some tables are defined by throttle position. I know the the voltage scales from 0v to 5v, and the bits scale from 0 to 256 accordingly. The TPS is set at .54v at idle. At .54v does the ECM see this as (.54/5.0) 10.8% throttle? I don't think so. So how does the ECM view throttle? I know there is an EGR constant in my bin that has a throttle % value around 6%. This is below the 10.8% seen at idle. so how how the throttle % work? What is considere 0% throttle and what is considered 100% throttle?


this is all related to my other post:
https://www.thirdgen.org/messgboard/...ML/001928.html

James

------------------
1985 Z-28, 350 TPI, T-Tops, edelbrock 6085 heads, ZZ4 cam, accel base/runners & 24 lb/hr inj., ported plenum, everything gasket matched, crane AFPR, SLP 1 5/8 headers, single 3" flowmaster catback, 3" Catco cat, modified tranny, 165 ECM & ARAP code, MSD 6AL/wires, edelbrock STB, Spohn SFC/LCA/PR, GW "wonderbar"

 

I think this may be a more difficult question than you think. I have seen on various cars the throttle % displayed in various ways at idle. Some show 0% at idle and some show 6-10%, but all show 100% at WOT. Also, some of the tps % tables are by % change in tps, not tps % itself. I hope I didn't confuse the matter even worse.

 

I understand the need for change % of throttle: to anticipate rapid changes and try to make things transition well in a rapidly changing dynamic environment.

I'm sure that the ECM has a definition of 100% throttle: like a TPS voltage >4.0v and a definition of idle like a TPS at<.60v. That is the stuff I am after.

I know my TPS will never see the whole 5v ref voltage. Hell I'm lucky if with an idle at .54v that I can get more than 4.2v by flooring the accelerator. ==> 4.5/5.0 = 84% throttle .: My ECM would never see WOT or 100% throttle.


James

 

First, the max value for an 8 bit byte, as used in these ECMs is Hex FF or 255. 0-255 represents a combination of 256 (2^8).

As for the question of what the ECM does, a lot has to do with the Scan Tool. Diacom always considers idle as 0% (even though on my car reads .65 volts @ idle) and @ WOT I read only 4.21 volts which is interpreted as 100%.

But, what you REALLY want to look at is where the Eprom is set to engage PE. Once PE is engaged, it could give a hoot what the TPS voltage is. You need to look at the %TPS vs RPM for PE.

This adjusting the TPS to get "extra voltage" above 4.0 volts so you can get "more fuel" is wrong. As long as the ECM detects that you have crossed the threshold that you have set in the %TPS vs RPM for PE...you are PE, and you won't get more fuel that you have set in the eprom.

Too many guys adjust the TPS when there is absolutely no reason to even touch it. Another "myth" in the quest for power. This is one of most useless mods, unless your TPS is truly out of adjustments IMO. Maybe that is why the TPS is not even adjustable on SD 7730?

 

What I was really after was how does the ECM determine 0% throttle and 100% throttle. I didn't know if there were fixed points or floating points. It appears that they are somewhat floating points. I asked this question on the GMECM mailing list and recieved this response:

0% is the lowest TPS reading the ECM has seen in a while. If the TPS
goes lower than the "lowest seen" value, then the new value becomes the
"lowest seen" number. Some ECMs have code that tries to pull this value
back up if it never gets that low, but this can't work very well. This
is why the ECM should be reset whenever the TPS is changed/adjusted.

100% is anything over "lowest seen" plus x where x is a value specified
in the PROM. It is usually set so that 100% is achieved at quite a bit
less than 5 volts on the TPS.

--
Ludis Langens


I am using craigs software and want a more REAL throttle postion in my logs than just the a throttle position based off the counts from the TPS. When I'm at idle I want 0% throttle not 10%, and when I floor it I want 100% throttle not 90%.

I guess the best way for this to work is to have min and max counts listed in the ECM definitions file and use the counts obtained using his software to update/re-iterate/correct those counts and would therefor give a better throttle % accuracy.


James

 

I believe this is a "display issue" in Craig's software as Diacom always display 0% on idle and 100% on WOT.

There is a "byte" on the SD ALDL Datastream which takes that actual %TPS from the ECM. This is calculated by the ECM. I haven't dug into the MAF system, but I would suspect that there is a similar field on MAF cars in the ALDL Stream.

It strikes me that Craig has chosen not to use this field, but simply take the A/D TPS and take a percentage of 5.0 Volts. This is probably a preference of Craig's or he is unaware of where the field is on a MAF car. Best to talk to Craig on the matter.

Since Diacom reads MAF cars the same as SD cars, they are obviously utilizing this field since how would they know what 100% is @ WOT without using this field in the ALDL.

So I conclude it is a simple "display issue" with Craig Moate's software. Talk to Craig or modify the code yourself as Craig does supply the source code from what I understand.

[This message has been edited by Glenn91L98GTA (edited August 31, 2001).]

 

that's what I'm doing. I'm modifying the code so it can at least make it a little more accurate than just basing it off the TPS datastream and its count limits.


James

 

Correct. Scaled TPS, auto-zero is an available value coming off the 730 SD system. Didn't see anything like that in the 165 datastream, just the raw TPS signal.

 

Over the weekend, I was helping a friend tune his new 383, AFR Competition Heads, Miniram, yada yada engine.

Though we eventually plan to go to SD (or let's say I am recommending it), we are also initially starting with MAF (just to see how far we can push it and to compare our results to SD should we ultimately go to SD).

In using Diacom, I noticed on MAF cars that Diacom doesn't even list %TPS, so I double checked what is in the ALDL data stream, and the %TPS IS NOT included on the data stream.

I having "dug" deep enough, but I do believe that %TPS is "inside" the ECM, but GM chose not to give that info in the ALDL datastream. I do not know where the %TPS is in the ECM's ROM (I will dig around to find it), but I am sure it is there.

If %TPS is in fact, in the ROM, then there you will have to modify the ALDL stream's data to include this and then have Craig's software modified to use this information. If I find out which ROM byte has the ALDL stream, then you can "poke" the instructions of the ALDL data stream to replace one of the other bytes with this info.

Alternatively, Craig could modify his program to determine when your car is idling and using the Volt reading of the TPS while idling as the "base" for 0% and then make an assumption of 4.2 Volts for 100%. Then when you "boot it", Craig's software could modify the voltage necessary for 100%. This is a lot of work for Craig and still is not 100% accurate.

Pity GM did not feel the %TPS was worthwhile to include in the ALDL stream for MAF cars.

 

Excel can not only plot, but it can add and subtract too, among other things.

Con't worry, I'll make the change at some point. Let the user put in what their zero and WOT TPS voltages really are...

 

Mike Davis already did this and documented the results at his web site.

SD, won.

 

Heh, heh, I predict the same results too.

But sometimes you got to go through the "long process", SD just scares people for some silly reason. I fully expect that the "full potential" will not be realized until we go SD. I am also using the process to fully understand MAF...the good, the bad, the downright homely.

 

Don't forget there are still lots of us "MAFFERS" out there running a 165 ECM with good results. My car has it, and will continue to be a MAF car for a long time. I do not have BIG hp (not yet), heck my valve covers or manifolds have never been removed. There is no way I am going to spend the cash to switch over to SD. Not unless my entire engine management system failed. SD is good for folks going from carb to TPI, or retrofitting an older car with FI. My car runs good, better and better since I have been burning chips. At least I am going in the right direction. The only improvement I might consider to my MAF car, would be installing a better MAF sensor itself, but probably not until my stock one fails.

As far as the original post, my Ease scan tool shows the TPS voltage, 0-5 volts. It would be nice if this could be converted to %TPS. But I can figure out where I am, by comparing the TPS volts to other parameters. I know what the volts are at idle and WOT, so I can take 70% of that number to figure when it goes into PE. It's kind of obvious when it happens, since several factors come togother in PE. IE 02 volts maxes, learn control off, BLM/INT =128, load goes high.

Just my 2 cents. I dont want to start the MAF vs SD debate again.

------------------
Best ET 14.413 @95.57 without
pulling valve covers or manifolds.
Also with stock 2.77 rear end!!!

 

No debate whatsoever. We are trying to just see how far we can push MAF and if it does not give the results we want, then SD.

Remember, this is not a stock application, but a 383 Miniram, AFR 195 competition heads w/ 2.05 intakes, yada yada yada. On a reasonably stock L98, I wouldn't change unless the MAF wasn't doing what I wanted it to do.

[This message has been edited by Glenn91L98GTA (edited September 06, 2001).]