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1992 LS400 - Cherry red exhaust - this may be the end for it

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So I have to get your opinion on this.  Took it to get gas yesterday but did not make it.  would not accelerate past 25 mph with foot to the floor.  turned around and took it home.  Idle in neutral down to 500 rpm.  Rev engine several times and it will go to 5k.  Noticed smoke coming off the engine.  turned off and looked under car. exhaust pipe on drivers side bright cherry red for about 2 feet starting at engine.  Any thoughts?  It has 2 coils, one for each side of the engine.  I'm hoping it just lost a coil and unburned gas is getting in the exhaust pipes.  But of course, the coil on the drivers side is nearly impossible to get to without removing the battery.  I'm really getting tired of working on this car.  Any thoughts?  Please don't tell me plugged cat. converter, that would be the end.
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It's not the coils. Just replaced both with my good spare one at a time.  No change.  Next stop, computer, spark plugs, junk yard.  It may be time.

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Let’s explore some possibilities based on the symptoms you’ve described:

  1. Fuel Delivery Issues:

    • The loss of power and hesitation during acceleration could be related to fuel delivery problems. Consider checking the fuel filter, fuel pump, and fuel injectors. A clogged fuel filter or a failing fuel pump might cause insufficient fuel flow, leading to poor acceleration.
    • Additionally, dirty fuel injectors can affect engine performance. You might want to try using a good fuel injector cleaner to see if it helps.
  2. Air Intake and Throttle Body:

    • Inspect the air filter and throttle body. A dirty air filter or a clogged throttle body can impact engine performance.
    • Cleaning the throttle body and mass airflow sensor (MAF) could improve acceleration.
  3. Exhaust System and Catalytic Converter:

    • While you mentioned not wanting to hear about a plugged catalytic converter, it’s still worth considering. A restricted exhaust system can cause poor acceleration and overheating.
    • The bright cherry red color on the exhaust pipe suggests excessive heat, which could be related to a partially blocked exhaust.
  4. Ignition System:

    • Since you mentioned two coils (one for each side of the engine), check the ignition coils and spark plugs. A failing coil or spark plug could lead to misfires and poor acceleration.
    • If one coil is indeed malfunctioning, it could cause unburned fuel to enter the exhaust system.
  5. ECU and Error Codes:

    • Sometimes, the engine control unit (ECU) can go into “limp mode” to protect the engine when it detects a serious issue. This mode limits power but allows you to drive to safety.
    • Consider checking for error codes using an OBD-II scanner. The codes might provide insights into the specific problem.
  6. Belt and Timing:

    • Ensure that the timing belt is correctly aligned. A slipping timing belt can affect engine performance.
    • Perform a power balance test to check if any cylinders are not firing properly, which could indicate distributor issues.

Remember, diagnosing car issues remotely can be challenging, and it’s always best to consult a professional mechanic. They can perform a thorough inspection and provide accurate guidance based on hands-on assessment. 


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Typically, a hot exhaust means a lean mixture.  However, a rich mixture will also make a catalytic converter run hot.

I'm going to assume that you've never opened up the ECU and inspected the capacitors for leakage.  All LS400's are prone to this.  In 1997 and earlier models, the problem is extremely common.  Click the link for information overload.


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Thanks for all your replies.  I have replaced capacitors but that doesn't really mean much as I have a friend who is working on his 4th ECU.  I do have a spare with new capacitors but haven't had time to put it in.  And don't get me started on professional mechanics.  My Lexus dealer replaced nearly the entire back suspension and ruptured the universal boot chasing a vibration which $3000 later, was actually just a bent rim.  And then he had the nerve to claim he didn't rupture the boot.  Well there wasn't grease all over the rear wheel well when I gave you the car.  That's the last time this car has seen a "professional" mechanic and the last time it ever will.

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