LS400NL

Dear Lexus fans,
Recently my Lexus started having issues, which was new for me in this car. It's a '95 LS 400, but it's still an UCF11, so no OBD II. It has about 300.000KM (186.000 miles) on the ODO.

My troubles started when the check engine light suddenly lit up. The car was still running fine however, and the light didn't always light up or turned off after driving a while.
After some time the car started to hesitate, or stutter, when I floored the throttle. However most of the time full throttle was still fine, the stuttering only occurred rarely.

Disaster struck a couple of weeks ago when all of the sudden the stuttering occurred while cruising at a low speed on the highway. It went downhill quickly, when I would push the throttle just a little the revs would simply drop to idle. The engine was running so rough it felt like I was driving on a very, very bad road. Luckily I made it to a parking spot where the car stalled when I came to a stop. It would still start, but ran extremely rough and had absolutely no power at all. I didn't even had enough power to drive up the ramp of the flat-bed truck that came to rescue me.

Reading the diagnostic codes resulted in:

• 13 - RPM signal no. 2
• 28 - Main oxygen sensor signal (on right bank)

However I decided to start with:

• Changing all spark plugs
• Changing both ignition coils
• Checking the ignition wires, they seem to be fine

The spark plugs on the driver side (LHD) seemed to be in much worse condition than the ones on the other side.
Changing the coils and plugs didn't resolve my issue. It's still running as bad as before.

Now I'm thinking about replacing the oxygen sensor. Could this sensor be the cause of my issues? And does anybody have other ideas on what to check or replace? Especially the cause of error 13 in relation to my problems isn't clear to me.

Thanks in advance!
- Paul

dicer

RPM signal is the clue.
Changing spark plugs yes good idea if they are very old. Changing the coils waste of $ except for having some spares laying around. And if not done in a long time a fuel filter would be a good thing too.
But the cause of the problem is probably the crank sensor as that is the rpm signal source. Though other things can contribute to the problem as well even the ecu capacitor issue, wiring, cam sensors, timing belt, reluctor etc. So you fixed a lot of things that probably didn't need fixing.

LS400NL

Thanks for your reply. The plugs were quite old and needed replacing anyway. I measured the resistance of both coils, the driver side coil didn't seem okay judging by the results (in hindsight it may have been fine anyway). Since the coils are so cheap I decided to change the other one too while I was at it.

Can a broken crank sensor cause these, at first, vague problems and then suddenly go completely bad?

dicer

Yes, a failing cam or crank sensor will do that. Also a loose timing belt jumping time will cause the code per the manual.
Taking care of the rpm signal is the first thing to do. Then if the O2 throws a code deal with that.

LS400NL

Thanks, I knew about the this error in relation to a jumping time belt, just found it a bit hard to imagine that happened.

I'll check out the crank sensor once I figured out where it is exactly and how to to get to it. I read somewhere that a coolant leak in a specific area could cause these sensors to fail. My LS 400 does seem to have a very small leak somewhere, so that might be the root cause.

blkstealthpaid4

I am thinking Cam Sensors thatn the crank.When my crank went out, I had hard start unless, I sprayed the intake with starting fluid.I have read those symptoms with a bad Cam sensor.I would change both.A bit harder to change than the crank sensor.BTW, I have the same year car

Stereorob

95 is a ucf20.

this is how ive always looked at it

90-92 ucf10

93-94 ucf11

95-97 ucf20

98-00 ucf21

but officially its

90-94 ucf10 , ucf11 air suspension
95-00 ucf20 ucf21 air suspension.

PureDrifter

iTrader: (10)

OP lives in the Netherlands, he can have a UCF11 with the 95 model year due to the registration being the year the vehicle was registered rather than produced. We would need op to post a picture to confirm.

You are close, the x1 desination actually refers to if the car was a C-spec (fully loaded with reclining rear seats and air) car. There were no UCF11 or 21 imported into north america.

blkstealthpaid4

Can we please get a resolution/outcome to this?