tjcypress

This is my first post, however I have read many and have fixed many a problem from this forum. Forum has save me $$$$$$$$$ over the years. This time I have exhausted my research and need help!
96 lexus 400 149K miles. Over the years at times it would run rough. and I have diagnosed and solved the problems. Some of the things done. New TP sensor, plugs and wires clean EGR sytem etc . The car has started running rough and started throwing random misfire 300 ans cylinder 1 2 and 8 misfires. When it first started acting up this time it also had lean bank 1. I have cleaned the EGR valve inside with throttle body cleaner, ran sea foam through the vacuum system, cleaned the throttle body, cleaned the mass air flow sensor,changed the fuel filter which I felt didn't have good flow. So I think it needed it. If I run carb cleaner through the throttle body with the car running and reset the codes they stay off for about 30 40 miles then it acts up and all over again. I have tried things and reset the codes about 6 7 times and still get 1 2 and 8 with the 300 random. So I checked my plugs they looked good and got a good spark. swapped 1 and 3, Still same codes. Swapped coil packs and swapped 1 and 3 fuel injectors. Still same codes. I also replaced all the caps on the ECM board as directed in the forum. Same codes. I am going to run a compression test after I borrow the tools tomorrow from a friend. ALWAYS 1 2 and 8 with 300. I need HELP!

Aeok18109

damn sounds like you have run the gauntlet narrowing it down to see if an issue exists with a certain plug/coil. hope you get it figured out asap

tjcypress

Yeah me too! I have been working on it for 3 weeks when can. I am going to check compression tomorrow and see if I can get a test light to make sure the injectors are getting a good signal from the ECM. I am starting to suspect the ECM even though I changed the caps as directed in the forum. It may be another faulty component. Any suggestions on ECM replacement.

LScowboyLS

in spite of the capacitors being replaced, it still sounds like an absolutely classic case of failing ECU capacitors, and 96 is the most common year of all for this issue., and the deep south is the most common geographical location.

so my question is, did you use the exact capacitors I specified in the thread, ordered via those links provided in post #1? - was there any visible leakage or corrosive damage when you replaced the caps?

can you do Yamae's ECU ripple test and post the results?

those misfires are on two different cams (banks) and two different coils, two different igniters and 3 different injectors - not much they have in common besides ECU and crank sensor, or perhaps jumped timing belt, have you checked timing belt alignment and tried a new genuine Toyota crank sensor and verified the integrity of the crank sensor wiring?

tjcypress

Yes I used the exact components. When I first fired the car up after replaceing the caps one blew. I knew when I heard it go pow what it was . I was an electronics tech in the navy years ago and I have heard that sound before. When I opened it up it was one of the 100s that blew apart. I ordered another and it didn't blow. I just pulled it apart tonight and confirmed.

Yes there was leaking from almost all the caps. I am going to have to check out the ripple test and see if I have the tools and do it. I have not changed the crank shaft sensor. I haven't found how to test it yet. I would like to test it if possible for i think that one is a relatively challenging job. If I must di it I will though.

By the way LScowboyLS
I am in Mobile now just bought a house there. almost neighbors!
I am looking for a thread on crank shaft sensor. Where is it? Can you test it for resistance, I had red once a long time ago I thought that it was haed to get to?

PureDrifter

iTrader: (10)

I noticed you didn't mention the distributor rotors and caps, nor the coils/ignitors...

LScowboyLS

if a cap popped, you likely had it in backwards, the only other scenarios are that some stray solder or something was left and completed a circuit via the now exposed copper of the corroded traces, or that the corrosion has caused shorted traces in the ECU itself.


not sure what you mean, the crankshaft sensor is extremely easy to get to!

however, I am becoming convinced that the issue remains in your ECU, it sounds like there was already a lot of leaking/board damage, that can require a lot of experience to recover an ECU from that and save it.

At this point, I recommend not worrying about the crankshaft sensor etc. and find a virgin ECU at the junkyard or ebay or wherever that has never been worked on (a "virgin") that can be verified that it is all original by myself or Yamae via photos the seller provides, and then carefully install new caps in that one. - I think this ECU may be toast, caps popping etc. is not cool. The caps on my list don't just "pop" - they have a defective rate when new of something like 1 in a quarter of a million.

LScowboyLS

very unlikely to be any of these, as I previously mentioned, because the 3 misfiring cylinders encompass both banks, both cams, both coils, both igniters, and 3 different injectors. very unlikely that for example, both caps, or both rotors or both coils, etc. having an issue at the same time, all of a sudden. Would be a different story, say, if all misfire codes were consistently on the same coil, for example, vs. this situation where they are consistently on both coils (cylinders, 1,2,8)