CODFISH or Pulse and Glide?

[Kraig]

I tried COFISHING on my last tank and am a little disappointed in my results. I only went from 52.08 to 53.78 mpg. I would CODFISH over about a 22 mile distance of a 37 mile drive home home each day. On the way to work in the morning I didn't do it so I wouldn't be late. Anyway I would speed up to about 50-55 mph then coast with engine off to about 35 mpg, bump start, speed up and start all over. It would take about .4 miles to get back up to speed and then about .3 miles to slow down to 35 mph.

Is this to fast a speed to do this? (Should I try Pulse and Glide?)

Should I be able to coast farther than I am? (Is something dragging me down?)

Should I coast to an even slower speed before speeding up?

Should I speed back up quickly or slowly?

I think I need a SuperMid (not in the budget currently :mad: ).

Any other technique suggestions? (I'm costing to stoplights trying not to stop, turning it off when I do stop, driving the speedlimit etc.)

Thanks for any input!!

[Brian D.]

Boy, I sure suck at 'search'. What the .... is CODFISHing, and why does it always appear capitalized here?

If I start talking about it I'm going to type "Codfishing" and be a rebel. Then again, if I were a hotdog I'd probably smear mustard & relish all over me & eat myself. hmm.

[omgwtfbyobbq]

Coast On Demand Forced Ignition Shutoff. Ideally, accelerating in your engine's minimal BSFC are will maximize engine efficiency, and shutting off/ dropping in nuetral will remove driveline friction losses (everything spinning) from a portion of your drive. So, you can do one, the other, or both. You can do coast down tests over a portion of road to figure out how much more energy keeping the car in gear requires, and as a rule of thumb, accelerating in the minimum BSFC region roughly doubles engine efficiency.

Edit- When coasting, the injectors will turn on once the car gets down to a certain rpm, which is really inefficient, so you'll want to stay above that rpm if you're coasting in gear.

[MetroMPG]

I distinguish between CODFISHing and P&G like this:

P&G is what I do when I could otherwise just be cruising along at a constant speed unmolested by other cars or stops. It's a continuous, repetitive process.

CODFISHING is more for sub/urban driving where you kill the motor and coast approaching turns, stop signs, lights, etc.

The difference is: to someone watching me P&G would think I'm insane, whereas CODFISHING is pretty much invisible to anyone observing (unless you do it and hold up traffic with extended coasts).

[Silveredwings]

...(unless you do it and hold up traffic with extended coasts).

You say that like it's a bad thing. :D

I tried killing my VW engine on a couple of drives and it started acting very strangely. A blower that I didn't even know existed started running for 30 seconds every minute or two, even when the car was turned off. It's supposed to add air to the exhaust manifold to burn excess HCs when the engine is running rich (cold mode). If it fails, the OBDII will tell on me next time I get it inspected, and it's expensive to replace (damn VW complexity). Ideas?

[MetroMPG]

Interesting. Do you know what kind of sensor control the blower uses?

If it runs off a temperature sensor, that might explain it. You likely killed the engine immediately after being under load, and cooler exhaust hasn't had a chance to flush the manifold. Just a theory.

[Silveredwings]

Interesting. Do you know what kind of sensor control the blower uses?

If it runs off a temperature sensor, that might explain it. You likely killed the engine immediately after being under load, and cooler exhaust hasn't had a chance to flush the manifold. Just a theory.

I'm pretty sure it's temperature controlled (but which temp. sensor, I'm not sure). It's run by a relay that's controlled by the ECU.

By burning the extra HCs in the manifold/head pipe, it probably has a side benefit of heating up the cat. a little faster.

I dealt with it at the time by unplugging the blower motor (no fuse would kill it) to keep it from killing the battery when the engine is off. It's since returned to normal.

[Kraig]

None of the replies really answered any of my questions.

[MetroMPG]

We can't answer some of the specific questions, because we don't know your car. E.g. whether it's coasting well or not, or what your best rate of acceleration is (though omgwtfbyobbq mentioned if you had a BSFC map for your engine, you'd have the answer).

I can tell you that the higher your upper pulse speed, the smaller the benefit of doing it. If you P&G below speeds where aero penalties are worst, you'll have better results.

So that would mean an upper speed of around 45 mph I would say, and a lower speed that would let you engage 2nd gear a little below its best BSFC engine speed.

But again, I don't know how your car is geared. So this is kind of guesswork. Sorry.

[Kraig]

That helps some, thanks. I noticed it does seem to slow down pretty quickly from 55 but if I'm in town it seems to coast fairly far. So CODFISHING is basically for slower speeds? I should try the pulse and glide at speeds above 45? S far as my BSFC I need instrmentation to figure this out? I guess I can't complain, I've averaged almost 52 mpg for over a thousand miles now.

[diamondlarry]

Is this to fast a speed to do this? (Should I try Pulse and Glide?)

No, it's not too fast. That is roughly the speed I have used occasionally. In fact, when I made a highway trip a couple of weeks ago, I would speed up to 60 then coast(engine off) down to 50 then bump-start and start over again.

Should I be able to coast farther than I am? (Is something dragging me down?)

That does seem like a very short coasting distance. I think my coasting times are actually longer than what it takes to get up to speed. I would check your air in the tires and make sure you don't have any brakes dragging.

Should I coast to an even slower speed before speeding up?

That speed seems about about right.

Should I speed back up quickly or slowly?

I've found that somewhere around 1/2 throttle seems to be about right for accelerating.

Any other technique suggestions? (I'm costing to stoplights trying not to stop, turning it off when I do stop, driving the speedlimit etc.)

Sounds like you are on the right track. Keep practicing and good luck.

[MetroMPG]

I noticed it does seem to slow down pretty quickly from 55 but if I'm in town it seems to coast fairly far.

Our cars are very light, so they slow down faster at higher speeds due to relatively low momentum. Aero drag kicks their butts when you take away the power. That's why the car decelerates more gradually and coasts noticibly longer at lower speeds.

Don't worry about what to call the technique. It's a fine distinction, and it doesn't matter a heck of a lot.

As far as BSFC, you'd probably be safe accelerating at about 1/2 throttle in the range of 2500 RPM, +/- 300 RPM.

But that only applies if you don't have a stop or slow-down immediately after accelerating - but you probably know that already. Try to avoid accelerating into any situation that requires you to get on the brakes. Coast in N to burn off your speed instead, if you can.

[Kraig]

Thanks for the replies! I'll check tire pressure and make sure I don't have any brakes dragging etc. I'd like to be able to get to 60 mpg with technique before starting to make any mods to the car. I guess I really need to save up for a SuperMid and get a tach.

[MetroMPG]

My first Firefly had sticky front calipers (corrosion on the piston - wouldn't retract smoothly). The car would come to a very slight but noticible STOP when coasting down to zero in neutral. I changed them, and that fixed it, but I suspect even a mechanic wouldn't have said the drag was serious, or even a problem.

Once your tire pressure is up, you should be able to push the car VERY easily with one hand on a level smooth surface. When coasting to zero, it should glide to a practically imperceptible stop, no "lurch" or jerk at the end.

[Kraig]

Thanks again.

[Silveredwings]

Oh, and I thought was normal for my brakes to throb like a trans-warp drive set to overload. Next you're going to tell me my tire tread is too worn when the steel belts make sparks on the road going around corners.

[Peakster]

Well instead of making a new thread, I thought I'd hijack this one :D

During my last fillup with the scangauge in use, I was codfishing like mad all over town, turning off the engine at virtually every available coast (that was 5 seconds or more). When I went to fill the tank, the Scangauge displayed that I used 3.8 gallons, but it took 4.3 to fill!

That combined with less-than-aspiring 52mpg I began to wonder if codfishing makes any sense in a city like mine where there are virtually no hills at all. I can only coast with the engine off for a mere 2 or 3 city blocks at most before coming to a stoplight, so is it even worth it to shut off my engine while coasting those short distances? Keep in mind that it's winter time here with lots of snow so my coasting distances have diminished. How many seconds of codfishing should be a minimum for best effect for FE?

[James]

Pulse and glide and codfishing is best done in the summertime. When you turn off the car in the winter, it is sometimes so cold that the engine has cooled off by the time you restart. I would not shut the engine off until you have driven for at least 10 minutes when it is below 20 deg F out. I think you might as well continue to warm up the oil, coolant, etc and leave it idling most of the time during winter. I would still coast at any given opportunity.
In the winter aerodynamic drag is greater, and since your car is very light and not very aerodynamic, the slower you go the better your economy will be (to a certain point).

You might also want to make sure your car idles at the right speed once it is warmed up. If it idles high it will use a lot more fuel while coasting (w engine running of course).

[James]

I notice that my father's 06 HCH II does not autostop until everything is warmed up--usually 5-10 minutes after starting. If that car does that, probably the engineers figured it wasnt worth the extra wear and tear of cold startups to save a little bit of fuel.

[Peakster]

What about when the engine is fully warmed up? How long should the engine be shut off to offset the extra fuel required to bump-start and/or key-start the car?

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?

[SVOboy]

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

[diamondlarry]

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! :mad: 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]

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 :thumbup:

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 :thumbdown:

[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]

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 :thumbup:

[diamondlarry]

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]

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 :(.

[kickflipjr]

I will pulse and glide if I don't have anyone behind me, but it is too crazy of a way to drive if a person is behind you.

[kickflipjr]

I will pulse and glide if I don't have anyone behind me, but it is too crazy of a way to drive if a person is behind you.

[MetroMPG]

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.

I usually max in the high 2000 RPM range in the burn.

[MetroMPG]

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.

What's your max RPM in 3rd or 4th at those speeds? I wonder if you're holding it a little too low.

I'm in 3rd gear up to 60-63 km/h. With the taller tranny and tires, my RPM is 25% lower than yours, which tells me you should be at 45-47 km/h before you shift out of 3rd if you were copying my approach.

And don't be afraid to use plenty of throttle in the burn - 1/2 of max TPS is no problem.

AH! Just thought of something else: this may be ScanGauge related. Doesn't your SG stop recording speed/distance data when you key off? And take a while to reboot when you key on again? If so your apparently lower MPG may just be a calculation error. That was the main reason I installed a kill switch - to keep the 12v always on to the SG.

[Peakster]

What's your max RPM in 3rd or 4th at those speeds? I wonder if you're holding it a little too low.

5th gear @ 50km/h is around 1500 rpm
4th gear @ 50km/h is around 1800 rpm
3rd gear @ 50km/h is around 2500 rpm

I usually don't pay attention to RPM, I just shift whenever the engine sounds buzzy. I've always thought that MPG is pretty much always better in higher gear rather than lower (eg. flooring the car and lugging it in 5th @ 50km/h returns ~28mpg while at the same speed in 4th, flooring it only returns ~22mpg)

And don't be afraid to use plenty of throttle in the burn - 1/2 of max TPS is no problem.

I usually press 1/2 of the way down to the floor on the accelerator, or just enough for the engine not to lug in gear.

AH! Just thought of something else: this may be ScanGauge related. Doesn't your SG stop recording speed/distance data when you key off? And take a while to reboot when you key on again? If so your apparently lower MPG may just be a calculation error. That was the main reason I installed a kill switch - to keep the 12v always on to the SG.

My SG does turn off during the P&G (or there's a medium pause before it calculates MPG again when the ice is off), but for the past several months the 'gallons used' indicator on the SG has been very accurate. So whenever calculate my MPG between fills (such as my sig) I take the miles traveled from the dashboard odometer (as the SG 'miles traveled' is always wrong whenever I CODFISH within the tank) and divide it by the 'gallons used' on the SG.

Perhaps a kill switch is in order. How does a person rig one up?

[MetroMPG]

Yup, my advice then is 2 part:

1) accelerate to a higher speed before shifting during P&G runs than you have been

2) the MPG calcs you're seeing are the reason you think P&G isn't working for you. The SG may well be calculating fuel used closely, but it's not recording distance traveled for a portion of your glide (until it reboots), and that's where the error is.

Do a search for kill switches. I did mine on the coil pickup wire (on the distributor); other Metroids have used the fuel injector signal wire (TBI = only 1 wire). I'd be inclined to do the TBI wire switch. Trying to remember who did theirs this way, but I can't at the moment.

Also, you want a momentary off switch, not an on/off switch. IE you press and hold until the engine quits, then release and you're ready to restart whenever.

[MetroMPG]

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.

Whoops - just realized I didn't answer the second part.

15-40ish range is 2nd & 3rd gear for me - but remember, I've got the longer legs.

[diamondlarry]

Actually, I could almost do the 15-40 mph burn in 4th only.

Do a search for kill switches. I did mine on the coil pickup wire (on the distributor); other Metroids have used the fuel injector signal wire (TBI = only 1 wire). I'd be inclined to do the TBI wire switch. Trying to remember who did theirs this way, but I can't at the moment.

Was it me you were thinking of?

[MetroMPG]

I was thinking of someone with a Suzukiclone who posted a picture.. May have been jwxr7... Or Skewbe.

[EHRGEIZ]

Is it normal for the ICE to idle higher when the car is in motion? At least on my PT Cruiser, part of it has do with the power steering set-up. There is a sensor that detects PS load on the engine. It automatically adds fuel to increase engine RPM when the PS pump is engaged... Maybe its the same?

[Peakster]

Since the filling up the Geo last night, I've been P&Ging everywhere I go. And I mean EVERYWHERE. Man alive, does it ever wear out my feet/legs! :o I was totally set out on proving that P&G doesn't work for my car, but the next fill shall be interesting. In city streets with a 50km/h maximum, I accelerate in 3rd gear to 60km/h, and then kill the engine and coast to 45km/h or so. That way I don't have people tailing me (pretty much the exact same technique I used with the Chrysler).

The SG is flickering on/off all the time and it's not correctly calibrated for the Geo anymore (was in the Chysler) but so far it says I've used 2.0 gallons and the dashboard odometer reads 104.8 miles driven ~52mpg. The Chrysler was much better at both accelerating and coasting.

Once the gas gauge reads at the 1/2 tank mark (3-4 gallons used) I'll fill up and see if this crazy style of driving was worth my time.

[MetroMPG]

Peakster - it's a proven technique for any normal gasoline, manual transmission car. If it's not working for you, there's a problem with the car: either rolling resistance, or the nut behind the wheel. :)

You could save yourself a lot of trouble with a kill switch - so you could use the SG and you'd have your answer in a few km.

[diamondlarry]

In 36.4 miles today I was able to acheive 62.6 mpg by using 4th gear between 30-35 mph. Occasionaly my start and stop speeds varied but for the most part it was 30-35.

[trebuchet03]

Since the filling up the Geo last night, I've been P&Ging everywhere I go. And I mean EVERYWHERE. Man alive, does it ever wear out my feet/legs! :o

Rev match to get out of gear -- if you perfect it, there's no resistance when getting out of gear ;) That will reduce your footwork quite a bit :thumbup: Just don't go the other way around (unless you're ballsy)... It's like catching a softball with your mouth, it's doable - but you're likely to break a few teeth :thumbdown:

[Peakster]

Okay, I guess P&G does work in the Geo too :o. 66.97 MPG fillup using the technique nearly 100% of the time in the city. At first the gas gauge fell like a rock, but then I was like: "Is it stuck? It's not moving and I've been driving for hours!!" I just wish the Geo could coast a little longer than 2 blocks :rolleyes:.

And here I thought I was going to need to make another video :)

[MetroMPG]

Ladies and gentlemen: I think we have a convert! :)

Glad you got your answer.

[BeeUU]

Ladies and gentlemen: I think we have a convert! :)

Glad you got your answer.

Peakster-

My last fill for the Peugeot (relatively old, big, heavy and nearly 2 liters!!!) was nearly 44 mpg, I had one hand on the steering wheel and one hand on the ignition key!!!! If the engine was not working hard it was off.

P&G works baby!! :thumbup:

But it is way too much work, forgetaboutit. Stick with acetone.