Prediction Coefficients

[rao]

Yes, what James is saying both SD and MAF are tuned according and operate properly independently. But when both are being utilized and its running the normal blended dynamic airflow mode, it goes stupid sometimes. The most common issues I've experienced is what James was pointing out about on boosted cars. Below the dynamic threshold before hi speed mode gets forced, the stock prediction coefficients are problematic. Most commonly I have seen it basically cut the air flow in half in boost at low rpm, which causes the car to go way lean and won't run. The quick solution is to lower the hi speed force rpm low enough to avoid the problem.

I made some posts about this stuff back in like 09-10, but no one wanted to acknowledge the problem or discuss it back then. I was doing lost of maggies in those days when the 5th gens first cam out. With boost at low rpm and trying to keep the SD functional with a high rpm disable in the 2-3k range it just wouldn't work. I tried playing with the numbers with little success. Tried numbers from a ls9 tune which obviously didn't exhibit the problem. Nothing worked for me short of setting the disable rpm to like 1K. I assumed it was a os bug or like always due to tables we couldn't see or get too. I later came up with a set a coefficients that I use, but still occasionally have issues and have to drop the disable rpm lower than I'd like.

Would love to see this cracked and us know what the real math behind it is. Many times Id like for the SD to play a heavier weighting in the blending or would like to filter the maf signal more heavily due to a dirty signal.

I had this exact problem with my car.

MAF only fueling was solid, VVE only fueling was solid, blended the afrs would go over 20:1 drove my crazy for quite a while.

Zeroing out the predictive coefficients solved the problem.

Thanks to everyone who posted in this thread.

[alexl226]

I zero'd them out. Still have the lean spike after entering boost...

what bluecat said about lowering the disable rpm has my interest peaked. What's the downfall of this?

[rao]

Wherever you set the disable RPM, above that point the PCM will switch to MAF only, so you are "losing" blended calculations.

[itsdaveonline]

So what if your running MAF only or VE only with no blended mode. Do the prediction co-effecients do anything in either of those scenarios? Or do these only come into play in the blended mode. Trying to understand this more, so forgive my stupid question haha

[rao]

I'm no expert but I believe that the prediction coefficients are only used in "blended" operation to move between the MAF's fueling and VVE fueling when conditions dictate that the PCM has to go from MAF to VVE. I don't think they would come into play if you are using MAF only or VVE only, which is why in my case everything worked fine until I put it in blended mode..

[ttz06vette]

Don't forget transient fueling...

[schpenxel]

Transient fueling can suck my you know what

[rao]

This does not appear to have an impact on transient fueling.

[ttz06vette]

LOL...feel the same way. Unfortunately as is usually the case, she is agnostic to oral

[mowton]

Just finished up a 2010 Camaro that the customer installed a Kenne Bell Liquid Cooled Supercharger. Had a lot of issues, not related to this thread, got them finally worked out, closed the loop (Dynamic Hi RPM = 4000) and on the first pull, saw a huge (2 sec) lean (1.20-1.30) lean spike at PE enable....updated the 105 -200 kPa VE hoping that would help...nope! Finally zeroed the VE Prediction Coefficients and problem solved...

So here is my question which is based on the my understanding that if the Prediction coefficients are zeroed than you can't predict the future.... but what about the present? The whole concept of the blended mode is to be able to compensate for the shortcomings of the MAF airflow values during transient states (hard acceleration/deceleration). Do we now lose that feature? And If so, then just leaving it in MAF only (400 rpm) wouldn't this do the same thing?

Ed M

[rao]

That's a great question.

I know on my car the fueling was different between MAF only and "blended" with the prediction coefficients zeroed out so the PCM is making adjustments, just not using the prediction coefficients.

Easy enough to verify.

[sssnake]

I have found that high numbers make the problems I see in boost less pronounced but not necessarily cured. But also seem to have an effect on how the MAF is filtered, even after the high rpm disable.

I do believe Bluecat is right. The filtering is affected. I zeroed prediction coefficients to see what happened and all air estimation and fuel trims got MUCH more reactive. Fuel trim swings with transients were worse (for me) but perceived throttle response was better. Now I am not convinced the transients will be worse for everyone but I do believe the MAF and VE data is MUCH more dynamic (less filtering). In my case too dynamic. I am now working a compromise set of prediction coefficient based upon what Bluecat mentioned. I thought I had things cured but then I found this in a couple of places.

2015-12-21.png

I know it is hard to see from this pic (I was screwing around with my scanner setup) but the cyl air value just leveled out initially on tip in to boost then KNOCK, KNOCK. You could argue that the PE should kick in earlier but there wasn't a ton of boost in this situation and these low boost scenarios seem to cause a lot of the problems that I am seeing. Presumably PE is masking issues where the boost is more aggressive. In the scan you can see the MAF and the SD/VE model both increased their airflows substantially but the cyl air from the ECM remained constant. Not good. Removing the prediction coefficients seemed to rid me of this issue but that caused other issues. So I am trying to find a happy compromise with the coefficients. Right now I am trying things with .6, .4, 0 for base, current, and old with the corrected coefficients set as Bluecat mentioned. So far pretty good. I will say that any inclusion of "old" seems to cause a noticeable lag in response both tipping in and getting off of the throttle.

[mowton]

I have just seen a great example of the effects of this anomaly as I normally don't do a WOT pull on the dyno in closed loop...Open loop you will not see this phenomenon and I guess the road tests after the tuning session when we have returned to closed loop blended operation never identified this problem, at lease not to the severity of this example on a 2010 Camaro with a KB SC'r installed. I wish I had more time to play with it to try different coefficients but we have had so many other problems with this setup and have worn out our reasons not to deliver :-)

The top scan is before zeroing the predictive coefficients and the bottom is after. You can really see the effects of the predictive algorithm on a very large transition and the fact it hangs around for almost 2 seconds. The MAF generated Cylinder Airmass is 1.2 g/cyl where as the Dynamic cylinder air mass is only .7....The other interesting finding is it seems to correct itself in one motion....not a linear correction back to reality????

[jsllc]

It appears HPT does not give a complete picture in this area. Below a is a pic from EFI Live. It has several more. As well as some others under a filter category.

[rao]

I thought I was able to find them all in HP Tuners but it was a while back. It is definitely easier to zero them out using brand X.

[sssnake]

In an effort to put all of the information concerning prediction coefficients in one place on this forum I want to put this out there.

In review of the Brand "E" software I found the following data values that are not normally present in HP Tuners:

Estimated MAP Maximum
Estimated MAP Minimum
Intake Manifold Volume
MAP Estimated 1 Error
MAP Estimated 2 Error
Zone RPM Hysteresis
Zone RPM Hysteresis, AFM Mode
Steady State RPM Threshold
Steady State RPM Threshold, AFM Mode
Steady State MAP Threshold
Steady State MAP Threshold, AFM Mode

It appears that Manifold Volume is available upon request on most tune files. However, the other parameters are not. The parameter that appears to be of most concern is the Estimated MAP Maximum. In my logs where the dynamic airflow and/or cylinder air values flat spot they all do so within about 7% of the VVE airflow for a MAP of 105 KPA. This is the GM default for Estimated MAP Maximum on non FI engines. I have posted about this in another thread http://www.hptuners.com/forum/showth...ine-Parameters and have a request out to the support folks to include access to the Estimate MAP Maximum parameter.

I am not absolutely certain that this will address all of our issues with prediction coefficients but I do feel this will be a LARGE step in the right direction.

BTW - I did examine in detail the gain values in the prediction coefficient tables and there is a fairly logical pattern to these (at least on the tunes I have examined). Once we get the Estimated MAP Maximum access I will post a fairly long write up on my findings.

[NorCal06GOAT]

I think I just popped a brain vessel...GOOD STUFF fellas...

[jsllc]

In an effort to put all of the information concerning prediction coefficients in one place on this forum I want to put this out there.

In review of the Brand "E" software I found the following data values that are not normally present in HP Tuners:

Estimated MAP Maximum
Estimated MAP Minimum
Intake Manifold Volume
MAP Estimated 1 Error
MAP Estimated 2 Error
Zone RPM Hysteresis
Zone RPM Hysteresis, AFM Mode
Steady State RPM Threshold
Steady State RPM Threshold, AFM Mode
Steady State MAP Threshold
Steady State MAP Threshold, AFM Mode

It appears that Manifold Volume is available upon request on most tune files. However, the other parameters are not. The parameter that appears to be of most concern is the Estimated MAP Maximum. In my logs where the dynamic airflow and/or cylinder air values flat spot they all do so within about 7% of the VVE airflow for a MAP of 105 KPA. This is the GM default for Estimated MAP Maximum on non FI engines. I have posted about this in another thread http://www.hptuners.com/forum/showth...ine-Parameters and have a request out to the support folks to include access to the Estimate MAP Maximum parameter.

I am not absolutely certain that this will address all of our issues with prediction coefficients but I do feel this will be a LARGE step in the right direction.

BTW - I did examine in detail the gain values in the prediction coefficient tables and there is a fairly logical pattern to these (at least on the tunes I have examined). Once we get the Estimated MAP Maximum access I will post a fairly long write up on my findings.

These have been added to HPT:

[ECM] 34971 - MAP Estimated Max: Estimated maximum MAP value.
[ECM] 34972 - MAP Estimated Min: Estimated minimum MAP value.
[ECM] 12003 - Intake Manifold Volume: The volume of the intake manifold. Used as an input into the transient fueling model.

You have to request them though. Info you need is above and tell them they can find them on a 2012 ZL1 E67

[ttz06vette]

Who has been successful increasing intake manifold volume to fix lean tip in on the E38's and if so what % did you multiply the tables by? Thinking about updating to newest version of HP Tuners if this in fact works although I will need to do to update my PID's and such in the scanner. Currently on 2.4

[cc-rider]

Who has been successful increasing intake manifold volume to fix lean tip in on the E38's and if so what % did you multiply the tables by? Thinking about updating to newest version of HP Tuners if this in fact works although I will need to do to update my PID's and such in the scanner. Currently on 2.4

I was successful. I have a PD blower and I put the manifold volume to what the stock ZL1 tune says. It worked. I've got a nice transient shot now that I can see on my wideband.