UPDATED!!!!

Hi guys,

1996 ls400 178000 miles.

Just to clarify just incase that I have done extensive research before posting this and tried/ spent good amount of time trying to diagnose this problem by my self and with my tech friends at the dealership. Anyhow i'll explain what's wrong with it.

Around 2 months a go the car drove fine as usual then 1 day it started miss firing so i had my friend scanned the for codes immediately. Came back cylinder 6 was misfiring. And if i was to drive it normal condition the trac light and CEL would blink ( this is a sign to stop driving) so i just babied it home.

At this time the car has new spark plugs but original spark plug wires. So I had a set of wires that i didn't get a chance to put on the car i installed it to see if i can rule out the wires to be the problems. It wasn't the spark plug wires and the problem were still there. I made sure them wires were installed correctly.

After wards i stopped by the dealerships and my friends hooked up the TIS machine to see what the car was actually doing during LOAD. Cylinder 6+8 were in the 150+ range the trac and CEL lights were blinking again.

I've done research and I don't want to throw parts at it until fixed, although i do have a set of caps and rotors sitting waiting to put ont but I honestly think that wouldn't solve the problem. I want to say it's the distributor it self or my tbelt jumped a tooth which i would like to get that check out too.

So how my request is that can someone show me how to test these few parts to see if they're in specs?

cam sensors
distributors
ignitors ( top and bottom)


Any help would be appreciated, i want to get this car back on the road properly and throwing parts + money at it for no reasons.

Thanks guys

MODS: can some one correct the title for me, my bad. Thanks!


So, after I've tried everything to fix the car, it still wasn't fixed and i decided to open up the ECU and see if I have leaking caps. Well, what do you know I do have leaking caps, so I ordered the right caps per the instructions in here.

Replaced caps and now all of my issues are gone. With the exception of my moon roof not functioning right. Here are pics of leaked caps.



This one has the most leak out of all of my caps. And actually out of 6 caps, only 4 seemed to have corrosion and leaked. The other 2 seemed fine but i went a head and replaced them anyway.



I wonder if that burned resistor at C110 will do any damage to the ECU down the road, i tried cleaning everything as much as i can.



Here we can see the corrosion.



This one seemed fine.



So is this one.



Another of the most damaged cap.

Replaced all the caps and everything is back to normal. Idles great without random misfire and car drives just like before. I wish I opened up the ECU earlier to check during my elimination process, and if it was fine I would've known that the ECU couldn't be the culprit.

I'd say if you're experiencing any kind similar problems that I had, open up the ECU just to make sure that it doesn't have leaked CAPS before throwing money / time at the car. All the parts i replaced were all original anyway so that benefit me so I wasn't wasting money since I planned to do all that soon. Now she's back on the road healthy again I can continue with my plans to make her better.

Thanks to LScowboyLS for this thread.and help. And of course CL too.

 

A misfire on a single cylinder that is repeatable is typically not a cam sensor, or igniter or distributor, as these would typically affect all of the cylinders in that bank or coil respectively. It's possible, but not probable. Also, cam sensors, nor igniters, nor distributors, neither one tend to be failure prone on LS400.

this could easily be something completely different, such as bad injector, for example, or the LH distributor cap (which fires cyl 6)

I also don't think this is a jumped timing belt, but I would go ahead and first thing install the new distributor caps & rotors (make sure these are genuine Toyota parts i.e. Denso) and while the cam pulley covers are off, go ahead and rotate crank a few times (always clockwise) and verify that the timing belt has, in fact, not jumped time.

Then I would install new wires (NGK or DENSO only) and I wouldn't call any of these things throwing parts at it, as all of this needs to be done anyway if it hasn't been done lately. - Also were the plugs you installed either NGK or DENSO, I am not real fond of straying away from OEM on ignition or fuel injection parts. If you need low cost online sources for OEM parts, let us know, several dealerships will discount genuine Toyota parts as much as 30 or even 35% online

Next thing I would do is to test the injector on cylinder 6 at least, if not all of them.

Then I would proceed to a compression test of all cylinders

do you have the factory (paper) service manual?

also, not saying this is your problem necessarily, but BE ADVISED - 1996 LS400 as well as other years nearby have a known issue with leaking ECU capacitors

 

sounds more like cap/rotors if it's only one cylinder. It could be a fuel issue (injectors for cyl 6) but it's far less likely than the cap and rotor which are wear items.

 

My thought is ignition wire and or plug. Tracing back inspect the cap and rotor. Unless the cap is warped or of marginal quality having one contact point wear faster than the others would seem unlikely. Strange stuff happens so the contact point in that cap may have sheared off so the rotor is not making contact to trigger spark.

 

That is right up there with parts left over from an install job.

 

All parts are OEM (Denso) , i replaced the spark plugs 2 years ago when I had to replaced the starter but didn't do the wires. So i installed OEM wires last week and the problem is still there. So as of right now i still have caps/ rotors to install but i just have a feeling that won't be it. But i guess i won't know until I dive into it and try to figure it out. I just want to know what else i can do while im at it to eliminate other possibilites.

My spark plug wires are installed correctly, last time having it at the dealer connected to the TIS machine # 6+ 8 were going crazy and 6 &8 are on different distributors. I was also advised that although running on different distributors misfire can cause other cylinders to react differently. Anyway, I want to know how to test the distributors when I replace the caps and rotors just to rule them out of the possibilities.

Also used a spark tester to test both of the ignitors and all sparkplugs, their is spark and fuel. The only think i haven't tested is distributors, caps, and rotors. Probably be doing that at the end of the week and report back here to you guys. Also, any idea why the trac off light is blinking like crazy?

Thanks for the inputs.

 

what does that mean exactly?

another thing I would do is to clear the codes and then drive the car and then rescan codes, clear codes, etc.

if you repeat this cycle you can assemble a collection of different codes which can be useful when taken as a group

you didn't say if you had the factory service manual or even a scanner

you also never mentioned whether you tested the injectors or if you did the compression test I recommended - what we are trying to explain is that a misfire can have several different causes, and many of them have nothing to do with the ignition system, yet you seem to be convinced the problem is ignition related, why?

PS: to repeat what I said earlier in post #2, distributors tend to be extremely reliable on LS400, so that part being bad would be highly doubtful.

 

what exact code did u get when u hooked up the scanner

 

Codes i get frequently are P0306 and P0308, and at times a few other cylinders misfire too.

As in going crazy is when I hook up the TIS machine to see what the codes are and what the engine is doing at the exact moment the feed back on the computer says that those 2 cylinders a lone are just going off and misfire like crazy. And we cleared the codes so many times that day and it will come back within a few minutes of driving, same condition, same codes.

I don't know how to test the injectors but i will look it up and as for compression test i'd do that this weekend. Started a new job this past weeks so I haven't had time at all to work on the car.

Thanks for the inputs

 

Update. No good news but some news lol

Replaced caps/ rotors today as i had sometime finally. Started her up and left running for 30 mins, seems normal, idle great, drove around town, locally and finally decided to get on the highway and it was still fine. Then right when i got off the highway at a traffic light she started showing signs of the same problems. Since then it all came back, trac light + CEL flashing.

Don't know what to check next, might just give in and open up the ECU to see what's up.

 

leaking or failing caps are often obvious once you open it up, but not always, I have seen early stage cap failure that showed no obvious signs - my 1996 ECU looked fine the first time I opened it, and I spent months trying to find the problem elsewhere on the car, after deciding the ECU looked fine, only after the problem got so bad that I couldn't even drive any more, did I go back into the ECU and have another look, and by that time the caps were not only leaking, they had almost completely ruined the main ECU circuit board!

 

did the techs do a compression test? what do the spark plugs look like? the color and condition of the plugs can say a lot about whats going on in those cylinders.

 

Yea, i might just have to open it up and check to see if this could be a possibility.


Haven't done a compression test yet. Sparkplugs were brand new a year ago. NGK OEM. I can open it up and look again to see what has happened since.

 

Did compression test today, all were between 175-180 across the board. Spark plug looks fine and were just moist from running really rich. Going to get the ohm meter out and test both ignitors tomorrow

 

zero the codes and reset ECU memory by disconnecting negative battery cable for at least 15 minutes, then drive again and rescan for new codes since the running better happened after the new caps & rotors

this is sounding more and more like ECU caps, but still a few things to rule out - did you test the coils? they are more apt to fail than the igniters - also, I would do a spot check of the voltage across the battery, with car on and car off

report back the new codes that appear and voltages across battery terminals with car on and car off