Hi All! I have a bit of a weird problem that has popped up over the last couple days after I took my 1998 Mercury Mountaineer 5.0L V8 into a local shop for some repairs. A bit of a back story first… Over the last weekend the engine started misfiring on me on the way home from work. I won’t go into details on the misfire because it was easy enough for the shop to diagnosis and fix when I took it in (This is a local shop here in Austin that I’ve taken the vehicle to a couple times now and always been happy with… They also get quite good reviews from most people on the internet). Anyway, they call to tell me that when they read the codes, #7 was the main culprit with a couple other cylinders having a random misfire, I don’t remember which. They said they got to digging around and somehow my #7 plug wire had melted in half, their theory being it had come in contact with the exhaust manifold.
Long story short, I had them replace all the plugs and wires and do a tune up and the car is running great! Here’s where the weirdness comes in. I have an aftermarket stereo that I installed (a Pioneer if it matters) and since I picked up the car there has been a moderately loud popping noise coming through the speakers when I have the receiver set on certain inputs. The noise is sort of a popcorn popping… It increases in speed with higher engine RPM and decreases at idle sometimes going away almost altogether but it is always the same volume no matter the RPM. If I lower the volume on the receiver the popcorn volume drops accordingly.
This might be getting too far out there, but the last thing I’ve been able to figure out is that the popcorn noise is there when I have the receiver input set on “CD” or “USB” (such as with an ipod plugged in) but if I set it to “Radio” or “AUX” (the little headphone style connection) there is no popping at all.
I wanted to get some advice before I go tearing apart my dash/engine compartment… My first thought was that I need to check the grounding on the stereo receiver, however it was perfectly fine before the plug repair and started as soon as I got in the car from the shop. My other thought was that perhaps somehow the new plugs/wires are sending a spike in voltage through the electrical system, but I’m no electrician so I don’t know how this could happen, or if it was happening why it would effect the stereo.
Does anyone out there have any idea what is going on in my car?!