i bought a 91 ls400 off someone who let it sit for a year, i had to put a fuel pump in it to get it running. but it isnt running right, its burning black smoke, which i believe means its running rich, and it wont rev over 2500rpm, and it has not to much power, and i did a diagnostic on it, it came up code 31 which means mass airflow. it does idle nice, but doesnt start on the first try. will this happen if the mass airflow sensor is bad??? what else could be a possibility? i scored the car for 800 bucks and i dont have a lot of $$$ i could use some suggestions. thanks in advance. mike

 

I would start with a replacement used MAF.
They are usually not that hard to find. Remember to check SC400 Forums as well for this part.

When the MAF ceases to work you will have a bucking bronco.

 

Ok, before you invest in a replacement MAF, which is $1000 from the dealer, try disconnecting it first - the car should run almost normal with the MAF disconnected. If it runs normal after you disconnect the MAF, that means your MAF or/and your O2 sensors are shot. However, if it still runs the same, then its something else. Could be the ECU, injectors, spark plugs, wires, ignitors and ignition coils.

The problem that you are describing is most often related to the ignition coil. Your LS has two of them, one on drivers side and one on top of the engine. Most likely you're only getting spark on one coil, so your engine is running on four cylinders and dumping the gasoline from the other four into the exaust. Check for spark on both coils.

 

Buy a new distributer cap rotor , wires and plugs to tune it up before being able to figure out the issue. A maf may be bad but it would need more of a problem to burn black.

 

i was curious why i would get the code 31, mass air flow code, could i have a diff. problem and it would trip that code?????

 

look on the internet for companies that rebuild them for about 150-200 dollars.

 

thanks guys, i bought a used one, im putting it in tomarrow, ill keep everyone posted...

 

it worked, i never knew that little unit could cause big problems!!!! thanks for everyones help in my ls issue...