Ghost in the machine?
09-25-2008, 09:40 PM
#1
Pro
Thread Starter
Ghost in the machine?
Think I may have a computer gremlin... after driving my 85 auto for the week, I've noticed the trans goes in and out of lockup mode. (I don't know what exactly to call it, so until someone corrects me I'll call it lockup) I assume this is the TC lockup, but don't know for sure. I do know it exhibits the same behavior when my speed drops below 40, feels like it unlocks or comes out of overdrive or something and the RPM's rise. I know very little about auto trannys and torque converters, so I hope that explanation makes sense!
I notice this randomly for random periods of time. I noticed it once last weekend, as I was cruising down I85 at about 75mph, it did it for a couple of seconds then locked up again back to normal cruising RPMs. Today it has gotten more frequent and lasts for minutes instead of seconds. No rhyme or reason at all. Today, with it stuck in the unlock mode I exited off I85 and when I got to the light, it was idling (in Drive) around 1000rpm- usually it's around 560rpm.
The last symptom- under hard accel, I noticed severe knock which it never does. I haven't noticed any knock under light/normal acceleration. I did have to put a few gallons of 87 oct to make it to a station that actually had 93 oct (damn SE fuel shortages), but that was Saturday and it hasn't knocked any all week long til today.
EDIT: I'm talking about spark knock, like it's badly out of timing.
To me, this seems to be computer or sensor related, but how? The actual ECM? Just the chip in the ECM? Any advice???
I notice this randomly for random periods of time. I noticed it once last weekend, as I was cruising down I85 at about 75mph, it did it for a couple of seconds then locked up again back to normal cruising RPMs. Today it has gotten more frequent and lasts for minutes instead of seconds. No rhyme or reason at all. Today, with it stuck in the unlock mode I exited off I85 and when I got to the light, it was idling (in Drive) around 1000rpm- usually it's around 560rpm.
The last symptom- under hard accel, I noticed severe knock which it never does. I haven't noticed any knock under light/normal acceleration. I did have to put a few gallons of 87 oct to make it to a station that actually had 93 oct (damn SE fuel shortages), but that was Saturday and it hasn't knocked any all week long til today.
EDIT: I'm talking about spark knock, like it's badly out of timing.
To me, this seems to be computer or sensor related, but how? The actual ECM? Just the chip in the ECM? Any advice???
Last edited by c4_4ya; 09-26-2008 at 11:27 AM.
09-26-2008, 12:21 PM
#2
Burning Brakes
The only way you are going to discover what is happening with the Knock issue is to drive it around while scanning or datalogging. This assumes that whatever is going on doesn't set a code, eventually. The SES light Does work, right?
As for the lockup - several things cause the ECM to unlock the convertor. The most Obvious would be the switch on the brake pedal- are you Certain that the brake switch isn't becoming un-adjusted and doing this to you? Does the Cruise control work normally (same switch..)?
Both of these problems really only "share" one thing - One thing that Could (possibly) be causing Both issues - the TPS switch. Really out of sync TPS readings could cause a greater liklihood for spark knock (if the ECM was dialing back lean, or Trying to), and the ECM will unlock the convertor at either extreme of TPS travel - nearly closed to idle or beyond some percentage of travel going towards WOT. BUT -If the TPS was messing up I would expect you would have Other driveability problems, and the SES light ought to be lighting up anyhow.
Of course these Could just be coincidence, and not related. The TCC solenoid could be dying and the Knock sensor could be failing too. Something like that.
As for the lockup - several things cause the ECM to unlock the convertor. The most Obvious would be the switch on the brake pedal- are you Certain that the brake switch isn't becoming un-adjusted and doing this to you? Does the Cruise control work normally (same switch..)?
Both of these problems really only "share" one thing - One thing that Could (possibly) be causing Both issues - the TPS switch. Really out of sync TPS readings could cause a greater liklihood for spark knock (if the ECM was dialing back lean, or Trying to), and the ECM will unlock the convertor at either extreme of TPS travel - nearly closed to idle or beyond some percentage of travel going towards WOT. BUT -If the TPS was messing up I would expect you would have Other driveability problems, and the SES light ought to be lighting up anyhow.
Of course these Could just be coincidence, and not related. The TCC solenoid could be dying and the Knock sensor could be failing too. Something like that.
Last edited by rons85; 09-26-2008 at 12:34 PM.
09-26-2008, 01:57 PM
#3
Pro
Thread Starter
Thanks Ron for the TPS idea, I didn't realize it had anything to do with TC lockup, good to know. I guess it's possibly going bad, as the last time I tried to adjust it, I had to adjust it as far as possible to get the correct reading (.54 I believe?) Is this a sensor a parts store (Oreilly's) can test?
09-26-2008, 04:03 PM
#4
Burning Brakes
Sure - the ECM decides when to lock or unlock the TPS based on Tables that compare %TPS to speed - separate tables for lock and unlock and for both 3rd and 4th gears. These can be edited in the PROM program.
There are also Several constant set values for TCC lock and unlock speeds (for each gear), TPS thresholds for TCC enable and Disable, TCC enable/disable Delta TPS constants, a Force Lock Speed and a TCC Unlock Pevent RPM. All of these are editable. You can dial yourself right out into left field with all of it.
All the TPS consists of is a variable resistor - same idea as a slot car controller. You can measure or "test" it with a multimeter, or check it on the car with a scan tool (or laptop/software/cable for OBDI). We don't Have O'reilly's around here in the Northeast - but checking the TPS is simple enough that about anyplace, or anyone, ought to be able to do it.
How it works is the ECM provides a 5v. reference signal out to the TPS, then measures the voltage it gets back. That voltage, as a percentage of 5.0, is the TPS value the PROM uses. (since the TPS theoretically could only "show" a max voltage of 4.5, the % Might be based on That, not 5.0 - I'm not certain on that one..) When a scan tool Displays the reading, it is the Voltage coming back to the ECM.
BTW - there is also a PROM table for TPS vs. RPM to enable WOT mode...which can be triggered at about Any %TPS you might want. The Factory threshold values are all set at about 70%, which would be about 3.5 volts - that's the TPS value where the ECM switches to WOT or "open loop" operation.
If the TPS was Completely faulty one of two codes would set - low TPS voltage or High TPS voltage (depending on how it failed - open or shorted). This will light the SES lamp and prevent normal closed loop operation. Other things could be happening, obviously - a bad wires someplace in the harness (hey - it's a 23 year old car!), a bad wire Connection, the ECM itself doing something goofy, like not holding the 5volt reference correctly, etc. A Bad "spot" in the TPS Might be your TCC problem, only scanning or datalogging is going to tell you that.
Here's another odd possibility - the ECM "knows" when the transmission is in 3rd or 4th gears - and Needs to know that for the TCC to operate. That switch (inside the trans) or connector At the trans, could be causing what's going on. Again - Scan Tool
There are also Several constant set values for TCC lock and unlock speeds (for each gear), TPS thresholds for TCC enable and Disable, TCC enable/disable Delta TPS constants, a Force Lock Speed and a TCC Unlock Pevent RPM. All of these are editable. You can dial yourself right out into left field with all of it.
All the TPS consists of is a variable resistor - same idea as a slot car controller. You can measure or "test" it with a multimeter, or check it on the car with a scan tool (or laptop/software/cable for OBDI). We don't Have O'reilly's around here in the Northeast - but checking the TPS is simple enough that about anyplace, or anyone, ought to be able to do it.
How it works is the ECM provides a 5v. reference signal out to the TPS, then measures the voltage it gets back. That voltage, as a percentage of 5.0, is the TPS value the PROM uses. (since the TPS theoretically could only "show" a max voltage of 4.5, the % Might be based on That, not 5.0 - I'm not certain on that one..) When a scan tool Displays the reading, it is the Voltage coming back to the ECM.
BTW - there is also a PROM table for TPS vs. RPM to enable WOT mode...which can be triggered at about Any %TPS you might want. The Factory threshold values are all set at about 70%, which would be about 3.5 volts - that's the TPS value where the ECM switches to WOT or "open loop" operation.
If the TPS was Completely faulty one of two codes would set - low TPS voltage or High TPS voltage (depending on how it failed - open or shorted). This will light the SES lamp and prevent normal closed loop operation. Other things could be happening, obviously - a bad wires someplace in the harness (hey - it's a 23 year old car!), a bad wire Connection, the ECM itself doing something goofy, like not holding the 5volt reference correctly, etc. A Bad "spot" in the TPS Might be your TCC problem, only scanning or datalogging is going to tell you that.
Here's another odd possibility - the ECM "knows" when the transmission is in 3rd or 4th gears - and Needs to know that for the TCC to operate. That switch (inside the trans) or connector At the trans, could be causing what's going on. Again - Scan Tool
Last edited by rons85; 09-26-2008 at 04:10 PM.
09-26-2008, 04:10 PM
#5
Pro
Thread Starter
No SES indicated, and last I checked it did work. Interesting stuff on the lockup and TPS, etc. Any possibility the TPS could be hosed (or loose) this badly and not trip a code?
09-26-2008, 04:47 PM
#6
Burning Brakes
I'm not sure.. I suppose it Could be flakey in a way that would cause the TCC issues, but would Not set a code. Anything is Possible..
Parts will fail in the weirdest ways, sometimes.
I don't know - I think I'd Really have to be sure of other things, in your case. Transmission gear switch is high on that list. The Brake pedal switch.
A scan tool would show you weather or not the ECM was Commanding the TCC to be locked, or not. That would be a good place to start
Parts will fail in the weirdest ways, sometimes.
I don't know - I think I'd Really have to be sure of other things, in your case. Transmission gear switch is high on that list. The Brake pedal switch.
A scan tool would show you weather or not the ECM was Commanding the TCC to be locked, or not. That would be a good place to start