mikemikeo

This is from my ECU. 1996 ls 400




Looks blown to me. I could be wrong. Not sure what I’m looking for.

Another pic

Another pic

SoIllSam

Definitely blown. Appears to be a Zener diode. Also take a close look at those electrolytic capacitors. If the end is swollen, the cap is bad and could be the cause of the diode blowing out. These are all replaceable.

Yamae

It's one of Zener diodes used at the injector driving circuit. The purpose of those are to protect injector driving transistors from the surge. I imagine that your engine's one of cylinders is not functioning.

timmy0tool

iTrader: (7)

impressive you know all this stuff yamae!

yeah it's a diode because the label tells me as it starts with a "D". capacitor is "C", resistor is "R", transistor is "T" etc...that's the extent of my knowledge haha!

deanshark

That's funny, cuz ya know what, I didn't even know that. That's why when it comes to computer stuff I leave it to the experts, like Yamae. (the best I've seen) Way above my pay grade.
Even as I get older I learn something knew every day.

RA40

iTrader: (6)

Yamae could you describe some of the trouble symptoms of this diode going bad?

This may explain the P0301 code that remains persistent in mine. I've checked that the cylinder is getting good spark, the injector is ticking/pulsing like the others. I'm unable to get individual injector output from my code reader so that remains an unknown. There is a distinct smell of gas at the tail pipe. Short and long term fuel trims fall in "normal" range but I suspect that that particular cylinder the injector is delivering excessive fuel for the misfire condition.

Yamae

The Zener diode dumps the peak voltage as is explained in the attached waveform which can be seen at 11:42 of the Youtube video below. It is used to reduce the over voltage stress of the transistor which drives the injector. Your problem definitely needs to observe the waveform of the transistor in accordance with this video. The poster ScannerDanner is explaining things very well except some minor affairs. The judgement can be done easily comparing other injectors waveforms.

Yamae

Sorry that I was not fully answering your question and I think I need to add these. When the Zener diode went bad, the drive transistor is stressed by the excess voltage and damaged resulting the poor performance of the injector driving. Depending on the damage, sometimes the drive is partially stopped, completely stopped or done more than the normal. All these can be judged comparing with other well working injector drivers. I hope your P0301 problem would be fixed quickly.

RA40

iTrader: (6)

Thanks Yamae.

Will need to pull the ECU to inspect those diodes. I really dislike how slow the code reader is to run the scan, in that time it is dumping lots of gas through that cylinder. The alternate path would be to pull the injector but that's not a task I look forward to for a quick session. All that brittle plastic concerns me when pulling the intake plenum and fuel rail to check the injector.

Yamae

I don't want to hijack the thread but what I write from now on would be probably related to the original poster. The possibility of the Zener diode failure is mainly caused by some extra stress from the coil of the injector such as the too much current to it. The over current makes extra higher voltage spike when the current is stopped and damages the diode. At the same time, the transistor may be damaged too.

The best confirmation is to observe the waveform. If not available of it, there is a way to measure just the voltage of the injector using a multi meter. The voltage varies depending on the engine's load and the rpm but all the cylinders should show almost the same voltage. Compare the voltage and if there is the difference, the injector itself or the drive circuit in the ECU is not OK.

Also there is another way to check when the engine is off. Use an ohm range and measure both the resistance of the injector and the resistance of the drive side removing the 2 pin connector coming from the ECU to the injector. These measurement results and the comparison may tell you that it's the injector or the ECU that is causing the problem.

RA40

iTrader: (6)

Thanks Yamae, that is also helpful for me to be aware of this.