ankurdave

Oh, I didn't mean to suggest I thought it was normal for a cat to glow. I was just wondering why, if there were misfiring cylinders across both banks (as I think would happen if the distributor rotor were backwards), I only saw one of them glow and not both. It seems to me that the one with less heat shielding should start to glow first in that case, which is what did happen.

ankurdave

It turned out the LH distributor rotor was indeed backwards! I fixed it and put everything back together, and the car idled smoothly with no more glowing cats.

However, after idling for about 20 minutes I revved the engine up to about 4500 RPM, and when the RPMs came back down to idle, a noticeable vibration persisted for about 30 seconds. After a few more minutes of idling, the check engine light illuminated and the TRAC OFF light began blinking slowly. I checked the codes and there was a confirmed P0307 (cylinder 7 misfire).

I cleared the code, then shut the engine off and started it back up again. It idled fine, no roughness. I looked at some of the OBD2 sensor readouts and two things looked abnormal: (1) Two of the four O2 sensors were not oscillating in voltage as they should, but staying around 0.1 V (too much oxygen in the exhaust). (2) The long term fuel trim was +6% on bank 1 and +10% on bank 2 (adding more fuel to compensate for lean condition).

I believe my timing is correct (pictures below). Here are my guesses:
- The spark plug or wire for cylinder 7 could be damaged. I ensured the wiring was correct and all wires were secure when fixing the distributor rotor, so I don't think it's just a loose wire.
- The two O2 sensors might have been damaged by overheating when the cats were glowing. That would explain the O2 sensor readings and abnormal fuel trim. However, it wouldn't explain the misfire code, which I gather comes from the timing of events reported by the crankshaft position sensor. Also, the two O2 sensors did run through the normal voltage range when I revved the engine to 1500 RPM.
- I suppose I could have damaged the crankshaft position sensor wire when trying to route it behind the fan bracket. That would explain the misfire code as a phantom reading, but doesn't explain the vibration at idle, which sounded to me like an actual misfire.

I wonder if you have any suggestions? Let me know if I should move this to a new thread.


Here are pictures of the crank and cam pulleys at TDC:

Banshee365

Your fuel trims can't be looked at until you fix the misfire. I would swap the caps and rotors from left to right and see if the misfire follows. Cylinder 7 is fired off the left distributor. It's possible the cap or rotor was damaged by installing it backwards.

Swap the caps and rotors and see if the misfire moves to #3. If you have a spark tester make are it actually is spark that your not getting.

ankurdave

I haven't swapped the caps and rotors yet since I wanted to be sure I could reproduce the misfire first. I've driven about 60 miles so far with no signs of misfire, but I did get P0420 and P0430 codes (catalyst system inefficiency) and a mild sulfur smell in the exhaust. Performance and fuel economy were fine otherwise.

Do you think the ignition system is likely still causing this, or is it more likely that the cats were damaged from overheating? My plan at the moment is (1) check for exhaust leaks, (2) replace the spark plugs and distributor caps and rotors, which I wanted to do at some point anyway, (3) consider replacing the cats as a last resort.

Banshee365

I've worked on LS400's that the cat's got hot like that and they were fine. The OEM cats are very very very stout on these cars. I would put my primary focus in looking at the spark distribution system. The most common cause for 420 and 430 codes is a leak at the between the o2 sensors typically at the rear flange on the cats. My personal car also struggles with intermittent 420 and 430 codes. I am still trying to sort that out. It would be more likely that the o2 sensors were damaged with the heat rather than the cats. My problem followed the engine to another car with different downstream o2 sensors but the same upstreams. I'm going to look into that more after the trans overhaul is complete.

ankurdave

Thanks again for your help. I think I have this resolved now:
- I found an exhaust leak at the outlet of the LH cat, which is OEM. After replacing the gasket, the P0420 code hasn't come back, and the LH post-cat O2 sensor moves slowly as it should.
- I'm pretty sure the RH cat, which is a cheap aftermarket one, has a genuine problem. The RH post-cat O2 sensor oscillates quickly, tracking the pre-cat sensor, and the P0430 code continues to appear. I'm planning to replace this cat.

Update a month later: I replaced the RH cat with a Walker 81846 and both codes are resolved now.

Elless400

Bumping for appreciation, very late to the party. If you have a 95-97, this is the best DIY ever, for this job. I really appreciate the accuracy, attention to detail and the good writing.

Exceptionally helpful DIY.

traducian

HI BANSHEE,

My 97 wasn't running right from the day I bought it.I just did my timing. Now I am firing at about 20 degrees btdc and idling really high. I am concerned that the last guy that did the timing had put it on the exhaust stroke and not the compression stroke. How can I identify that my engine is on the correct stroke is correct if I suspect he did this?

Brian

nvturbo

^^^ you mean he couldn't' set the cam gears correctly ???

Banshee365

Uhm, did you work on the timing or someone else? I'm confused. If the engine was timed 180 degrees off it would not run at all. I show the marks on the cam sprockets and crankshaft pulley in my tutorial. The crank marks can be hidden pretty good in grime sometimes. Pay close attention to the steps in my tutorial and you'll see how they are timed properly.

nvturbo

if the timing is off by 180*, the markings on the cam gears would not line up to the factory markings on the plastic indicators. I believe he (or whoever did the work) didn't know what they were doing.

Safari

Thank you Banshee! I know this thread is a few years old. However, this is the best tutorial on changing the water pump/timing belt and accessories on the 95-97 LS400 1UZ-FE, any where. I just used this to change the water pump, timing belt, cooling fan bracket all pulleys, tensioners, belts, hoses and power steering pump, etc. on my 1996 LS400. I'm retired from the communications field, not a mechanic. It took me 30+ Hours. It came out beautifully, No leaks and purrs like a kitten. If you are considering this, have a clean place to work, follow step by step, also read all the comments from this thread there is more helpful advice and as stated have patience. Take photos to refer back to helped me also.

Banshee365

Thank you for the kind words. I have moved on from LS400’s after selling my last one that I built out of a wrecked car. I wrenched a lot on those cars including 2 tranny overhauls. To this day the LS400 is the best quality built vehicle I have ever worked on. Absolutely amazing. I’m still wrenching in Toyota’s on my wife’s 2013 Lexus LX 570. Amazing vehicle as well but it doesn’t quite have the same ‘no expense spared’ feeling as the LS 400’s did.