5speedLS

*Fixed* Post #11

1990 LS400. After pulling my ECU and replacing the capacitors, I threw it back in the car and it wouldn't start up! I figured I did a bad job soldering or something, so I ordered a junkyard ECU for $50 and tried that. Same thing no luck. At the same time it turns out my starter is sticking on even with the key out *yikes* but I never noticed till now because the engine always fired up first try. So I decided I could use this to my advantage and let the thing keep cranking while I sprayed some starter fluid in the intake. It didnt make so much as a pop. So I am suspecting spark is not happening. I have to pull off the neg battery terminal just to get it to stop cranking. I wonder if that could make it too hard for the ECU to learn everything.

I did jumper the circuit opening relay and could hear the fuel pump coming on when ignition was turned to on. I could not hear the fuel pump running without jumpering it, but from what I read the ECU will open the relay when it senses something is amiss. While the relay was jumpered I tried cranking and no start. I did open the second ECU to inspect it and there was no leakage visible or signs of tampering.

Why would simply taking an ECU out and putting it back in (effectively) have this effect? Did I just get a second bad ECU? I wouldnt think so because most "bad" ECUs only run rough, not don't run at all. What are the chances that something else went wrong when I pulled the ECU? I am stumped here. Thanks for reading.

dicer

If you didn't unplug, disconnect the battery first, then you could have fried, burned out, wrecked both ECU's. Also if you replaced the capacitors and didn't use a wrist strap, especially in a dry cold area like Wisconsin, then you could have ESD damaged the IC's on the board of your ecu. Maybe the one you got from the Junk yard was the reason the car was at the junk yard in the first place.

oldskewel

iTrader: (1)

Perhaps obvious, but maybe it is as simple as a blown fuse.

After that, I'd start trouble shooting relays, confirming spark, etc. You know you have fuel pressure since you can hear the fuel flowing, but that does not mean the injectors are firing.

I would be surprised if both ECU's are completely dead. From your description, it is just not likely.

Good luck.

YODAONE

[QUOTE=5speedLS;9811999]1990 LS400. After pulling my ECU and replacing the capacitors, I threw it back in the car and it wouldn't start up! I figured I did a bad job soldering or something, so I ordered a junkyard ECU for $50 and tried that. Same thing no luck. At the same time it turns out my starter is sticking on even with the key out *yikes* but I never noticed till now because the engine always fired up first try. So I decided I could use this to my advantage and let the thing keep cranking while I sprayed some starter fluid in the intake. It didnt make so much as a pop. So I am suspecting spark is not happening. I have to pull off the neg battery terminal just to get it to stop cranking. I wonder if that could make it too hard for the ECU to learn everything.

I did jumper the circuit opening relay and could hear the fuel pump coming on when ignition was turned to on. I could not hear the fuel pump running without jumpering it, but from what I read the ECU will open the relay when it senses something is amiss. While the relay was jumpered I tried cranking and no start. I did open the second ECU to inspect it and there was no leakage visible or signs of tampering.

Why would simply taking an ECU out and putting it back in (effectively) have this effect? Did I just get a second bad ECU? I wouldnt think so because most "bad" ECUs only run rough, not don't run at all. What are the chances that something else went wrong when I pulled the ECU? I am stumped here.

YODAONE

[QUOTE=YODAONE;9812194]What is P.N. on original ECU?

What is P.N. on replacement ECU?

Htony

First thing after putting back the ECU, you need to initialize the board. Takes about 30 mins. Peruse Youtube about how to do it.

5speedLS

Thanks for the replies. I can confirm that the PN of both ECUs are the same.

I did always disconnect the battery before pulling or putting in the ecu.

I checked all fuses in the fuse box on the drivers side of the engine bay and the drivers footwell. All were good. Are there any im missing?

I was able to get a constant blinking check engine light when pulling codes, so at least the ecu is doing something. I think I have to be botching this install somehow, because its the only thing that changed.

Does the ecu have to be grounded to the chassis? I was just letting it sit on the lower glove box cover.

I didn't think it took 30 min to initialize but I will do some homework on it.

dicer

Where in the manual does it say to do that? This is the modern computerized world. There is no computer that I know of that needs 30 minutes to accomplish anything.
Not even a smart tv which is way slower than any old vacuum tube tv that I ever had in the old days even 50 years ago. Oh and this is a gen 1 ecu not a fancy CAN system one that does require it to communicate with other ecu's in the car. So sorry to disappoint but its just plug and go.

RA40

iTrader: (6)

Cowboy's post in the ECU thread mentions this:

https://www.clublexus.com/forums/ls-...capacitor.html

YODAONE

Lexus shop manual images depict ECU mounting bracket(s) as a groundpath to the chassis suggesting the ECU grounds here...

5speedLS

So I put in a 3rd cheap ecu from Ebay cuz I was just convinced it was a bad ECU. So I crank the car a few times and the same thing, no start, although when I modulated the throttle, I noticed little pops. So I said screw it and floored the throttle. After about 2 seconds of cranking with the throttle floored, the thing roared back into life. Of course it idled like junk and died unless I revved it like a LeMons race car . A week later it idles fine.

I hear that when you floor a car when cranking it goes into clear flood mode. I wonder if that helped it default to some pre-programmed fuel map instead of having to rely on sensors. I hope this helps somebody in a similar situation.

Thanks

Htony

If you don't initialize the ECU after installing it, it'll never work. I am mentioning it already second time. Ask a knowledgeable techs. about this. Also peruse youtube
regarding how to do it. Takes about 30 minutes. If one knows anything about processor chips, ought to know what initialize means. Without initialize, the ECU is like
a brain dead animal. Can't perform as an ECU.

dicer

YAMAE we need your input on this one.

Banshee365

This hasn't been my experience with the ECM's. I usually just mount them, plug them in then leave the key on a minute or two and I've never had a problem. I don't know what you're talking about regarding 'initializing' the ECM. I'm certainly not going to go watching YouTube videos about it. Half of the stuff on YouTube is garbage.

Htony

Depends how it is designed. If boot loader is in NVRAM, as soon as power is applied it can wake up and initialize itself or powering up will trigger the initiallize. My back is in eletronics. Lived through electronic evolution from vacuum tubes to nanotech. in my professional career. Hobby is ham radio, licensed in the '50s, still active on the air using ll mode. You are just speaking for yourself. Yes, Internet is full of garbage, it is our individual responsibility to distinguish between good and bad information, same with daily news on MSM.