91 Ls400 Engine Misfire

[jqzhang]

Hi,

I have a 1991 Lexus Ls400 with a mileage of over 150k. The problem is the engine misfire especially when it's hot, I mean after warming up.

1) the radiator is 2 or 3 years old, copper or brass;

2) newly changed thermostate valve;

3) newly rebuilt starter (pain in the neck job);

4) Check Engine light has been on for a couple of years: main oxy sensor at the right bank, replaced but the light won't go away;

5) converters are sort very old but doubt they will cause missing;

6) plugs and ignition wires 2 years old;

7) one of the ignition modules a few months old;

8) when doing 40M to 50M per hour, the car starts jerky. It feels like a tranny lock-up failure but at other speed range, it would be fine.

Any suggestions? A mechanic told me it's sort of common for early model of LS400. My 95 LS400 behaves similar but not so obvious. When the engine misfires, it will get worse.

Thanks in advance

John Z.

[91 and Smoooth]

Check this thread

http://us.lexusownersclub.com/forums/index.php?showtopic=64831

[jqzhang]

Check this thread

http://us.lexusownersclub.com/forums/index.php?showtopic=64831

Thanks. But I clean the throttle body and it did not solve the problem. I have to try something else.

Thanks again.

[dcfish]

Hi,

I have a 1991 Lexus Ls400 with a mileage of over 150k. The problem is the engine misfire especially when it's hot, I mean after warming up.

1) the radiator is 2 or 3 years old, copper or brass;

2) newly changed thermostate valve;

3) newly rebuilt starter (pain in the neck job);

4) Check Engine light has been on for a couple of years: main oxy sensor at the right bank, replaced but the light won't go away;

5) converters are sort very old but doubt they will cause missing;

6) plugs and ignition wires 2 years old;

7) one of the ignition modules a few months old;

8) when doing 40M to 50M per hour, the car starts jerky. It feels like a tranny lock-up failure but at other speed range, it would be fine.

Any suggestions? A mechanic told me it's sort of common for early model of LS400. My 95 LS400 behaves similar but not so obvious. When the engine misfires, it will get worse.

Thanks in advance

John Z.

Why only 1 ignition module replaced ?

[AndyLowe]

I truly believe you are describing a failing Ignition Coil.

I have bought them on Ebay, with shipping for $22.

I would buy one if I were you and replace one and then go for a ride.

If it continues to fail as you describe, then use the one you removed and install it on the remaining original coil.

Voila!

I truly think you will be surprised to learn it's fixed.

As for the O2 Sensor being replaced and still not being able to clear the light, I would confirm with a volt meter set on 1 volt range, at the Diagnostic Connector on top of the engine, the voltage being produced by your O2 Sensors, while engine is warm at idle.

You can buy a subscription to www.alldatadiy.com and look at the electrical wiring diagrams to learn which connector pin to put your meter's red lead, and just ground your meter's black lead.

You SHOULD see your O2 producing a signal/voltage that porpoises around .5vdc.

(Lean is Low .2v, .3v. .4v.....

(Rich is High .6v .7v .8v.....

It should always be going above and below .5v if your engine is running correctly.

If it's running lean, look for a vacuum leak.

If it's running rich, consider a stuck open thermostat......read your temp guage......it should be just slightly below the halfway point on its range when the engine is warm.

Hope this helps,

Andy