Questions and Answers
Mitsubishi Running Lean
Q. I recently had my car to a garage and got a diagnosis done to see why it was hesitating and starting hard. The diagnosis came up with nothing wrong. The technician said he knows something is wrong because of the hesitation.
He said that it is running a lean mixture. I don't know how to fix a lean mixture. I will go into what the problem was when I took it to the garage.
When I would press on the gas, it would hesitate and buck as it tried to accelerate. It would do this when it was cold, and when it was warm. Also when I go to start it, it takes a long time to turn over. The starter is working fine but it just doesn't seem like it is getting enough fuel. It will only start if I pump the gas pedal. Then as it does turn over, it starts real real hard and feels like it is going to shut off.
Please tell me what you think could be the problem. I have gone to a couple different garages and they all say they have no clue. Thanks so much. If you might only know how to help the problem that would be a great help cause anything is better than now.
1993 Mitsubishi Eclipse GS
2.0
Automatic transmission
90,900 Miles
Fuel Injection
ABS brakes
P/S, P/W, P/DL- A/C - Cruise controlJustin
A. A lean fuel mixture would definitely cause the problems you are having. And since the fuel mixture is non-adjustable, we have to find the cause of the lean mixture. There are a number of causes of this condition however.
The first, and easiest to check is the Idle Speed Control Valve (ISCV). This can be removed and cleaned. Most often this is the cause of the problem you are having. Over time gums and varnish build up inside the valve and keep it from operating correctly. A good cleaning usually restores it to proper working order. Of course it is possible the valve is bad and needs to be replaced.
Another common cause is a vacuum leak. This will allow unmeasured air to enter the engine and lean out the mixture. Something as simple as an oil dipstick that is not fully seated may cause a problem.
The spark plugs may be the problem as well. I would use only NGK BPR5ES-11 gapped at .039 - .043 in. in that engine. It does not like aftermarket spark plugs and simply installing the right plugs could help immensely.
Another thing to check is the O2 sensor. An O2 sensor sending the wrong information to the computer will cause a drastic change in the fuel mixture. Either causing it to be too rich or too lean.
Another thing that can cause the problem are the air intake and engine temperature sensors. If they are bad or out of calibration, they will send the wrong information to the computer and cause a lean condition. Low fuel pressure, caused by a bad fuel pump or fuel pressure regulator can cause a lean condition as well. A test with a fuel pressure tester will pick this problem up.
A scan tool will be able to check the ISCV and sensors to see if they are operating properly.
Additional Information provided courtesy of ALLDATA
