: Strange ignition problem. Thoughts?



taken
10-07-11, 07:43 PM
So, got a strange one here. When I run the car enthusiastically (not redlining every gear, just enjoying the throttle response) I have a strange thing happen when I shut the car off. When I turn the ignition off, the car continues to run. Sometimes for a few-10 seconds. Once it happened until I tapped the gas and then it stalled out. The first few times it happened, it was pretty unnerving. You shut off the car, wait a second or two, and then let out the clutch assuming it's shut down. This is met with the car jumping forward which can be pretty scary if your not ready for it or close to a curb. So, if I just drive it at low rpm's, say on a rainy day, this never happens. Only when you've been on the gas a bit. That to me eliminates it being the ignition switch or wiring issue. So, what could cause this? I brought it to the dealer once when the run on ignition caused it to throw a CEL. The code they pulled indicated that "modules lost communication with each other." I guess that made as much sense to them as it did to me because the car is back home and not fixed. They offered to keep it for a while and try to replicate it, but I didn't have time for that when it was in so I figured I would wait til it happened more frequently. Thoughts?

stabie
10-07-11, 08:11 PM
Whenever I have weird problems like this, I really try to nail it down. My last CTS would very occasionally not do what it is supposed to when you open the driver door, IE, radio off etc. So I watched tried various things and after I figured out how to reliably replicate it, I took it in and fixed in half a day . So in your case, when you turned it off, did the radio go off, unfasten seat belt cause seat belt warning, ie all the things that change when the car is turned off? If you turn the car back to run, and let it run for a minute, does it shut off? If you press the accelerator, does it rev? Does the steering lock? If you kill it and restart does it do it again? Just try every test you can think of over a week or so.

Intermittent problems like these are some of the toughest to fix. You can get your car fixed alot faster if you can isolate it.

taken
10-07-11, 09:41 PM
Whenever I have weird problems like this, I really try to nail it down. My last CTS would very occasionally not do what it is supposed to when you open the driver door, IE, radio off etc. So I watched tried various things and after I figured out how to reliably replicate it, I took it in and fixed in half a day . So in your case, when you turned it off, did the radio go off, unfasten seat belt cause seat belt warning, ie all the things that change when the car is turned off? If you turn the car back to run, and let it run for a minute, does it shut off? If you press the accelerator, does it rev? Does the steering lock? If you kill it and restart does it do it again? Just try every test you can think of over a week or so.

Intermittent problems like these are some of the toughest to fix. You can get your car fixed alot faster if you can isolate it.

Radio the same, don't wear a seatbelt, if I start it back up it won't do it a second time, if I press the accelerator it stalls, and when it does shut down, it's a very slow crappy kind of a shut off. Not a crisp off, more a tapering, skipping, sputtering shutdown. The only variable is how I drive it before I shut it down. I agree, it could be a pain so I'm just going to keep an eye on it and wait for it to get worse.

stabie
10-07-11, 10:29 PM
So it sounds like most of the modules think it is off. Radio will not shut down till door is open, so check if it turns off when door opens. If system thought car was running, opening door would not shut off radio. I don't care if you wear seat belt or not. My point was in the run position dash will show seat belt warning. If ignition is in off position, seat belt warn should not be on. Is it? It sort of sounds like the module that fires the plugs does not know car was turned off. I wonder which module that is and what else it controls?

qictrk
10-08-11, 02:03 AM
Could be a few things. Running a poor grade of fuel, timing out of syc, slipping serpentine belt, running to hot, and the most likely, its a injector that is staying open. Cecil..........

taken
10-08-11, 07:47 AM
I like the injector idea. Don't think it's the fuel as I fill up at different places all the time which has no effect. Will try the opening the door idea and see if it shuts off the radio or stalls the run on ignition. I don't know about the seat belt warnings as I have the harness' unplugged from both front seats so I don't have to deal with the warning ding. As I said, it only happens if you have run it a little hard. Never if you drive it slow and steady. This kind of makes me think it's not a module as it would seem that if it was, it would happen every time. So far, the check engine light only came on once and that was when it ran on for about 30 seconds and only stalled out when I touched the gas pedal. I may have to leave it with the dealer and let them play at some point. Maybe when I go on vacation next. Hate to be without the car when I'm home!

stabie
10-08-11, 10:21 AM
I like the injector idea too:) Dieseling makes more sense if car got hotter, and there is probably some fuel in the lines that would leak thru the injector after the fuel pump was cut off. Any thoughts out there for an experiment to confirm?

tedcmiller
10-09-11, 07:10 PM
The pressure in the fuel rail is maintained for a certain amount of time after the fuel pump shuts off (ignition off). If the spark plugs are very hot, dieseling can occur as fuel leaks passed a faulty injector (or injectors). All of the 2004-2007 CTS-Vs dieseled a little bit (my 2004 and 2005 both did), but I have not observed it in my 2009 CTS-V.

taken
10-09-11, 07:29 PM
So, I've been experimenting. It's def not dieseling. It's running with spark and all. Again, only after I drove it a little harder. Drove it easy all the way to a car show and shut off normally. Went through the gears on my street on the way home and had running after shutdown. Am going to bring it in while on vacation later this week and let them spend some time with it. Will report back....

Kluch
10-10-11, 12:27 AM
Taken,
Do you live in New Hampshire, the land of no state income taxes and no seatbelt laws? Just curious. Not to derail your thread, because I sincerely hope you get your ignition issue sorted out, but why don't you wear a seatbelt?

taken
10-10-11, 07:56 AM
Taken,
Do you live in New Hampshire, the land of no state income taxes and no seatbelt laws? Just curious. Not to derail your thread, because I sincerely hope you get your ignition issue sorted out, but why don't you wear a seatbelt? No, live in MA. Don't wear one because I don't want to. Thanks for the support on the ignition issue. Will post when I hear back. I go on vaca from Friday to Tues so hopefully I'll have an answer Tuesday afternoon.