Can you force the PCM in to open loop at idle?

[Eddie-98GTP]

As I posted in another thread, closed loop can be a problem with a bigger cam...

With the bigger cam, it's going to idle rich especially when in closed loop. The O2 sensor monitors oxygen level in the exhaust (duh!). With a bigger can (big enough for a rough idle), you will have cylinders that do not fire at lower RPM (Idle). This pushes raw fuel (HC's) and Oxygen (since we didn't burn the fuel, we still have almost 14.7 parts of O2) past the O2 sensor. The biggest problem here is the PCM. The O2 sensor will tell the PCM the engine is running lean (not enough fuel to burn all of the O2), and the PCM adds MORE fuel.

If we could etell the PCM to go into open lood at idle, we could adjust the fueling without having the PCM compensate for what it thinks is a lean condition.

Thanks for any advise on this.

[Russ K]

Try this set up, the PE enable delay is zero, the 0-800 rpm PE enable TPS is at 0%. Then the Base AFR is 11.5 which is good at WOT on a SC 3800, but would be very rich at idle. To lean out the lower TPS AFR, I set the Add vs. TPS table to 3.2 up to 40% TPS. Note that this is an adder, so 3.2+11.5=14.7 AFR at the lower TPS. You could change the Add vs. TPS to be greater than 3.2 to lean the commanded AFR at idle some more. Also I always zero the Add vs. Rpm table on the V6 cars. Then I use the Maf AFR Error% histogram to adjust the Maf table to get the actual AFR to match the commanded AFR.

Russ Kemp

[JerryH]

Also I always zero the Add vs. Rpm table on the V6 cars. Then I use the Maf AFR Error% histogram to adjust the Maf table to get the actual AFR to match the commanded AFR.

Russ, very interesting way to do it!

The one thing that I would be leary of is that if things are so far off that the MAF table starts to get more than a certain percentage variance over stock settings, I can vouch that there is some hidden table in there that checks for excessive MAF table variances, and if its past a certain amount (this amount is different on various years of 3800 bins), that you will start to get some really strange things happening. This has a greater chance of happening if you are using an aftermarket MAF like the LQ4 where the differences over stock are already significantly greater over stock from a basline position before you've had a chance to dial it in.

By strange, I mean things like the TCC not consistantly locking up while cruising, inconsistant ability of the fuel trims to lock in at 0 in PE and a couple of other interesting happenings.

Edit, changed my train of thought... question for you: Since we know that when the PCM is in PE mode, the fuel trims are ignored... how is the engine going to adjust for temperature varaiances? This may work down south were temps vary 5 degrees from day to night... but that would not work in Canada, where in the summer we can get 90 degree days and 55 degree nights.

When enabling PE mode form 0% TPS, you are in effect talking about a race car only, I hope? On the street, this would be a car that drives well only under 1 very narrow set of humidity/temp conditions. Outside that range, since it now has NO way to compensate for it... it would run poorly, IMHO.

Please correct me if I am off base on this one.

[Russ K]

Jerry,

All I'm doing is changing the commanded AFR at idle & low TPS settings. The Maf table shouldn't be adjusted any more than a normal tune. There is an open loop table, just not available in the editor at this time. On the V8 vehicles & the V6 trucks, the richer of the open loop table or PE table is used. So at the colder temps, the open loop table will be adding to the AFR during cold engine operation. This is the only way to idle in open loop.

You can read about my open loop maf tuning at the top of the V6 forum.

Russ Kemp

[z34phoenix]

if your runing rich cause of the cam at low rpm... why not add timing advance! that will give the fuel more time to burn.

some times i have learned i can even out my AF by adding and removing timing to get the specific RPM AF dialed in cause most AF tables jump 400 rpm or so when spark timing can be 200 and then do fine adjustments with the MAF table too

[Eddie-98GTP]

Russ, this is very insightful. I have not thought about forcing PE at idle, I'll have to try this, thank you!

There have been different trains of thoughts about how PE and open loop corralate. Are the open loop tables you are referring to used while in PE?

Jerry, I believe what he is suggesting is to force PE at 0 - 800 RPM, leaving the rest of the enable points the same. This will force the PCM in to open loop (PE) at idle, allowing you to use the Add vs. TPS table to modify the AFR.

z34phoenix - The problem with idling rich is due to the overlap in the cam causing the mixture from the cylinders that did not fire to pass by the O2 sensor. The O2 has no way of knowing how much fuel is in the exhaust, it just knows there is a lot of O2. Raising timing may help smooth out the idle a little (or make it rougher depening on the car and how much you have raised timing), but you are still going to get the misfire due to the cam. In closed loop, the PCM tries to compensate for the perceived lean condition by adding fuel. This only makes the engine run richer causing poorer fuel economy (in stop and go traffic like I sit in EVERY FREAKING DAY!!!), carbon problems, and you oil gets dirty a lot sooner.

[JerryH]

if your runing rich cause of the cam at low rpm... why not add timing advance! that will give the fuel more time to burn.

1-2 degrees may help, but if you go above +3 degrees on a 3800 (at least the 2 that I tried it on), this increases idle roughness very noticeably.


Russ, thanks for the input... more reading for me it is.

[JerryH]

Jerry, I believe what he is suggesting is to force PE at 0 - 800 RPM, leaving the rest of the enable points the same. This will force the PCM in to open loop (PE) at idle, using the Add vs. TPS table to modify the AFR at idle only.

That then the obvious part that I overlooked. Makes a LOT more sense to me. Darned interesting none the less.

Not having the HPT yet is hindering me... lol. I usually open the program and "follow through" on a process. Its coming, though!

[Russ K]

if your runing rich cause of the cam at low rpm... why not add timing advance! that will give the fuel more time to burn.

some times i have learned i can even out my AF by adding and removing timing to get the specific RPM AF dialed in cause most AF tables jump 400 rpm or so when spark timing can be 200 and then do fine adjustments with the MAF table too

The V6 cars don't have the Base Idle spark tables in the editor like the V8's & V6 trucks.
The V6 car spark tables are used when the throttle is not closed.

Russ Kemp

[Russ K]

There have been different trains of thoughts about how PE and open loop corralate. Are the open loop tables you are referring to used while in PE?

PE is open loop, and the richer of the PE or open loop table is then in use. I heard that the open loop tables will be added
to the V6 cars on the next release.

Russ Kemp

[Eddie-98GTP]

Very good!

[JerryH]

Looking forward to testing that out.

My car (Eddie's too), has the XP cam. Not the most aggressive (I have a local friend that has or is just about to order the HPT, runs around with the XPZ cam. Darn thing feels smoother than my XP, but then again he is running a set of Stage IV heads), but still does exactly what we were talking about.

[bilemke]

PE is not the same as normal open loop.. Call it an open loop mode if you will, but is using PE tables and not open loop.


Attachment 9804

For those of you who have or are about to get a HP Tuners, use the above on our cars to keep it in open loop but not be in PE.

A side note, while it is not in HP Tuners for us V6 guys yet, the open loop tables are available in PowrTuner.

It is kind of funny that way, each tuner has half of what is is need to tune open loop, but not the other half.

[Eddie-98GTP]

Posted in another forum...

Here is what I plan on doing to start with...

PE AFR vs Time - Zero out all columns in the 0 - 800 RPM range

PE Enable by TP% - Setting this to 0 for the 0 - 800 RPM cells

Base PE A/F is currently set to 11.44629 from 50* to 120*

PE A/F vs TPS - Setting 0% TP to 3.557617 - trying for 15.0:1 to start with. May lower this a little and adjust with Open Loop AF by RPM vs Air Mass once I see how this works.

I'm going to leave the open loop base AF alone for now, to see if this table affects the AFR when idling in PE. Currently the table is set to 12.4 from 50* to 110*

I've never played with the Open Loop AF by RPM vs Air Mass table, so I'm starting out simple (with things I have played with) to see if it makes a positive difference.

I'll let you guys know how it turns out! It may be Monday before I get some good driving in (we're usually in the wife's Jeep on the weekends).

[bilemke]

Eddie, just a note, by doing the above, the best you will get is tuning the lowest part of the PE RPM vs Time at the longest time period.. You cant forget, PE RPM vs Time, after x amount of seconds, you will just be using the last time frame of the table at what ever RPM you are at..

This not an alternative way to Open Loop.

Also, to note, HP Tuners currently can scan a status bit (something like "PE Status") that shows when PE is active.. This is not active when in open loop the way I described above.

In the end, if you want to run your car without fuel trims and dont mind that you will hit the end of the PE RPM vs Time table a few seconds after you turn the car on, yeah, you could run a non-stoich afr.

When you are actually goes in to open loop, these are not the tables it will be using. BTW, I know from experience with the PowrTuner and the goofy partial writes that through countless DTCs each time i write. I knew when I had forgotten to resent the DTCs as I would start driving and never get out of the Startup AFR tables. Well, actually, I did. It was staying in open loop.

[Bill@HPTuners]

PE is not the same as normal open loop.. Call it an open loop mode if you will, but is using PE tables and not open loop.

Just remember that open loop means your getting no feedback from your o2's.

Whether talking about cold start or wot fueling its all open loop and wot would be pe ALSO so they do go hand in hand once cold startup is done and pe can ALSO go hand in hand with cold startup if you set it up as such.

Also look at it like this you can switch back & forth from your PE tables & OL tables at any point that your in PE mode ie lets say at 5000 rpms & 100kpa your pe commands 12.9:1 and your ol table commands 13.0:1 the pcm will choose the pe table, if at 5200 rpms & at 100kpa your pe commands 13.1:1 and your ol table commands 13.0:1 the pcm will choose the ol table. In the end they work side by side no matter how you cut it.

[bilemke]

Bill

Yes, "open loop" by definition would be when the PCM is not using the PCM or not getting feedback form the O2 sensor. Just saying, from what I have heard from Eddie in the past, he is aiming for the actual continuous Open Loop tables in our PCMs. To activate them, so far, I have only been able do this by using the real time controls and set Close Loop to off.

Otherwise, the startup values are of course used for a few seconds each time you start the car. And yes, PE (as described above) open loop of a sort, but it is not using the open loop afr tables. For that matter, I have never seen my car go and/or stay in open loop to this day. I only was able to force it there with the real time controls.

Before, with the PowrTuner, i swore noticed my car go to open loop once (it was before PE Enable) while driving. Shortly after getting my HP Tuner, I noticed (by scanning several status bits) that it was not open loop tables or PE causing a odd commanded AFR. It was COT.

Given the odd chance that Open Loop would actually come in to play, I havent bothered to comment on them here or ask for the tables in the request sub-forum. Would be interesting at the track though, if you had your HP Tuner in the car and forced closed loop off.

[Chris@HPTuners]

here's the detail:

By default you cannot make the PCM go into openloop at idle regardless of having the openloop table. Once the openloop temperature and the O2's are working the PCM will go into closed loop. It's the same for the V8's.

You can trick the PCM to go into openloop at idle by enbaling PE mode, some tuners do the same on the V8's, you just need to make sure that your PE table and the higher RPM area's of the TPS enable are tuned so that when you really need PE you get it and not some tricked idle AFR, thankfully the RPM range generally allows for this.

[bilemke]

Yes, the startup tables will prevent it from staying in open loop. Once it warms up it is done.

I am just saying, using PE as a trick is not really a good option for tuning the actual open loop tables.. You will be in open loop (PE) if you set PE Enable low enough, but you will be tuning PE tables instead of open loop tables. That is all i am saying.

[Chris@HPTuners]

yeah i was just answering the original question, using PE is the only way i can see in the code to force openloop at idle, but still retain closed loop during part throttle.

There is no way to use the openloop tables at idle unless you disable closed loop.

Chris...