I am attempting to trace down the cause of a misfire on my 2002 mitsubishi lancer, but I can seem to find anything that gives me a definitive answer. Heres whats going on: The engine seems to run on 3 cylinders whenever you rev it up by flooring it and letting off while in neutral. (Not rev limiter, when i say floor it, im talking just a blip), the car idles alright, its had a slightly rough idle at times, and its been that way since I bought it two years ago. Also, whenever I am driving down the highway in 5th gear, and above 3k rpm, there is no manipulation of the throttle that I can do, that will make the engine misfire. However, if I am below 3k, and floor it, or go past about 50% throttle, it will begin to misfire. Another thing that I noted is that if I am in 4th gear, and above 3k rpm, and floor it or go past aprox 50% throttle, it WILL misfire and run rough. That part baffles me.
I cant find any vaccum leaks, so I dont think thats the issue. I put some new (used but in good condition) injectors in thinking that the old ones were clogged, however that did not fix the issue. I checked fuel pressure and fuel flow, and it is good and within spec. This seems verified to me by the fact that the car runs fine under WOT when in 5th gear on the highway (above 3k of course). Fuel trim is +12.5 percent, and its been that way for a long time, so no change there. O2 sensor values are correct and around 0.8V. The Throttle position sensor seems to be reading correct values as well. The MAF sensor is reading values between 0 and 8 lb/min when driving, and the values dont seem to be jumping around whenever its misfiring. One of the things that I did to that seemed to help the issue was replacing the spark plugs. Also, if I steadily roll on the throttle, the misfires seem to be less frequent.
So does anyone have any ideas on what the issue could be? Maybe coil packs? Im at my wits end…
I would do that, however, the leads for the plug wires are setup so that the coils are not interchangeable. Coil pack 1 for cyl’s 2 and 3 and coilpack 2 is for cyl’s 1 and 4.
+12% fuel trim is out of spec. That could be caused by the misfire though, and once you get the misfire corrected that will correct itself. knock on wood. It says the compuer is having to add more fuel than it thinks it should have to b/c there’s more o2 in the exhaust than should be But that o2 may be b/c the o2 in the intake air isn’t being burned up b/c of the misfire. Single cylinder misfires are usually diagnosed by swapping stuff between cylinders and seeing if the misfire moves to the other cylinder or not. Common misfre causes
weak or no spark
air leak
fuel problem
low compression
head gasket problem allowing coolant to enter the cylinder putting out the bang
Thanks for the insight. Ive known that the +12% fuel trim was out of spec for a while, but I dismissed it since the max value was 25% and I do have an exhaust on the car so I figured, maybe its slightly more rich to make up for the increased flow. However awhile back I started getting a p0171 system too lean code every once in a while (I dismissed it as a freak thing because the code seemed to be thrown very randomly) anyway, this kinda makes me think that ive had a coil pack on the way out for a long time now, and perhaps its been weak spark, and ive not been getting a complete enough burn, so the poorly burned gasses screw with the O2 reading. Again, I really appreciate the insight!
My advice to swap coils was based on looking up your coils and both Rock Auto and Advance Auto and seeing individual coils. Are you in the US? The books show only 1 engine for the Lancer, a 2.0 liter.
Old_timer11, I am in the US, and yes there is only one engine for the lancer, the 2L 4g94. I realized this last night when I ordered new coilpacks, but the wires on the coil packs are removable, so I actually can switch the coil packs around. Ill give it a try later today.
Ok4450, the car has 225k on it, but the motor has 80k on it. Ill also try a compression test later today, though I dont think thats the issue since it misfires under a constant circumstance. If it was low compression, then I would think that it would run poorly under all circumstances, and at all RPMs.
Tcmichnorth, at first I thought the wires on the coilpacks were nonremovable, but that is not the case, so Im going to try to move them later today.
