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Stalls If Hot Weather And/or Low Gas Tank


NJ Bob
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Hi, new to the forum. Am original owner 1991 LS400. Great car, 160k miles. No real problems until about 1 yr ago.

Noticed last summer the car would stall while driving. I found that it only stalled after driving about 20 minutes minumum AND the gas tank was low (maybe 1/3 tank or less) AND it was hot/humid. I replaced the external fuel filter last September or so and it seemed to go away (thinking of the old vapor lock situation). BUT now that the warmer weather started to come back it has returned.

There's definitley a relationship between the outside temperature/humidity, the amount of gas in the tank, and the length of time the car has been running. Short stops of 15 minutes or so also seem to make it worse (ie- no prblem satalling, make quick stop somewhere, then stalling problem happens when accelerating).

As time has gone by it has gotten worse. The tank can now be more than half full and the weather might be slightly warm and the stalling occurs. MOST IMPORTANT- it has NEVER EVER happened with a full tank or close to it. If stalling is occurring, I can pull into a gas station, fill it up, and leave knowing that it will definitely not be stalling.

I cannot afford to have repair shops do trial and error to find the problem. Has anyone heard of this exact scenario? Other posts seem similar, but no one has mentioned the low gas tank connection, or even the ho/humid wether situation.

Any help would be appreciated as I would love to keep this car for as long as possible.

Bob Z

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Wow, this is a good one. My first thought was to agree with the guy from Spain who mentioned the loose gas cap possibility. The last time I didn't tighten the cap properly, gas spilled in my garage. But I always keep the tank pretty filled. The LS balked a little, and squeezing the cap fixed the problem. I'll be really interested in the solution.

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I had the same problem with a Mercedes I had. It was a 1985 S-Class. I loved the car, but occasionally when I would stop at a traffic light, or turn into a parking space, it would stall. It would always restart though. It never did it when it was cool out... only warm/hot. I took it to a MB tech and he said it was the injector seals. I am sure this is not the case on the LS though.

Good luck.

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Hi, new to the forum. Am original owner 1991 LS400. Great car, 160k miles. No real problems until about 1 yr ago.

Noticed last summer the car would stall while driving. I found that it only stalled after driving about 20 minutes minumum AND the gas tank was low (maybe 1/3 tank or less) AND it was hot/humid. I replaced the external fuel filter last September or so and it seemed to go away (thinking of the old vapor lock situation). BUT now that the warmer weather started to come back it has returned.

There's definitley a relationship between the outside temperature/humidity, the amount of gas in the tank, and the length of time the car has been running. Short stops of 15 minutes or so also seem to make it worse (ie- no prblem satalling, make quick stop somewhere, then stalling problem happens when accelerating).

As time has gone by it has gotten worse. The tank can now be more than half full and the weather might be slightly warm and the stalling occurs. MOST IMPORTANT- it has NEVER EVER happened with a full tank or close to it. If stalling is occurring, I can pull into a gas station, fill it up, and leave knowing that it will definitely not be stalling.

I cannot afford to have repair shops do trial and error to find the problem. Has anyone heard of this exact scenario? Other posts seem similar, but no one has mentioned the low gas tank connection, or even the ho/humid wether situation.

Any help would be appreciated as I would love to keep this car for as long as possible.

Bob Z

Hey Bob

I currently have the same sputter stall problem on my 94 LS400 but this only happens when the humidity / temperature outside is high. The problem happens on a full tank but only after I drive for about 20 minutes or so and then turn the car off and on. Did you ever resolve this issue?

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Hi, new to the forum. Am original owner 1991 LS400. Great car, 160k miles. No real problems until about 1 yr ago.

Noticed last summer the car would stall while driving. I found that it only stalled after driving about 20 minutes minumum AND the gas tank was low (maybe 1/3 tank or less) AND it was hot/humid. I replaced the external fuel filter last September or so and it seemed to go away (thinking of the old vapor lock situation). BUT now that the warmer weather started to come back it has returned.

There's definitley a relationship between the outside temperature/humidity, the amount of gas in the tank, and the length of time the car has been running. Short stops of 15 minutes or so also seem to make it worse (ie- no prblem satalling, make quick stop somewhere, then stalling problem happens when accelerating).

As time has gone by it has gotten worse. The tank can now be more than half full and the weather might be slightly warm and the stalling occurs. MOST IMPORTANT- it has NEVER EVER happened with a full tank or close to it. If stalling is occurring, I can pull into a gas station, fill it up, and leave knowing that it will definitely not be stalling.

I cannot afford to have repair shops do trial and error to find the problem. Has anyone heard of this exact scenario? Other posts seem similar, but no one has mentioned the low gas tank connection, or even the ho/humid wether situation.

Any help would be appreciated as I would love to keep this car for as long as possible.

Bob Z

Hey Bob

I currently have the same sputter stall problem on my 94 LS400 but this only happens when the humidity / temperature outside is high. The problem happens on a full tank but only after I drive for about 20 minutes or so and then turn the car off and on. Did you ever resolve this issue?

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Hi, new to the forum. Am original owner 1991 LS400. Great car, 160k miles. No real problems until about 1 yr ago.

Noticed last summer the car would stall while driving. I found that it only stalled after driving about 20 minutes minumum AND the gas tank was low (maybe 1/3 tank or less) AND it was hot/humid. I replaced the external fuel filter last September or so and it seemed to go away (thinking of the old vapor lock situation). BUT now that the warmer weather started to come back it has returned.

There's definitley a relationship between the outside temperature/humidity, the amount of gas in the tank, and the length of time the car has been running. Short stops of 15 minutes or so also seem to make it worse (ie- no prblem satalling, make quick stop somewhere, then stalling problem happens when accelerating).

As time has gone by it has gotten worse. The tank can now be more than half full and the weather might be slightly warm and the stalling occurs. MOST IMPORTANT- it has NEVER EVER happened with a full tank or close to it. If stalling is occurring, I can pull into a gas station, fill it up, and leave knowing that it will definitely not be stalling.

I cannot afford to have repair shops do trial and error to find the problem. Has anyone heard of this exact scenario? Other posts seem similar, but no one has mentioned the low gas tank connection, or even the ho/humid wether situation.

Any help would be appreciated as I would love to keep this car for as long as possible.

Bob Z

Hey Bob

I currently have the same sputter stall problem on my 94 LS400 but this only happens when the humidity / temperature outside is high. The problem happens on a full tank but only after I drive for about 20 minutes or so and then turn the car off and on. Did you ever resolve this issue?

Hi Bob,

I was a lexus tech for a long time. I have seen two things cause these symptoms, first oxygenated fuel or high achocol content fuel mixed with warm weather can cause the fuel to boil in the rail. Usally worst after trying to restart a warm engine after 15-30 min of sitting. try a different brand of preimum and see what happens. Second and more common the check valve in the in-tank fuel pump allows fuel pressure to bleed off. let it sit an hour and crack open the fuel line at the rail if you don't get a good high pressure squirt replace the pump.

Rusty

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Sorry, I don't have direct experience with this one (yet).

Attached is a rough guide to checking the fuel pressure in the line, the proper way is to hook up a gauge but this is really easy. Refer picture below. The special service tool is a piece of wire that jumpers the 12V at the B terminal of the check connector to the pump. Please be very careful as the instructions highlight, as the 12V will harm circuits on the other terminals if you accidentally contact them.

I have looked through the manual and the most common cause of trouble starting hot is the water temp sensor, followed by vacuum leakage, then fuel quality. If you can start eliminating these factors you will hopefully solve it.

The water temp sensor is listed as quite an involved job, eliminate the other 2 first. If you are still stalling on acceleration when hot (I don't know how the tank level affects this) then come back for more help.

post-21092-1209067128_thumb.jpg

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  • 7 years later...

Lexus LS 400, '91: hot days, virtually, stop in go traffic...hesitates, jumps rpms up/down, 1/4 gas or less. loss of power, stalls and turning car off and cool--restarting seems to reset its self. I have recently been following this "TAG" 1st hand experience, January 2015 - present day, I have paid cash--not credit cards, sum of, $20,000.00 plus, attempting to rid my vehicle of this ongoing problem the others are also having. LET ME TRY AND SAVE YOU $$$. I have had the following repairs/replacements: Engine building/balanced, $6,500.00: hoses, starter, TPI sensors (2), fluid leaks, cables, battery, alternator, lines, steering pump, knock sensor, EGR transducer, cam sensors, and etc.--after all that...Problem still exist!!!!!!!!

Has anyone out there, found a solution(s) yet, I would like to trust my inadiment item that I love and enjoy driving...loves to be driven hard and fast.............

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I have studied this problem a bit. One of the things that always comes up is the fuel pump was changed to fix it. Another thing that comes up is the fuel pump resister, and since I have zero information on 93 to 94's I have no idea if they have that resistor on not, nor do I know where it is on those cars. The resistor is for low powered driving and lets the fuel pump run slower. So it is possible that if that resistor drastically changes value and lowers the pump speed too much then there would be more susceptibility for vapor lock.

So when you have this problem simple things first, and start with good clean battery connections, an experiment can be done by bypassing the resistor to see if the problem clears up. But fuel pump life is degraded if that resistor is not there, so let it be a short experiment.

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