Short and sweet. Did a rebuild. Engine would idle around 650/700 once warmed up. Kinda seemed like a possible miss or something. Anyways. I bumped idle speed via the screw that was originally plugged. Been messing with diy prom data logging. Chose to try and reset the idle speed/IAC via the writeup here on TGO. Not liking what its doing. Tried a different way, somewhat similar to TGO writeup but slight differences in instructions. Either way I don't like whats goin on and not sure if its a byproduct of me trying this IAC reset. First thing. Once warmed up idle is like 1000 in park. Drop to drive or reverse and idle drops to like 650ish but climbs back up to like 1000ish. If I drop outta gear into neutral or park RPM'S shoot up to 1800ish and really slowly come back down to 1000ish. Doesnt seem right. When I follow reset procedure I set the idle around 600ish. Does whats goin on sound normal? Plus my BLM and especially my IAC counts seem odd.

 

Did you try setting it like this


Reset the IAC valve pintle position by performing the following.

- Depress the accelerator pedal slightly.

- Start the engine and run for 5 seconds.

- Turn the ignition switch to the OFF position for 10 seconds.

- Restart the engine and check for proper idle operation.

That's it.
Also if you mess with the idle control screw than I believe you must adjust the TPS .(Throttle Position Sensor) maybe someone can verify that.

 

I have not...

I set it this way.. https://www.thirdgen.org/tpimod2 followed by this way... http://www.gmcmidwestclassics.org/We...0the%20TBI.pdf

I have a tendency to over analyze.

As stated before. Initially bumped just RPM via the throttle stop screw. Then I started to think that in doing this without resetting the IAC my readings might be skewed. So I followed the TGO method. Didn't like what it was doing with my RPM's so I assumed maybe I reset it wrong. Tried again using the PDF stated method (slight variations). Either way right now I know it's wrong. BLM's are 128 across the board and IAC counts 1. Don't think that's right.

I will try the method you stated. Thanks

 

To set the IAC, warm up the engine and with no other loads on it set the idle stop screw so that the steps are between 5 and 10.

If you want to raise the idle speed it should be done in the PROM.

Unless the proper IAC parameters are changed the ECM will only control the idle once at 195 - 200*F.

If pins A & B on the ALDL connector have the 10K resistor between them, the ECM will target a higher idle speed.

RBob.

 

RBob. Just to clarify. Do I need to use the reset procedure (or any steps in the reset procedure like disconnect IAC) in conjunction with your suggested method or just warm up, set steps between 5 -10 and be done with it?

Idle speed seems like it needs to be higher, some mods. Guess I'll bump in PROM.

Engine temps never exceed 190.

As far as the rpms.. so if I have my aldl cable plugged in (switch on resistor) it will automatically raise rpms vs not connected?

Thanks.

 

That's it. Do this after you increase the idle speed in the PROM.

That could be an issue, it is calibration dependent. Has to do with the IAC step table versus kick down steps. See the IAC Logic write up in the DIY_PROM Tuning Guide Book sticky.

If the resistor is in place the ECM will target a higher idle RPM. No need for the resistor to be used when data logging the '8746 ECM.

RBob.

 

Thanks, Now just gotta figure out which one is the exact idle spped entry in the .bin as I believe there are 4 listed.

Interesting, I will take a look. Makes me wonder how guys are running 180 stats.. Maybe thats addressed in the IAC logic sticky you suggested

I guess i misunderstood in my reading as I had it set with resistor switched on. Thanks

 

I run a 180dF therm. Today temps were 45-50dF environment. I ran 189 on Xway at 70 mph. At 75dF I see 190. At 85dF I see 195. Coolant temps are determined by more than just a therm(radiator capacity, air flow, coolant, load).

I enter CL at 155dF.

 

I haven't run on the highway since the mods... 2 reason. Not ready to and no hood. As far as the temps... Pretty consistent at 175ish to 190. Have yet to exceed 190. I don't know what the fan switch parameters are or how it necessarily works but while driving (around town) when I monitored the temps they reached like 190 and cooled to about 178ish... What I find odd is when I key off the fan keeps running and continues to cool to like 165 or so... Not sure if that's normal or not.

I assume this "IAC step table versus kick down steps" in my prom is "IAC steps vs Enigne temp"?

The steps from 166 through 298 are all listed as 65. So my understanding is that no matter whether the temp is 180, 190 or 220 the steps are the same... Unless there are other tables to be considered on top of the step vs temp table.

 

Note that Ronny is running an EBL Flash ECM. The IAC logic is completely different then the '8746 stuff. And much better.

> I assume this "IAC step table versus kick down steps" in my
> prom is "IAC steps vs Enigne temp"?

Most likely, but there is another parameter that it is related too:

LD527: FCB 65 ; Kickdown steps

This is covered in the IAC Logic write up, at the very end.

RBob.

 

This is borderline turning into PROM discussion and maybe should continue in my thread in the DIYROM section. Either way.... I tried searching and either I missed it or couldn't seem to find an answer... What would you label this as? (---->LD527: FCB 65)<----- Would this be considered an address, code, hex? Other question, I cant seem to find a way to search for (LD527: FCB 65) in tunerpro unless i just don't know how. This is your post from the IAC logic... Where is this code from? How is the ECM read in this format? Sorry if it's a repeat question but I couldn't find an answer. THANKS



FYI, have reverted the IDLE screw back to where I believe it was. No more rpm's hanging.

 

The way I did the hac the LD527 is a label along with the virtual address of the parameter. Take the LD off for the physical address of that parameter within the PROM:

$527

The dollar sign is to designate that address as a hex value.


The format above is source code. Which gets assembled into binary code that the ECM understands. Which is how we came up with the .BIN extension for the stuff the ECM understands, it is in binary.

IIRC, there is a patch method demo thread in the DIY_PROM Tuning Guide sticky that further explains this stuff.

RBob.

 

Thank you... As always, RBob, you the man.

....and thank you again. I understand nothing from the readings yet but I'll keep reading until that light bulb in my head lights.

I have no 527 physical address (unless the "7" is translated through hex with a letter like "A" or "B") but instead I have a value of 538 (IAC - Max throttle follower steps)

 

IAC throttle follower is a different table than the one RBob refered to(coolant)

 

Well then I see no kickdown steps in my ECM/tunerpro and/or cant find it.

 

Must be there. Used the search function in TP? Maybe listed under RPM vs coolant temp? For instance if coolant is 20dF you can command a higher RPM during warm up?

 

Then the parameter doesn't exist in the XDF file. This is not unusual. Here it is in the hex editor of Tuner Pro (CTRL+H). Changed it so that it View's as decimal. Also note the values in the steps vs. coolant table.

RBob.

 

Steps in the table are not much different at normal operating temps in the pic you posted as compared to my table...

So then should I look into adding it?

 

Can either add it or use the Hex Editor to view/change it.

RBob.

 

So I went ahead and added it. Not sure if I did it right or not. Used a $42 mask as a template. (see pic). Questions....

1) I used same parameters from the $42 and applied to $61. Will this be okay? (note pic)

2) Is the $42 (IAC Position vs Temp) similar to the $61 (IAC Steps vs Engine Temp)? As in with me adding the IAC kickdown to my $61 is the IAC steps vs temp table fine (will new kickdown parameter recognize/work with it) or do I also have to add the $42 IAC position vs temp table and eliminate the $61 IAC steps vs temp? Hope this is a clear question.

3) Depending on the answer to my #2 question.. If just the new kickdown parameter is fine and no other changes necessary, if you note the pic the $42 kickdown is 25 and IAC position is different from my $61 kickdown of 4 and Steps table. Should I change the kickdown in the $61 to 25 and adjust the Steps vs temp to mimic the $42 IAC positon table?

Thanks,
ROB

 

In the $61 XDF, need to change the address of the kick down steps. It isn't in the same location as the $42 mask. See the editor entry of "Address (Hex)", change the address to "0x527"

RBob.

 

Thanks RBob. Address changed. Pic posted.

The fact that a parameter as "kickdown steps" was not included in the XDF makes me question/curious how many other parameters are lacking/not shown.

1) So in following the IAC LOGIC thread, if you note the pic, my steps at 166F+ are 65 and so are the kickdown steps. So the ECM as you stated in the IAC LOGIC "attempts to control the high idle rpm once steps are below kickdown value". So with the kickdown at 65 does that mean that the ECM will not attempt to control the high idle rpm at all?

2) I assume the "IAC" values (steps) are the same values seen when datalogging (IAC count)? If I remember correctly a higher "IAC" count corresponds to something like a vacuum leak, so you'd basically want lower IAC counts? So would I wanna change my steps in the "IAC vs coolant"?

Or am I just totally confused right now?

 

A lot, the EBL systems have nearly 400 parameters in the XDF file and documented. Which is also a negative as it can be overwhelming. I tell folks to just change the ones that need to be changed, just because they are there doesn't mean that they do need to be changed.

The P4 and SFI-6 systems have a reduced XDF along with a full XDF to help in this regard.

The IAC Logic thread is the '7747 ECM, not the '8746 ECM. Although similar there are differences. It may be the test & bra for the kick down versus steps table is different. Too early in the morning to look at code to see.

The 65 kick down and 65 in the table is likely OK, it will control the idle at that point. If you are concerned about it, make the kick down steps 66.

The IAC steps in the ALDL stream are the current commanded step position. If you have opened the throttle blades to get the steps within the 5 - 10 range, then lowering the Steps vs CTS table can be helpful.

That will allow the ECM to more quickly obtain the proper idle RPM.

On a side note, check the IAC steps at key-on, engine-off. See if it stays at the park position or if it moves according to the engine CTS. The '7747 cranks at the park position, the '8746 may or may not.

No, just over thinking it a bit.

RBob.