I'm going to be dyno tuning my ZR-1 to get the calibration right after some airflow mods, but I am concerned about what happens when you burn a new chip and redyno without giving the ECM time to 're-learn' the BLMs.

I'm worried that the ECM will lock down the BLM's at the wrong values when it goes open loop and cause my WOT fuelling adjustments to be way off.

Am I right to be concerned about this?

 

That shouldn't happen as long as your tuner does a good job. If he leaves everything super lean except for a nicely tuned wide open than you will have high blm's at wide open and it will dump extra fuel.

If hes got the part remotely close it shouldn't effect wide open blm's.

 

Alvin,

Thanks for the input.

Just to give a little more background, I've done a port and polish job on my intake and heads, so I assume that the stock %VE figures (LT5 is speed-density) in the tables will now be on the low side (I have not done any scanning and have not changed any of the %VE figures). So with more air going in and stock VE values, the engine I figure will be tending to run leaner, but the ECM will compensate in closed loop by increasing the long term fuel trim (BLMs). That's my understanding of how it works.

My concern is, what happens if you don't give the ECM time to do the block learn and then try to calibrate for WOT? What will the BLMs lock down to in PE mode (128 or some other figure?) Does it depend on whether the engine is running lean or rich just prior to going open loop?

I figure that if you calibrate the WOT fuel curve before the ECM has had a chance to block learn, you could be lean or rich at WOT depending on what happens to the BLM figures subsequently when the ECM has learned.

Maybe I'm barking up the wrong tree, I suppose if the short term fuel trim always goes to 128 in PE mode, then tuning for the correct AFR with a wideband will always ensure the correct fuel curve at WOT?

Hope you can shed a little more light on this, I'm having to do the tuning myself and wanted to be clear about this before progressing.

 

For me when I tune ZR1's and for any chipped ECM, I use a emulator to tune the VE tables on my chassis dyno that is set up to run in vehicle simulation mode. By this I mean that my Mustang Dyno is actually simulating real road load on the engine as if it was cruising down the highway. I can even add load by simulating a grade. Or I can tune using a preset vehicle speed setpoint. If your tuner is using a DynoJet dyno, attempting to tune part throttle on a DynoJet is going to be hard to do. Once the drums are up to speed, there is virtually no load on the engine.

Using the emulator to run the engine I can make changes in the VE maps and watch the fuel trims via my TECH2 scan tool. You don't have to use a TECH2, you can use any good scan tool that can display at reasonable update rates. Thus you can make changes to the maps, then watch the reaction from the fuel trims. When I am tuning in this manner, I can watch the fuel trims change. It does not take long for the ECM to learn. This fuel trim strategy can also be termed as a predictor, as it is more of a predicitive control strategy, or adaptive strategy. The ECM uses the O2 sensor input(s) and with its internal alogorithms it uses the fuel trims as a predictor for adding or subtracting fuel.

I also tune so that the Long term trims will correct slightly by taking fuel out. In other words I intentionally tune it so that the VE maps are slightly rich. I look for trims around 125 to 126. After I feel comfortable with the trims I then tune for WOT. I also use a wide band that is installed directly in the exhaust stream with a weld in bung.

 

Thanks for the input tj. I'm going to be checking the fuel trims with Datamaster by driving on the road and adjusting the %VE values to get the BLMs right. This is the right way to do it as you described.

But to get back to my point about what happens to the BLMs when it goes into PE mode and the BLMs are not perfect. Do you know what the fuelling strategy is when it goes into PE, i.e. what does the ECM lock the BLMs down to in PE mode and how is it affected by the engine being either lean or rich before it goes into PE?

I hope I don't labour the point, but some tuners don't seem to scan and adjust the %VE tables and only modify the 'PE % CHANGE TO FUEL vs RPM' table using a wideband to get the WOT fuelling right. Is there any significant risk with this approach?

 

I think both of us answered your question, you are just looking a bit too far into it. No problem in that. As long as the tuner got the part throttle tuning right the wide open should stay at 128. The computer hardly EVER change wide open fueling at wide open.. its more of a "well, everything has been lean up to that point so far so wide open must also be lean" You can still have a car that runs 128 at wideopen but say .700mv (which is very lean) and the car will do nothing about it.

As long as your tuner tunes the part throttle. You should be fine. Part throttle tuning definately requires VE table changes.

 

Calibration strategy in a LT5 is not like that of a LT1/LS1. There are 4 VE tables, 2 for port closed(secondarys closed) and 2 for port open(secondaries open). When you go WOT the calculated PW is multiplied by a Secondary inj pulse width multiplier constant (.512 in a stock bin) and applied to both injectors.

If you are going to try and do this yourself I would recomend you invest some money in a FJO wideband and data logger(It can be put in place of your stock O2 and routed to the FJO which can turn it into a NB signal and routed back to your ecm). You can use datamaster et al but you will spend a lot of time and money chasing your tail without a good WB02 AFR to work with. The thing with the FJO is that you can use a PDA to log rpm, map, and afr during normal driving to get the port closed figures right. Once you get this right your WOT tuning will be greatly simplified with the FJO. This will greatly reduce dyno time.

Tyler

 

OK so it sounds like to avoid lean or rich conditions at WOT you need to get the part throttle tuning correct, which I can understand and is the way I would do it, but I'm still puzzled as to why some people bypass (i.e. ignore) the part throttle tuning and just do the WOT tuning by adjusting the PE %FUEL vs RPM table to get a good AFR with the wideband at WOT.

In a sense, why do you care if the part-throttle tuning is out, as the closed loop will compensate for this and if you've checked the fuelling at WOT with the wideband, you're good to go right?

 

Fuel control for all the FI GM engines is a PID loop that takes its error correction
from the O2 sensor feedback.

There is a brief intro to PID here:
http://www.expertune.com/tutor.html

There is some technical discussion of O2 feedback design going on here, see p.2:
http://www.thirdgen.org/techbb2/show...hreadid=263280

The stock GM code is designed to be an inherently unstable (i.e. oscillating) loop.
That is, the proportional gains are setup in such as way to force the fuel rate to
crosscount (O2 switch rich-lean). The system requires this instability in order to
function properly.

As such, the fuel control program is designed around having a fairly accurate VE
look-up table as its starting point.


If you take away the accuracy of the VE data set, you are forcing the computer to
operate in a region for which it is not programmed. The consequences of this may
or may not be dire, depending entirely on blind fortune's careless aim. If one feels
'lucky', trusting to chance to make things work is one possible tuning philosophy.

On the other hand, if one is trying to get the best possible performance from the
engine, a good deal of trial-and-error MEASURING is the way to realize ACTUAL
gains from the hardware, at ALL engine speeds.



BTW, fuel tuning is in fact the easy part of engine/ECM modification. Adjusting the
spark tables for new conditions is where one derives improvements to drivability,
fuel usage, and power.


The precise details of your ECM program can only be found in a commented hack of
the GM program - and I am not aware of such a hack for the LT5 code. Here is some
background reading for a similar VE design used in L98 engines of the same era - your
program will be analogous, but NOT exactly the same:


Inj PW calc
http://forums.corvetteforum.com/show...m_id=82&arch=1

How 3D Tables Work
http://forums.corvetteforum.com/show...m_id=82&arch=1


As a final point, there is some info here on dyno operations that might be of interest
to you - look in the technical articles referenced toward the bottom of the home page:
http://www.pumaracing.co.uk/mainmenu.htm

Have fun.

 

Fuel control for all the FI GM engines is a PID loop that takes its error correction
from the O2 sensor feedback.

There is a brief intro to PID here:
http://www.expertune.com/tutor.html

There is some technical discussion of O2 feedback design going on here, see p.2:
http://www.thirdgen.org/techbb2/show...hreadid=263280

The stock GM code is designed to be an inherently unstable (i.e. oscillating) loop.
That is, the proportional gains are setup in such a way to force the fuel rate to
crosscount (O2 switch rich-lean). The system requires this instability in order to
function properly.

As such, the fuel control program is designed around having a fairly accurate VE
look-up table as its starting point.


If you take away the accuracy of the VE data set, you are forcing the computer to
operate in a region for which it is not programmed. The consequences of this may
or may not be dire, depending entirely on blind fortune's careless aim. If one feels
'lucky', trusting to chance to make things work is one possible tuning philosophy.

On the other hand, if one is trying to get the best possible performance from the
engine, a good deal of trial-and-error MEASURING is the way to realize ACTUAL
gains from the hardware, at ALL engine speeds.



BTW, fuel tuning is in fact the easy part of engine/ECM modification. Adjusting the
spark tables for new conditions is where one derives improvements to drivability,
fuel usage, and power.


The precise details of your ECM program can only be found in a commented hack of
the GM program - and I am not aware of such a hack for the LT5 code. Here is some
background reading for a similar VE design used in L98 engines of the same era - your
program will be analogous, but NOT exactly the same:


Inj PW calc
http://forums.corvetteforum.com/show...m_id=82&arch=1

How 3D Tables Work
http://forums.corvetteforum.com/show...m_id=82&arch=1


As a final point, there is some info here on dyno operations that might be of interest
to you - look in the technical articles referenced toward the bottom of the home page:
http://www.pumaracing.co.uk/mainmenu.htm

Have fun.

 

This is great information everyone, thanks for your input.

 

Tod Pepmeter has done an excellent TunerPro .ecu file (Mostly the hard way) for the 90-91 LT5 code. He was reciently provided a commented hack that can be used for further work should it be necessary. In the course of doing the .ecu he found that a lot of the routines in the L98 were reused in the LT5 calibration however as explained previously there are some key changes brought about by sequential injection, 2 injectors per cyl and DIS wasted spark.

Tyler

 

TT,

Thank you for that info, it's very interesting.

Regarding spark control, I'm currently playing with a Northstar(Son-of-LT5)
ignition package for an L98.

So far, it looks like the DIS logic is mostly in the ICM rather than in the ECM - but
I'll know more in a few weeks. I believe there is a lot of common code in the SD
P4 ECMs. Spark logic didn't change significantly until the LS1 design, and even
that leaves the dwell calc to the coils rather than the main CPU.


Regarding VE and fuel control, your code guy might be interested in another
experiment that's running now, if he hasn't already seen it:
http://www.thirdgen.org/techbb2/show...hreadid=296415

DrJ

 

I think you right. Have you seen this little gem?

http://cgi.ebay.com/ebaymotors/ws/eB...spagename=WDVW

I am biding on it right now for a friend as I got one some months ago to troubleshoot a problem in my 88 prototype zr1. It also works with a GM 4.6 L engine code 9 DIS system which I think is the caddy.
http://www.sirgalahad.org/tyler/misc/dis_1.jpg

It simulates the crank and cam and ecm signals and you can see them on a scope. I have the pattern for the LT 5 from this manual:
http://www.sirgalahad.org/tyler/prototype/page09.jpg
http://www.sirgalahad.org/tyler/prototype/page11.jpg
http://www.sirgalahad.org/tyler/prototype/page12.jpg
It can also be used to troubleshoot the injection system the timing of which on an LT5 is controled by the DIS module. IE it is a sequential system so the same logic that calculates timing for each cyl is used to time the injector firing. Is the caddy sequential?

Tyler

 

TT,

Not to hijack the thread but yes, Northstar is indeed the 4.6L V8 9 engine.
It's evolved some from the LT5 design, and uses sequential inj.

Northstar wheel & cam sensors:
http://www.thirdgen.org/techbb2/atta...postid=2202395

NStar signals:
http://www.thirdgen.org/techbb2/atta...postid=2203657


That is a clever device you have. Just to be clear, it simulates the engine sensor
signals and sends those to the ICM??? If that's correct, it is something I could
possibly use...

I had a pseudo-NStar trigger wheel made up at a machine shop last month. It
and an ICM are going on my test bench as soon as I get the boat in the water for
the summer. I was wondering how to test the module to be sure it was good
before I sank too much time in it... Hmmm. Is there any more detail in the
operating manual about its signals for the NStar??

I was simply going to force a simulation of the DIS engine inputs by spinning
the wheel on a drill-press, then reading the wave forms on the O-scope.
From that I think I can get an interface to the 727 ECM - with a little luck

Thank you for sharing the references.

FWIW, here is some detail of an earlier ignition project - making a 4X crank trigger
for a small block out of GM truck parts:

http://www.thirdgen.org/techbb2/atta...postid=1425055
http://www.thirdgen.org/techbb2/atta...postid=1425057

Having DIS on an L98 seemed like an interesting experiment, and the next step
up in technological evolution - or something like that.

DrJ

 

I made a connector for the crank signal input and disconnected the cam sensor input and connected the simulator. You leave the ecm connected and turn on the ingition. Once its turned on you can adjust the siginal input from crank to idle to cruse and it simulates those signals to the DIS module. I put plugs in all 8 wires and laid them on the plenum so I could watch the spark across the plug. I found the first DIS I had was completely dead and the second one would give good spark at 400 rpm but went random above that. Both of these were 'engineering samples'. I am using a rewired 90 DIS at the moment but just got 2 more engineerin samples yesterday which I am going to try.

The paperwork does not include just what the signals look like for the respective modules but you can put a scope on the inputs to get an idea then scope the actual input to see if it matches.

This is the DIS pin setup, (sorry its upside down) how close is to the caddy module?

http://www.sirgalahad.org/tyler/prot...90_ign_mod.jpg

This info comes from a GM STG Course manual for the LT5, I assume they have the same for the Caddy Northstar moter.

Tyler

 

Holy hoard! Where are you finding all those LT5 ICMs??? I always heard they were
unobtainable - or maybe it was you that said that? Looks like you have the market
cornered...

A complete set of NStar diagrams (from the GM tech manual) is here:
http://www.moates.net/files/6)%20Mis...star%20DIS.zip

(Paste the whole line into your browser.)

Were you thinking about trying to lash-up a NStar ICM in place of the LT5??

Hope that helps.

DrJ

 

Well what I have are 'engineering samples'. They are from different sources (read junkyard, GM throwaways etc) and are even more unique than you realize. They are in fact prototypes, some were made in 87 and none are later than 89. The car is a 88 ZR1 with a Phase 2 motor. They only built 24 of them and the rest were destroyed. It took 2 years for me to figure out why I could not get it to crank and run due to a lack of documentation and test equipment. If anyone is interested it will be at Carslile with the ECM development stacks that were used before the advent of laptop computers.

http://www.sirgalahad.org/tyler/prot...gEquipment.jpg

I am interested in the caddy setup used in conjunction with the megasquirt DIY ecm. If anyone wants to learn EFI or convert a street rod to efi its the way to go. Thanks for the Northstar document link.

Tyler

 

OK I got the Datamaster scanner plugged in and did some WOT pulls on the street in 3/4/5th gear, looking at the data you can see the long term and short term fuel trims locking down to 128 when the ECM goes into PE.

In closed loop mode the fuelling was generally a little rich, with BLMs around 122-125. I wonder what happens with the fuel trims in PE if the fuel trims are a little lean in closed loop?

If it still locks down to 128 in PE, then it would prove that the fuelling in PE is independent of the closed loop operation.

Time for more experimentation...

 

A narrative recently prepared for a fellow new to tuning is located here
(with even more references):
http://forums.corvetteforum.com/show....php?t=1069644

I'd modestly suggest reviewing the parts about 'getting the low-speed
fuel tables in good working order FIRST, before doing the WOT tables'.

In my experience, it's generally true that if the foundations are correct,
the high-speed fuel will sort itself out with little further anguish.


The reasons for this are several, but I'll burden you with only one now:

In most GM programs, PE and AE are ADDERS to the base fuel term.
(The equation for fuel load was given in a previous reference.)

That is, in the PE vs. CT and PE vs. RPM tables, GM typically adds ~ 25%
EXCESS fuel to the BASE engine load (or some number like that). Thus
if the base fuel calculation is reasonably correct (VE tables) - there is
scant danger of the engine running lean. Hence there will be less need
to fret over where the 'BLMs are locking' - since the BLMs will already
be ipso facto in the proper range.

Good luck with your project.