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Ok all of you boosted fanatics! I received my digimoto ODBII scantool today and did a little playing around / investigating! For those of you who did not know I bought the digimoto datalogger / scantool for my laptop (http://www.digimoto.com). Only cost $100, and its a great deal because it does dynos as well (sort of like G-tech).

I drove around with my laptop logging data. Here are some results. The ECU goes into OPEN LOOP mode only on three different occasions:

1. Under accelleration, if the engine load is great enough the ECU will go into open loop. I don't know how great the load has to be, but under soft acceleration the scantool said the ECU remained in closed loop. Only when I applied a more vigorous throttle did the ECU go into open loop. My guess is that it is using feedback control analysis (ie, if the car load is a certain % or the RPM vs vehicle speed is greater than a certain # the ECU will revert to open loop).

2. Upon ANY deceleration. If you are driving, and take your foot off the gas, the ECU goes into open loop. Fuel injector duty cycle at this point is 0, the car stops dumping fuel into the cylinders. I'm guessing this is also based on the tach signal, as when I down shifted, the injectors started injecting fuel again.

3. WOT - again, this is sort of like #1.

I also logged fuel trims as well. It appears that our cars attempt to maintain a -10 long term fuel trim. Mine bounced around from -10 to -11 once in a while. The short term fuel trim was all over the place. As I stepped on the gas it would shoot up, meaning rich. As I dropped off of the gas, it went to 0, as it stopped injecting fuel into the engine. This makes me wonder (and wish) that the E-manage could do this based upon RPM signal as well - it can if you plot RPM vs the TPS signal, but I will be basing my fuel injector signals upon boost.....hmmm.

The cool thing about this tool is that it allows you to log the data, and export it as a TXT document. I took the data, cleaned it up a little, and plotted the O2 sensor voltage (from the front O2 sensor) vs the short term fuel trim. The results are interesting! The short term fuel trims mimiced the O2 sensor voltage a bit. The plot shots that when the O2 sensor voltage rises, the fuel trim begins to rise. Like I said before, the STFT is all over the grid - but its mostly centered around -10 to -15 A/F.

I plan on trying to log some more before installing my turbo to see exactly where things are beforehand......

 
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sweet post thanks...there is also a good one at www.scantool.net

Brandon

 
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Its the same thing - the one from scantool.net

 
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someday id like to get one with a small pc in the car perm mounted and be able to display the data via my alpine iva-d900 deck. There are some sweet programs available for free that if your interested ill try to locate them.

 
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That is such a sweet find Travis! I watched the flash demos and it looks bad ***. What does the installation consist of?

 
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we have a REAL mechanic here people, that was just over my head

 
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^^^

 
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After this, it seems you have a good starting knowledge of how the ECU actually works. There are an amazing amount of fuel enrichment and spark retarding maps in there.....

Just a few things: when on closed throttle, are you implying zero fuel is being delivered? If this were so, you would lose combustion... There is gas, albeit very little, being put into the motor upon deceleration... Think about if you ever started a car by popping the clutch while rolling (damn starters)... The throttle is closed, but gas is still getting delivered to start it....

Very good points on open loop, which is what one would be tuning for max power (WOT)... switching between open and closed loop really are based off TPS voltage and motor temp. When you first start a vehicle it starts in open loop until it reaches temp... Again, another fuel and spark curve...

Closed loop maps are very interesting as you can really improve driveability (sp?) on modded motors... You can adjust for things like larger cams, port work, larger injectors, etc.... It helps with things like gas mileage (who cares on honda's, right???), idle surge, fuel pooling on warm starts, etc.....

The A/F ratio is another huge part that the ECU controls.... This is all based on O2 sensor info.... Think of how any A/F meter works (voltage changes in O2 sensor).... Again, based on O2 voltage, the ECU can adjust fuel and spark to compensate....


Keep up the learning, there are tons of sites out there with this type of ECU info, including maps....

 
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Woah...pretty interesting stuff man. Keep us posted cuz as you know we're starving for new knowledge around here all the time.

bawwwwrr-eautiful work.

 
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According to the Helms manual, upon decelleration the fuel injectors shut off - to conserve fuel. logging with this confirms it (as well as the E-manage, which can track injector duty cycle whereas this cannot directly monitor the injector duty cycle).

Yes and no. The Scantool even says - whether its in open loop or closed loop, due to driving conditions such as accel or decel. The IAT pretty much remained the same throughout the test. It varied by about 10 degrees at most. At idle I measured 190....It appears that the ECU takes into account a few of the sensors, such as TPS, RPMs, and Speed. This may all correllate to how it calculates the engine loading, which in the end could determine the actual transfer from closed loop to open loop.

Actually it is open loop maps you are thinking about - the ECU will run in open loop when the car is cold (ie as you stated before - until it reaches operating temperature). It does not depend on the readings from the front O2 sensor at this time, only the hard programmed fuel maps. Once it reaches optimal conditions it jumps to closed loop, which allows the O2 sensor feedback to control fuel (in addition to the other sensors).


Which is why a wideband is sooooo much better (0 to 5 volt output vs 0 to 1 volt for a narrowband) - much more precise measurements of A/F ratio.

 
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But if you have no fuel, how can your motor continue to run? If there is no fuel, there is no combustion--no combustion means the crank is not rotating or you are seriously leaning out. You know that if you have-say 730 rpm while in idle or anytime that the clutch is depressed then you have to have crank rotation. The crank won't spin on it's own, it has to have combustion.

I take it you are using the stock narrowband sensor then? I agree 100% on this though, a wideband unit is the optimal piece to use but using a wideband with this datalogger sounds like it would work great. Thanks for the info and review on the part, this can make tuning much easier with a good datlogging tool.

 
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Andyman is correct on the deceleration fuel issue....

On the others, we are essentially saying the same thing...

The IAT has a small portion to do with open and closed loop, the actual engine temp does. This was in reference to the warmup mode you spoke of. Obviously this varies as the termostat and ECU-controlled electric fan will keep operating temp within the specified range...

Again, closed loop comes into play when the vehicle is up to temp and you are driving "normal." Closed loop utilizes more information and therefore you can adjust for daily driveability issue on built motors... Open loop is again only for the situations above which is basically WOT (or close to it) and warmup.... Two compltely different things with two different purposes....

I've been dealing with ECU's fuel, spark, and sensor correlations for 10 years. Obviously not every ECU is exactly the same, yet they all utilize the same set of sensors and principles....

Try sites like this, you would be amazed at the number of things going on in that ECU...
http://www.diy-efi.org/diy_efi/

Good discussion.... Anyone else want to pipe in???

 
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Opto, I think something that you may be overlooking by reading what the Helm's says or what the datalogger is indicating is that it may register at 0 for the injector pulse due to the fact that the amount of fuel consumption is so low that it either registers at 0 or 0 is the amount of the duty cycle for idle or deceleration. Reading at 0 may not necessarrily mean that the injectors are closed but they aren't opening as they would if you were under acceleration.

 
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I just ordered the digimoto too on Monday. I'm using a pocket pc though. Everything about it is amazing for the price.

 
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As I've stated above, I've noticed that the D17 ECU goes into open loop when the throttle is released, or when there is a large enough difference in speed or load. I've witnessed this. Other ECU's may be different. I can take a picture of it if you want to....The ECU also bases its changeover from open loop to closed loop based on coolant temp.

I am just reading what the manual (and the empirical data) are telling me....Most likely you are correct, the injectors are probably at like a 1% duty cycle.....

 
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?¿?¡ Damn, i wish i has a clue on how to read all this stuff

 
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To imply that the motor will continue to run with the injectors shut off, would imply that Honda has created an engine that does not need fuel to run. Its just not possible to shut off fuel flow to the engine and have the engine continue to run.

But this is an intresting find none the less

 
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I don't think any of you understand this concept. Quoted straight from the HELM Manual, page 11-35, sub heading Fuel Supply System:

"During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at engine speed over 850 RPM. Fuel cut-off action also occurs when engine speed exceeds 6900 RPM, regardless of the position of the throttle valve, to protect the engine from over-revving. With the A/T model, when the vehicle is stopped, the PCM cuts fuel at engine speeds over 5000 RPM."

Straight from the horses mouth. Another member wrote me and brought up a good point, if you are traveling, and take your foot off of the gas, injector pulse goes to 0. NO fuel is being injected into the cylinder (as stated from the book, and proven from my experiment). The enigne continues to run only because the clutch is engaged. When you take your foot off of the clutch the RPMs drop significantly until idle speed is reached whereby the ECU starts injecting fuel again. Its not voodoo or rocket science people.....

 
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No, it's not voodoo, it's just very hard to believe when thinking about it in a real world setting even if the helm manual says it, thats all.....

 
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What this is saying is that when you decelerate and your rpms are above 850 rpm (throttle is closed), electrical current to control injector pulse width is cut off. In other words, when you let off of the throttle and are decelerating at an engine speed of over 850 rpm, the ecu is no longer opening the pulse of the injector. That's how it saves fuel. It doesn't continue dumping the same amount of fuel into the cylinders while decelerating that it would if you were at WOT.

Also, the rev limiter is set at 6900 rpm apparently so there's a fuel cut when your engine hits that speed. I'm sure alot of us have hit that limiter and seen what happens, right? It bogs because there is no fuel so you can't continue to accelerate past the set rpm.

Then it goes on to say that if you are stopped that there's no fuel over 5k, so you can't rev your engine over 5k while you're stopped (and I would assume that means if the clutch isn't depressed, either.)

As far as completely cutting fuel, it's impossible. Your piston will not fire without fuel in the cylinders. You won't have a combustion. What would happen if you unplugged all of your injectors and tried to start the car? Nothing. It won't start for that very reason.

 
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I think that imply's for automatics. u cannot rev them in neutral at a stop.
either way tho, My car hits the REV limiter.
Its not fuel cut off.
The fuel cut off occurs at top speed. Not Rev's. I can Hit the fuel cut off in 4th gear at 120mph. Not the rev limiter. If i switch to 5th gear then its at like 4k RPM's and still stops at 120mph. That is the Fuel cut off.
so how could it say that it stops fuel while ur stopped? It doesnt. The ECU stops the engine when X amount of RPM's are detected.

please correct me if im wrong

 
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wouldn't the inertia of thew engine just keep it running

if an angine was at XXXXrpms and the you disconect the battery, i woudlt not stop (or would it)it woudl just decelarete rapidly and he totally stop, but not 5000-0 rpms in a tenth of a second

 
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he said that when you reach 850 rpms fuel is delivered again, and it was said that fuel was cut of when decelaration or rev limiter occured, not when idling...

 
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you took my statement out of context. i wasnt referin to opto.

 
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Interpret this however you like, I know exactly how it works....I just posted this for everyone's information.

 
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It isn't interpretation. What you're saying isn't correct. If you have any understanding of how an internal combustion engine works, you will understand the basic principle that you must have air and fuel to burn properly and cause your pistons to fire. You don't just burn air, you have to have fuel in it. Period. It's that simple. When you decelerate above 850 rpm, your injectors flow as much fuel as they do at idle. That's all that this is saying.

As far as automatics, I can't say for sure if it works the same but your fuel does cut at redline which is 6900 rpms. It does the same thing when you hit top speed at 120 mph or so. If you are in a 7th gen with a standard transmission, try revving it while in neutral and the ebrake is on. See if you can get it over 5 grand. From what this helms says is that you can't due to fuel cut. I haven't tried it myself but I will tonight.


Civic Mexicano: Yes, the engine will continue to run for a few crank rotations if you shut it off but after that the engine is no longer running. Your tires still move if you have the clutch in but it isn't because the motor is powering them, it's because you still have momentum.

I'm not trying to argue or flame anyone here but there seems to be a big misunderstanding of what is being said.

 
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its ok i just wanted to see if my argument was correct or not....

 
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Another good way to test this theory would be this....

Get up to about 50 mph in fourth gear. Let off the gas and clutch. Turn the engine off while you're decelerating. Guess what will happen? Say goodbye to your motor. Your crank will stop suddenly and tear your motor up. Now, if there's no fuel being delivered, it shouldn't matter, right? Wrong. Still don't believe me, give it a try then.

 
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Thank you Andyman, that's the best real world scenario I was looking for....

 
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It's no problem man. Not to bash anyone but there's no point in arguing just to argue. The way a motor runs is not that complex. And I can't say I know everything there is to know, no one does, no matter what they say. But just because you think that you know is no excuse posting mis-information just to argue a moot point.

All in all, I think this board is great. There are alot of people that know what they're talking about. And I'm not pointing any fingers but I think there are alot that think they know alot of things that they don't. Nevertheless, people shouldn't believe everything that they read if they don't truly understand it. Great discussion, nevertheless. I think this is the first technical discussion that I've been involved in that hasn't turned sour......