91 Ls400 Stumbles/misses On Moderate Acceleration

[Juddly]

Hi!

This is my first posting to this forum.

I'm looking for help diagnosing engine trouble with my 1991 LS400.

The engine accelerates fine under light load, like city driving. Under full throttle (petal to the metal) it also performs flawlessly.

But under moderate acceleration, like passing within the city, or accelarating on the freeway on-ramp, the engine "stumbles" or "misses". Warm or cold engine makes no difference.

I've changed the plugs and wires. No change. No codes are displayed.

Any suggestions?

Juddly

[ToddLS400]

Dirty injectors? Try using some high quality injector/octane booster like C5. I get that stuff at a local performance shop. They don't sell it at Schucks or any of the run of the mill auto part stores. If that doesn't clear it up, you may have to have them removed and cleaned professionally.

[bennie]

Hi,

check the egr pipe, maybe there is a small leak.

Bennie

[Juddly]

What is the possibility of the problem coming from one of the two coils?

[Juddly]

Hi:

Follow-up...

I tested the coils with an ohm meter last evening. The left coil was OK and well within specs. The right coil was way out of specs,... twice the resistance in both the primary and secondary coils.

I've ordered a new coil from the local dealership and will install it tomorrow. Will let you all know what the outcome is.

TTYL,

Bill

in Saskatoon

[Juddly]

Hi again:

It wasn't the coil either. I put a new coil in and the same trouble with hesitation/stumbling persists.

Gotta keep looking...

Bill

[VBdenny]

I gotta agree with LS Todd. I would add a can of either Slick 50 Fuel System Treatment, or Valvoline Fuel System treatment. If you don't pay $10, you have the wrong stuff and nothing else works as well. My friend had the same probem with his Cadillac and have a tune-up, and the computer replaced and it still did the same thing. He said go drive it. I did, right to the auto parts store where I dumped in 2 containers. The next few days his problem was gone. He couldn't believe it.

[ToddLS400]

My '90 LS400 wasn't always giving me full power at WOT (pedal to the floor). Sometimes it would kick down and give me normal power. Sometimes it would act like it didn't want to shift down. I ran 2-3 tanks of fuel injector cleaner and a tank of C5 octane booster. The problem is now gone. I thought it was my kick down switch under the pedal but it appears to be solved. I think the previous owner before me used regular unleaded gas for the few years they had it? I always use premium in my cars. I believe his wife drove the car most of the time too. They have a few kids so I'm sure it was drove very conservative. I like to get on it when on the freeway. It eats gas when I drive it like that but it's fun accelerating with these tuned Toyota V8's. They have quite a bit of power.

Now I need to take off those horrible stock 15" rims/tires and get some 18" rims/tires. I've spent a lot of money lateley so I just have to wait about another month to get them. I think I'm going with the Enkei LM1 18" rims with Kumho Supra tires?

To sum it all up, the car is running great now.

[SKperformance]

sometimes under moderate accel

the stumbling is caused by a gap or tear int eh intake piping

check it for cracks and see

it might be an easy fix