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Old 07-08-2014, 01:09 AM   #21 (permalink)
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Digging up an old thread but interesting (to me anyways) new to me info on dfco.
While my old Saturn was picky when it would go into and drop out of dfco my newer Pontiac Vibe loves going into dfco. The Saturn cut out below about 1400 rpm or below 32 mph. This (Toyota 1.8 liter) Vibe goes in easily, stays in, if out-jumps back in easily, will stay in all the way under 1000 rpm, doesn't seem to care about speed. Basically anytime (in closed loop) I want it, it is there. It is a 2007, maybe that is a big part of the difference. Better programming for more often used to help battle the CAFE standards?

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Old 07-16-2014, 05:06 PM   #22 (permalink)
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My Del Sol ('93 Acura engine) drops into DFCO whenever you let off the gas, in any gear, and the RPM is above 1000. It's really as simply as that. Warm or cold, 1st or 5th (or even reverse!). I believe it detects "letting off the gas" via throttle position, because I was having some trouble getting it to go in for a while and found the screws on my TPS were a bit loose. After adjusting it back to the position it was supposed to be in, and tightening it, everything again worked properly.

It seems a similar system is used in my Insight but I've only had the car a few weeks and am not 100% sure yet. I only use the onboard instrumentation, and not an MPGuino, which reads the injector grounds and tells you when they're not firing.
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Old 08-18-2014, 04:19 PM   #23 (permalink)
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CRX - '91 Honda CRX HF
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the ugly one - '97 saturn SL just sl,not sl1 or 2
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Well, the Vibe is gone and now I'm driving a 99 Saab 9-3 (5 speed 2.0L turbo).
I don't know what the manufacturers fuel economy ratings are but the first tank gave up just over 32 mpg. I have since fixed the pixel screen (replaced ribbon wire) and am using the average mpg on the dash. I have eeked it up just over 34 over the last couple hundred miles (mixed driving) with a tiny bit of eoc and some dfco.

This one, I don't think Saab was ever known for high fuel economy, is a little pickier as to when it wants to cut out the injectors. I got out the chassis ear again for a listen today. It will not go into dfco at all in first or second. I even tried running second way up (to get speed above dfco range in third gear) to around 4k rpm and it would not go into dfco. It seems to want to be real close to 2000 rpm or higher to go into dfco and will drop back out around 1300 or so. If coasting all the way down (below 1300) like I do approaching my driveway I now know to dfco down to about 1300 rpm then bump to neutral rpm (just under 1000) for the rest of the coast.

By far, the most aggressive that I have driven (easy to keep in dfco) has been my sons old (270k miles) 1993 Toyota corolla (automatic trans).
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Old 08-18-2014, 04:56 PM   #24 (permalink)
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My Aygo wouldn't go into DFCO under 1400 either, although it was happy to stay in it until just over idle (~950).

Be careful of shutting the engine off when running due to Turbo temps - once the engine is off the oil is no longer circulating and oil in the turbo can overheat and cause seal problems.
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Old 08-18-2014, 05:09 PM   #25 (permalink)
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Quote:
Originally Posted by Arragonis View Post
Be careful of shutting the engine off when running due to Turbo temps - once the engine is off the oil is no longer circulating and oil in the turbo can overheat and cause seal problems.
I know very little about turbos. Is the turbo temp close to the same at all ranges of boost? I mean, with my light driving the boost gauge on the dash, for what its worth, stays low almost all the time. My driving doesn't ask for the boost or horse power. I also rarely eoc, often once per trip for the last half mile of my road where I have to come to a stop anyways. I find p&g/dfco added to neutral coasting more than adequate to appease my desired mpg.
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Old 08-18-2014, 05:34 PM   #26 (permalink)
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The temp will go up with the level of exhaust boost employed so yes a lot of use will raise temps.

In the mid-late 80s a lot of high performance cars with Turbos had issues when drivers would blast down the motorway, then stop for a pee and shut the engine off straight away - the oil would stop circulating and the oil in the turbo would "boil" and cook. A few Escort RS Turbos had this issue early on.



Eventually this would lead to premature issues with oil seals becoming brittle, fail to seal, and then lots of blue smoke as oil leaked into the turbo on boost - and eventually turbo failure.

Translate this to ecomodder style driving - maybe a harsh pulse and glide with EOC might not be too great for a turbo, although the material seals are made from is much better these days.

When driving a car with a turbo I still tend to slow down gradually from high speed so the turbo has time to cool before shutting off completely.

On the positive side you are driving a SAAB. Although it is based on a GM product it still has a SAAB engine (not a GM one Thor be praised) and SAAB were early into turbos and making them reliable for large mileages. People here regularly get 400hp+ from a 2.0 SAAB without it going pop even after 100K+
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Old 08-18-2014, 05:42 PM   #27 (permalink)
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If you want to see how GM did it in a previous generation, the ecm for the 86-87 turbo 3.8V6 Buick Grand Nationals has been completely cracked and decoded. It is OBDI, not II. Go to Turbo Regal Web Site, resources, tech info, ecm and sensors, ecm secrets revealed (this is the disassembly of the code in the rom and the 2K of code in the removable 4k chip). Then get chip secrets revealed and more chip secrets revealed, these are the 2k of data tables in the chip with descriptions and formulas, in spreadsheet form. This ecm used both dfco, and for throttle closing conditions not quite vigorous enough for dfco it also did dfe, decal fuel enleanment, where it cut the fuel 10-15% but didn't turn it off. Anyway, you can see the control parameters in the spreadsheets and the code if you want the real explanation :-). GM tended to reuse code so I imagine other ecms from this time frame were pretty similar in their control strategies. No telling how it evolved later, though.

Two other web sites with lots of gm ecm info is the Welcome to diy_efi/efi332 site and Mark Mansur's site, TunerPro and TunerPro RT - Professional Automobile Tuning Software. Tunerpro is a freenware (basic version) and shareware) full version chip editing program, and he has lots of definition files for various ecms so you can browse for yours and see what data tables are accessible. I've done lots of chipmaking for the buick TR's, starting with a calculator and doing manual hex conversions and editing and then using several freeware packages as they were released, and the free tunerpro is very good. I've never had to deal with obdII so I don't know what its capabilities are there, sorry.
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Old 08-18-2014, 05:58 PM   #28 (permalink)
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No matter what brand of vehicle, I've always been told that you should allow at least 30 seconds of very light throttle or idle after making any boost, to allow the turbo to spin down and cool off. I've always tried to do that and so far have never lost a turbo seal, knock on wood (25 years of spirited driving and drag racing a Buick TR and 6 years so far with a turbo Duramax diesel pickup).

Also, a spark ignited gasoline engine has maximum pumping losses when the throttle is closed. It isn't that the engine compression is slowing the car down, it is the pistons being forced down with the intake valve open and the manifold at maximum vacuum, so the vacuum is pulling upwards on the pistons. Any air that is ingested will be compressed as the piston goes up on the compression stroke, but then on the expansion stroke the air will be re-expanded and minus friction losses the work down on compression is recovered, at least until the exhaust valve opens and you lose the rest of the stored energy. Diesels do not have throttle plates (in general, I know there are a few but ignore them so we can keep this simple :-)) which is why they are so efficient at idle and light throttle; they don't have the pumping losses of the spark ignited gas engines. That's also why when you lift off the accelerator on a diesel you don't get nearly as much engine braking. Diesels move the same amount of air at a given rpm no matter how much fuel is being injected, at least without a turbocharger. The power level is controlled by how much fuel is injected. That is one of the advantages of the direct injected gas engine, which is why manufacturers are working so hard to develop it; it lets them do away with the throttle and inject the fuel at the last possible moment to effectively raise the octane so they can raise the compression ratio to raised the efficiency. You could test this with a fuel injected engine and a kill switch, just do a short coast down test in gear with engine off and throttle closed, and then repeat with throttle wide open. Yes, you will be injecting fuel at wot but if you only do this once each way it shouldn't hurt any thing, and you should coast a good bit further with the pedal to the floor which will demonstrate how great the pumping losses are at idle. Just don't turn the kill switch back on with the pedal still on the floor :-).
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Old 08-18-2014, 09:35 PM   #29 (permalink)
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Had to go out for awhile, and right as I was leaving I realized I didn't give a complete description of the coast down test to show throttle closed vs. wot with a kill switch. If the kill switch is wired into the injectors then no fuel will be injected and the test is completely safe. If it is wired into the spark side of the ignition system then fuel will flow while the pedal is down and the engine is being driven by the car so when you turn the kill switch back on there might be a backfire from the fuel in the exhaust system, so make sure the throttle is back at idle position before restarting. If the kill switch is wired into the crank sensor then the ecm won't see pulses and won't inject fuel, so again the test is completely safe. Sorry to be so longwinded.

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