Diagnostic question
- Thread starter dylan
- Start date
What happens when you enter diagnostic mode is the microprocessor outputs from a specific memory location a timing value based solely upon CPS position. This value is called different things here but the correct term is Initial Timing. The Initial Timing signal is output through a back up chip inside the ECU, a chip also used to start the engine, control it below 500 rpm, and allow it to run should the microprocessor inside the ECU fail. This "hand off" to the back up chip is also what disables the ESA (Electronic Spark Advance) system when the jumper is put in.
The simple answer to your question is only the ECU gets affected. The CPS does not, nor do other sensors. Course, the moment the CPS is moved the initial value in memory changes. There is one important thing to remember though: Initial Timing will not be sent to the igniter in diag mode unless the IDL contact in the TPS is closed. The system also uses it to set idle speed in preparation for timing. It's no different than the old days when timing involved setting idle speed and disconnecting vacuum advance except now the electronics do it for you.
That said even in diag mode the ESA system will be enabled when IDL becomes open. It's why you can drive the car in diag mode and not notice a performance change other than maybe in idle. Anyway, all this is why you should never attempt to time the engine without first verifying there isn't a code 51 being displayed on the MIL. Course, it's best to avoid timing with any codes present.
The simple answer to your question is only the ECU gets affected. The CPS does not, nor do other sensors. Course, the moment the CPS is moved the initial value in memory changes. There is one important thing to remember though: Initial Timing will not be sent to the igniter in diag mode unless the IDL contact in the TPS is closed. The system also uses it to set idle speed in preparation for timing. It's no different than the old days when timing involved setting idle speed and disconnecting vacuum advance except now the electronics do it for you.
That said even in diag mode the ESA system will be enabled when IDL becomes open. It's why you can drive the car in diag mode and not notice a performance change other than maybe in idle. Anyway, all this is why you should never attempt to time the engine without first verifying there isn't a code 51 being displayed on the MIL. Course, it's best to avoid timing with any codes present.
jetjock;1061852 said:
Thanks for the answer I have a 87 supra turbo and when I try and time it I plug the wire in and the timing only moves just enough to notice it moved and there are no error codes I tried another ecu I had but same thing What would cause the IDL contact in the TPS not to funtion and what would I try to cure this Thanks Barry
Not sure I follow. Do you get a normal code? Is the CPS in the center of the bracket? What timing do you see from one extreme to the other?
What is the idle speed?
What is the idle speed?
you need to put the jumper in. loosen the cps bolt. turn it until you get the mark at 10 degrees carefully tighten the cps bolt and then remove the jumper and it will advance it 2 degrees which will be at 12 degrees. do this with the motor running.
It blinks constantly this came out of nowhere I was thinking old wiring but there is nothing wrong it runs starts and revs nicely I never thought to check the timing light that will wait for the sun to come up Thanks for the time Later barry
dylan;1062094 said:
eather the timing marks on the cam gears are off or yes you need to back the cps a tooth back. it will jump a tooth on the cam gears when the timing belt tensioner is bent or the tighting bolt is loose