1. Make sure key is not in the "Run"position
2. Shift into appropriate gear
3. Engage Clutch
4. Move key to run position

Apparently, the Prius has a similar startup sequence when starting up its ICE. Not sure why, but I suspect it's to get oil pressure and flow on the wear components (journals et. al.) before putting them under load.

Is it normal for the ICE to idle higher when the car is in motion?

When I had my SW2 (auto), it did the same exact thing

[MetroMPG]

Trebuchet - I would think that bump starting method is going to be kind of harsh.

I tend to re-start the car with the *briefest* (and only partial) engagement of the clutch in at least 1 (usually 2) gears higher than my road speed calls for. As soon as the engine catches, clutch in again, then shift to the right gear.

---

Peakster: to get the high numbers with P&G, I limit my upper pulse to around 60 km/h (40 mph-ish), and re-engage around 25 km/h. For my transmission, that's a 2nd-3rd gear pulse.

The stupid high numbers come with a 2nd gear only pulse from 25-40 km/h.

[trebuchet03]

Originally Posted by MetroMPG

Trebuchet - I would think that bump starting method is going to be kind of harsh.

I tend to re-start the car with the *briefest* (and only partial) engagement of the clutch in at least 1 (usually 2) gears higher than my road speed calls for. As soon as the engine catches, clutch in again, then shift to the right gear.

Doh! I said lower gears again... I did mean higher - usually 4th... Not 5th as it's overdriven.

I've been going by the butt meter on how hard it engages... Once engine starts turning, it acts just like an engine brake... And because I'm typically doing this in 4th, my engine speed never goes above 2000

[diamondlarry]

Originally Posted by MetroMPG

Peakster: to get the high numbers with P&G, I limit my upper pulse to around 60 km/h (40 mph-ish), and re-engage around 25 km/h. For my transmission, that's a 2nd-3rd gear pulse.

The stupid high numbers come with a 2nd gear only pulse from 25-40 km/h.

Metro, about what rpm's are you running when pulsing like this? If I'm figuring correctly(15 mph to 40ish mph), this would be a 3rd-4th gear pulse for me.

[Peakster]

Originally Posted by MetroMPG

What gear(s) during the pulse?

I shut off the engine at 50km/h, bump start in 5th gear @ 35km/h. I go into 3rd gear, accelerate from 35km/h - 40km/h, shift into 4th and accelerate from 40km/h to 50km/h. Shut off engine. Repeat. Remember I have the stock Metro tranny.

How fast is the acceleration (time spent accelerating relative to the glide length)?

for every 1 unit of distance pulsing, I can usually go 2, possibly 3 units of coasting.

How's your tire pressure?

Just checked: ~43 psi all around... granted I just came back from a drive, so they're probably not cold... perhaps I should check again in an hour. EDIT: Tires are now at 50 psi cold.

Make a video

I just might, if I can't figure this out! I bet I'm missing something real simple.

BTW, I just drove in city traffic today just keeping a steady 0.4 GPH @ 30mph, coasted with the engine on but shut it off at a complete stop at traffic lights and came out with 63.2 mpg trip average. Compare that my P&G'ing which gets around 50mpg .