A question of timing...

[Tannhauser]

...and piggybacks and large injectors.

 

I was reading a thread on Supraforums in which someone was explaining why he didn't think much of piggybacks for controlling oversize injectors. As far as I understand it, I think the argument went like this:

 

1. Piggybacks such as the emanage deal with larger injectors by adjusting the airflow signal to the ecu. The emanage tells the ecu that there is less airflow than there really is. The ecu therefore reduces the pulse width for the injectors. This compensates for the fact that the injectors are delivering more fuel in a given amount of time.

 

2. The stock ecu has a timing map, which determines what advance there will be at any given amount of airflow. At lower boost, there is more advance; at higher boost, there is less. This is to prevent the possibility of detonation at higher boost pressures.

 

3. As stated in (1), the piggyback is messing with the airflow signal, making the ecu believe that the car is running less boost than it really is. So at high boost, the ecu -referring to its timing map - continues to run a high degree of advance. It thinks the car is still running at low boost due to the fudging of the airflow signal.

 

4. OK, now the ecu can get round this because it can sense if knock is starting and can back off on the timing. But this creates the following problems:

 

a) if the knock sensor fails, there is a much greater danger of damage to the engine than without the piggyback

b) if the ecus learning is reset e.g. pulling the whatsit fuse, then until the ecu learns, there may be dangerous amounts of advance

c) letting the ecu determine timing by continually using the knock sensor may not be the best way of extracting power.

 

Obviously, the bigger the discrepancy between the original injectors and the new ones, the worse the problem could be. The emanage can adjust timing, but guess what? It can't monitor it: it doesn't know what timing the ecu is running. So if you try to get around this problem without additional equipment, you're groping in the dark.

 

I've got an emanage and 850cc injectors .

 

Any views on if the argument holds up and if it's a real potential problem?

[CJ]

Nothing to add - but interested in the replies.

[Wez]

Have a look through this thread :-

 

http://www.mkivsupra.net/vbb/showthread.php?threadid=28949

 

[Matt Harwood]

From what I've seen, this doesn't seem to affect too much. The stock ECU does seem to do a very good job of keeping the timing under control. No matter how fudged the airflow has been. (to a degree )

However, the theory is correct, and that's one reason why I'd NEVER suggest ADDING timing at the top end of a fuel map, with a piggyback system, but if you want to retard it a couple of degrees for safety it shouldn't cause any problems, and in theory, that should bring you back to standard.

All IMHO of course

 

 

Disclaimer - I'm not suggesting that anyone should just play around with things like timing without the correct equipment to monitor what's actually happening with the engine.

[AeroMatt]

I've also heard that the ECU messes around with the timing if the airflow signal is fudged by a piggy back system.

 

However, with the emanage (I don't know about the other piggy backs), there are two methods of altering fuelling; changing the airflow that the ECU sees or simply adding extra pulsewidth to the injector signal. Therefore, if you are only adding extra fuel to your map, then you should be fine just to use the injector map which won't alter the timing.

[Matt Harwood]

The add injector duty feature is only really for upping the fuelling when the stock MAP sensor is out of it's range.

Most piggybacks are used when the new injectors fitted are oversized, hence the reason for altering the airflow signal, which in turn, may alter the timing slightly, depending on how much the airflow signal has been altered.

[Tannhauser]

Originally posted by AeroMatt

However, with the emanage (I don't know about the other piggy backs), there are two methods of altering fuelling; changing the airflow that the ECU sees or simply adding extra pulsewidth to the injector signal. Therefore, if you are only adding extra fuel to your map, then you should be fine just to use the injector map which won't alter the timing.

 

and from Matt:

 

 

 

The add injector duty feature is only really for upping the fuelling when the stock MAP sensor is out of it's range.

 

I would have thought that the 'add injector' could only be used in isolation if your injectors were smaller than stock?

 

I might be mistaken, but I thought that with oversize injectors you would need to use both airflow adjustment AND add injector, even WITHIN the stock sensor range.

 

The adjustment map makes the ecu trims fuel by a % that you tell it to. But it does so for a given throttle position and rpm. However, thiis trimming won't be the same for all boost pressures. The 'add injector' allows you to reduce this trimming for higher boost. So this allows you to map the fuelling quite flexibly.

 

Wez, thanks for that link. It all seems to depend on how the ecu goes about pulling timing when it detects knock.

 

Matt: As my current injectors are twice stock size, or as near as dammit, Is uspect that the timing aslteration might be signifiacant, seeing as huge alterations are being made to the airflow signal.

 

Thanks for replies

 

Cliff

[Matt Harwood]

You are correct in your description, my comment was more of a generalisation.

 

As a rough guess, you'll be making roughly a 50% reduction for the size injectors you have. At the top end of the rev range, it won't be quite as much of a reduction as that because you do want/need the extra fuelling.

Bear in mind the stock ECU will throw in as much timing as it thinks is safe for stock full-boost level, (0.8 bar), I doubt your 'fudged' reduction will be too disimilar to that final figure, and as such, I don't think the timing will be too far out.

 

That's the way I understand it anyway.

[eyefi]

the problem with all this is that no-one really knows what the stock ecu does with timing. yes, it's obvious that it retards timing when it see's knock but how does it retard, does it remove 10 deg from the entire timing map and then start to add timing back in gradually, or does it adjust only the timing in the cell that the map is currently in. it's anyones guess and in the end im sure only the toyota ecu techs really know (maybe mines aswell). i personally dont beleive the notion that it retards alot of timing (which would b safe but bad for power) then nudges it forward again gradually until know is seen again.. this system seems too complicated to me, i would imagine a simpler system would have been implemented.

 

this system was never designed to be relied on, it is a backup or safety measure, what if the knock sensors begin to fail or deteriorate or the wiring gets damaged. how does this system work when above (approx) 4krpm when the knock sensors r pretty redundent and there is alot more engine noise that could b confused with det?

 

at the end of the day i don't think u get an ideal ign map when using big injectors (a big airflow correction) and i think it's risky. having said that standalones also carry certain risks. my ecu safety net for bad fuel is to flash a warning light, it leaves the ignition map as the tuner intended.

 

2p

[Chris Wilson]

Good post from eyefi, if you don't mind me saying so, and the reason I just won't get involved with things like the Emanage.

Once you start changing injector sizes, fitting bigger turbos, and even, ideally, when fitting even mildly timed cams, you need to re address the whole timing and fuelling maps, which means a proper mappable ecu.

 

Don't blow it up!

[Tannhauser]

OK, from the above comments, I'm reluctantly coming to the conclusion that if I'm sticking with the emanage (which I have to ), it might be prudent to swap the injectors for smaller ones.

 

However, I don't want to do this if because of the hassle, expense and need for remapping.

 

Matt, you said that the timing adjustment probably wouldn't be major, but a 50% reduction in airflow sounds pretty major to me. Parts of my airflow map ARE reduced by that much iirc. You may be correct that the final figure is not that different, but it's hard to see how to determine this.

 

Another troubling thing is that this 50% figure is right at the limits of the trimming that the emanage can do. (without using the global reduction thingy). It makes me uncomfortable to be maxing out the system.

 

How about this as an alternative (it's not my idea!): lower the fuel pressure using the regulator and re-map the emanage at that pressure. With lower fuel pressure, ess fuel will be delivered per unit time and therefore the airflow adjustment need not be so drastic . Less fudging of the airflow signal would be required. Can anyone see problems with this? I know it's not ideal, just trying to think of a cheaper way of tackling this issue.

 

Ta

 

Cliff

[Guest Terry S]

No Cliff this unnecessary. It will just require more adjustment with the e-manage map with 850's as the ECU is looking at a different part of the map. The Stock ECU throws timing at the car. Then when it senses det it wil pull up to 7 or 8 degrees of timing, but that is the MAX it can pull AFAIK. You can however pull timing in the cells of your e-manage, making AFAIK, the car perfectly safe.

[Tannhauser]

Originally posted by Terry S

The Stock ECU throws timing at the car. Then when it senses det it wil pull up to 7 or 8 degrees of timing, but that is the MAX it can pull AFAIK. You can however pull timing in the cells of your e-manage, making AFAIK, the car perfectly safe.

 

So there is a maximum amount of timing that the ecu can pull. I didn't know that. Does this mean it may not be able to pull enough timing to prevent det? I'm suggesting that the car might be running so much advance at high boost, because it is working off the 'wrong' part of the map, that it can't correct the discrepancy.

 

 

The problem with trying to pull the timing using the emanage is that there's no way of monitoring what's going on. If you dial in, say, -5 degrees, how do you know if that is sufficient/too much?

 

I'll admit that I might be being paranoid about this, but I'm not sure that I'd recognise any untoward symptoms until it was too late.

 

Is anybody using a Techtom unit to look at timing in their car?

[Guest Terry S]

IF it were me I would pull a global say 3-4 degrees and see how it went, remember the ECU advances then retards dependant on knock. You have the concept correct. you are better of pulling some, then tuning with det cans and adding it back in in various places. dont go too made, to little timing can be detrimental too. If you can get to Matts and some point there are a few bits we'd both like to check. Also, do you know what static fuel pressure the car is running??? There is a set of det cans there too

[Tannhauser]

Originally posted by Terry S

IF it were me I would pull a global say 3-4 degrees and see how it went, remember the ECU advances then retards dependant on knock. You have the concept correct. you are better of pulling some, then tuning with det cans and adding it back in in various places. dont go too made, to little timing can be detrimental too.

 

Would there be any advantage in retarding across the entire range, though? I don't want to lose power/increase EGTs unnecessarily at lower revs/boost.

 

pm'ed about getting car to Matt's.

[Guest Terry S]

only retard intially, then add back in with the det cans on, does that make sense?

[Tannhauser]

Sorry, I didn't read your post properly. Yes, it makes sense.

[Guest Terry S]

No worries Cliff. Will check my PM's in a min mate.