[ceokingcobra]

Alright this issue is weird

Over the past couple of weeks, every once in a while when i park the car and shut it off the engine DOES NOT shut off completely. It seems to idle at ~300 rpm but i have no way of telling since the tach is dead when the key is off. I recently replaced the fuel pump since it was due to be replaced (was making loud whining noises and groans on priming) and the problem is worse now (I also have a p0172 code as well as soon as the pump was replaced). The car also idles a bit rough when sitting as well.

If i "turn the car off" the engine seems to "idle" at around 300 rpm and will do so for atleast 2 minutes, i haven't tested any longer but it shows no signs of shutting down. The way I turn the car off is I pull up to a space, leave the car in drive, turn the key off (the engine will turn off due to car being in drive and not moving stalling the engine) and then put it in park.

Stuff I've done:
1) Tested fuel injectors (Did the resistance test with multi meter and listened to them with a screwdriver), all 4 were good.
2) Checked the 2 grounds by the driverside headlight. Both grounds showed resistance meaning they are good. I already did the common problematic ground under the passenger headlight. Going to do more research before I look at other grounds
3) Spark plugs were checked and were good.

Going to clean the throttle body this weekend.

I can post a video of this happening it's a bizarre problem to have in my opinion.

I have a 2007 Jeep Compass with 4x4 and the 2.4L engine. Any help/suggestions is greatly appreciated.

 

[Newt]

I'm not a mechanic, but it sounds like something I've heard called detonation. Here's a definition I found:
Detonation, or engine knock, occurs simply when fuel pre-ignites before the piston reaches scheduled spark ignition. ... Detonation is generally caused by excessive heat, excessive cylinder pressure, improper ignition timing, inadequate fuel octane or a combination of these.

 

[KF2M]

I'm not a mechanic, but it sounds like something I've heard called detonation. Here's a definition I found:
Detonation, or engine knock, occurs simply when fuel pre-ignites before the piston reaches scheduled spark ignition. ... Detonation is generally caused by excessive heat, excessive cylinder pressure, improper ignition timing, inadequate fuel octane or a combination of these.

That would have been true with carbureted vehicles with mechanical fuel pumps. This was a common problem back in the day when no-lead fuel was being phased in, and engines getting smogged. With electronic fuel injection once the power is cut the injectors, and the fuel pump should not be functioning to allow this to happen.

 

[mr_et2]

Not to sound condescending or anything, but my mother claimed that the same thing was happening with her Saturn Ion last year. She told me that it happened almost every time she shut the car off. I had her bring it over and was out in my driveway when she arrived. She parked, shut it off, and then got out and said "see, it's doing it now". Turns out it was the radiator fans still running after she shut the engine off. They were really loud and caused some vibration in the vehicle, and they did indeed sound similar to the engine at a very low idle.

In order for a modern engine to keep running after the vehicle is shut off, there would have to be quite a few failures occurring simultaneously, the fuel pump would have to keep running, the fuel injectors would have to be getting power still, the ignition coils would have to still be getting power and timing signals, etc. If that's really happening, it's a one in a billion occurrence. Or it could be something as simple as a faulty key switch.

 

[Newt]

That would have been true with carbureted vehicles with mechanical fuel pumps. This was a common problem back in the day when no-lead fuel was being phased in, and engines getting smogged. With electronic fuel injection once the power is cut the injectors, and the fuel pump should not be functioning to allow this to happen.

That's why I am not a mechanic.

 

[ceokingcobra]

Not to sound condescending or anything, but my mother claimed that the same thing was happening with her Saturn Ion last year. She told me that it happened almost every time she shut the car off. I had her bring it over and was out in my driveway when she arrived. She parked, shut it off, and then got out and said "see, it's doing it now". Turns out it was the radiator fans still running after she shut the engine off. They were really loud and caused some vibration in the vehicle, and they did indeed sound similar to the engine at a very low idle.

In order for a modern engine to keep running after the vehicle is shut off, there would have to be quite a few failures occurring simultaneously, the fuel pump would have to keep running, the fuel injectors would have to be getting power still, the ignition coils would have to still be getting power and timing signals, etc. If that's really happening, it's a one in a billion occurrence. Or it could be something as simple as a faulty key switch.

This sounds like a grounding issue then or a faulty key switch like you said. I doubt its the key switch tho because the key barrel is functioning properly when the key is off as in the cabin shuts off everything (lights go, radio turns off, dash shuts off like normal). Ive had to redo the infamous g110 (I think its g110) ground since my passenger head light went out, I think this could be another ground that is going bad.

 

[ceokingcobra]

I'm scouring google right now but if anyone has a diagram of all the grounds in the engine bay it would be greatly appreciated

 

[Sandstone]

After the fuel pump replacement, did you disconnect the battery cables to reset the PCM? If not you might try it.

Here's the manual info on P0172:

 

[ceokingcobra]

I did a PCM reset via disconnecting the battery twice the day i changed the fuel pump. Reading the serivce manual you have provided, my O2 sensor voltages are off from the last time I used my scan tool. Ill have to check them this weekend.

 

[ceokingcobra]

So I cleaned the throttle body and it was FILTHY. Full of carbon deposits and gunk and even some oil?

The car drives really well now, better throttle response and all but it made the "turn off issue" worse.....
Before i could "stall" it by leaving it in drive and turning the key off but now i can't even do that.

Going to take it to my mechanic on monday and just eat the bill.

 

[ceokingcobra]

So it is DEFINITELY an evap issue.

I disconnected the evap line that goes to the intake manifold (located just under the airbox) while the car is running and the car shuts off normally. The evap solenoid was already replaced a couple months ago but it gcould have gone bad again.

Still taking it to the mechanic.

 

[Sandstone]

Nice find!

 

[John W Davis]

I'm not a mechanic, but it sounds like something I've heard called detonation. Here's a definition I found:
Detonation, or engine knock, occurs simply when fuel pre-ignites before the piston reaches scheduled spark ignition. ... Detonation is generally caused by excessive heat, excessive cylinder pressure, improper ignition timing, inadequate fuel octane or a combination of these.

If it is detonation, you have leaking fuel injector .

 

[ceokingcobra]

If it is detonation, you have leaking fuel injector .

Fuel injectors aren't leaking to my knowledge. I'm certain its an evap issue, car is at the mechanic so I will know for sure soon.