Festyk

None of the caps that I had on board was leaking, I just read that even if they look fine it is recommended to replace them.
The reason I replaced only 7 of 9 caps is because I ordered only those listed in first post and the list was missing two 15uF capacitors.
Yesterday I tried to resolder old capacitors to the board and the result is the same - engine doesn't work well. I am sure that I done soldering in a good way. I have electronic education and done many computer main boards repairs before.
So right now I am thinking about two posibilities:
- I have damaged some tiny traces near the soldering holes of caps.
- maybe static discharge has done some damages.
In both cases I have no idea how to check it and fix.
What would be the consequences if I connect the 89661-50351 ECU to my car? I could have it really cheap and if it is safe for engine maybe it is worth trying?

Yamae

There was a design change of the ECU in September 96. The ECU 89661-50351 is not designed for earlier models. I don't know what will happen if it's used for earlier models.

Festyk

I followed RA40 advice and checked the error codes. Dashboard blinked mi codes: 21,27 and 28 which are connected with oxygen sensor. I really don't know if I had those before my resoldering operation and I doubt that this is just a coincidence.
I also inspected again the circuit board, corrected soldering pads and still the same result.

Yamae

You must remember that codes related to the O2 sensor are obtained in two totally different reasons. One is by the failed O2 sensor itself and the other is by the bad engine running.

Incidentally what was the original situation before you replaced capacitors?

Festyk

Well, before my operation, the engine run very smooth with no vibrations and any pulsations.
Sometimes just the idle rpm was dropping to 350-400 and I suspected that ecu could be the reason.
Also the gear shifts were not very smooth. I don't have a comparison but I am thinking that this could be better working.
I suspect that my error codes are related to improper engine works, rather that failing three lambdas.

williamb82

Run continuity tests from the pins of the capacitors to the other soldier points on the same trace. You may have broken a trace. I did on one joint and had to run a jumper to fix the connection.


As for my cold starting issue, Well, it is solved. Sunday morning it wouldn't start. Opened the hood, and it would. So I put a piece of foam that I lined with electrical tape on top of the coil/coil wire connection and closed the hood. it started. opened the hood and removed it, closed the hood. Wouldn't start again. Coil has no cracks, and has been swapped for another known good coil previously with the same result, and coil wire is new. I guess the hood blanket is sagging and when it is wet with condensation etc.. it provides a ground and the damn coil arcs to it. Well, I put the cover I made on it and taped it over it. I left it all week. no issues, I will find a different style boot for the coil wire connection to the coil and see if that solves it. Gonna try to find one where the rubber boot slips OVER the coil post like my supras have. Still need to grab another ECU to replace the caps on though. Car ran much smoother on the ecu I replaced them on except the occasional fuel dumping issue, which may have been something I caused, or pre-existing that just got worse wit hthe new caps, idk.

Najeeh

My dad was doing some research and found polymer typelow ESR capacitors. I've got 2 ECU to repair. One is from a euro spec '93 LS400. All of the caps have leaked. The other is my '90 Celsior. The caps have not leaked on it yet. I was wondering if the polymer ones were a better replacement instead of the aluminum ones?

Yamae

You have to be careful that too low ESR capacitors often cause an oscillation and the circuit becomes unstable due to the continuous phase rotation up the higher frequency when used at a regulator circuit. Some polymer type capacitors are so. The Bode_plot tells the story and this page may help you to understand more and the actual problem.

Najeeh

Well as it turns out my father selected polymer type capacitors with a very low ESR. I'm making a list of capacitors that are needed and found that some are not in the list. Can you suggest me some good replacement ones of the following:

From instument cluster of the Celsior (Capacitances on the circuitry):
1uF 50V
4.7uF 50V
180uF 35V
470uF 16V
820uF 25V
33uF 35V (this is also in the ECU of the LS400)
I'am replacing the ones of similar capacitance with the ones recommended for the ECU. I'am hoping that this doesn't destabilize the circuit.

Yamae

A good EE should be OK to find good capacitors for the LS400 without asking others.

Najeeh

He has found some, I was just asking for suggestions as to which would be the best.

waseem3000

Highly recommended for even 1998 up cars where my ECU had no leaking capacitors but had low power and rough performance. After the ECU recap which was a very hard task due to the stubborn dried soldering finally the car is smooth and gear shifting is crisp and will see the changes that happen over the days.

Total 11 capacitors were changed in the car which are:

Qty. 2 of 10μF - 50V
Qty. 3 of 47μF - 63V
Qty. 2 of 100μF - 10V
Qty. 1 of 220μF - 16V
Qty. 1 of 33μF - 35V
Qty. 1 of 47μF - 25V (special BP capacitor) - high reliability capacitor, replacement recommended but not critical
Qty. 1 of 330μF - 35V - high reliability capacitor, replacement recommended but not critical

(taken from the first post)

Changed them all and works like a charm.

Thanks Yamae and LSCowboyLS.

PS Where is LSCowboyLS... is he ok as he is not on the forum for a while now!

Yamae

Thanks for the report, waseem3000.
Your report will be encouraging owners of 98 and after. The ECU for a 98 and after was totally redesigned and consumes less current but still those QAS capacitors were used.

Due to the smaller load, those QAS capacitors are not stressed as serious as earlier models, but it has been already 18 years or more since the production. As LScowboyLS and I recommend, it would be smarter to replace those capacitors before the problem happens. As far as I have experienced, the initial problem for a 98 and after is mostly the rough gear shifting. Owners seldom notice the low power but after the capacitors change, they notice the better running and the better gas mileage as well as the smooth gear shifting. Some of them amaze at the improvements like you. LScowboyLS is fine but not here but I often communicate with him on the Facebook and the email.

waseem3000

Thank you Yamae.

My car is a 1999 btw.

A few things I wanted to add is that I had the A/C compressor not working after the ECU recap because the technician who repaired the ECU did not solder one leg of a capacitor and I went back and fixed it up. So if anyone has any issues in the list on the first page, go back and check the soldering work done on the ECU. I should have done the work myself as I was doubting my soldering skills but had to do it eventually

And some of the capacitors were not coming out so I just went ahead and cut the old caps off and left those leads there to avoid excessive heat from the soldering iron to damage the board and just attached the new caps to those leads and did the fix. I know it is the not the best way to do it but I did not want to risk any damage to the ECU and the soldering on the ECU is top notch and not easy to remove at all or maybe I was just unlucky with it. It was not for all Caps but a few and attaching the new ones was much easier and fix was done in a shorter time.

And I would encourage everyone to go ahead and do the fix because it really helps and the car performance changes a lot and even gas mileage is better despite me needing maintenance on the car.

Anyone in UAE wants the Caps for 98-00 I have a few spares I had ordered so PM me and let me know.

And love this forum and the discussions and the helpful members! Keep up the good work guys!

dicer

To remove a component like a capacitor you will want to remove the solder using either a solder wick or sucker.
If you keep trying to work it out with out removing the solder that does over heat stuff. Cutting the leads works if you can reach them, but the holes need to be open to put the new component back in.
There is a case where you want to leave the solder on the board, that is the climate control LCD.