ECUs & Ignition Timing

[Roland Jacques]

Does the ECU change (Retard or Advance) timing independently form RPMs.
In other words does the ECU determine that the fuel we are burning would distribute its power best at a cretin timing and change to that timing?

Will it retard to a limit or will it retard past TDC if that is where the fuel burns best?

[JojoJaro]

Does the ECU change (Retard or Advance) timing independently form RPMs.
In other words does the ECU determine that the fuel we are burning would distribute its power best at a cretin timing and change to that timing?

Will it retard to a limit or will it retard past TDC if that is where the fuel burns best?

Gas engine ECM will adapt timing based on o2 reading and knock sensor.

Diesel engines will operate the same way based on the values in the calibration tables. Diesel engine do not have a mechanism to detect fuel quality. It does not adapt to it because it can't.

[Jaxom]

For most vehicles, the spark tables are preprogrammed into the PCM's memory. Timing varies based on RPM, throttle position, engine load, and O2 feedback voltage. RPM and engine load are the primary factors. There is also an algorythm that retards timing when the knock sensor detects detonation. The timing is limited in both the advance and retard directions by the PCM's programming. There is very little feedback control in the timing routines, other than the knock retard.

[Roland Jacques]

I've read that some tests indacte that a 5 degrees retarding happens when they added HHO. (they did not give amounts of HHO details)

I am assuming that 5 degrees retarding happens due mainly to the anti knock sensor. This raises a questions.

1. IF ideal timing is say 6 degrees before Knoking occures does the ECU sence the knock, then retard to that 6 degrees. Then it waits to sence another Knock. Or does it retard just enough to stop the knock?

The changing HHO to air/fuel ratios & ...must really make that Knock sensor work over time. Thanks for helping me get a good handle on this.

[Jaxom]

Most of the knock routines I've seen will retard timing until the knock signal drops, then slowly add it back till it knocks again, then retard it again and slowly add back in a cycling manner, until it can get back to the "normal" timing without picking up knock.

[Roland Jacques]

Need some more input, Is this logical ????

Ive seen some post of extra ordinary results (1976 1/2 ton Chevy truck getting 74 mpg hwy and others) with HHO boosting. The common thyme seems to be retarded timing. TDC is where they set their timing.

(I’ve read some places that HHO boosting speeds flame by 10 Xs. And since HHO burns 1000 times faster than gasoline. So 10xs quicker burn does not seem out of line.)

If the ideal crankshaft position for power to start being applied to it, is maybe 4 degrees after TDC. And HHO increases speed 10 times we should subtract the advance by that much. I’m now thinking that timing may be better 2 or 3 degrees AFTER TDC.

If Normal timing is
At 650 RPM 6 BTDC should go 3 ATDC

At 2000 RPM 20 BTDC should go to 1 After TDC

At 3000 RPM 30 BTDC should go to TDC

So if I can figure a way to eliminate all timing Advance I might be better off.

What do you guys think?


At 650 RPM 6 BTDC should go 3 ATDC

At 2000 RPM 20 BTDC should go to 1 After TDC

At 3000 RPM 30 BTDC should go to TDC

So if I can figure a way to eliminate all timing Advance I might be better off.
What do you guys think?

[hydrotinkerer]

The 76 chev. truck has no electronics, has a carb., has a mechanical and vacuum advance. The engine package as a whole is a lot easier to tinker with than an OBDII vehicle. To eliminate timing controls on OBDII is to eliminate a detonation problem(if it occurs). Considering grades of gas, HHO output, cyl temp, not all detonation is audible to your ears. The chev. example can ping a certain amount and won't hurt the engine. You let these newer OBDII vehicles ping a little bit and poof its torn up. What kind of vehicle are you trying to adjust?

[Roland Jacques]

Mainly im speaking in general for all ICEs.

But my vehicals are
2001 GMC 3500 Savanna Box van
1999 Ford Expedition
1993 Lincon towncar
1991 Ford Bronco (Four door)

It Was mentioned that ECU/OBD can be Reprogramed by a tuning shop. (chip mod?) Not sure if they can totaly program Timing And advance rate.

[Jaxom]

They can, although it takes time and skill to get it right. I can go into the programming in my IROC and set the timing to 5* ATDC all the way across the board if I so desire. The base map can be changed, and the timing adders for RPM and load, as well as WOT mode and other parameters can all be modified if you have a decent tuning package.

Also, IIRC, for maximum efficiency, peak cylinder pressure should occur at 22.5*ATDC. This is the point where the velocity of the piston and the leverage angle of the crankshaft throw match up best.

[Roland Jacques]

22.5 degrees ATDC sounds right to me.

With that in mind I’m thinking that 22.5 ATDC should be the middle of the burn.

I read that burn duration is cut by 30%, with relatively low HHO quantities.
I don’t no how long the normal burn duration is. (what degree mark ATDC it normaly ends) I'm thinking the 30% reduction in duration should be kept in mind. Making sure the burn does not end to soon, in relationship to 22.5 degrees ATDC optimum power transfer point.

Example; If the burn only last for 30 degrees of rotation, The timing should be adjusted so that 22.5 ATDC falls in the middle of burn (or power part of the burn ).
Starting the burn at 15 degrees before 22.5ATDC and ending 15 degrees after 22.5 ATDC. So the burn should start at 7.5 ATDC in this example. Does this make sense?


Jaxom, have you played with different timings setting on your IROC with HHO?

[Chris65]

I know this isn't a lot of help. but if you take a look at www.msdignition.com you will see that they have timing retard modules for some OBDII cars. The drawback is that you need to use their ignition box for these modules.

The reason I point this out is that if they are doing this type of thing on OBDII cars, then there should be some way to add a manual controller similar to the MAF/MAP enhancers.

My electronics skills are near nil, so I won't be of much help, but maybe someone can figure out a way to do this.

[Jaxom]

My IROC is not equipped with HHO as of yet. It will likely be the last of my vehicles to get the system, as it is primarily a "toy" and doesn't get many miles put on it anyway. I have done quite a bit of playing with the settings running straight gas though....I've had to make numerous changes to the programming as I've changed engine and drivetrain configurations. The car is not quite stock.

One of the problems with figuring out the timing is that the burn duration is not a set value. It changes with engine RPM and load conditions, and is based more on actual time than on degrees of crankshaft rotation. The faster the engine is turning, the more degrees of rotation it goes through while the fuel is burning.....this is why timing has to be more advanced at higher RPMs. Peak pressure also doesn't always occur midway through the burn....it can be earlier or later depending on how rich/lean the fuel mixture is. So you see, timing can get pretty complex.....engine dynamics is a very in-depth field and my knowledge of the nuances is only fair.

[hydrotinkerer]

22.5 degrees ATDC sounds right to me.

With that in mind I’m thinking that 22.5 ATDC should be the middle of the burn.

I read that burn duration is cut by 30%, with relatively low HHO quantities.
I don’t no how long the normal burn duration is. (what degree mark ATDC it normaly ends) I'm thinking the 30% reduction in duration should be kept in mind. Making sure the burn does not end to soon, in relationship to 22.5 degrees ATDC optimum power transfer point.

Example; If the burn only last for 30 degrees of rotation, The timing should be adjusted so that 22.5 ATDC falls in the middle of burn (or power part of the burn ).
Starting the burn at 15 degrees before 22.5ATDC and ending 15 degrees after 22.5 ATDC. So the burn should start at 7.5 ATDC in this example. Does this make sense?


Jaxom, have you played with different timings setting on your IROC with HHO?


22.5* atc is way to far advanced. Take your 91 bronco and advance the base timing and see what I mean. You are to far fast the optimum power stroke. Hydrogen has an octane rating of 130, it will resist detonation but not much better than some racing fuels. When I had my drag racing car my max timing @6200rpm's was only 30* atc and was rich enough to prevent detonation on pump gas. Even with a HHO cell at 1lpm about 5* atc base for a curve of 20* advanced.

[Roland Jacques]

Jaxom, you absolutly right. The duration is more time dependent. Humm that does make it even more complex. i going to need some time to digest this. Thanks

[Jaxom]

Tinkerer I think you're confused. ATDC is AFTER top dead center. When people talk about adjusting timing, it's normally referred to in degrees BEFORE top dead center. There is a huge difference. A base timing of 22*BTDC would indeed be far too advanced for most engines, but we're talking about retarding the timing, not advancing it.

[Roland Jacques]

hydrotinkerer

22.5 ATDC was talking about the point at which piston combustion power transfer point at which the most power can be transfered to the crankshaft. That is 22.5 degrees AFTER TDC.

I think you mixed ATDC and BTDC

Anyway im not sure that you can look at HHO boosting the same way you look at 130 octain Race fuel. i think it may be burning faster than RF (but i'm not sure) The 74 MPG 1976 C-10 is adding 7-9 lpm of HHO so i think it burning fuel faster than RF.

[hydrotinkerer]

Tinkerer I think you're confused. ATDC is AFTER top dead center. When people talk about adjusting timing, it's normally referred to in degrees BEFORE top dead center. There is a huge difference. A base timing of 22*BTDC would indeed be far too advanced for most engines, but we're talking about retarding the timing, not advancing it.


Your right thats what I get trying to do two things at once.(read post, watch hurricane) I live about 180 miles north of Houston. Sorry I misread post.