Driving in idle loop mode

[steve5309]

Excellent forum you have here so much information on the 6.5.
I have a 1999 c3500 that I got for a couple hundred bucks.
I was told it needed an injection pump, so when I got it, it started but it ran really rough
I had an extra 2 pumps in my barn. One of them I pulled from a running truck, and as far as
I can remember the engine light was not on. ( from a seized engine).
So I put the IP on and it started and ran ok. I hooked up the autel bluetooth scanner and
set the timing. 10.8 degrees and, the suggested was close to that. Ran it up to temp (192 degrees) and tried to set the
TDCO because it was on -2.46. I tried a few times, It would not change at all. So I drove it around a few days
with no CEL light on cause it seemed ok. ( also added the relay for fuel pump so I get 5-7 psi fuel pressure)
So just under a week the code pops up I think it was the p0216 ( trying to remember or the p1214)
IDK but it seems to be in Idle loop mode? but it runs good. So checking out the stepper motor now and i pull off
the pump servo advance mechanism because I took out the IP to check it. So I can see that the plunger in the advance
mechanism is pushed all the way in so that it should read its in full retard mode. I noticed the one in the pump that came
with the truck was nice a freed up, so that one went in.
Ok so now the serve advance mechanism seems ok lever works pushing in piston
to retard timing, so at rest its in advance mode now ( Lowest point in the pump Im sure water collects there as my 2 spare pumps
had stuck servo pistons) and btw I broke the ring that keeps the little locking pin in place to keep the little piston in.
OMG but I still have one left. I've looked everywhere to get a spare one and no luck on hard parts.

So I start the truck it comes up to 170 degrees and shuts off ( trying to relearn I guess Idk) So i take my extra stepper motor
and plug it in and let it rest on top of my coolant manifold. ( ground wire too on the stepper motor case) Fairly sure my servo motor
hasnt pushed the plunger in because my timing is still set at 10.8 around there Start the truck and a few moments later the servo
is pushed all the way out and still under 170 degrees. but truck comes up to temp and runs ok. timing is good too and the TDCO
is again set at -2.46. and the truck is running good. ( with the servo advance mechanism at rest, which is advance) So as a test I plug
in the servo on the pump and the timing changes 3.5 degrees, suggested 10.8 and the truck doesnt want to start.

Questions: does the CPS operate in idle loop mode (before 170 degrees)or does the optical sensor run the timing?
and can I run in idle loop mode or do i care if the computer doesnt advance or retard timing? as long as its at 10.8 and TDCO is -2.46
CEL will be on always but whatever
So what I have to do now is unbolt the stepper from the mount move the plunger in, so the servo advance mechanism
isnt pushing on the plunger and the timing will go back at rest and will read actual 10.8.
Is the stepper motor more for cold weather starting? or that purpose


found this too:
94-95 (ODBI) acceptable TDCO range of -0.25 to -0.75

96-97 has a wider range of acceptable values... something like -0.1 to -1.9

98-02 wider still... +2.46 to -2.46.

I also noticed that the PCM plug into the computer only has an A9 and A10 male prongs which indicate coil 2 on the stepper motor
there is no A7 and A8 male prongs or wires for the coil 1 in stepper motor. So one coil pulls in and the other pushes out in the stepper motor
? IDK because my extra stepper motor pushed all the way out when out of the mount. Red and blue female plus on the PCM ( is this an aftermaket one)?

 

[dbrannon79]

Welcome to @steve5309.

I have no experience with the newer 6.5's setting TDCO, but on mine (obd1) I seem to have better luck when during the timing process before you trigger the learn process you can do the time set which zero's out the PCM's stored timing setting and then you adjust the IP as close as possible to 3.5 degrees for the "actual timing", 10.8 might be a bit much. there should be three values to watch when setting timing. "Desired" "Actual" and "offset" I use a program called GMTDscan that is designed for the older pre 96 obd1 systems, but iirc you will need a GM Tech 2 in order to see and set timing on the newer systems.

others have mentioned where some android apps like torque pro can do this. I thing Quadstar has some instructions posted on his site on how to set the app up.

others should chime in here soon to help. just keep in mind, these trucks and engines take a lot of patience. so take it slow. I have found that getting the TCDO right where you want it can take a LOT of tries. It's like a crap shoot of getting it right in the first couple of attempts. remember moving the IP 1mm is like changing the timing about 3 degrees! especially when the timing chain has little to no slack.

oh yeah, don't do like I did trying to bump the IP with the engine running LOL I did that after several attempts of back and fourth. it worked for me but later I found out that if the IP had moved too far while running, it could have cause catastrophic damage!!

 

[Big T]

Welcome to @steve5309.

I have no experience with the newer 6.5's setting TDCO, but on mine (obd1) I seem to have better luck when during the timing process before you trigger the learn process you can do the time set which zero's out the PCM's stored timing setting and then you adjust the IP as close as possible to 3.5 degrees for the "actual timing", 10.8 might be a bit much. there should be three values to watch when setting timing. "Desired" "Actual" and "offset" I use a program called GMTDscan that is designed for the older pre 96 obd1 systems, but iirc you will need a GM Tech 2 in order to see and set timing on the newer systems.

others have mentioned where some android apps like torque pro can do this. I thing Quadstar has some instructions posted on his site on how to set the app up.

others should chime in here soon to help. just keep in mind, these trucks and engines take a lot of patience. so take it slow. I have found that getting the TCDO right where you want it can take a LOT of tries. It's like a crap shoot of getting it right in the first couple of attempts. remember moving the IP 1mm is like changing the timing about 3 degrees! especially when the timing chain has little to no slack.

oh yeah, don't do like I did trying to bump the IP with the engine running LOL I did that after several attempts of back and fourth. it worked for me but later I found out that if the IP had moved too far while running, it could have cause catastrophic damage!!

I am reluctant to even respond here. After much effort, I got my ‘94 set at -1.94 TDCO and thanked my lucky stars, because I can’t tell you how I did it.

 

[steve5309]

Thanks for the welcome and the replys. Im sure the answer can be found here. I took a look at the autel scanner again it lists desired, and actual pump timing. Little word mix up.
Pondering if i should just get a new cps, but i dont want to just throw parts into it, and see what happens. (180,000 miles)
Not sure if if the cps is used in idle loop, so i dont know what is commanding the stepper motor before 170 degrees
As of now when its running the stepper motor pushes the plunger as far as it can go, so it goes to full retard LOL. and the tdco shows 3.5. I could make a bracket and set the tdco wherever. But it would be nice to figure it out.
I have the 1998 wiring diagram I think they are the same

 

[ak diesel driver]

To test the CPS unplug the OS (optical sensor) and try and start it. It will take extended cranking and when it starts it will be running in limp mode. If it doesn't start or if it doesn't run smoothly then the CPS is bad. You can test the OS by reversing the procedure and unplugging the CPS.

 

[steve5309]

To test the CPS unplug the OS (optical sensor) and try and start it. It will take extended cranking and when it starts it will be running in limp mode. If it doesn't start or if it doesn't run smoothly then the CPS is bad. You can test the OS by reversing the procedure and unplugging the CPS.

I'm making some progress and learning more. So i took a long sharp pin and pierced the signal side of the CPS, put a meter on it and saw it was on/off 5 volts ok. (I turned the crank manually) whats strange is the 5 volts seems to be on when the sensor is NOT on the high side of the cam. So the trigger is when the 5 volts is off, I believe. And looking on other forums and posts it looks like this being looked at for testing too.
Another one I discovered is that when the stepper motor extends outward ( in full retard position) it will hold there even when power is disconnected. whoa ( wish I knew that earlier) ok so now I have moved my IP, when the stepper is in the full retard position and redo the KOKO. and low and behold I now have -1.23 degrees. So I'm close and not sure where to set the TDCO for my 99 6.5. I had no idea the stepper motor would hold position, but I can see now that Its when you step on the pedal the stepper relaxes and slightly advances.
So I'm still looking on if I should go up to -2.02 or where?
On a side note, both of the IP's in my barn had advance servo pistons stuck all the way inward, so the advance mechanism wouldn't work, even if the stepper worked ok. And I drove the truck with this IP in it ( and IP other from junk yard). I can see why they get stuck because its the lowest point in the IP where water and grit can collect, and over time if it sticks, you lose that computer advance

 

[Big T]

I'm making some progress and learning more. So i took a long sharp pin and pierced the signal side of the CPS, put a meter on it and saw it was on/off 5 volts ok. (I turned the crank manually) whats strange is the 5 volts seems to be on when the sensor is NOT on the high side of the cam. So the trigger is when the 5 volts is off, I believe. And looking on other forums and posts it looks like this being looked at for testing too.
Another one I discovered is that when the stepper motor extends outward ( in full retard position) it will hold there even when power is disconnected. whoa ( wish I knew that earlier) ok so now I have moved my IP, when the stepper is in the full retard position and redo the KOKO. and low and behold I now have -1.23 degrees. So I'm close and not sure where to set the TDCO for my 99 6.5. I had no idea the stepper motor would hold position, but I can see now that Its when you step on the pedal the stepper relaxes and slightly advances.
So I'm still looking on if I should go up to -2.02 or where?
On a side note, both of the IP's in my barn had advance servo pistons stuck all the way inward, so the advance mechanism wouldn't work, even if the stepper worked ok. And I drove the truck with this IP in it ( and IP other from junk yard). I can see why they get stuck because its the lowest point in the IP where water and grit can collect, and over time if it sticks, you lose that computer advance

The TDCO range is -0.50 to -1.94, so I’d call it good at -1.23.

 

[dbrannon79]

I second that notion. call it good and leave it at -1.23

 

[steve5309]

I second that notion. call it good and leave it at -1.23

Ok, thank you I'll drive it around a see how it goes