ZYTRAM

Hi all,

New member from Australia, on my 4th UCF10.

Background:
Following an overtake on the highway, my UCF10 that started misfiring. Symptoms: All cylinders firing upon cold start but once the car warms up it cycles between 6-8 cylinders. This occurs at idle as well as across all RPMs.

So far I have:
- Replaced Fuel Filter
- Replaced Spark Plugs
- Cleaned distributor points
- Cleaned rotor arm
- Tested with known working coils
- Re-capped ECU
- Checked timing belt position
- Tested with CTS and o2 sensors unplugged
- Disassembled and Cleaned Idle Air Valve

It definitely is spark and not fuel related. I am testing using a timing gun and testing across plug leads from the distributor. The misfire is not limited to individual cylinders or bank of cylinders either - completely random.

By this point I'm totally stumped, does anyone have any ideas?

Known

If needed find the rep- Manuals at http://lexus-doc.ru/
What about the resistance of the High-tension cords (limit is 25k Ohm).
Are there no error codes stored?

timmy0tool

iTrader: (7)

i too would check the spark plug wires next. how many miles (kms in your case)?
cleaning the dist points and rotors can only go so far, why not just replace them while you were in there?

also check your AFM, but am unsure if you are allowed to clean it. certain AFMs are sensitive to cleaners.
https://www.clublexus.com/forums/ls-...0-afm-maf.html

Yamae

If it has a tendency to happen when the engine is warmed up, the suspect would be the ignition coil or the cable between the ignition coil and the distributor. I'd check it observing the spark which should travel almost a half inch when you test it in the air.

PureDrifter

iTrader: (10)

Probably the coils going bad, they start to die when heated then eventually give out completely.

Test as per the FSM and how Yamae suggested, both when cold and once the engine was warmed up.

What do you mean to cleaned the "distributor points"?? These cars have electronic ignition...

ZYTRAM

Thanks for the responses guys! Fixed the issue, it was the ignition leads 😁

Yamae

Thanks for the update, ZYTRAM.
Which leads were causing the problem?

ZYTRAM

I replaced them all - coil and spark plugs. Cheers!

afanboy

For future use, please post the model and year of your car, what codes it's giving on OBD, and what is the recent service history. Not everybody knows what UCF10 is.

PureDrifter

iTrader: (10)

We actually have a naming reference thread in both of the generation FAQs stickied at the top of the forum