I have a 1997 Mitsubishi Eclipse 2.0L non turbo. It has a 130,000 miles on it. The car seems to be be hesitating when I push the throttle in half way to full throttle. The check engine light is on and the codes are: PO300, PO301, and PO302, which is multiple cylinder misfire. The car drives good if I barely hit the gas peddle but if I push the gas halfway to full throttle, it begins to hesitate and misfire. The car idles good but once in a while it sounds like it misfires for a slight second. I replaced the spark plugs with NGK, the spark plug wires look to be in good shape. They are Excel performance wires. The coil pack looks new. The EGR valve isn't sticking. I think the guy I got the car replaced the wires and coil pack. I ran a fuel pressure test and the pressure is high. The car doesn't use coolant or oil as well. Also ran a compression check and all the cylinders have high compression. It seems like the car is running lean. The plugs are not carbon fouled at all and are burning really clean. The car has an automatic transmission and if I keep the RPM relatively high, the car seems to drive better. Another words if I keep the overdrive off and rev up first and second before hitting drive. Another thing to note is when I turn the AC on, the car will stumble and sometimes die at idle. I don't drive the car with the AC on. The guy I got the car from said the ECU computer was programmed to run performance specs dont know if this relates to the problem. If anyone has experience this kind of problem any input would be greatly appreciated.

 

altenator

 

I hooked up a multimeter to my battery. When the car isn't running the battery is putting out 12 volts. When the car is running and I rev up to 2500 RPM, the battery is putting out around 13.5 volts. I also unplugged the negative battery terminal while the car is running, and the car doesn't stall out. Is 13.5 volts sufficient voltage for this car when running? Could the alternator still be bad?

 

id want higher but should be alright for a 2l.
Perhaps the ecu was flashed with wrong mappings.
Trace through the ign system, testing as you go, but yeah, if its not power shortage it starts looking like computer. Bugger.

 

The car seems to run good when the ECU is in open loop mode. Another words when I first start the car when the engine is cold. When the car warms up to normal operating temperature this is when the problems start to occur, closed loop mode. It sounds like the computer to me. Like it isn't using the data from the sensors properly in closed loop mode. It would probably be best just to get another ECU but I was wondering if there is a way to keep the car running in open loop mode all the time in order to test this theory?

 

unlikely without a bit of electrical know what. And i dont know what, but i imagine a 555 time gate and some triacs somewhere on the pcb.. Desolder a few pins...

 

Do you think that a ECU that was reprogrammed with performance specs could operate fine at first then start to develop problems over time as a result of it being reprogrammed? I think there is good indications that the computer is bad so I think I'm going to hunt down a decent used ECU sometime this week and give it a shot.

 

absolutely. Flashing boards (technical term for reprogramming firmware) is rort with potential *****-ups.
You could try re-flashing with a closer-to-stock map, probably cheaper than an ecu swap...

 

Well I found a ECU that is from a junk yard. He says its in working condition but he also said that some ECUs are vehicle specific and need to be programmed for the car its going in. Its from the same car as mine. Has the same motor and transmission as well. Do you think if a get this ECU that I well just be able to plug it in and be good to go or does it have to be programmed specifically for my car? I called around all the mechanics in my area and none of them have the right equipment to do the flashing for my car. I think Im going to check out my exhaust real quick to see if its clogged first, then try a different ECU.