junkcltr

iTrader: (1)

I have an LT1 throttle body that I am using with a 730 MAF ECM. I will be firing up the engine in a couple of weeks so I am starting to look into changing some code so that it will work with the LT1 TB (non-adjustable TPS).
The LT1 PCM reads the TPS when the ign. is turned on and adjusts from this point. The 730 wants to have it adjusted to about .5V at idle.
I could take the easy way out and slot the LT1 TB TPS, but figured it shouldn't be that hard to have the 730 act like the LT1 PCM in terms of the TB TPS.
Anyone else messed with this yet? Searched the boards.....didn't find anything.

J

Grumpy

Start the engine and set the min idle and see where you are.

If you have a big cam, or have to open the butterflies alot, then you'll want to drill a couple small holes in the butterflies to close them back down. The relationship of the butterflies to bore is somewhat critical, since changing that changes the percentage of air the IAC will bypass at a given opening.

RBob

iTrader: (1)

The '730 with the $8D mask does the same thing, reads and stores the lowest seen TPS position and uses that as the 0% setting.

RBob.

junkcltr

iTrader: (1)

Thank you for letting me know the 730 already does this. I have been using strictly 165 MAF ECMs so the 730 is new to me. I have read the hac a few times, but never in detail.
I am still going to read through it better though to get a feel of how it does things.
So what you are saying is that the 730 does not need the TPS adjusted, because it does it's own closed throttle calculation.

J

11sORbust

If your tps is over like .65mv then I would slot it. The 730 ecm does use the (existing)tps setting as 0% throttle angle. I think the ecm does this every time the car starts. BUT there is many reasons to keep the tps to about .65 or less. So just slot it if you are getting a high tps reading. Fyi, I have a friend that uses a lt-1 tb for his 3rdgen. It works OK but I wouldn't suggest it.

junkcltr

iTrader: (1)

Why not over .650 volts? You mention that there are many reasons to adjust the TPS.......shouldn't everything be taken care of inside the ECM with the 0% correction it does?

Why do you not suggest using the LT1 TB? They work just as well as the TPI TB.

I may end up slotting the TPS though, or I could do what Grumpy says and start filling the blades full of holes, but that is just a hack for doing it right inside the ECM.

11sORbust

Maybe someone else could explain why better than me. But from what I understand AE can be effected. .650 is no set amount but at some point you'll lose resolution or some sheet.

Because my friend has some crazy throttle cable/return rigged up. I would ASSume that's because of the lt-1 has a different cable setup or linkage.....but if that's all you can get then it'll work...

MrDude_1

tell your friend to get a LT1 throttle cable, and its a bolt in that looks factory.

junkcltr

iTrader: (1)

I am going to look into the code and see if there really are thresholds for the TPS in the 730 ECM. I just figured I would ask the board if anyone had already looked into this.

The throttle cable setup is straightforward and I don't need to rig up anything. I put it all together using factory parts but this in on an LT1 intake.
Thank you for the help.

11sORbust

What about the T/V cable and cruise? Thanks !

MrDude_1

93 LT1s had a TV cable... i dont know about the cruise. you would have to look into that...
if you can get someone to pop the hood on their LT1 car to look, that might tell ya what you need.

RBob

iTrader: (1)

I wouldn't steer you wrong:

L83E5: FCB 48 ; 19% TPS IS LOW TPS

Comment may not be exact, but that is the parameter used to init the TPS at key on.

RBob.

junkcltr

iTrader: (1)

I checked out what you said and it appears to be correct that the 730 does adjust to make the ign. on TPS to be the 0% point.....but there is more.
The $8D hac has some stuff at 0xE45C that sets some errors if TPS is out of range. Actually, thinking about it makes sense. The A/D has a 5V and 0V reference and therefore the ign.-on TPS value must be within a set range or the A/D would saturate.......much like saturating a MAF at high RPM/big engine combos.
For example, suppose ign-on TPS was 2.5 V, and the ECM called this 0%. As the throttle is pressed the ECM "sees" full throttle way before the TB is physically at full throttle. So the 730 does need an adjustable TPS or a larger voltage reference on the A/D.

J

RBob

iTrader: (1)

OK, the TPS can't saturate the A/D convertor because they both use the same REF Hi voltage.

If the TPS was at 2.5 volts at key on the ECM would not use that value, it would use .94 volts for 0%. In the cal shown above the init term is 48, or .94 volts. ( 5v / 255 * 48 = .94 volts). That is the maximum minimum the tps can be.

RBob.

jeepguy553

What is the conversion to percentage? Would you simply use the +5V as the reference and derive the percentage TPS from there?

junkcltr

iTrader: (1)

RBob,
you are correct. it would not be saturated, degree opening resolution would suffer. That appears to be why GM limited the max. value for the TPS at idle to be .94V and not something like 3.0 volts.
The code shows that the TPS voltage must be below .94 volts for everything to work properly. I am guessing I won't have to slot the TPS at all.
Thank you for the insight.

RBob

iTrader: (1)

The ECM uses a gain term, in $8D found at L83E4.

Goes something like this:

(("TPS A/D from idle" * gain) * 4) / 256 = TPS%

Simplified:

(("TPS A/D from idle" * gain) / 64 = TPS%

RBob.

jeepguy553

Looks like I better get in the code to figure that one out for the $61 and/or the $42. I was just wondering if it could be that simplified for an ALDL definition so that instead of seeing TPS voltage, you could see TPS%.

11sORbust

I was .29mv off, lol.

junkcltr

iTrader: (1)

yes, your guess was good. Most of the manuals I have read say between .4 and .6 volts, but I wanted to know the 'real' value that the ECM uses.

Grumpy

You guys are also totally ignoring the mechanics of it.
Yes, the software is a critical item, but you want the delta TPS stuff for AE to somewhat correspond to the air flow, for a given delta. You have to remember that 30% of throttle opening is like 60% of possible air flow. While you have so much adjustment in the code for AE you can still get a poor combination of lining up TPS to code to engine.

A general rule of thumb I use is that the min idle setting should just allow a 1/4" ribbon of paper to be drawn thru between the butterfly and it's bore. If you see much of an opening, then you need to close it back down some, and that'll probably take some mods to the butterfly itself. But this is just if you want things correct.

11sORbust

Knew sombody would explain it better than me. Think about it, if you are close to .940 mv then you are losing (aprox) 1/4 of the tps resolution.....

junkcltr

iTrader: (1)

I agree with you Grumpy in terms of how far the blades should be opened before doing mechanical corrections.
In my case the 224 degree at .050 cam will not have problems that will force me to do a large correction with min. idle.
The thread was more aimed at how the 730 ECM deals with a TPS that can't be adjusted. RBob told me some good stuff and pointed me in the right direction. I was more concerned about a high TPS voltage with pretty much normal TB blade openings due to manufacturing variances in the TPS.
If I did go to a much more radical setup, then the secondary TB mechanical effects you describe would need to be taken into account.

also, .94/2 = .47.....pretty much what the manuals call out for TPS setting. This allows for the greatest margin of error.
J