Help please – misfire when hot
Posted: April 16th, 2006, 8:04 pm
I could really use some help with a very frustrating misfiring problem. I call it a misfire, but I’m not sure that’s what’s happening. It’s a 93 MX-3 with the 1.6 L SOHC 16 valve engine.
The motor runs great when it’s cold, but after it warms up and runs above 3000 rpm for a few minutes, the problem starts. When I tip into the gas a bit, it hesitates and gasps. The car bucks violently unless I ease off the gas and feed it gently. Then, when it exceeds 3000 rpm, the engine is strong and smooth. When I park it after such a run, it usually stalls. It will then restart only by flooring the gas and even then requires rapid pumping of the gas to catch and stay running – usually only above 3000 rpm. At lower speeds its very rough, misfiring and hesitating – trying to stall.
I’ve modified it with a short, aluminum 3 inch intake and 6 inch K&N. There’s a 2-1/4 inch Pacesetter cat-back system. Everything else is stock. Partly to chase this problem and partly to bring components back into spec, I’ve replaced the Idle Speed Control Valve, the Purge Control Solenoid, the Fuel Pressure Regulator and related Solenoid Valve, the Oxygen sensor, the thermostat and the Coolant temperature sensor, as well as plugs, wires, distributor cap/rotor and ignition coil. The Throttle Position Sensor tests OK and looks good inside. The Air Flow sensor tests OK on all combinations of contacts except wide open E1 to FC, which is 0.3 ohms instead of zero.
I have also by-passed the Idle Speed Control Valve and Intake Manifold with the coolant pipes in an effort to solve the problem, but in vain. The spark plugs (NGK V-Power) turned black in the course of 2-3 test drives. The exhaust tip is also black. Compression is 180, 175, 135, 165 – ring job next winter! Check Engine light remained ON throughout all of this. I just read something on another forum about how to read codes with a paper clip so I’ll try. I can’t find a used or new Code Scout code reader.
By my reckoning, the only thing left would be the ECU or a bad wire somewhere. I have tested all the W/R wires to the solenoids, injectors, ISCV and main fuse and they’re all good. I am really stumped and would appreciate any suggestions or observations anyone might have.
The motor runs great when it’s cold, but after it warms up and runs above 3000 rpm for a few minutes, the problem starts. When I tip into the gas a bit, it hesitates and gasps. The car bucks violently unless I ease off the gas and feed it gently. Then, when it exceeds 3000 rpm, the engine is strong and smooth. When I park it after such a run, it usually stalls. It will then restart only by flooring the gas and even then requires rapid pumping of the gas to catch and stay running – usually only above 3000 rpm. At lower speeds its very rough, misfiring and hesitating – trying to stall.
I’ve modified it with a short, aluminum 3 inch intake and 6 inch K&N. There’s a 2-1/4 inch Pacesetter cat-back system. Everything else is stock. Partly to chase this problem and partly to bring components back into spec, I’ve replaced the Idle Speed Control Valve, the Purge Control Solenoid, the Fuel Pressure Regulator and related Solenoid Valve, the Oxygen sensor, the thermostat and the Coolant temperature sensor, as well as plugs, wires, distributor cap/rotor and ignition coil. The Throttle Position Sensor tests OK and looks good inside. The Air Flow sensor tests OK on all combinations of contacts except wide open E1 to FC, which is 0.3 ohms instead of zero.
I have also by-passed the Idle Speed Control Valve and Intake Manifold with the coolant pipes in an effort to solve the problem, but in vain. The spark plugs (NGK V-Power) turned black in the course of 2-3 test drives. The exhaust tip is also black. Compression is 180, 175, 135, 165 – ring job next winter! Check Engine light remained ON throughout all of this. I just read something on another forum about how to read codes with a paper clip so I’ll try. I can’t find a used or new Code Scout code reader.
By my reckoning, the only thing left would be the ECU or a bad wire somewhere. I have tested all the W/R wires to the solenoids, injectors, ISCV and main fuse and they’re all good. I am really stumped and would appreciate any suggestions or observations anyone might have.