1991LexMan

So this **** keeps happening like a few times a month, and ONLY when it's hot. My car will run fine for a little while, then when i'm idling it will choke itself and drop the rpms to like 200 and either catch itself and shoot back up to like 1400 real quick then idle normal for a second or two and do it again.... or it will simply die... it doesn't (or hasn't yet) happened when its cool, or when its raining, only when its 80 + out... when it happens it still drives sometimes, but when i hit it it bogs down for a few and either dies or shoots up to like 3000 or wherever it should be if it hadn't been bogging itself down. Any help or advice or 2 cents would be nice because i'm kind of puzzled right now

Yotarip

Does your check engine light some on when the problem starts?

hobojoe

I have had this problem also but never shot up in rpms when i caught just caught and went as normal always happened when the car was Hot and it was hot outside or the car had been running for a long time.

^^ Nope never has for me it just dies.

JimsGX

1991LexMan,

Does it stop doing this in hot weather if you keep the tank close to full, or at least above half full?

1991LexMan

its weird you mention the gas becuase it USUALLY only happens when its 1/4 tank or so left, but i had a little under 1/2 tank the other day when it did it... and i noticed (or remembered) it will stop if i throttle it for a few minutes, when and if it doesnt die

ZenkiFace

My car (1990 LS, 160k) is having this exact problem, started happening when it warmed up here in Seattle a couple weeks ago. It seems to run fine for about the first 30 minutes of driving, then will begin with the idle dipping to around 500, then surges to 1100, settles back at 650, and repeats.

As the OP explained, when attempting to accelerate from a stop the car will severely hesitate like it isn't getting spark or fuel, then will 'kick back in' for a second or two, only to return to the no power condition.

No CEL, no codes.

I have been scratching my head on this one, at first I suspected an ignition problem, but went through troubleshooting coils, wires, etc, and am now suspecting intermittent fuel delivery issues.

I will update this as soon as I find out what the problem may be, and will certainly check back if anyone can make an educated guess.

ZenkiFace

My problem was diagnosed today: Failing fuel pump

$986 parts & labor at the dealer...OUCH!

JimsGX

Was it really hot out the other day when it did it with just under half a tank? we're in close proximity to each other and the days have been pretty hot lately... I've had the problems you're experiencing in the recent past. I took the MAF out of the car (91LS) a while back and cleaned it up with MAF cleaner. Also reset the ECU at the same time. I haven't had the problem occur again since, but I've also been running at no less than about 5/8 of a tank because I know the problem had always cropped up when I let the fuel get below a half when it was hot out.

I'm not ready to start throwing parts and $ at the problem. I've seen a half dozen posts of the problem but no one has posted a solution. I remember reading one post that someone had replaced a bunch of components, including the fuel pump, but it didn't solve the problem.

1991LexMan

Yes it was the other day, the first hot day we had in a while... my friends brother said his 240 used to do the same thing and it was his fuel pump, but im not spending 900 something dollars for it, ill replace it myself... i'm going to do the fuel pump, fuel filter, and keep it above 1/2 tank and see how it goes. maybe ill clean the MAF and stuff like you did while i'm playing with everything

JimsGX

Fuel pump, ls400, denso 90-94 List: $381.31 Cost: $263.63

hobojoe

Zenki Did you do the replacement and did it fix the problem??? Just had this happen to me again.... Super hot here today and inbetween 1/4 and 1/2 tank of gas.

hobojoe

Ok guys sooo after much research here is an idea of a possibility of our first gen problems....I have never taken out my fuel pump but the concept behind it is its electric so it 95% of the time works the other 4% of the time when its broke it doesnt = no going at all. Then maybe there is 1% all of us that have our weird problem......

My idea is that for somereason the pump is worn out just enough that once the tank is below halffull since its a vertical mounted tank and the pump is not always close to gas that the heat is exxageratting the worn pump and causing us this issue....

any thoughts?

ZenkiFace

Yes, I had my pump replaced. My problem was very intermittent. It seemed to happen more often on hot days. Sometimes you could drive 50 miles with no problem, other times 4 miles in the same behavior would start up.

The techs ended up connecting a fuel pressure gauge and a multimeter to the pump circuit and driving the car around. After a few miles they saw the fuel pressure dropping to ~ 18-19psi and the voltage on the circuit dropping. I had replaced the pump in my old 1996 240sx, it wasn't inherently difficult, but a nasty job to say the least. The fumes really get to you after a while! They seemed to agree with the above diagnosis that our pumps are nearing a total failure condition, but are at a point of limbo where certain environmental conditions exacerbate the worn part. I've gone about 1500 miles now and no problems, it had stayed fairly hot in Seattle afterward, and I have taken my tank down below 1/4 a few times and no issues.

FisforFast

Thermostat, fuel pump and lastly... headgasket?

fourthmeal

First guess is fuel pump (diagnose before buying one.)

Do you have any codes stored? A code of any kind will point the direction you need to take. Obviously we're not talking OBDII codes here, but 15, 13, 71, etc...any at all?