QuestionQUESTION: On a 1997 Grand Prix SE (3.8 efi Non SC) what will cause the injectors and IAC not to pulse? JUST CHANGED-Fuel Pump,MAF sensor, Cam Sensor, ECM. It is getting spark and will run on fuel poured into the throttle body. I did not install the FUEL pump, but when the key is turned to "on" position, it does come on and pressurize the line, but it doesn't shut off, it keeps running. I know the prior fuel pump did not operate in this manner. The car would not start after a visit to a mall , which prompted the fuel pump change. There was no fuel pressure at the schrader valve, therefore it was changed. Got pressure, but now no pulses on the injectors or IAC.
Already Tried:
I'm the second guy to work on it;I went after the MAF because it did have a MAF code months ago before the "no start" occured at the mall. Then I checked the injectors/IAC with my NOID light and get nothing; then I went after the CAM SENSOR first before i TRY THE CRANK SENSOR. Trying to PINPOINT the ROOT CAUSE and not give the car a complete "emissions overhaul". Plugs are not perfect but are not fouled as it will run on a little cup of fuel into the throttle body.
ANSWER: Hi there:
welel lets start with the parts you replaced and an explaination of things. The ecm need to be programmed if you put in a used ecm or a new remanufactured unity it need to be programmed to match the car. this has to be done at a AC delco repair shop or the delaer. if the ecm was not programmed that could be you issue of no injector pulse. THE IAC does not "pulse" it's a bidrectinal motor in runs in and out to control the idle speed. It will not have anything to do with injector pulse. You need a true scan tool to look at engine data when the engine is cranking to see if indded the engine computer sees that the engine is cranking. If it doesn't see engine speed input then either the wiring between the ignition module and the ecm is bad or the module is bad or the engine computer is bad. If it doesn't see engine speed it will not pulse the injectors. As for the fule pump it should not run all the time when you turn the key to run it should run for about 1 second as a prime. if it keeps rnning it would look at the fule pump relay as being bad ot again backto the computer not being programmed. good luck :)
---------- FOLLOW-UP ----------
QUESTION: So the orig ECM lost it's programming from sitting in a parking lot? Because that's what prompted all of this. What causes that to happoen? I'm confused that the ICM could be bad since the car is getting spark; remember it does run when I hand feed fuel into the throttlebody.
ANSWER: No you said you replaced the ECM and that is what prompted me to say that it need to be programmed. I think you may have mad this issue worse by throwing parts at it instead of diagnosing it properly. The ICM does multiple things besides control the coils it converts the crank signal to a signal that the ECM need for fuel control.
---------- FOLLOW-UP ----------
QUESTION: I understand that replacing the ECM prompted you to say that, but from the original problem, a "no start" condition that made the fuel pump stop working, the ICM ultimately controls the fuel system as well? So why now does this make the FUEL PUMP keep running after priming the system? Is it "FLOODING" the cylinders and causing the "no start"; would this circuit be looked at as failing in the "open" position?
AnswerThe ecm controls the fuel pump relay. so either the driver in the ecm is bad keeping the relay on, or the relay is stuck on. either thing is not going to make it so you have no injetor pulse. As stated before the injetor control is based on an RPM signal from the ICM. the duration of the pulse is based on a bunch of things like coolant temp throttle position map readin MAF reading etc... But the cog that gets it all going is the rpm signal from the ICM. you really need a scan tool to look at the engine data to see ehat is missing or is reading incorrectly untill you have that it's just a guessing game.
