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Old 08-11-2011, 10:50 PM   #1 (permalink)
Underground Man
 
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P&G gave me 1 MPG increase

Just did 450km of of P&G around the city in my 91 metro, and I only gained 1 MPG over normal driving.

I was pulsing with normal (~3/4) throttle, in normal shift range, timing my pulses for as little braking as possible, no EOC. Basically it was all going smooth (other than my slightly jerky revmatching skills), lots of my glides were 3-4x longer than pulses, and I was hoping for better results.

My car seems well mechanically other than (I believe) a dirty/corroded fuel tank, where sometimes the fuel supply (accelerator) is weak.

What can be wrong?

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Old 08-12-2011, 12:26 AM   #2 (permalink)
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What rpm do you shift at?

How do you measure/validate consumption?

What was your average speed?

a problem with no EOC is that: you have a fixed consumption, so the slower you go the "worse" your mileage.
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Old 08-12-2011, 01:42 AM   #3 (permalink)
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No tach but I upshift approx around...
1-2 20km/h
2-3 35km/h
3-4 50km/h
4-5 75km/h
Didn't check the manual lately but I know that's the recommended shift speeds for 1st and 5th.

For my pulsing and gliding, speeds were not planned ahead, I just did it on the spur of the moment within traffic conditions. Maybe part of my problem is that P&G has to be planned to use the best acceleration areas, so it's not always beneficial? When I was coming out a glide, I was being more lenient to avoid extra shifting. For example if I came out at 40 km/h I would go into 4th, instead of going into 3rd and then upshifting again after a few seconds. Although there is no lugging at that point, now that I think of it it's probably in a slightly lower efficiency area of the BSFC than 3rd gear would be.

I guess one of my main problems in general is never knowing what RPM and load I am driving with, so it's hard to use the BSFC graph specifically. Can MPGuino display those?

Other things to consider... rev matching coming out of a glide uses fuel, so I try not to do very short glides. How hard/fast do you accelerate out of a glide?

I fill tank at exact same pump/position until it auto-shuts off so hopefully my measuring is ok.

Average speed I'm guessing around 60km/h - 70km/h.

Supposedly the fixed consumption to idle is low enough that it shouldn't be a huge deal to P&G without shutting off engine. I should mention that I always have the radio and amplifier powered when driving, so that probably adds some load. In fact I was planning to wear headphones for my next tank to test how much effect it has. My radio/amp is older than the car, so I really don't know how efficient it is.

Last edited by actwithclarity; 08-12-2011 at 01:53 AM..
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Old 08-12-2011, 05:45 AM   #4 (permalink)
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I find that doing P & G whit a lot of traffic around tend to lower my mpg's compared to doing it without the traffic on the same route. My main problems are people cutting in front of me, causing me to brake, and trying to stay ahead of semi's trying to run over me at the end of a glide. It seems that in some situations, DWL should also be considered.

I hope you can see some better figures soon.
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Old 08-12-2011, 09:38 AM   #5 (permalink)
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Sorry, that must have been frustrating. I have two ideas. one about technique and one about instrumentation. 1) If you don't combine engine-on P&G with engine-appropriate DWL you won't get the best results. Your margin between idle and in gear is closer, of course, at low speeds. Without gauges, you are mostly guessing at load, and if your guess is off... well. I know from driving my wife's auto trans and trying engine on P&G that the instrumentation is critical. So... (2) How about getting yourself an aftermarket tach and vacuum gauge?
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Old 08-12-2011, 03:38 PM   #6 (permalink)
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Quote:
Average speed I'm guessing around 60km/h - 70km/h.
That's pretty high average speed for city driving - for example my avg. speed in city area is about 25-30km/h and I see noticeable difference between "normal" driving and P&G (with lower speeds ratio for P&G is better).
Another thing is mentioned by California98Civic instrumentation - I have only vacuum gauge installed but without this one I bet my results would be worse than now.
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Old 08-12-2011, 10:09 PM   #7 (permalink)
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Ya I'd really like to get instrumentation but I don't know what I can do, car is OBD-I so MPGuino looks like the only option, and I'm pretty sure it's beyond my electrical skills (0) to install it properly. I'm not really sure what a vacuum gauge does, or what you hooked it up to, but that seems even harder to install.
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Old 08-12-2011, 11:05 PM   #8 (permalink)
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Quote:
Originally Posted by actwithclarity View Post
Ya I'd really like to get instrumentation but I don't know what I can do, car is OBD-I so MPGuino looks like the only option, and I'm pretty sure it's beyond my electrical skills (0) to install it properly. I'm not really sure what a vacuum gauge does, or what you hooked it up to, but that seems even harder to install.
Vacuum gauge shows engine vacuum, the wider the throttle opening and higher the load, the lower the vacuum so basically what you are working for is the highest level of engine vacuum.

All that's involved with hooking up a vacuum gauge is finding a vacuum line with a good source of constant manifold vacuum and placing a T in the line to run a line to the vacuum gauge. Takes less than 15 minutes to install.

I have one installed in my '88 Escort. The engine vacuum at idle is about 20-21 inches, deceleration is about 23-24 inches, WOT is 0 inches and all other conditions vary depending on throttle plate opening and load. The vacuum gauge just makes you more aware of the pressure you're applying to the pedal. I know this isn't a very scientific explanation, but maybe it helps you understand it's benefit.
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Old 08-13-2011, 12:49 PM   #9 (permalink)
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Quote:
Originally Posted by actwithclarity View Post
Just did 450km of of P&G around the city in my 91 metro, and I only gained 1 MPG over normal driving.

I was pulsing with normal (~3/4) throttle, in normal shift range, timing my pulses for as little braking as possible, no EOC. Basically it was all going smooth (other than my slightly jerky revmatching skills), lots of my glides were 3-4x longer than pulses, and I was hoping for better results.

My car seems well mechanically other than (I believe) a dirty/corroded fuel tank, where sometimes the fuel supply (accelerator) is weak.

What can be wrong?
What were the actual MPG figures both before and after, could you actually get exactly the same MPG on the same route or tank to tank ? I ask because a 1 MPG difference seems within any margin of error to me. I'm probably not the most precise around here but I think any tank to tank with a difference of under 3 is probably no change at all.

I'm interested in the techniques you may use though, I have switched from a TDi to a small petrol car and the pulses take a lot longer than they did. I used to be able to go from 60-80 in about 3-4 seconds. Now I don't go much above 65 and it takes a good 5-10 second pulse to get there.

Also do you have any other mods, e.g. tyre pressures higher or aero mods / deletes.
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Old 08-16-2011, 06:58 PM   #10 (permalink)
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I have been experimenting with EOP&G for the last few weeks. What I have found is that I seem to be better off is running high RPM's for the pulse (2500 to 3000 in my truck) to get the pulse part over with fast. Then I end up gliding about 3x as much as a pulse. The average seems to come out a lot better than nursing it up to speed at OK mpg and gliding less of the time. If I accelerate too slow, the average seems to come out worse than constant speed.

Also, I read the terain like a hawk and glide dow every slight down grade I can and keep it under at least some power on every incline.

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Last edited by graydonengineering; 08-16-2011 at 07:03 PM..
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