Ls 400 Engine Stalls When Warm

[Ambrose]

I have a 1990 LS 400 that stalls, only when warmed up. It starts just fine and runs like a smooth champ until it gets warmed up and then the fun starts. It has high mileage, (280K) but has been pretty well kept up.

I originally thought it was because of something in the gas, because it seemed to start stalling only when the gas was under a quarter of a tank, so I put some gas treatment in the tank which didn't help much, if at all.

The weird thing is that initially when it acted like it was going to cut off, I could put more gas in the car and it would run just fine again. But now after a week or so, it's stalling every time the car warms up regardless of the amount of gas in the tank.

It cut off completely while driving a couple of times, but it always started right back immediately like nothing was wrong. But it would do absoutely nothing when I pressed the accelerator, as if it's out of gas

I remember reading a thread about the "limp mode" on the LS and that's exactly what has been happening...it has never left me stranded, but it "limps" home going no faster than about 20 MPH after acting like it wanted to cut off, then 20 MPH; stall, 20 MPH, stall back and forth.

It also fails to rev above a certain RPM, when I put it in neutral or park and try to rev up the engine. Very frustrating! Any clues?

[ROYT]

Has the fuel filter been replaced?

If all filters are clean, including air, have the fuel line pressure checked, the pump may

be failing to supply correct pressure.

Assuming plugs HT cables, rotors,distributor caps all good etc.

[Ambrose]

Has the fuel filter been replaced?

If all filters are clean, including air, have the fuel line pressure checked, the pump may

be failing to supply correct pressure.

Assuming plugs HT cables, rotors,distributor caps all good etc.

No, but I actually purchased one yesterday on a recommendation from a friend. Haven't installed it yet, will reply when done.

Thanks,

[soundchaser100]

Has the fuel filter been replaced?

If all filters are clean, including air, have the fuel line pressure checked, the pump may

be failing to supply correct pressure.

Assuming plugs HT cables, rotors,distributor caps all good etc.

No, but I actually purchased one yesterday on a recommendation from a friend. Haven't installed it yet, will reply when done.

Thanks,

This sounds like it could just be our old friend the throttle body again. Take the air intake pipe off and give the throttle butterfly and the inlet pipe a good clean, then see what its like. Paul