The car feels underpowered and shifts slowly as if clutch is slipping?

JMTW

MEMBER
1994 LEXUS LS 400
4.0L
V8
2WD
AUTOMATIC
198,000 MILES

I checked the codes and found DTC 13 (rpm signal #2), DTC 51 (knock sensor #1), and DTC 55 (knock sensor #2). I changed 1 knock sensor, both cam sensors and crankshaft sensor. I rebuilt the heads a while back due to them being warped and causing overheating issues. What could be the source of the codes? I checked timing and it is on time.

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,813 POSTS

Hi,

The knock sensors manipulate timing. Did you replace both or only one? Also, the transmission could be causing an issue as well. When you day a delayed shift, is it slipping or does it just seem to take longer to shift?

Next, when I think of power loss, one of the first things that comes to mind is a partially plugged catalytic converter. Are there any odd sounds or odors coming from the exhaust?

The other thing to consider is the signal plate on the crankshaft. The NE signal plate has 12 teeth and is mounted on the crankshaft. The NE signal sensor generates 12 NE signals per engine revolution. The engine control module detects the standard crankshaft angle based on the G1, G2 signals, and the actual crankshaft angle, and the engine speed by the NE signals. It could be loose or damaged. Have you checked it?

Also, according to my manual, DTC51 is a switching-related issue. I attached the information below along with diagnostics. Let me know if you are finding something different.

Let me know.

Joe

See pics below.

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