Low 5v ref

[fixkick]

Ok mr,

  she ran GREAT sat.  Now she’s dropped the ref vol AGAIN.
Totally rewired tps. Maf ect and o2 pulled from back of ecu.
She’s definitely in limp home mode now.  
Don’t know why it ran so good sat.  (just running is easy, the limp mode does that, on all cars made (1989 up EFI) that is  the purpose of LIMP to limp home with dead sensors on the car.
it has no other purpose,  15MPG in limp home will make you go broke fast. on gas costs,  it is just to get you say out of snow bank, at -10 F and not walk home and freeze to death
that IS its only purpose, (nor stall dead in front of Logging truck with bad brakes) see?


Didn’t seem to affect it at all that the other sensors weren’t on there (you do no understand what LIMP IS or DOES) but could smell that it was runn rich- lean... something.
Wasn’t getting any black smoke. Ummmm.  (well the CAT eats up  the mess glows red hot and burns up the cat) that is what it does. in limphome mode.,)

 Ref is down to .08 now.  Totally lost again....  bad ecu???  
The +5vdc refr, is just a power source and like all sources of power, even batteries, solar cells , or generators of any kind
I'd guess max load is 1amp (even less)

1. the source is bad. (ECU) (or can be intermittent all by itself )
   
2. the wires cut. from TPS to ECU will make +5 go dead at TPS, called and OPEN circuit. (called a bad connection)
   
3. the load is shorted that means in terms of cars the sensor is shorted.
   

 if the +5vREf fails at the ECU actual pin named that, then it can not be #2, see why?  



Had a rebuilt one in there ran great for couple days without the maf plugged in minus the hiccup at say 3500 rpm then it dropped the ref.
    This time..sat... it ran even better with the rewired tps...and no maf ect and 02 sensors. 
    
  Maybe this ecu is shot????  And the other rebuilt one blew because of the bad maf??  (again the MAF  does not use +5VREF, it uses 12vdc battery power,only) forget MAF.(in this context)


  
    Bout ready to scrap this ol girl. Tired of throwing money at it.  (yes old cars are for sure a huge money sink, for sure bad ECU that costs $400 for  real one from CARDON1 refurb top source)


   Definitely appreciate your insight.    Thanks

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[b]Yukonjay[/b]  
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#18
02-16-2021, 05:16 AM 
Also.....

I had the ecu on the floor so I could access it for testing. Is it missing a ground by not being screwed in??  (yes there are 2 grounds, earth(case) and 1 battery ground.)

the case ground is only for noise reduction.  ECU runs fine like that for testing, and wise to do that way.    The inputs on the ECU have noise reduction caps to earth ground case)

sure seems to me bad +5ref inside ECU,  the TPS can not  short out, (inside it is pure carbon inside on top pure ceramic base) it will not short. wires yes.
nor ECT ,IAT (super rare to short this, but wrong sensors can, here,  but some ECT are switches inside, and no good here stolen from other cars, see folks do that, and bad to the bone it is.)

most times it is BAD WIRING,  and us super common that, on cars this old, ratty nasty wiring. (and there connector pins bad)

the MAF can NOT Short out +5vREF, it can not do that,  ever , the MAF is a 12vdc powered sensor not 5v. see?

all other sensors use 5v directly or indirectly.

for sure finding bad ECU or finding any kind of INTERMITTENT short is not easy on any car for sure moving.

the +5vref is bad inside the ECU
or the loads on it are shorting to ground,  if  shorted to 12vdc that blows the ECU +Vref up to H3LL.
Many ECUs do have bad +5vREF, and is the first test done, and DTCs or Dead CEL lamp.


this PC has mode called BACKUP mode, and tons of black smoke (or cat burning up, eating all that crap)
Backup mode is like 1960s lawmower engine, no controls at all much.

the clue is CEL lamp is totally dead.
so now you know the 3 modes of ECU, Backup, Limphome and normal.

The ECU does not know why it fails only that it DOES.

good luck finding the cause or  good  used cheap ECU,. rare that. now.