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Pete, Buick Technician
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Experience:  15 years Buick Technician experience and training.
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I have a 1990 Buick Century Limited 3.3 I have no injector

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I have a 1990 Buick Century Limited 3.3 I have no injector pulse. I have changed the crank sensor, witch is a duel purpose sensor, there is no cam sensor. I have also replaced the ECM and the ICM. I have ohmed out all wiring from the ECM to the ICM, and all wiring from the ICM to the crank shaft sensor as well. Also checked for power and ground at ECM all good. I do have 12v at ijectors. The injector drive signals from the ECM are putting out 12v positive power during cranking. Should'nt this be ground pulses? I consider myself to be an exelant tech but this has me stumped. Please help!!Also have checked for power at ICM and I have it.
Submitted: 4 years ago.
Category: Buick
Expert:  Pete replied 4 years ago.
Hello,it sounds like you definitely know your stuff here,yes you are right the ecm should be pulsing ground signals to one wire at the each fuel injector,the other wire should be hot with key on,since you have already replaced the ecm the only other thing I can think of is a shorted injector harness,it almost has to be shorted to voltage as you are getting power on the pulse side.If the power is constant then this should be the case,I have seen this once before,unfortunately it also took out the new ecm that was installed in the vehicle from being shorted to voltage.I found my short believe near the alternator,I cant remember whether it was under the alternator or behind it,I know some of these vehicles had a shorting issue behind the alternator near the firewall,it was rubbing through I believe on a power steering hose.Your going to have to trace the engine harness on top of the engine all the way to where it goes in through the firewall to see if you can locate this short.Hopefully you haven't damaged the new ecm,you may have since you have no spark once again.It pretty much sounds like you have covered almost everything,I suspect you may have a shorted harness here.I hope this information helped,if you need anything else let me know,if you feel satisfied that I have assisted please click the accept answer button as this is how I get paid,positive feedback is appreciated,Thanks Pete.
Pete, Buick Technician
Category: Buick
Satisfied Customers: 16435
Experience: 15 years Buick Technician experience and training.
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