MorePower

I have a 1993 Lexus LS400, 145K miles, that I haven’t driven for 3 years due to a starting problem. Just maybe someone may have experienced the same thing and have an idea what is wrong.

The problem is that about 10% (and increasing) of the time while starting the engine, it tries to “kick back” due to the ECM sending the firing signal to the wrong igniter, causing the next 3 firings during that crankshaft cycle to be out of the correct igniter sequence. At the next (third) camshaft signal, the ECM corrects the firing order of the igniters. This problem only occurs during the one revolution of the crankshaft cycle between the second and third camshaft signals to the ECM. The “kick back” is caused because four cylinders are firing 90 degrees advanced. If it wasn’t for the starter torque and the engine inertia, the engine would stop rotation during the “kick back.” Obviously engine damage can (and has) occur.

The engine can be started and will run normal using the signal from either one of the two camshaft sensors. The malfunction only occurs when the ECM is receiving signals from both camshaft sensors.

As a background, I have many years of auto repair experience. Lexus doesn’t have a clue what is wrong. No fault codes are stored in the ECM, therefore Lexus’ attitude is to “throw parts at it until it’s fixed.” (Their remedy could cost more than the car is worth.) I have spent hundreds of hours trying to diagnose the problem. I have videotaped the malfunction on my 4 channel scope, and I know exactly what is going on. I just don’t know which component is causing the problem. The following items have been replaced:

Distributor caps and rotors.
Crankshaft sensor
Engine ECM (tried rebuilt, then replaced)
Timing Belt

EDIT: Replaced timing belt tensioner 7-23-08. Didn't solve problem.

According to test equipment information, all sensors are functioning correctly. Since the malfunction occurs less than six times consecutively, the ECM will not record it. This problem began happening occasionally and over time (1 year) progressively got worse.

I would appreciate any information regarding the cause of this malfunction.

etex

Did you replace the timing belt tensioner when the belt was replaced? If so, was it pulled up tight equally on both sides with the two bolts?

MorePower

@etex
No, the timing belt tensioner was not replaced because it was within the specs as indicated by the factory service manual. And yes, the tensioner was very carefully installed and tightened equally as mandated by the service manual.

I will ponder the ramifications of the tensioner not working properly. It would initially seem that if the timing belt was the least bit loose, it would jump a tooth on one or more of the pulleys. All pulleys are still in time as indicated by their marks and confirmed on the scope. Thanks for your reply.

bigste

Did you do any work on the car before it started playing up? It does seem like there's a timing problem somewhere.

MorePower

@bigste
At 136K the timing belt was changed for the second time. A few months after the belt change, the first malfunction occurred. It would only happen very occasionally, and only after the engine had been hot for a while. During the following year, the malfunctions began occurring more and more frequently to the point that I decided that continued use of the car could result in major engine damage.

At 145K an inspection of the timing belt revealed that the “kick backs” had indeed damaged the timing belt. A new timing belt was installed and an intensive investigation began into what could be causing the malfunction. When the investigation indicated a component might be the problem, it was replaced. So far, the component causing the problem has not been determined.

MorePower

After changing additional parts and much more testing, I have decided that 3 years trying to solve the kickback problem is long enough. It’s time to dump the car. It’s the first time in 45 years that I haven’t been able to fix a mechanical/electronic problem within a reasonable time. The biggest problem here is that I failed to investigate the design and engineering of the Lexus before buying it. I clearly understand (now) that Lexus designed the car to only be repaired by a Lexus dealer. It’s bad enough to repair a reasonably engineered car, but a deliberately engineered mechanics’ nightmare is not something I want to voluntarily repair. Obviously Lexus determined that if one could afford a Lexus, they can afford to be ripped off in repair bills. I also understand that Lexus doesn’t have a monopoly on this method of operation.

It is true that generally a Lexus will operate for several years with little or no problems. However, the poor sucker (like myself) who buys one used really gets shafted. Just a routine dealer “major tune-up” costs over a $1,000. I’m going to pass this future money pit to someone with a bigger bank account than me. Fortunately I could do my own major tune-ups and fix the burned out speedometer needle light, another engineering nightmare money pit. (Another dealer $1,000 bill). I’m sure that if I kept working at it, I would eventually find the cause of the kickback problem, but life is too short for that.

It’s onward and upward………