ground issue ill bet

 

Read post #6 and start there.

 

We exchanged the battery with another car and the Lexus drained the replaced battery again. That was the easiest to check and ruled out a bad cell. The mechanic then disconnected a connection between the alternator and the fuse box and saw a large spark (this was a bit unclear to me what exactly he was doing). He then installed a new alternator and saw a small spark at that same connection. He was encouraged. I am cautiously encouraged. The next step is to run the codes.

Thank you and another member for the suggestion. I'll report any progress.

 

Excuse my limited English but I was in a mood to write some for those who suffer the problem.
Judging from my past experience, I suspect some electrical load is killing the ECMs. I once have fixed a problem that killed ECM next to next. The original problem was a rough and low idle issue in a cold day. Changing a ECM fixed the problem but within a few days, it was broken again. I was requested by a friend of mine who was a mechanic guy to find out the reason why and also the way to find out the root cause of it.

I am a electronics engineer and I have been fixing many different ECUs doing as a volunteer. The friend of mine is not very good at electronics affairs. This is common among mechanics in Japan. The situations there in US is almost the same or more serious, I know. He used to ask me to help when he needed to fix problems related to electronics affairs. That is the reason why I have started to fix cars and repair ECUs. Automobiles are now mechanical + electronics machines. Many mechanical units are now controlled by electronics units. Those who are good at electronics affairs are definitely needed at the auto repairs shops but the actual situations are not and a unit or a big block change is widely done and making it sometimes worse and charge you a big money.

The problem I mentioned at the top was caused by a broken IACV. It had two windings inside and one of them was partly short circuited. The resistance was less than a quarter of the good one. It was so small value that there went more than 4 times bigger current through the FET in the ECM. The too much current was enough to kill the FET within a few days. Without fixing the root cause, the FET in a good ECM would be killed again and you need another ECM.

In order to find out the root cause, you need to check the broken ECM carefully. I recommend you to check FETs. Don't you know anyone who is familiar to electronics affairs like me around you?

According to my past experience, the most common problem among broken ECM is caused by (a) electrolytic capacitor(s). Next comes (a) FET(s). Sometimes a resistor causes a problem shown below at my blog writing for my American DIY friends.
http://blogs.yahoo.co.jp/mae_yas/3189638.html

 

saying the problem of the broken ecm's are caps,fets and resistors is fine..but i would be more concenred as to what is the cause..without the reason u have nothing but a broken ecm and a reoccurring problem. you also said the iac valve was the issue,that must have been a chore to find...or because of a certain area in the ecm thats problematic..does that enable you to narrow down certain circuits in the electronics or certain systems. meaning if u have a cap thats blown in a certain part of the ecm..is that a clue whats wrong?

 

In order to narrow down the certain point、
1, Check what is broken in the ECM.
2, Trace the line which is connected to that broken part.
3, Find and Investigate what is connected.
4, Is the connected part OK?
5, If not, replace or fix it.

IACV is only an example. As far as I have fixed ECMs that were killed next to next, an external part of ECM was killing FET. Most of them are inductive load such as a solenoid and some by a shorted wire or a broken external circuit located outside of ECM. Without finding and fixing the external part, you will kill ECM again. So what you need to do is find out what part is broken in the ECM. I recommend you to check all FETs in it. This requires some skill. It would be better to be checked by a person who is familiar to electronics circuit. If you do not find anyone, try checking the resistances yourself between the source, the drain and the gate of each FET and compare the value with a good ECM. This is a passive way to check but 80% of broken FETs were detected in my experience.

Good luck.

 

This is a modded your photo. Red arrows indicate FETs. Most of FETs have 3 legs. Some have 8 legs and shaped like a dual in line package indicated by an yellow arrow. But some of those type are not FETs.

 

now that is a much more informative post! thank you

 

very cool blog! - very interesting reading!

 

Sorry python for my limited explanation at #19 and thanks for your caution.
I am mostly OK to deal with electronics affairs but I am not good at handling English still. I'd be happy if you could help me when I'd have difficulties to express things well enough. Your words taught me that my initial explanation was not enough and made me to write more for a better analysis.

I am not a professional mechanic nor a person working for automobile industry but my company has been supplying electronics key units to different automobile companies both in Japan and in US. So I know some about automobiles.

I sometimes help an auto repair shop near by just as a volunteer fixing electronics related problems when they are not OK to handle them. I don't receive any money from the owner but I can use special equipments and tools freely there without paying any money. That is wonderful to me and the shop owner is happy with it too.

Helping each other is nice and I find Club Lexus is one of those nice places to do so each other.
Best wishes.

 

I find your English to be quite good! - Everything you explained was quite clear and understandable!

 

Thanks LScowboyLS for your complements but I still have difficulties to write and to speak.
Hearings and readings are mostly OK but I know my limitation.

Anyway, I am glad that you find my blog interesting.

 

dont worry about it..u did just fine and ur english is better than some i know,thanks again for the info and clarification

 

Yamae, I appreciate your guidance on this matter. I have not found an auto mechanic that has experience in circuit board troubleshooting. I did find an electric engineer at my work that designs circuit boards and is willing to take a look at the damaged EMC board. Before he looks at the ECM, he requested a schematic.

Does anyone have or know where I can get a circuitry schematic of the ECM used in the 94 LS400?

 

I am sorry tbradford, for I don't have any circuitry schematics for Lexus although I only have one for another car. It is usually almost impossible to obtain circuitry schematics here.

So far I could have fixed ECMs without viewing them since I never have encountered any complicated problem such as a failure of micro processors, memories or key devices. Failures were related to electrolytic capacitors, FETs, resistors as I have mentioned before. Below is my simple way to find the cause and fix ECMs and I hope your friend can do some for you seeing this.

Failed capacitors were mostly leaking the liquid or the body itself was expanded. But some of them looked OK but the capacitance was far less and I have needed to use an oscilloscope measuring a ripple at the both terminals at the car. This type of an example can be seen here at my blog below.
http://blogs.yahoo.co.jp/mae_yas/993740.html

In case of FETs, the resistance between the source and the drain was much smaller and I could easily find out just using an Ohm meter. Sometimes a comparison was needed putting a broken ECM and a good ECM on my working bench. In case of a resistor, my eyes were effective to find the bad resistor since the enclosure or the resistor was changed the color as I have introduced before.

My method is not a fully professional way, I know. Without any schematics there wouldn't be a good way for me to help the repair shop owner. But so far I could have fixed all the ECMs requested by him. May be I can start to run an ECM repair shop soon but there would be no need for me to do so. My patents are helping my life enough and my wife doesn't want to leave me alone although my hands are always dirty with oils or dusts.