Tuning a/f on BBSC or other Blown NSXs

[len3.8]

Very helpful post. Thanks to all the insight that is posted here.
I may be off topic, I have a 6lb CTSC,Header,exhaust,and if it matters a 6spd trans with short gears, so I assume that it matters that I am getting in the rev range quicker than a normal trans.
My question, Comptech offers the Baschboost
ESM(Smart map) with it's kits now.(or $149) This unit gets rid of the Honda Mechanical check valve system,does it not? How much better off would the car be with this unit instead of the manual system? Would the car have a ideal A/F mixture because of this? Would the tuning of the system still need the type of aftermarket system that Steve and Ken have been discussing throughout this thread. My car too has been running rich. I have changed the O2 sensor that was giving the check engine light. I am hoping that that was causing the car to run rich. I also plan on tracking my car, and at the cost of maintenance for these cars, I do not want to hurt the car. I would rather spend the money to prevent the fire than to put it out. I am completely ignorant when it comes to these cars , read paranoid.
I want to have it running correctly.
Any advice is taken with great appreciation.
Len

[This message has been edited by len3.8 (edited 20 August 2002).]

[This message has been edited by len3.8 (edited 20 August 2002).]

 

[BryanZublin]

Originally posted by sjs:
"OK, that’s fine for the stock setup, but those factors aren’t part of the Split Second box maps, or any of the auxiliary injector controllers I’ve seen. So that still means they should be inadequate, using only manifold pressure and RPM, and all the more so since they magnify intake air temperature variations."

BZ: I think the general idea is that the stock ECU still applies a global correction factor (multiplier) to the final injector duty cycle for intake air temp and barometric pressure.

"That takes me back to the fact that, for example, I can get 5psi boost at 4k RPM under WOT acceleration but I can also get 5psi at 4k RPM but just ¼ throttle. Leaving air temp out for a minute, I’m trying to convince myself that fuel demand for a given RPM and boost is constant regardless of throttle position."

BZ: Yes, it is the same. The reason is that we are measuring boost in the intake manifold (that's the "M" in MAP) which is after the throttle.

"I got it dialed in nicely on a dyno, but out in the real world at part throttle as boost builds it goes decidedly rich. I’ve tinkered with the map trying to resolve it but without an AF meter it’s pretty tough, which is why getting a wide-band is my top priority. I haven’t given up entirely on the possibility that an acceptable solution can be reached with the parts at hand, but something about part throttle boost still worries me."

BZ: Have you performed dyno tuning at less than 100% load? What fuel management system do you have for your turbo?

"How does the volumetric efficiency of a boosted engine compare to the same engine normally aspirated? As I recall, it is typically somewhat different."

BZ: I guess it depends on how you define volumetric efficiency (I'd have to go back and look it up).

"It sounds like you are saying that the BBSC/Split Second setup still utilizes speed density on boost. But since you can’t send the ECU anything above the voltage that equates to atmospheric (zero vacuum zero boost) then it can’t ever calculate the actual airflow on it’s own (on boost). Or am I missing something? So as soon as you get to positive manifold pressure, what are you changing to increase fuel delivery? Must be either duty cycle or pressure. Sorry, I just don’t know anything about how the SS box is supposed to work, so please feel free to enlighten me."

BZ: The BBSC system replaces the stock 240 cc/min injectors with 440 cc/min injectors and retains stock fuel pressure. So, right away, the injector duty cycle needs to be scaled by 0.55 just for the NSX to run like stock from vacuum to atmospheric. What the SS box does is lower the MAP voltage that the NSX ECU receives (by the equivalent of "55% of the real load") so that it appears that the engine needs less fuel, so the injector duty cycle is reduced. With the NSX ECU receiving the max MAP voltage that it would normally see with an NA NSX, it will be injecting 83% more fuel than needed, so theoretically, it should be able to handle at least 11 psi of boost. The SS box performs the MAP voltage conversion over the entire range from idle to "max" boost.

One issue that I have not seen addressed with the SS system is now the ECU is being told that the engine is running at lower loads than it really is. This will impact when the ECU switches from closed loop mode to open loop mode. Closed loop mode maintains stochiometric fuel ratio (around 15:1) and is required for lowest emissions and good fuel economy. Open loop mode is used at high load for best power and safety. The point at which the NSX ECU changes from closed loop mode to open loop will happen *later* with the SS box in place than it would for a stock NA NSX.

Imagine an actual MAP of 1 or 2 psi, but the NSX ECU receiving a MAP voltage that indicates the engine is at part load. If the ECU remains in closed loop mode, it will attempt to maintain 15:1 AFR which is BAD for this boost condition.

Bryan Zublin

Updated 23-Aug-2002: I corrected some numerical errors in my orginal post when I was comparing the injector duty cycle of the stock 240 cc/min injectors to the 440 cc/min injectors.

[This message has been edited by BryanZublin (edited 23 August 2002).]

 

[BryanZublin]

Originally posted by Gerard van Santen: I have the following problem. When I shift up from 3 to 4 and 4 to 5 under WOT, I hear a bang coming out of my exhaust and sometimes big flames come with it.

I think many people would pay to have flames come out the back of their NSX!

The BANG and flame are the result of excess unburned fuel and air in the exhaust system igniting.

Bryan Zublin

 

[BryanZublin]

Originally posted by len3.8:
(snip)My question, Comptech offers the Baschboost ESM(Smart map) with it's kits now.(or $149) This unit gets rid of the Honda Mechanical check valve system,does it not? How much better off would the car be with this unit instead of the manual system? (snip)

Some info here: http://www.nsxprime.com/ubb/Forum1/HTML/003945.html

 

[Gerard van Santen]

Originally posted by BryanZublin:
I think many people would pay to have flames come out the back of their NSX!

The BANG and flame are the result of excess unburned fuel and air in the exhaust system igniting.

Bryan Zublin

Thanks Bryan,

It is pretty exciting for the cars behind me (fantastic at night), but will it give engine problems?

Gerard

 

[tunapie]

My project entails a modified Bell kit with air/water aftercooler and Greddy e-manage piggyback for ingition, fuel (RC 440's) and Vtec control. We are just starting the tuning and would like to know what deg. of timing you are pulling off at Vtec. I have the Tech-edge WB and a EGT that gives me a better picture of what is going on. Also a aftercooler inlet and outlet beta temp to figure out my upper boost limit. If everything works as planned I am shooting for 6.5 to 7 psi but right now 5. If you can, post your ingition and fuel graph. Thanks, Dan

 

[sjs]

Originally posted by BryanZublin:
... One issue that I have not seen addressed with the SS system is now the ECU is being told that the engine is running at lower loads than it really is. This will impact when the ECU switches from closed loop mode to open loop mode... The point at which the NSX ECU changes from closed loop mode to open loop will happen *later* with the SS box in place than it would for a stock NA NSX.
Bryan Zublin

Ah, perhaps that explains an observation made earlier by kpond talking about the BBSC when he said "Most important, IMO, is that 90% of the time you are in closed-loop mode ...".

So, what are the upside and downside possibilities of that? If the ECU is attempting to respond to MAP even under boost, is it up to the task in terms of response time and more importantly the nature of the response? It seems like it would always be fighting to achieve stoichiometric while you’re trying to tune for ~11.5/1

 

[sjs]

A few more comments and responses to Bryan’s most recent (and most informative) post:

I was not able to run at under 100% load because I ran out of time and figured that at least I was “safe”. I would have gone back but still had other problems that needed to be resolved first.

I looked that the SS site and gather don’t see anything like what the BBSC must have. They are all manual “pot” adjustment devices and the BBSC uses loaded “maps”. Is it a custom built unit? It would make sense in terms of “clean” and tamper resistant., but it still seems odd that SS doesn’t appear to have any retail units with loadable maps (yet).

You said: “I think the general idea is that the stock ECU still applies a global correction factor (multiplier) to the final injector duty cycle for intake air temp and barometric pressure.”

That makes sense if in fact it works on a factor basis, which I suppose is a logical assumption, but does anyone know for sure?

With the exception of the open/closed loop issue it sounds like a pretty logical approach, but I get the feeling you are not too crazy about lying to the ECU. Can you elaborate?

 

[BryanZublin]

Originally posted by Gerard van Santen: It is pretty exciting for the cars behind me (fantastic at night), but will it give engine problems?

The only issue that I can think of is the small explosions in the exhaust system might expel some of the packing material in the muffler.

 

[BryanZublin]

Originally posted by sjs:
>perhaps that explains an observation made earlier by kpond talking about the BBSC when
>he said "Most important, IMO, is that 90% of the time you are in closed-loop mode ...".

Yes, those were my exact thoughts.

>So, what are the upside and downside possibilities of that? If the ECU is
>attempting to respond to MAP even under boost, is it up to the task in terms of
>response time and more importantly the nature of the response? It seems like it
>would always be fighting to achieve stoichiometric while you’re trying to tune
>for ~11.5/1

At best, it would result in non-repeatable results during part throttle tests and cause endless grief during the tuning process. At worst, it could cause less than ideal AFR under boost resulting in detonation.

 

[BryanZublin]

Originally posted by sjs:
>I was not able to run at under 100% load because I ran out of time and figured that
>at least I was “safe”. I would have gone back but still had other problems that
>needed to be resolved first.

If you have access to a wideband O2 meter, put it on your NSX and just drive (long hills are best). This will give you tons of data.

>I looked that the SS site and gather don’t see anything like what the BBSC must have.

The programmable box from Split Second is not advertised on their web page. It is my understanding that it is somewhat of a custom part, tailored for each vehicle application.

>With the exception of the open/closed loop issue it sounds like a pretty logical
>approach, but I get the feeling you are not too crazy about lying to the ECU. Can you
>elaborate?

Here is another possible result of trying to fool the ECU:
At idle, the ECU itself will have to apply a large 55% reduction in injector duty cycle in order to operate at the same AFR as stock. This large correction factor may be outside the closed loop range of the ECU. Apparently this has not been a problem, since no one is reporting an error code of "bad O2 sensor", so I don't know how they have solved this issue. Perhaps the ECU does not log an error code if it can't maintain closed loop at idle. Running open loop at idle will increase emissions and could cause problems with the smog check.

The Split Second box is not perfect, but its approach to making a boosted application work is better than many other systems on the market. Short of an entirely new ECU, I believe the best solutions are:

1. Re-chipping the stock ECU like the Hondata system, assuming that the ECU can read boost. Too bad this didn't work out for the BBSC.

or...

2. An external box that connects inline with the fuel injectors to directly modify the injector duty cycle based on RPM, boost, etc. I believe the Emange box from Greddy does this. Timing would also need to be controlled by either intercepting the timing pulses into the ECU or the ignition coil drivers.

[This message has been edited by BryanZublin (edited 22 August 2002).]

 

[kpond]

Sjs,

You said, "It seems like it would always be fighting to achieve stoichiometric while you’re trying to tune for ~11.5/1"

That is exactly correct. In closed loop, the NSX only has the O2 sensors to "hunt-in" on 14.7:1 It can't differentiate 11:1 from 13.5:1. Conceptually, a vehicle manufacturer could have a design that uses two O2 sensors - one for the usual closed-loop running and the other for WOT. Man, that would be cool.

The ss box is not ideal becsues none of us - and I mean NONE of us, know what the algorithms are inside the ECU to deal with these values. Let me give a real example. In my current config, I go almost 1 full point richer right at 5K RPM. I have a good 12:1 or 12.5:1 and abruptly at 5K rpm I go to 11:1. I can assure you that from the SS box, there is no value change to warrant such a transition. So, for example, the ECU is clearly using something else for this data point. An average of previous numbers? A value it saw from closed loop? Yesterday's temperature? (I'm joking.) The reality is that none of know hy this change occurs and, more importantly, how to get rid of it. Various fuel maps tend to move this point around and some even seem to mitigate it somewhat.... but it's indirect trial and error to discover a better table. Grrrrr.

 

[BryanZublin]

Kendall,
Does your engine look like it is running in closed loop mode at idle? (see my previous post)

 

[len3.8]

Originally posted by BryanZublin:
Kendall,
Does your engine look like it is running in closed loop mode at idle? (see my previous post)

This is the reply that I got on a similar question. I think it is of the same line.
I hope Kp doesn't mind.


In “normal” driving, your ECU is increasing the pulse length of the injectors until the O2 says you’re under 14.7 (rich) and then it backs off a little until the O2 says you’re over (lean). It keeps doing this – several times a second and, consequently, it keeps you’re a/f at an ideal 14.7:1.
This is called the “closed loop” mode of the ecu. When you approach wide open throttle (WOT), the ecu jumps out of this mode and reverts to open-loop mode. In open-loop it ignores the O2 sensors and reverts to internally programmed fuel tables (painstakingly arrived at by the factory engineers) which are designed to provide a slightly richer a/f because of the higher load condition on the engine. This a/f is likely around 13:1. The reason it has to revert to this open-loop mode is that the O2 sensors are virtually useless sense they only can help the ecu hunt in on 14.7:1. This is the same reason your gauge is limited.
So, as you are idling and/or driving around at approx. 80% or less throttle – you’re a/f will show lean or at best stochiometric. You will be most lean when decelerating when the fuel injectors are virtually off. You should be rich (well, less than 14.7:1) when you are WOT… and whenever you go to WOT.
It is OK for you to be “lean” under partial throttle – but you should be very close to stochiometric… say no more than 15.2:1. This is normal and is the design. It’s closed-loop mode and the ecu is going to do what it wants to achieve this. If it can’t achieve it (and maintain it), it will turn on your check engine light to tell you. Under full throttle with your CTSC you are in open loop and the ecu just assumes the factory tables it is using to pulse the injectors are accomplishing their job. Fat dumb, and happy. Ideally, you would have a stable 12.0:1 to 12:5:1 during these conditions. However, you won’t really be able to know if you’re at 10:1 (almost too much fuel) or perhaps 13.5:1… which is arguably too lean. In both of these scenarios, you’re a/f will show rich (I think) so just understand the limitations of the gauge. Certainly if you ever see stochiometric or higher when under boost, you should let off right away. That IS the value of your gauge.
Just trying to be of value.
You guys keep talking/typing, I'll keep listening.
NSX at home and it passed emissions the
O2 was bad car was stuck at a point which had
my car running very lean)
Now it shows the AF patterns that KP talks of. With a little more tuning I should be at
optimal for my driving.
Thanks again KP,and all
Len

 

[nsxxtreme]

Has anyone tried the ECU from AEM? Would it work for boosted applications?

 

[kpond]

BZ,

Yes, I believe idle is in closed loop. However, as you are aware, there is a cold-start pre-programmed sequence as well as a warm-start one that is approximately 30 seconds in length. Also, during this time the ECU is working with the IAC valve. Occasionally, (usually a warm start after 30 minutes or so of not running), many of us are experiencing a minor idle-hunt problem. I believe this is due in part with the interaction between a reset of the IAC,MAP v. in, and the pre-programmed warm start sequence.

 

[kpond]

nsxxtreme,

IMHO, the AEM may have the best potential of ANY I have seen to be a viable ECU-replacement for the NSX. By design, it is literally a plug-in using the same connectors, sensor, etc.

The key will be the base programming and if someone can get these nailed down pretty good. If so, this unit may be the DREAM we are looking for.

Imagine an ECU that is a plug and play swap for the stock ECU that is programmatically controlled. Armed with a good a/f logging device, you would in theory tune for your add-ons - using DIRECT control (EFI pulse widths, timing, etc.)

As I understand the AEM owner himself has an NSX and is pushing for finalization of this unit. I am told it is a couple of weeks off.

I have VERY high hopes for this solution - and I sincerely hope they can get all of the base map stuff completed with good results.

 

[sjs]

“If you have access to a wideband O2 meter, put it on your NSX and just drive (long hills are best). This will give you tons of data.”
You probably missed my other posts where I said exactly the same thing and that a wide-band is now my top priority. I intend to purchase one but haven’t settle on which.
“At idle, the ECU itself will have to apply a large 55% reduction in injector duty cycle in order to operate at the same AFR as stock. This large correction factor may be outside the closed loop range of the ECU. Apparently this has not been a problem, since no one is reporting an error code of "bad O2 sensor", so I don't know how they have solved this issue. Perhaps the ECU does not log an error code if it can't maintain closed loop at idle. Running open loop at idle will increase emissions and could cause problems with the smog check”
Somehow that sounds backwards. A lower duty cycle would result from it thinking there was more vacuum at idle, so it would be below the normal closed loop range, not above. Which is also why you said it may stay in closed loop too long.

 

[BryanZublin]

Originally posted by sjs:(snip)Somehow that sounds backwards. A lower duty cycle would result from it thinking there was more vacuum at idle, so it would be below the normal closed loop range, not above. Which is also why you said it may stay in closed loop too long.

Here's my explanation of what I think happens with the SS box: At idle, the SS box can not reduce the MAP voltage to the stock ECU lower than a certain point (ie. can't go less than "full vacuum"). This certain point is the same for the stock MAP sensor, so to the ECU, it sees the same MAP voltage as stock. The ECU will set the injector duty cycle to its nominal starting point and then attempt to close the loop with the O2 sensor. With the 440 cc/min injectors and the stock idle duty cycle, the AFR will be very rich. The ECU will detect this from the O2 sensor reading, and then reduce the injector duty cycle to lean the mixture and bring the AFR closer to stochiometric. It will have to apply a HUGE correction (0.55) to the duty cycle in order to get back to stochiometric. Since this correction factor is so much larger than stock, the ECU might think that there is a problem with the EFI system and log an error code.

In actual practice, the ECU seems to be OK with the larger 440 cc/min injectors at idle based on no complaints from BB SC owners.

 

[sjs]

Ah, very good, thanks. Sorry to beat this to death, but it's quite interesting and I appreciate your indulgence.

I was visualizing an offset downward 55% for the entire range but of course that may not be practical if the voltage at that point is zero or the ECU can’t deal with something lower. In any case, the charts we've seen suggest that isn't a problem or they can tune around it.

Meanwhile, I've looked at the EGOR products mention above (http://www.interstice.com/~garfield/) and they just may have what I'm looking for. The "Pro" model monitors and logs dual O2 sensors and a bunch of other EOM sensors. They also claim to be the only (affordable) ones able to correct for exhaust back pressure and that it can be significant. Anyone know about these guys or their products? Has anyone dealt with the MaxQData products? (http://www.maxqdata.com/MQ100.htm) Their unit has inputs suitable for wide-band plus built in accelerometers, GPS input, OBD-II input, and other inputs for injector duty cycle or the like. Pretty neat stuff if it works.

Bryan, I'm surprised you haven't developed a basic wide-band meter. If I understand correctly, the common 5-wire sensors have a linear output so they should be simple to work with. I've considered just buying one of them and hooking up a good quality damped AVM for now to see how it looks. Any thoughts?