brandon26

Looking for some advice on a 1992 Lexus SC400 I recently got

Sorry for the lengthy post, just trying to provide as much information as possible for this situation

I have a misfire currently, this vehicle has only 82k miles. It has been driven less than 6-7k miles in the past 20+ years. So far currently I have replaced the full EGR assembly (was throwing a code 71), wires and plugs, fuel pump and filter, I had the ECU rebuilt by Module Mechanics.

Caps, rotors, and the PCV valve were replaced in 2010 at 79,500 miles

The fuel pump did go out on me randomly and left me stranded which led me to replacing that and the fuel filter.

When I did the pump and filter I drained the tank entirely and put a fresh tank of fuel in it, along with some injector cleaner.

I did try jumping FP and B+ to put the pump in constant high speed, and driving it around that way. It seems it ran worse, and got better when I removed the jumper

I've gotten the car to throw codes 25 and 26 after a lengthy drive only once (30 minutes at various rpms) and ive reset the ecu multiple times. It usually wont throw the codes even after 15-20 minutes. It's definitely rich because on startup you can see some black smoke out of the tailpipes, and it smells rich aswell. Idles okay when cold, but after about 30-60 seconds it starts getting worse and worse. Once fully warm the car stutters and runs bad. You can hear it missing bad all the way up to 3-4k rpm, seems to get better around 5-6k rpm. Idles around 1000rpm cold, and 500-700rpm warm (no ac on)

When I did the plugs on the car, the middle 4 cylinders had very black rich plugs (middle as in cyl 3,4,5,6) and the outer plugs were normal looking (cylinders 1,2,7,8)

I've tried ignition coils, unplugging both sides one at a time. The car ran both times on both coils so it shouldn't be those id think.

Unplugged the MAF while running, it ran worse with it unplugged and instantly threw a code, instantly ran better when plugged back in and code went away. Airfilter is clean



SECONDLY I DID THE INSPECTION OF MAIN OXYGEN SENSORS TEST

I jumpered TE1 and E1, got the motor to 2500 rpms, then tested VF1 and VF2 (+) and E1 (-)
Volts VF1 0.089 / Volts VF2 0.097 and not fluctuating at all. Staying the same volts

Removed the Jumper on TE1 and E1 and got the same exact results/voltage readings from VF1 and VF2

I disconnected the PCV hose, with no jumper on TE1 and E1, and I got fluctuating voltage for VF1 (2ish volts) and VF2 (3ish volts)

This lead to the "Repair (Over rich)" diagnostic on the diagram.

I also jumped FP and B+ to put the pump in constant high speed, jumped TE1 and E1 at the same time, and if I remember right I got fluctuating voltage for VF1, but not VF2? I cant quite remember. Or it was vice versa. I would have to perform that test again, but I do remember it read over 1v for both, and not over 5v



I've narrowed down potential issues to what I think are injectors (because of it sitting for long periods of time), O2 sensors, or maybe the ECT sensor maybe? What do you guys think? Has anyone had similar issues before? Again sorry for the long write up, hoping all of this information helps diagnose this issue. Cant wait to fix this and finally get to enjoy this car!

brandon26

Bump. Any ideas?

Tallyhoe

Ignitors. Check them both... I've had a misfire on both ends and it was only 1 that was the problem.. On my case 1 was cracked..

brandon26

Okay, thank you. I will check them and see what it looks like