Skip the auto shop - Our mechanics make house calls

Q: Black smoke, intermittent starting, overflowing coolant with cap off

asked by on

-2004 Jeep Grand Cherokee Laredo 4.7L V8. 134k miles

Codes: -P0420 (Catalyst system efficiency below threshold bank 1) -P0302 (Cylinder 2 misfire detected)

-Car doesn't usually start on first try. It'll either crank for 5-6 seconds and start weakly, or it'll just keep cranking. If it doesn't start after 5-6 seconds (but it does crank), then turning the power off and trying again starts it 90% of the time immediately (normal start). May or may not be unrelated - the battery is unlabled and undersized. It only takes up about 60% of the space of the battery tray. Black smoke from exhaust when accelerating (around 40%+ throttle) Strong gas smell from exhaust smoke at idle

-Not sure if this means a bad head gasket, but with the radiator cap off, revving the car to 1.5k makes the coolant overflow. The coolant level doesn't move at idle. Here is a quick gif (the level seems high because this was the second time it was revved. It sits a bit lower at idle): http://i.imgur.com/1Mx2B1U.gifv

My car has 134000 miles.
My car has an automatic transmission.

Hi there. We need to first determine the cause of the misfire; this is what most likely lead to the catalyst failure and is causing the hard starting. Data from the ECM would be helpful, but alone, like a code, will not provide a diagnosis. If you’re smelling fuel at the tailpipe then this is a pretty severe misfire. There could be a fuel, air, ignition, or mechanical concern. This truly needs an inspection performed by a qualified technician to avoid replacing unnecessary parts. Your Mechanic has several available technicians that can assist you with a check engine light inspection.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  • Home
  • Questions
  • Black smoke, intermittent starting, overflowing coolant with cap off

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: 07 Sequoia key only turn sometimes

Hi Jcrew. Thanks or writing in tonight to YourMechanic.com. Generally speaking, when the ignition cylinder is hard to turn, it means the cylinder is either dirty with excessive dust and debris or has broken pieces. If you can turn the...

Q: Car wont start up again once its warm 2005 Jeep Grand Cherokee

Hello - the first thing to check is for problem codes, whether the Check Engine light is on or not. Checking for spark during one of these "warm, won't start" conditions in the next step. Your symptoms are likely a...

Q: Brake lights are not bright, drivers can barely tell I am braking

Hi. There are 2 likely possibilities for your poor lighting. The first is a bad ground connection, limiting the power that can electrically flow through the light bulbs. The second possibility is that the wrong bulbs have been inserted in...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...