GM TBI Weak Signal

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  #1  
Old 03-11-06, 01:47 PM
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GM TBI Weak Signal

1987 2.5 4cy Olds Ciera rebuild her a year ago,
No Codes, after about 10 minutes with engine warm the TBI quits. A noid barely blinks very dim. Wait 10 minutes and noid will blink bright and it will run again. During the problem there is 12 volts on the red wire at the TBI. Seems like a bad connection but I can't find one. I pulled the ECM and all connections look fine. These GM 4 cyls are a hobby of mine and have never got me before. Also all sensors seem good and O2 is almost new. Was thinking about changing the ECM but I have never had a bad one. I thought they quit or give codes. Help!!!
 
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  #2  
Old 03-11-06, 04:44 PM
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so the injector has 12 volts is this with the injector still connected if you backprobe the injector connector you can check voltage with it still connected and when the engine does die it is obvious by reading the meter if it is a power supply problem or not to the injector.
have you tried tapping lightly on the ecm to see if it causes any difference either when the car is running and when the car will not start.
have you ever checked codes if so was there any?
is this car equiped with a distributer or is it a distributerless ignition system and have you checked for spark when the car dies does it still have good spark?
 
  #3  
Old 03-12-06, 07:55 AM
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12 volts from red wire to ground on TBI. Blue returns to ECM and it completes circuit with pulses. That is what is weak.
Have ECM hanging down so I can do that. I wish I had a circuit board diagram. I could understand it and would check it out.
No stored codes ever for this problem.
Car has DIS and I am pretty sure it works. Car will run on spray either.
One of my thoughts was that maybe crank sensor controls fuel pulses via ECM.
As you see this is a hobby and challange. I don't have to make it run and I don't care if I have to buy parts. I just want to find the problem. This car is like a stress reliever. I like to think I can find any problem on a GM 4cyl with out guessing and changing parts first. I have teenage kids and I am known as the GM fix guy. I am tyrying to teach them some values. Thanks!
 
  #4  
Old 03-12-06, 09:01 AM
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its not uncommon for ecms to go bad on older gm vehicles, so a bad ecm is very likely a scan tool can often help diagnose them as you are able to scan data from the ecm and see all the sensor data.
 
  #5  
Old 03-12-06, 11:41 AM
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agree with bejay ecm do go bad after some years, i just replaced mine on a 92 suburban 3 months ago i was driving on the freeway and engine died out of the blue, highway assistance guy had a scanner and said ecm most likely...he was right on the money ( $ 65 at autozone )
 
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