MY,1999-LIGHTNING SUDDENLY STARTED RUNNING ROUGH
AT IDLE. IT IS ALSO WAY DOWN ON POWER. THE CHECK ENGINE LIGHT IS ON CONSTANTLY! THERE WERE TWO FAULT CODES
ONE FOR LEFT BANK F/A, TOO LEAN AS WELL AS RIGHT BANK TOO
LEAN. THE TRUCK IS STOCK.

 

Mine did the same thing about three weeks ago. I had a couple of coils go bad, so the dealership replaced the whole drivers side bank (4). I replaced the other 4. The truck went back to running smooth, but the fault codes kept coming back. They then replaced my MAF sensor. This didn't stop the ses light from coming on. Fuel pressure seemed alright. So I put my 2# pulley back on instead of my six#er and put my other chip in. I then disconnected my battery and got the light to go out. If the light comes back I will check the o2 sensors and have my injectors cleaned as well as check my fuel pressure again. You probably only have a coil or 2 bad.

 

It could be a number of things, but my guess is a bad Mass Air Flow Meter.

 

If it were a bad coil or two or bad plugs, then I would think that you would be running too rich not too lean. Bad coils or plugs would be my guess IF you weren't getting a 'lean' code.

It might be a vacuum leak, a clogged fuel filter, too much EGR, or a bad MAF sensor..............

Dan

 

I would start with a new fuel filter, and while I was changing that I would check the fuel pump pressure. I've seen several pumps blow a line off and run real lean. After that I would check the MAS. Its all up to you just my two cents worth.

 

how can you tell if the truck is running too lean? or how to check the fuel pressure??

 

I didn't notice you have a 99 L---duh!

As usahooters said, it may be a loose fuel pump line inside the tank. This has happened on more than one 99 L. Th e clamps are at fault if I remember correctly. PSP has better/higher pressure pumps available. This would answer the lean codes situation too.

Dan

 

I have the lean codes now also. It gave me the code after driving about 50miles then going to a traffic light. At the traffic light the Check Engine Soon light came on. The code was bank 1 and 2 are Lean. If anyone knows what to look for please let me know.

 

ttt

 

Mine started pulling the 171 and 174 lean codes recently. Dealer claimed it was a bad MAF sensor but its still acting up. The ses light hasnt came back on yet (only drove maybe 40 miles since I got it back) but its doing some wierd things. At a dead stop I can push the gas half way down quickly and it'll stumble on itself for a second and then take off. Sometimes it'll do it say when you slow down for someone in front of you to turn off and then you hit the gas down halfway. Any ideas? FWIW its a dead stock 99 model with 20K on it. Almost seems to me as if its not getting fuel for a moment.

Billy

 

1. clogged fuel filter --easy to replace

or

2. Fuel hose off of one of the fuel pumps--have to drop the tank to investigate/fix.

Dan

 

I really believe its #2. Getting the dealer to believe me about it is another thing. Guess I might just have to do it myself.

Billy