Hello

[Scuba1x]

Hello all!
I have a 1992 K3500 7.4L 4l80E Dually.

I have attached a photo of the ECM service label.

This truck has an open loop at idle issue that I have been unable to resolve by use of a Snap On scan tool and changing suspected parts.


I have eliminated all vacuum leaks (new intake manifold gasket, new tbi gasket, all new vacuum hoses and fittings), converted to heated 02 sensor, new CTS, new ignition module, new cap/rotor, new plugs, new HD spark plug wires, checked timing 4deg BTDC, new TBI (reman from Carb X) with new TPS, new IAC, new EGR, all are AC Delco or NAPA Echlien.....and new CAT

The truck still reverts to open loop @ idle at ~15-20 seconds.....if i tap the gas pedal it kicks into closed loop, if in gear and I let off the pedal (no gas pedal apply, it kicks back to closed loop........ then ~15-20 seconds later...back to open loop.

I think the truck may have factory open loop @ idle that is causing me to fail the emissions test...or what else could it be?

To further debug this issue I have purchased the 12 pin OBD 1 to USB cable and TurnerPro RT..

I have installed TunerPro RT on the computer.......and now could use a little help to get started to pull the data stream from the truck.

I have found the xdf file on turner pro, but I guess I need additional files and am trying to locate the correct files to get started, any help or pointers appreciated.

[dave w]

Gearhead-efi information for the 16147060 PCM: http://gearhead-efi.com/Fuel-Injecti...Information-85

dave w

[1project2many]

Welcome,

The $D8 calibrations were built with open loop idle as an option in the calibration. AXRD is listed as a federal emissions compliant calibration. By comparison, BAMN is listed as a leaded fuel compliant calibration. Leaded fuel is gm's secret code for an open loop calibration. When comparing AXRD with BAMN there are several differences present. It's clear that GM used coolant temperature as the way to force the controller to remain open loop. AXRD is able to go into closed loop at approximately 85 degrees F while BAMN would require coolant temperature in excess of 303 degrees F.

Many of these trucks just didn't like to idle in CL IME. Is there an issue related to open loop operation that you are trying to resolve?

[In-Tech]

just change the parameters for close loop idle

[Scuba1x]

Welcome,

The $D8 calibrations were built with open loop idle as an option in the calibration. AXRD is listed as a federal emissions compliant calibration. By comparison, BAMN is listed as a leaded fuel compliant calibration. Leaded fuel is gm's secret code for an open loop calibration. When comparing AXRD with BAMN there are several differences present. It's clear that GM used coolant temperature as the way to force the controller to remain open loop. AXRD is able to go into closed loop at approximately 85 degrees F while BAMN would require coolant temperature in excess of 303 degrees F.

Many of these trucks just didn't like to idle in CL IME. Is there an issue related to open loop operation that you are trying to resolve?

Yes, the issue with the open loop @ idle is failing the smog test @idle.....other than that the truck runs and drives great.
Especially since I have replaced all sensors, complete tune up, installed all new ground cables to engine/chassis/body, changed out the intake manifold gasket and TBI gasket, changed all vacuum hoses and fittings, and installed a new TBI reman from Carb X......the truck has never run better............

I need to get this truck on the road for hauling and towing work and the open loop @ idle is a roadblock.

It seems the only solution is burning a custom chip to keep it in closed loop at idle....for the test and then revert back to factory chip after testing...

I purchased the ALDL to usb cable, downloaded tunerpro rt, and have the loaded the following files into tunerpro rt:
TP files V1.jpg

Now I will need to either pay someone to burn the chip to keep it in closed loop @ idle or buy the equipment to program and burn the chip myself.
I guess the moates equipment is highly recommended, but I see most of items for my application are on back order......

Is there an alternate equipment recommendation that I can buy that will do the same thing and is in stock....if I go this route I will need help to know what to modify to keep the truck in closed loop.

Thanks for any help..

[In-Tech]

Hello,
Here is a printout of the contents of that memcal(the blue chip enclosure).
I have those memcal's in stock, not available at GM for many years now.
Let me know if I can help.

[Scuba1x]

Hello,
Here is a printout of the contents of that memcal(the blue chip enclosure).
I have those memcal's in stock, not available at GM for many years now.
Let me know if I can help.

Hello Carl-

Thanks for the File!

AXRD.JPG

Under the ECM Constants, it would seem the following would force open loop at Idle:

Force Open Loop Fuel for Idle, (Speed) 2mph
-Does this mean if the speed is under 2MPH it will force open loop at idle?
Force Open Loop Fuel for Idle, (TPS) 2.3%
-Does this mean that TPS lower than 2.3% (or 1V) will force open loop @ idle?
Open Loop Idle Fuel Enable RPM Threshold 1500RPM
- Does this mean that below 1500 RPM it will force open loop at idle?
Open Loop Fuel Enable Enable Delay Timer 16 sec
-Does this mean that after 16 seconds it will force open loop if it meets the conditions above?

Are there any other CAL items/values in the AXRD that will force open loop @ idle?

For the MEMCAL do you have the AXRD? What is the price?

Thanks for all your help!

[Scuba1x]

Hello-

Here is a photo of the ECM MEMCAL:

20210719_102622.jpg

[In-Tech]

I have brand new GM memcal's I bought years ago. I can put whatever stock or modified file you want on them. I generally charge $100 for the memcal and then whatever for the tune. Locally if tuning on the fly with emulator I start at a charge of ~$500 for the tuning, cam/head changes etc. Just the closed loop idle stuff would be included for the hundy if you like.

[Scuba1x]

I have brand new GM memcal's I bought years ago. I can put whatever stock or modified file you want on them. I generally charge $100 for the memcal and then whatever for the tune. Locally if tuning on the fly with emulator I start at a charge of ~$500 for the tuning, cam/head changes etc. Just the closed loop idle stuff would be included for the hundy if you like.

Ok, I'll take the new memcal with closed loop @ idle.
When can you ship?

[In-Tech]

I'm not sure how this wonderful website works but I think you need 10 posts to be able to PM. I can ship within a couple days of paypal or zelle. As hard as parts are to get these days, a spare memcal is a good thing. Man, the junkyard hunting the last few times I have gone is horrible and the time lost :(

[Scuba1x]

I'm not sure how this wonderful website works but I think you need 10 posts to be able to PM. I can ship within a couple days of paypal or zelle. As hard as parts are to get these days, a spare memcal is a good thing. Man, the junkyard hunting the last few times I have gone is horrible and the time lost :(

Yeah, the PM button is not working yet....
I will make sure I have 10 posts and then try it again....

[Scuba1x]

This is post number 8.

[Scuba1x]

Post number 9.

[Scuba1x]

Post number 10....