Moarpower

The coils were not affected by water but show their age.
A look into the coil side of the lead. Looks a little old too.

Moarpower

I'm at a loss guys. Any tips on where else I should look. I don't want to just throw parts at it without trying to trouble shoot a little more.
I will he buying the o2 sensors the if anyone could tell me a part number for a good replacement.

Moarpower

Stumped. Appreciate some help on what I should do next

Moarpower

Ordered new o2 sensors online. Will update when they get here but I dont think these would be cause the misfire. . Will pull out the cats either today or tomorrow and inspect.

Could this be due to a timing slip? I would have thought that timing would be a constant miss and not get worse as it warmed up.

Yamae

I'd simply check the ripple voltage first.

Moarpower

Gone over the voltage when I checked the caps. Electrical output while running is all fine. Checks the alternator and battery. Definitely not a voltage issue at this stage.
Leaning towards a failed cat caused by either timing or 02 sensor fail. All plugs and rotors are working well. I will replace the caps and rotors as well as the leads, regardless, as I have no history of what has been replaced and having only 70k miles at 27 yrs old, Im going to assume its all original

Yamae

How much was it? Did you use an oscilloscope or a multimeter with a series capacitor to measure?
If it were the original capacitors, it would be old enough to lose the capability to work properly. Many QAS capacitors begin to fail after a bit older than a decade, you know. 27 years are long enough to fail.

Moarpower

I use an oscilloscope that iuse to test power supplies for server racks and pcs.
As you can see in the pic, the caps are old. Id say they are original.So I am replacing them once I find a supplier who doesnt have to order from japn or china. I will replace the whole ignition system minus the plugs over the next month.
The overheating cat is the killer. Something isnt igniting right so its fuel or ignition related. I wish there was a way to simplify the wiring on these things.

AlaskanLS

Hey man, I had the same problem not soo long ago. If you have already diagnosed the spark plug wire, rotor, ignition coil etc. I would suggest to check the spark plugs for hairline crack. Some spark plugs developed hair thin crack that are some time hard to see. My problem got solved after replacing coil wire. Check both of the coil harnesses to make sure that there is continuity of electricity in them.

Moarpower

Hey man, thanks. The plugs are brand new so I dont think thats it. I will replace the caps, rotors and wires when i find a good package deal. They all come with plugs which I already bought.

Moarpower

Replaced the o2 sensors but no change. Is there a chance that this could be caused by the 30 year old cats failing? When the issue gets really bad I get the cat warning light I showed earlier in this thread.

Yamae

That's what I thought.
I have experienced the cat warning light problems among several JDM cars and I was able to fix all of them quite easily. I already have given you an idea but you never informed me the actual measuring data. The answer must be there.

Moarpower

Pulled both cats off to find one on the left side very much melted. Going to replace them. I checked the voltage last week. Didnt record the data sorry but I know it was withing range according to the info I have. From what I remember it was 5.3 or 5.5. Something around there anyway I am not leaning towards this being an ECU issue right now. I have inspected the ecu itself and it looks fine and has been perfect up until now. I will pull it out again just to make sure and ill try measure with a multimeter also.

Yamae

It seems to me that you are only measuring the DC voltage. You should measure the ripple voltage setting the input mode of your oscilloscope AC.
Electrolytic capacitors can't be checked by eyes. How can you measure the ESR and the capacitance by your eyes?
Measuring the ripple voltage can be an alternative method to know the condition of capacitors. If it exceeded 100mVp-p, you'd better replace ECU capacitors ASAP.

Moarpower

Thanks for the little faith mate but I checked the ECU correctly. It is not the culprit in this case and I have now confirmed it to be working perfectly fine for the 3rd time since purchasing the vehicle less than 6 months ago. I know how often the caps may go bad but this is NOT my issue here. If you have any other tips thanks, but Im not chasing the ecu on this one anymore.