Closing in on a problem

[EagleMark]

Idle RPM is not accurate on this ECM, so at this point it needs to read higher. I need to send another chip with an additional 100 RPM. But until I get home I don't know of anoter way.

[1great40]

EagleMark, do you need me to mail the other chip to you?

[EagleMark]

Problem is I have been in hospital and rehabilitation since I did your chip and have no way to burn and mail another. But have someone who will, just need to contact him.

[1great40]

It's been a few weeks since I last posted. Eagle Mark said that the speed control on the ECM that I'm using is not too precise and that another bump in the idle speed would be in order. That got me to thinking. Once the truck is in gear if I'm stopped and I crack the throttle with my foot, and get the engine up to about 675 to 700 RPM, everything feels fine.

From what I understand, the ECM looks at the TPS voltage when the engine is started and uses that value as the idle TPS voltage. If you fiddle with the screw you can raise the idle speed, only for that one start/run cycle. If you stop and restart the engine after moving the screw, the ECM looks at the "new" TPS voltage and calls that the idle TPS voltage. So, once the minimum air is set, you can't play with it any more to try to set the idle speed.
But, once the engine is running, any movement of the throttle shaft has a corresponding change in the TPS voltage so the ECM doesn't try to force the engine speed, you're doing it with your foot.

My next step was to make a secondary idle stop so that I could "fake" the idle speed. I made a small block of aluminum with a second idle stop screw and attached it to the throttle body, right next to the minimum air screw. Once the engine is started and the ECM knows the idle TPS voltage, I could raise the idle speed with my new "idle stop screw". I could set the idle speed manually and it would return to the same speed every time the vehicle came to a stop. I would let the engine idle for several minutes in gear to see if the ECM tried to undo what I was trying to accomplish. Fortunately, I faked out the computer.

Obviously, it's highly impractical to back the screw off every time you shut off the engine and then reset it once the engine is restarted, but I did prove that the computer can be faked out and the idle speed can be set manually, at any speed I needed.

The next step is to automate this process. I ordered a continuous duty 12V "push" type solenoid from McMaster-Carr industrial supply. The solenoid has 30 oz. of force. I fabricated a bracket that attached the solenoid to the throttle body assembly. The actuating rod of the solenoid was set up to push on the boss on the throttle arm where the throttle cable attaches. I machined an eccentric cam that fit over the boss of the throttle arm and locked in place with a set screw. Rotating the cam with the solenoid actuated opens or closes the throttle plate. I have actuated the solenoid by connecting it to the battery and it moves the throttle no problem. Once the correct speed is obtained, the set screw can be locked.

My plan is to utilize the P/N switch that currently grounds the B-10 line to the ECM in park. I will add a SPDT relay and tie one side of the relay coil to a 12V signal that is switched with the ignition. When power is applied to the relay and the transmission is in park, the relay will actuate.
The B-10 line to the ECM will be connected through the normally open contacts to ground, so as soon as the ignition switch is turned on, the contacts ground the B-10 line to the ECM, just like a normal setup. Once the transmission is shifted out of park, the ground to the relay coil goes away, and the B-10 line is ungrounded, just like a normal set up. The other set of contacts in the relay now close and apply power to the idle stop solenoid, kicking up the idle when the truck is in gear.

As of now,the solenoid and the mechanical part of this set up is working. The next step is the wiring. Stay Tuned.

[damanx]

Love the ingenuity, but I have a couple of questions.

(Note that I am not an expert, but since I am running TBI with the 1227747 ECM on an engine that GM never made with the 1227747 and TBI combo, I had similar issues with finding the lowest, smoothest idle speed.)

In a thread you started about "setting up your tbi", you stated that you had set up the timing per the manual provided with the harness.

Where did that manual tell you to set the timing?

http://www.gearhead-efi.com/Fuel-Inj...ll=1#post21107

What I am curious about is that if you are running a pretty much stock engine with it's matching ECM and sensors, did the base timing adjustment in the painless manual match up with the base timing value programmed into the BIN file?

Unless I missed something in your posts, I did not see anything that indicated to what value you set the base timing at.

Also, in regards to the "open mode idle in drive" , my engine does that, and, seems to idle better, although I don't recall what all controls that. I do remember that it seems that in general, slightly rich at idle is what you want, but don't recall if that is idle park, or idle in drive.

If I am out of line asking any of the above, please let me know.

[1great40]

I think I used the term "manual" to refer to more than one book. The painless manual tells how to set the timing but the actual spec came from some other book I had.

I set the timing to 0 degrees.

I know now my setup is a round about way of addressing the idle issue but I thought it may be useful to someone else.

[Fast355]

I love the ingenuity but in this case it is simply not needed. To adjust the minimum idle rate, I open the throttle body screw 3-4 turns. Then jumper the ALDL A-B and turn the key on, wait 20 seconds for the IAC to fully close, then disconnect the IAC. Then remove the jumper and start the engine and work down from a higher RPM. Set the idle RPM for 750 rpm in P/N with the IAC closed off. Then when you reconnect the IAC and restart the engine it will idle at 750 and a little lower in drive. These older ECMs are pretty leniant with idle speed and setting idle speed control codes.

[damanx]

I think I used the term "manual" to refer to more than one book. The painless manual tells how to set the timing but the actual spec came from some other book I had.

I set the timing to 0 degrees.

I know now my setup is a round about way of addressing the idle issue but I thought it may be useful to someone else.

What does the base timing parameter show in TunerPro for the bin you are using? I am only curious because you had stated that the original eprom was a "AKMH" bin and wasn't sure of the new one.