# HELP: power transistors and coil on plug ignitions **URL:** \ **Category:** NYSpeed Automotive\ **Created:** [June 29, 2005, 5:41am UTC](https://forums.speedlife.net/t/help-power-transistors-and-coil-on-plug-ignitions/447 "2005-06-29T05:41:11Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![newman](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/newman/32/7569_2.png) [@newman](https://forums.speedlife.net/u/newman)\ **Post date:** [June 29, 2005, 5:41am UTC](https://forums.speedlife.net/t/help-power-transistors-and-coil-on-plug-ignitions/447/1 "2005-06-29T05:41:11Z")
how does a power transistor work. i know that it amplifies the signal from the ecu to the coilpacks, but how? I am working on a car and it will not spark. I havent yet checked tha CAS, but the ecu threw an ignition code but not a CAS code. What kind of an ignition signal does the ecu output before the transistor? Anyone? ---
**Author:** ![zwarbyt](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/zwarbyt/32/7623_2.png) [@zwarbyt](https://forums.speedlife.net/u/zwarbyt)\ **Post date:** [June 29, 2005, 5:48am UTC](https://forums.speedlife.net/t/help-power-transistors-and-coil-on-plug-ignitions/447/2 "2005-06-29T05:48:47Z")
[http://www.autonerdz.com/downloads/copman.pdf](http://www.autonerdz.com/downloads/copman.pdf) ---
**Author:** ![Carnut](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/carnut/32/7590_2.png) [@Carnut](https://forums.speedlife.net/u/Carnut)\ **Post date:** [June 29, 2005, 8:05am UTC](https://forums.speedlife.net/t/help-power-transistors-and-coil-on-plug-ignitions/447/3 "2005-06-29T08:05:47Z")
the power transistor is just like a solid state relay. It takes a small signal from the ECU to trigger a “switch” and then the transistor allows power to flow in this case it goes to the coils and provides power for the primary side of the coil. HHHHHHHHHHHHHHAAAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHH ---
**Author:** ![Daddie](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/daddie/32/7621_2.png) [@Daddie](https://forums.speedlife.net/u/Daddie)\ **Post date:** [June 29, 2005, 8:10am UTC](https://forums.speedlife.net/t/help-power-transistors-and-coil-on-plug-ignitions/447/4 "2005-06-29T08:10:24Z")
wtf? ---
**Author:** ![newman](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/newman/32/7569_2.png) [@newman](https://forums.speedlife.net/u/newman)\ **Post date:** [June 29, 2005, 8:20am UTC](https://forums.speedlife.net/t/help-power-transistors-and-coil-on-plug-ignitions/447/5 "2005-06-29T08:20:15Z")
> [@Carnut](#): > > HHHHHHHHHHHHHHAAAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHH AHAHAHAHAHAHAHAHAAaa but there is an ecu signal in, signal out and ground. does it act on the ground side of the coil. because i have power at the coil. i have ground at the coil. but when i put a test light on the signal wire, i get nothing. they tell me to do this in the manual, but i dont see where the power would come from, beacuse there really isnt any power coming into the ptu… maybe i could use your logic probe to check it vs the FSM, but i ran the test with a test light and battery and it didnt match, but neither did the replacement ptu that i tried… unless they are both bad… ---
**Author:** ![boardjnky4](https://avatars.discourse-cdn.com/v4/letter/b/96bed5/32.png) [@boardjnky4](https://forums.speedlife.net/u/boardjnky4)\ **Post date:** [June 29, 2005, 5:13pm UTC](https://forums.speedlife.net/t/help-power-transistors-and-coil-on-plug-ignitions/447/6 "2005-06-29T17:13:11Z")
do you have a 300zx? because i have the same problem with a 90 300zx, i order the power tranisitor unit and hopefully it will help. I was also told at the dealership that about 7 years ago they replaced a shitload of these units. mine is going in tomorow and ill let u know if it helps. I am having trouble on cylinder 4, i tested all others by plugging a spark plug into the end and groundng it on the motor and i got spark on it with another cylinder’s plug, if its not the ptu then its gotta be the ecu or a short in the wire i think, i guess ill ffind out tomorow. ---
**Author:** ![Carnut](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/carnut/32/7590_2.png) [@Carnut](https://forums.speedlife.net/u/Carnut)\ **Post date:** [June 30, 2005, 7:51pm UTC](https://forums.speedlife.net/t/help-power-transistors-and-coil-on-plug-ignitions/447/7 "2005-06-30T19:51:40Z")
> [@newman](#): > > AHAHAHAHAHAHAHAHAAaa > > but there is an ecu signal in, signal out and ground. does it act on the ground side of the coil. because i have power at the coil. i have ground at the coil. but when i put a test light on the signal wire, i get nothing. they tell me to do this in the manual, but i dont see where the power would come from, beacuse there really isnt any power coming into the ptu… > > maybe i could use your logic probe to check it vs the FSM, but i ran the test with a test light and battery and it didnt match, but neither did the replacement ptu that i tried… unless they are both bad… No you know what you are right i forgot there is power to the coils at all time on those engines. the transistor then completes the ckt for each individual coil.