Ls400 Help

[Jerjer]

Hey guys well Im new to your site and I need your help with my 91 ls400

My car is giving codes 25-26 and is running rich and fowling the plugs and mising really bad.

It runs better when cold the codes are rich and lean fuel condition Im not worried about the lean just the rich.

I have cheched the wires and coils and they are good I really dont want to geuss and throw parts at it

Any advice would help

[steve2006]

Hi and welcome to the LOC.

Your symptoms seem to suggest the problem is temperature related.

If the car seems OK when cold but not when warm it would point to the coolant temperature sensor.

When cold the fuel mixture is richened (used to be the choke on older cars) as the engine warms up the mixture is weakened to normal fueling levels. If the engine ECU, because of a faulty coolant sensor,thinks the engine hasn't warmed up it will continue over fueling and giving the problems you have.

You can check the sensor with a multimeter,either the voltage output hot and cold or it's resistance hot and cold, for what they cost just replace it but also check the wiring connections to it as well.

[Jerjer]

Well its better when cold but still runs like crap

[steve2006]

How did you check the coils,the drivers side one does fail

[Jerjer]

I checked primary resistance and secondary with a multimeter

[Jerjer]

Well problem solved and I cant believe what fixed it

Since it was do for a tune up I replaced the plugs and wires and its fixed

I never would have thought thats all it was, while I was at it Cleaned the throttle body and intake and installed a k&n filter and wow this thing hauls !Removed! way better then before