Chevy Impala SS Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
472 Posts
Discussion Starter · #1 ·
My 94 caprice stalled on me,it started back up but went into limp home mode.This was three weeks ago.I have no trouble codes and have replaced the following with no change.Opti,maf,tps,icm and pcm.The car car starts and runs normal then stalls and goes into limp home mode,third gear start and 1500 rpm idle.When this happens my lt1 scanmaster goes blank.All sensors show to be working fine prior to the car stalling and like i said earlier no trouble codes.What am i missing here? any and all help much appreciated, Randy
 

·
Premium Member
Joined
·
8,383 Posts
With your scanmaster does it show your ECT working? What is the fuel pressure? I know that fuel pressure wouldn't cause a limp home mode, but ECT may. Do both the fans kick on when it is in this mode? I will do some digging and see what I can find as far as what would cause limp home mode.
 

·
Registered
Joined
·
472 Posts
Discussion Starter · #3 ·
With your scanmaster does it show your ECT working? What is the fuel pressure? I know that fuel pressure wouldn't cause a limp home mode, but ECT may. Do both the fans kick on when it is in this mode? I will do some digging and see what I can find as far as what would cause limp home mode.
ect reads fine on the scanmaster and yes both fans do kick on.I just went out and started it up ,checked all sensors reading okay then stall,restart in limp home mode.
 

·
Registered
Joined
·
472 Posts
Discussion Starter · #5 ·
How long does it take to stall out? few seconds or minutes?
The only thing that I can think of would be system voltage, that would be battery, alternator etc, but I am still digging on the limp home causes.
I would say a few minutes,i checked the voltage also thinking that and it appeared to be fine.this is a really strange one and i keep going over my factory manual and not getting any answers.
 

·
Premium Member
Joined
·
8,383 Posts
Yeah I can't find it either, I will keep digging tonight and see if I come up with something, just sounds weird, what about the grounds at the drivers side head, what is boggling me it is like the PCM is shutting down since your scanmaster doesn't work.
 

·
Registered
Joined
·
413 Posts
If you have changed what you said with no change. I am guessing broke wire somewhere. As to what not sure. If 94MI9C1 can narrow down what could cause the limp mode that would help.
I know a work truck I drove did same kinda thing and it was bad ecm ground.
Id say check all your grounds. Then check all wires that run + power to sensors or control icm and pcm. I will have to say this sounds like a wire is bad somewhere.
Being the work you have had done I would suspect bad wire. You move old wires around enough they break and sometimes you dont know.
Cant bad trans temp cause limp mode or too high or low a voltage on a sensor.
Also ecm getting too much power or not enough?
Just taking guesses here.
 

·
Registered
Joined
·
472 Posts
Discussion Starter · #9 ·
Yeah I will see what I can find but can't guarantee anything. The ground point at the head FWIW it is worth is the system grounds for the PCM and all the sensors. Check there first and see what you find.
it looks okay and is tight,but i think i will take it apart and have a closer look,just seems like how this is happening could be caused by a short or grounding issue.
 

·
Premium Member
Joined
·
8,383 Posts
it looks okay and is tight,but i think i will take it apart and have a closer look,just seems like how this is happening could be caused by a short or grounding issue.
Very true, if the ground is shi*** and let's say a higher resistance, it will cause more loading on the PCM to accomplish the same thing. On other thing to note is to whether it happens once it goes to closed loop or not.
 

·
Premium Member
Joined
·
8,383 Posts
explanation of limp home mode
What is "limp-home mode" ? This is a fault mode in which the transmission either loses electrical power or the PCM deactivates all of the electronics. The transmission will default to max line pressure. The driver will have Reverse and 3rd, with manual 2nd available by putting the gearshift in 2 or 1 (doesn't matter). 1st, 4th, and TCC lockup will not be available. It will not hurt the car to drive it like this for short periods, but use manual 2nd to get the car moving, and be aware that the trans will generate more heat than normal while operating in limp-home mode due to increased torque converter slippage during 2nd gear starts and no lockup in 3rd gear. This explains the scanmaster shutting down and all that, just have to figure out why the PCM is shutting down.

also note did you check the fuses, the #5 fuse for the PCM in the U/H panel labeled TRANS sends power to the PCM as well as the Trans, FSM states that it only powers the PCM for ignition feed, but not exactly sure if that is entirely true as I don't have the internals to the PCM where as if it would run if this fuse was blown and the PCM would get the power from elsewhere. Still digging.
 

·
Premium Member
Joined
·
8,383 Posts
Also ignition switch could be causing this as in not passing enough power to the PCM and related components. Are there any other weird things not working, the wire that is feeding the U/H panel for the PCM power in the ignition on state is spliced inside and this also feeds, the turn signal, abs, chime, i/p indication, air bag, and pass key.
 

·
Premium Member
Joined
·
8,383 Posts
Could be a grounded internal harness to the trans causing a load in the PCM of sorts, as listed here in this thread http://www.ls1lt1.com/forum/showthread.php?t=33719&page=3 Still digging.


TPS and VSS can cause limp home mode as well. But I think that it is a ground power or short, something along those lines.
 

·
Registered
Joined
·
472 Posts
Discussion Starter · #15 ·
Could be a grounded internal harness to the trans causing a load in the PCM of sorts, as listed here in this thread http://www.ls1lt1.com/forum/showthread.php?t=33719&page=3 Still digging.


TPS and VSS can cause limp home mode as well. But I think that it is a ground power or short, something along those lines.
I think i have it !!! Took apart harness and found loose spliced wire,d3 pcm ignite feed,must have been connected just enough to pass current then lose contact.I will make proper repair tomorrow afternoon and report results. I really appreciate you spending the time here!! b-body people are the best !!!!!!!!! ,Randy
 

·
Registered
Joined
·
472 Posts
Discussion Starter · #17 ·
No problem Randy glad I could help. I am betting that internally the PCM if it senses a current draw issue on itself it shuts down to protect itself. Hope to hear good news from you tomorrow, good luck.
That was it,fixed wire and all is good!!!!!!!!!! Wow one little wire causing such a big ole head ache.....lol. ,Randy
 
1 - 18 of 18 Posts
Top