My mustang has around 140,000 miles. Took her to the shop after hearing a not so pleasant popping noise and ended up having the harmonic balancer, crankshaft cover, and drive belt replaced. Before this event the car ran perfectly. Immediately after these repairs the car started misfiring above 2000 RPM with the engine consistently throwing P0301 and P0305 codes with the occasional P0300 code. So far I’ve checked/changed out the spark plugs, spark plug wires, and ignition coils. So far, nothing has changed and the car continues to misfire above 2000 RPM in the same cylinders. Figured it’d be the coil pack given the misfire location but the mechanic told me the coil pack was fine despite 1 and 5 being next to each other and I decided to get some second opinions. Seems odd more than one cylinder would fail coincidentally after this repair but at this point I’m just looking for the most likely solution. Any help greatly appreciated!
Since the car uses the harmonic balancer and crankshaft sensor to determine cylinder misfires I suspect an issue with those parts, especially since the problem surfaced immediately after those were replaced.
Agree with @asemaster. The balancer has the crank timing toothed ring on it and the crankshaft position sensor mounted to the timing cover.
If you took it it back to the shop that did the work and they blew you off, you might want to find a better mechanic.
I’d take a good look at the crankshaft position sensor and its wiring. Rockauto sells a sensor WITH a new wiring pigtail. That might be a hint… it looks like this;
The shop that replaced the balancer and cover may have damaged the pigtail connector or even the sensor. Take a look, unplug it, and make sure the connector pins are all properly seated and clean.
I’d be looking at the teeth on the new harmonic balancer for the crank sensor to see if there’s something irregular with them.
Tester
I agree with the above reply’s…
I would look to make sure the balancer was bottomed out when installed since it is a interference fit if not mistaking… Possible the reluctor ring is damaged during shipping or even being installed somehow… looking at the reluctor ring it is just out there in the open…
I always test drove a vehicle after any kind of repairs were made and I would have caught the misfire and not released the vehicle until I figured out why/what happened, soo I don’t understand (I do but still) why they even gave you the car back…
But anything can break at anytime with no warning, so sometimes things just happen, but I think either the shop screwed up (well they did for not catching the misfire IF it really happened right after they worked on it) or you have a bad defective or damaged part…
Concur w/above, problem is most likely caused by a faulty crank position signal input to the drivetrain computer. As the crankshaft pulley rotates, a sensor attached to the engine produces a signal indicating the rotational angle of the crankshaft pulley. Requires the pulley be have a specific magnetization pattern, termed “reluctor”. If that crank position signal is corrupted, misfires expected. Could be a problem with sensor, the sensor’s wiring, the sensor is too far away from the reluctor, or the pulley ass’y isn’t compatible with the sensor, new pulley is wrong part number for the engine etc. OP can Google “reluctor wheel” if curious.