4l80e/6.5 NA limp mode??

[Roberttx13]

You should say don't always turn the light on. Some DO turn the light on for trans codes.

No, you will not have battery power to your aldl plug. Do not use a truck manual, use a van manual for 95. There are differences between a truck and van. Sounds to me like a power or ground issue to the controller(ECM, TCM, engine or trans controller, whatever you want to call it). GM many times used basically an engine controller for the 4l80e as it needed a good controller to run it with multiple PWM outputs. Failed controllers is not uncommon on obd1 generation controllers. They werenot the best built, and low voltage can kill them in a hurry. I wouldn't worry about anything else until you can get your controller to respond to the code check test. Verify you have power AND ground to all neccesary wires at the tcm. Use a test light with a decent size bulb to simulate a load. I've seen them showvoltage with a dvom, but go to 0 when connected dueto poor connections, so you need to verify the circuit can hold somecurrent load. Next up is unplug the tps, engine speed sensor, trans, and speed sensors. Any shorts to ground can short the controller and prevent it from working. The 1st goal you have to do is to communicate with the controller. If a shorted sensor or input is found shorti,g it, then you have to fix it. If you completely isolate all circuits to the tcm and still can't communicate with it, then theres a good chance you popped the tcm trying to start it with dead battery's. And you need to find out what is killing your batteries to prevent this from happening again.

Thanks everyone this is steps forward I'll set off tomorrow to see if I can get the obd to respond to the test I'll isolate all the curcits to find the problem. So if the tcm were to fail could it possibly cause the ses light to illuminate because weeks ago when it ran good there were no lights on at all. And is there a way to test the tcm once I have confirmed all bad wires and grounds are corrected in the system? Great tip about putting load on the circuit it makes good sense but never occurred to me!! First and foremost Ill get the obd to respond to the test!

 

[THEFERMANATOR]

Thanks everyone this is steps forward I'll set off tomorrow to see if I can get the obd to respond to the test I'll isolate all the curcits to find the problem. So if the tcm were to fail could it possibly cause the ses light to illuminate because weeks ago when it ran good there were no lights on at all. And is there a way to test the tcm once I have confirmed all bad wires and grounds are corrected in the system? Great tip about putting load on the circuit it makes good sense but never occurred to me!! First and foremost Ill get the obd to respond to the test!

You could build a simulator from pieces from diyautotune, but short of that there isn't much ypu can do other than go through the diagnostic tree in the shop manual. These old style single board controllers are pretty basic, but with being basic, also means something simple can take them out. And yes, the service engine soon light could very well be on because of a bad controller, but it could also be anything else it controls turning it on. I've lost count of how many times I've seen a crank sensor or something simple like that shorted out would leave a controller dead and unable to work with a scanner. The controller would fail the factory test, but the replacement would also not work. Go through and unug sensors 1 at a time until you found the one shorted and would allow it to communicate again with it unplugged.

 

[Roberttx13]

Okay gents im out here wire hounding and checking grounds I found that the engine speed sensor that y'all pointed out to me is not hot with key on...should this be hot? If so this curcuit may have the short. On the fuel heater one prong of the sensor plug reads 12v like the other prong however with a large test light one prong dims very quickly which I assume is a short and not something that's ment to happen. I feel I'm getting closer to knocking this out and being road Worthy again.checking voltage to the tcm next... Keeping fingers crossed as I replace messed up wires that the tcm will survive. Thanks for everything and I'll continue to update as i go along and when she's running

 

[THEFERMANATOR]

No, if it's a 2 wire sensor, it is a magnetic pickup, and it outputs it's own voltage signal to be read by the controller.

 

[Roberttx13]

Okay good to know thanks....I've checked and cleaned every ground on that vehicle and got rid of extra wires running to the back I've taken the entire harness out of the conduit to check for breaks and shorts all in vein.. the controller plug has 12v where it should with key on and off on pin 12. I've cleaned every sensor except the crank position sensor because I can't find the damn thing haha so the tcm has power the transmission has 12.5 volts at the harness plug but still won't flash codes with the ses light only get a code 12 with the abs terminal grounded I've traced the black and white wire and nothing seems amiss in it's curcuit. Next step I'll be unhooking sensors until it will communicate with the aldl if not I guess a reman tcm from cardone will do the trick. This is a whole new world for me I appreciate everyone for hanging with me and for the advice!!!

 

[WarWagon]

You should say don't always turn the light on. Some DO turn the light on for trans codes.

Best way I can think of saying the damn thing may have codes in it without turning the SES light on. Several cratered transmissions and never seen the light on my 1993. This includes TPS out of adjustment, ratio error as 4th/OD scattered, overtemp, speed sensors plugged in backwards... I have only seen the light flicker IMO due to speed sensor wire(s) shorting - it was totaled before we could track it down. I am sure there are exceptions to everything including ECM fault that may turn the light on.

Regardless getting the "diagnostic mode" via a flash of code 12 to work is task #1. X2 on disconnect every sensor. With the rodent damage a short causing this is very likely. IMO you are doing a good job tracking this down.

New parts don't mean good parts. So even as best practice replace the ECM last. It may be bad and not entering diag mode is one strike. Note there is a calibration chip in it under the 2 bolts holding the door on. Do not exchange the ECM without keeping that chip!

One more thing. Key off power: you should have 12v to the ECM for "code memory" when the key is off. So key on is two 12v power wires. Old fusible links fail and this memory circuit should have one.

 

[Roberttx13]

Best way I can think of saying the damn thing may have codes in it without turning the SES light on. Several cratered transmissions and never seen the light on my 1993. This includes TPS out of adjustment, ratio error as 4th/OD scattered, overtemp, speed sensors plugged in backwards... I have only seen the light flicker IMO due to speed sensor wire(s) shorting - it was totaled before we could track it down. I am sure there are exceptions to everything.

Regardless getting the "diagnostic mode" via a flash of code 12 to work is task #1. X2 on disconnect every sensor. With the rodent damage a short causing this is very likely. IMO you are doing a good job tracking this down.

New parts don't mean good parts. So even as best practice replace the ECM last. It may be bad and not entering diag mode is one strike. Note there is a calibration chip in it under the 2 bolts holding the door on. Do not exchange the ECM without keeping that chip!

Thanks for the warning on that I'm assuming that chip is the prom? Will one prom go right into another ecu and become plug and play compatible? The rat damage is pretty severe I've found one eaten glo plug wire, the radio, a ground from the water temp sender, several wires going to running lights and a corroded ground. I just hope the tcm wasn't killed by trying to start low voltage as mentioned before is possible.
I'll replace the tcm with a good reman as a final resort. I've ordered the 4l80e internal and external harness for under 50$ just for security. Ill continue the hunt for lost and hopeless wires and report back. Thanks again!

 

[Roberttx13]

Best way I can think of saying the damn thing may have codes in it without turning the SES light on. Several cratered transmissions and never seen the light on my 1993. This includes TPS out of adjustment, ratio error as 4th/OD scattered, overtemp, speed sensors plugged in backwards... I have only seen the light flicker IMO due to speed sensor wire(s) shorting - it was totaled before we could track it down. I am sure there are exceptions to everything including ECM fault that may turn the light on.

Regardless getting the "diagnostic mode" via a flash of code 12 to work is task #1. X2 on disconnect every sensor. With the rodent damage a short causing this is very likely. IMO you are doing a good job tracking this down.

New parts don't mean good parts. So even as best practice replace the ECM last. It may be bad and not entering diag mode is one strike. Note there is a calibration chip in it under the 2 bolts holding the door on. Do not exchange the ECM without keeping that chip!

One more thing. Key off power: you should have 12v to the ECM for "code memory" when the key is off. So key on is two 12v power wires. Old fusible links fail and this memory circuit should have one.

Fusable link to the ecm, should it be near the fuse block or coming off the tcm? I'd like to check that for sure I'll confirm the volatage right now

 

[EWC]

The battery feed is A12 , Orange with batt voltage . The ign feed is C16 and batt voltage with key on and also with engine running . This is in the 32 pin connector in one corner with a BLU/WHT wire next to it . There are 10 open cavities in the row and then 4 more wires . The only other item is battery feed to the trans , pin E at the trans connector . The reason I mentioned A8 is that wire could be broken and then no codes . I'd pull the TCM connector and check that wire back to the ALDL . The PROM pulls straight up . Make sure no pins are bent and then straight back down to replace .

 

[Roberttx13]

The battery feed is A12 , Orange with batt voltage . The ign feed is C16 and batt voltage with key on and also with engine running . This is in the 32 pin connector in one corner with a BLU/WHT wire next to it . There are 10 open cavities in the row and then 4 more wires . The only other item is battery feed to the trans , pin E at the trans connector . The reason I mentioned A8 is that wire could be broken and then no codes . I'd pull the TCM connector and check that wire back to the ALDL . The PROM pulls straight up . Make sure no pins are bent and then straight back down to replace .

Awesome thanks so much for walking me through this... I'll trace that wire back and confirm that's it's good from the tcm plug. Is there any kind of vacuum pump sensor? I just found a piece of small black hard plastic cap tubing coming from what looks like the vacuum pump and it was sucking air like crazy is this correct on a diesel I assumed manifold vacuum leak and plugged it now the engine isnt running as high in the rpm range

This is a dumb one but do the proms go bad or just the control modules? And no flash needed if I used my existing prom in a new tcm?

 

[WarWagon]

Post a pic of what you think is the vacuum pump part that was sucking air.

ECM = TCM for you. we call it diffrent things , but, same stupid computer controller.

 

[THEFERMANATOR]

Very rarely do proms fail. It's happened before, but it is highly unlikely. And the prom is what tells the controller what to do. Without it, it does nothing, so make sure it is swapped in.

 

[Roberttx13]

Post a pic of what you think is the vacuum pump part that was sucking air.

ECM = TCM for you. we call it diffrent things , but, same stupid computer controller.

I'll get that pic on here I'm the morning yeah thanks to this forum I learned that they're all pretty much like you say a stupid computer haha I love my '65 Pontiac for it's simplicity.

And thanks Fermanator if I have to get another module I'll definitely keep the prom to swap in. This one has BLUE molded in the underside of the prom... aftermarket? Shouldn't it be Delco or subcontractor of gm?

 

[MrMarty51]

You could build a simulator from pieces from diyautotune, but short of that there isn't much ypu can do other than go through the diagnostic tree in the shop manual. These old style single board controllers are pretty basic, but with being basic, also means something simple can take them out. And yes, the service engine soon light could very well be on because of a bad controller, but it could also be anything else it controls turning it on. I've lost count of how many times I've seen a crank sensor or something simple like that shorted out would leave a controller dead and unable to work with a scanner. The controller would fail the factory test, but the replacement would also not work. Go through and unug sensors 1 at a time until you found the one shorted and would allow it to communicate again with it unplugged.

I have one of those simulators setting in My tool box. Also have a DIY standalone controller.

 

[Jaryd]

I'll get that pic on here I'm the morning yeah thanks to this forum I learned that they're all pretty much like you say a stupid computer haha I love my '65 Pontiac for it's simplicity.

And thanks Fermanator if I have to get another module I'll definitely keep the prom to swap in. This one has BLUE molded in the underside of the prom... aftermarket? Shouldn't it be Delco or subcontractor of gm?

The know stock ones have “blue” molded into them. I don’t know if aftermarket ones do or not. Picture of the stock chip out of my 95 parts truck

 

[Roberttx13]

The know stock ones have “blue” molded into them. I don’t know if aftermarket ones do or not. Picture of the stock chip out of my 95 parts truck View attachment 53352

Looks exactly like mine!! And can someone explain to me the diy standalone controller? Isn't that pretty much what mine is since it's just an tcm is mine "standalone"? Thanks guys!!!

 

[EWC]

I've got one of those EPROMs , BLUE means nothing . It's the letter code on the other side that's important .

Yes , you basically have a standalone ECM .

 

[Roberttx13]

I've got one of those EPROMs , BLUE means nothing . It's the letter code on the other side that's important .

Yes , you basically have a standalone ECM .

Okay thanks for answering that for me. I'm back under this damned thing again I'll keep everyone posted!

 

[Roberttx13]

Post a pic of what you think is the vacuum pump part that was sucking air.

ECM = TCM for you. we call it diffrent things , but, same stupid computer controller.

The green vacuum cap is where it was pulling air like crazy about 1/4" or smaller ID of the tubing coming from the pump.

 

[WarWagon]

Do the door controls for HVAC (Heat, AC) use vacuum on the van? Other than the doors for HVAC vacuum would (could) control the turbo waste gate (not likely), EPR on the exhaust driver's side back of manifold, cruise control, and EGR. Does your van have either EPR or EGR? EPR is exhaust pressure regulator via a valve in the driver's side end of manifold that adds more EGR flow and flows gas through the intake manifold's EGR ports from driver side to passenger side to help warm up.

As an aside EPR and EGR are items that were on my 1988 1/2t burb controlled by a hard to research even today Command Control computer of some kind. You wouldn't have this rather it would be part of that ECM we are looking at.