- 674
- 1,284
- 93
- Location
- Mesa, Colorado
Steel Soldiers now has a few new forums, read more about it at: New Munitions Forums!
What's weird is that it only bumps up a small amount of rpm's, barely noticeable but clearly as a result of the switch activation.There may be some condition not met for it to enable/allow fast idle, like throttle position not low enough, or neutral or some such. Not specifically familiar with the specific requirements for fast idle, but it may be something like this causing your issue…
It's definitely going into fast idle mode but the rpm change Varies greatly. Normally to about 1200 rpm but half the time it only goes up by 50-100.Conditions for Engaging the Fast Idle System
When all of the following conditions are present the idle speed will increase to the selected value and the FAST IDLE lamp will illuminate.
The engine is running
The transmission is in Park (P) or Neutral (N)
Vehicle speed is not detected
The FAST IDLE switch is depressed and released
Conditions for Disengaging the Fast Idle System
When any of the following conditions are present the engine speed will return to the normal engine idle speed and the FAST IDLE lamp will turn OFF:
The engine is not running
The transmission is not in Park (P) or Neutral (N)
Vehicle speed is detected
The FAST IDLE switch is depressed
I tried this today. Needle is off zero to begin with, then goes to zero on ignition switch on. No change if I cycle mode once the truck is running. However, this speedometer does act squirrelly at times when driving. It's gone to zero a few times while on the street and I have to stop and cycle ignition to get it back. More dirty connectors I gather?here is an alternate theory for you all to crunch on…
I have come across a few people who have had intermittent issues with the transmission throwing speed sensor codes, myself among them when I select mode. What I am theorizing might be happening is that there is a weakness in the pass-thru connector on the transfer case. That connector carries the transfer case lockup solenoid signal and the output speed sensor signal… The Allison uses a 7Khz PWM signal to control the solenoid valves. It sends it all the time. At a low PW, it uses it to test the circuit and higher PW to actually activate the solenoid. What is happening in my case when I select mode, my speedo needle twitches and my TCU throws a fault as it is sensing output speed with no transmission turbine speed as the vehicle is not actually moving… I havn’t gotten a chance to scope it yet and see exactly where the crosstalk is occuring…
So what I am theorizing, since what I have read indicates vehicle speed detection inhibits fast idle, if there were some crosstalk in that connector on yours, it may be sending back enough signal on the output speed line to tell the ECU that there is vehicle speed, which might be inhibiting the fast idle?
so here is a test or two for you:
While watching your speedometer very closely, does the needle move when you turn on the ign, or after you start the truck?
while watching your speedometer needle very carefully, after it is running, select mode. Does the needle move?
I suppose another check in your case might be to simply disconnect the transfer case cannon plug on the front of the transfer case and then see how your fast idle behaves…
Dirty or failed, what I am getting is 7KHZ differential solenoid PWM signal being fed back thru the speedometer signal lines. These 2 signals share a 4 pin passthru connection on the front of the transfer case. If you were getting something similar, the rogue speed signal input might be great enough that the ECU detects it and restricts fast idle… if you unplug the transfer case connector, does your fast idle work consistently?I tried this today. Needle is off zero to begin with, then goes to zero on ignition switch on. No change if I cycle mode once the truck is running. However, this speedometer does act squirrelly at times when driving. It's gone to zero a few times while on the street and I have to stop and cycle ignition to get it back. More dirty connectors I gather?
I haven't tried this specifically yet. The next cold day start will be the best time to test it as that's the only time there's an issue. Never happens above 40F.Dirty or failed, what I am getting is 7KHZ differential solenoid PWM signal being fed back thru the speedometer signal lines. These 2 signals share a 4 pin passthru connection on the front of the transfer case. If you were getting something similar, the rogue speed signal input might be great enough that the ECU detects it and restricts fast idle… if you unplug the transfer case connector, does your fast idle work consistently?
My C7 will change idle a little in the cold similar to what you describe but no where near the rpm of the fast idle switch. I'd guess a few hundred rpm change. This is including down in the single digits.Our 2003 M1078A1 does on its own cycle to high rpm (though I haven't yet checked exactly how fast) when starting in colder weather. Though it does so after running a bit and doesn't stay there long. Clicking the high low switch always works while in neutral (1,350 rpm) and goes back when clicked again (700 rpm). It worked today—
Hhhhhmmm - you sure your grid heater is working? My experience down to the ether set temp (about 20) has been that if you wait till the grid heater light goes out they will start right up. I've never once had to run the starter more than one time. Even down to 16 degrees where the Ether kicked in.Well, in the last week I replaced my fuel hand primer, fuel lines, IDP and high pressure sensor. Last night was in the low 30’s, this morning I started the truck. Initially It had a hard time staying running, had to restart three times. However once a good idle was established, it idled right up as it never has before.
I took a video, no movement detected on the Speedo.
IDP? I must be having a senior moment. Not recalling what you are referring to.I believe the grid heater is working. But I can check it. I wonder if there is a learning curve with the ECM for the new IDP, the old one certainly was not functioning properly. The ECM I’m sure was trying to compensate for it somehow.
We get it, advertisements are annoying!
Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!