Very rough engine from cold

JMan69 · #1 09-18-2010, 11:09 PM

When my car has been sitting in the driveway for maybe a day or so, maybe over the weekend. I start it up to drive after that time period and idle is extremely choppy, the revs are at the normal level but the engine sounds almost like a lawnmower "chuff chuff chuff chuff" I starting driving and the "chuffing" doesn't go away it just gets faster. It has actually made me stall at an intersection at some point. After about 5-10mins of anxious driving it finally returns to normal. It has happened consistently the last 3 start ups. Any ideas?

JDW-SVX · #2 09-19-2010, 01:21 AM

Sounds like one or more cylinders aren't firing. That could be caused by a bad coil pack, or a bad injector that is leaking when the engine is shut off, and is fouling the spark plug in that cylinder.

The first thing that I would do is to pull each of the injector connectors off each cylinder to determine which cylinders are causing the problem. Once you have determined that, you may want to pull the spark plug and coil from that cylinder and have a look at them.

The ignition coils used on the SVX coil-on-plug ignition system can and do go bad. Usually, the spark burns through the plastic on the coil, and shorts directly to ground through the cylinder head instead of through the plug.

Alternatively, you may just need to replace your spark plugs.......

Jason.

JMan69 · #3 09-19-2010, 02:47 AM

Good to know will look into it

dannal1113 · #4 09-29-2010, 11:59 AM

Was this resolved? My dad runs a shop and we did some injectors after unplugging 2 with no effect on the idle however it didn't resolve the issue. He doesnt have time to look at it because he is quite busy but I have all the tools to diagnose. I'm thinking coil packs but I don't see why this would be limited to a cold engine.

Edit: we have checked the spark plugs and they do not appear fouled. Curious as to what I can look for on the coil to verify.

SoCal LS-L · #5 09-29-2010, 08:56 PM

Quote:

Originally Posted by dannal1113

Was this resolved? My dad runs a shop and we did some injectors after unplugging 2 with no effect on the idle however it didn't resolve the issue. He doesnt have time to look at it because he is quite busy but I have all the tools to diagnose. I'm thinking coil packs but I don't see why this would be limited to a cold engine.

Edit: we have checked the spark plugs and they do not appear fouled. Curious as to what I can look for on the coil to verify.

The coils can fail from the internal contacts corroding or developing cracks from thermal stress. Metal contracts when cold, opening the circuit and killing the coil. As the coil gets hot from the engine block, the metal expands and can restore contact between sides of the fissured connection, making it work again.

dannal1113 · #6 09-29-2010, 09:06 PM

Makes sense... I had a similar situation with my starter once actually when I think about it. Except it was opposite. Once it had warmed up it could no longer make the connection so you had 1 good start to get where your going then you have to wait a couple hours XD. Anyways I'm gunna pull it in to an open bay tomorrow and pull some coils and check em out.