Turn key and POP!
 

I'm wondering what might be the cause of this POP I hear sometimes when I turn the key to on. It wont do it every time, but sometimes when I turn the key to on I hear a loud "POPP" and the car shakes a little. Then I turn the key all the way and it starts right up.

Is this called "intake backfire"? Could this be something major going on? Kinda sounds major, but it happens daily and no problems yet.

Any ideas?

My car does this occassionally as well....I know the half ass answer but don't wanna post it since I'd probably look like a tard ;)

Are you guys running MS? If so, its a known "issue" with the hardware. Nothing you can do about it and it won't hurt anything.

I am...and from what I gather, all the spark plugs fire upon energizing, sometimes igniting fuel that has found its way into the cylinder (Leaky injector??)....maybe I'm completely wrong, idk but who cares as long as it doesn't cause any grief...

It's because you have some unburned fuel vapors in the cylinders from when you last shut it down, and when MS powers up it causes a pop due to the ignition circuit design. This thread discusses a circuit mod by Joe Perez that addresses the issue.

Fuck me! Fast responses guys, nice! :bigtu:

Ok so I wont worry about it then. It doesn't do it all the time, but I'm pretty sure it does it at least once a day. If that's all it is and its not going to hurt anything then I can live with that.

I've had it pop before with people around and they always ask "wtf is that" lol.

For some people the pop will occasionally foul a plug or two making starting it a bit more of an issue. I had this problem and had to do the new spark out circuit.

There was a long thread about this issue that was hopefully heading towards a solution. I'd really like to see a solution as this sometimes blows vacuum caps off my intake manifold. Once had one land 30 feet in front of the car.

No shit ehh? Good thing I keep spares in the trunk, amongst a million other spare pieces and tools.

I have a MSPNP though. Should this issue still apply to me?

Yeah, I'm pretty sure it does. Read the big thread by Joe Perez that I linked earlier. I'm almost positive that info is in there and you'll know for certain.

BTW this thread reminded me that I needed to post about how my car shuts down with my higher than normal capacitance built into my COPs harness, and if that can be exploited to help y'all. I posted the details in Joe Perez's thread since it seemed appropriate to add it there.

It has to do with the fact that the MS automatically fires the coils when it powers up for some reason. Joe's mod reverses the signal to the coils, which means they don't trigger when you flip the ECU on, which means no more poppy poppy.

not entirely true. PWNT!