Lexus SC 1992 SC300 cold start problems

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hi. First owner of a 92 SC300. Never had problems till my gauge cluster died and I ran out of gas. Now cold start is a problem - 3/4 turns to get it started in the morning. Changed IACV, fuel filter and cleaned the throttle body. No improvement. It’s driving me crazy. Anyone have an idea? Thanks!
 

mmcartalk

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Welcome to LE.:)

Are you using the correct grade of fuel for it? Premium gas is not only different in octane from regular, but also has a different vapor-pressure, which can make a difference in fuel-vaporization on a cold start. Also, a bad coolant-temperature sensor could fool the engine computer into giving the engine a leaner-than-required fuel mixture (or, in some cases, richer), which will hurt cold starting and warmup.
 
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Using 95 octane. Never had issues with the start Tull I ran out of gas a while back due to a faulty gauge. After that it started acting up
 

mmcartalk

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Using 95 octane. Never had issues with the start Till I ran out of gas a while back due to a faulty gauge. After that it started acting up


I'm not sure exactly how your fuel tank and pump are designed, but it if is the pump-submerged-in-tank system, that could also explain at least part of it. With that system, gasoline flowing through the tank helps keep the pump lubed...if you run the tank dry (or the level of fuel in the tank gets below the tank's intake-port), the pump is electrically-operated and, in some cases, keeps running for awhile, sucking nothing but air, which can damage or degrade the pump, lessening its performance even when the tank is filled up again. I'm not saying that's exactly what happened to your car, but it has been known to happen in similar circumstances. That's why some Owners' Manuals caution against letting the tank go dry....though, obviously, if the gauge failed, that's not your fault. Still, it's a good idea to fill up based on mileage, not just a gauge-reading, which could be off. Fill the tank every 150-200 miles or so, and you generally won't run it dry, no matter what the gauge reads.

Using 95 octane

Also, if my memory was correct (I once had an IS300 with the same 3.0L in-line 6) that engine was designed for 93 octane.
 
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Using 95 octane. Never had issues with the start Tull I ran out of gas a while back due to a faulty gauge. After that it started acting up
I'm not sure exactly how your fuel tank and pump are designed, but it if is the pump-submerged-in-tank system, that could also explain at least part of it. With that system, gasoline flowing through the tank helps keep the pump lubed...if you run the tank dry (or the level of fuel in the tank gets below the tank's intake-port), the pump is electrically-operated and, in some cases, keeps running for awhile, sucking nothing but air, which can damage or degrade the pump, lessening its performance even when the tank is filled up again. I'm not saying that's exactly what happened to your car, but it has been known to happen in similar circumstances. That's why some Owners' Manuals caution against letting the tank go dry....though, obviously, if the gauge failed, that's not your fault. Still, it's a good idea to fill up based on mileage, not just a gauge-reading, which could be off. Fill the tank every 150-200 miles or so, and you generally won't run it dry, no matter what the gauge reads.



Also, if my memory was correct (I once had an IS300 with the same 3.0L in-line 6) that engine was designed for 93 octane.
 
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Using 95 octane. Never had issues with the start Tull I ran out of gas a while back due to a faulty gauge. After that it started acting up


Still don’t get why it would be the pump if he car runs fine when its started....thanks
 

mmcartalk

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Still don’t get why it would be the pump if he car runs fine when its started....thanks

Good question (and I'm not an engineer)...but, with my admittedly limited knowledge, it takes more gas (a richer air-fuel mixture) for a cold-engine start and early warm-up than it does after the engine warms up a little, where things lean out and a weak or damaged pump can supply more gasoline per unit of time. That's because, up to a point, the colder it gets, the less fuel can vaporize in the cold air, and the more gas is needed to get the cylinders to fire up.
 
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Good question (and I'm not an engineer)...but, with my admittedly limited knowledge, it takes more gas (a richer air-fuel mixture) for a cold-engine start and early warm-up than it does after the engine warms up a little, where things lean out and a weak or damaged pump can supply more gasoline per unit of time. That's because, up to a point, the colder it gets, the less fuel can vaporize in the cold air, and the more gas is needed to get the cylinders to fire up.
Good point. Does the SC300 have a cold start valve?
 

mmcartalk

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Good point. Does the SC300 have a cold start valve?


Don't know that right off the bat. Here's a '93 video (not me, but someone else)....is this what your SC300 is doing? Note, in the video, that the Check Engine light stays on long after it should have gone out. That could indicate a sensor problem, like I mentioned earlier.

This engine, BTW, also, from my memory, has quite an appetite for gas. Its average mileage was comparable to that of the 4.0L V8 found on some other Lexus models of the period.