So, on my 2001 Jimmy, it's gotten to where, in 1st or 2nd gear, if I really gun it, it bogs down, like it just can't burn off the fuel. Also, when it does this, it'll FLASH the check engine light, for about 20 seconds, then it goes out. FWIW, my milage has been crappy this winter, only getting about 200 miles per tank.
A guy at Advance said that sometimes the coil gets tired, and needs replaced, and that it won't throw any codes for this.
Any ideas? Is there a way to test the coil for being weak?
THANKS

 

Bump?

 

If the service engine light is coming on at all then it should be storing the code that caused the light in the first place.

However even without the code there are steps that you can take to diagnose the problem without resorting to the shotgun mechanic method that the parts stores are so fond of.

Lack of power issues are most often caused by air flow problems either into or out of the engine. So the first step is to check for restricted airflow into the engine.

Start by checking that your air filter is clean and is not restricting the air supply. Then move on to the intake ducting and check for blockages and soft intake hoses that could be collapsing. You'll need to take them off anyways so you might as well look them over when you do.

After that move on to your Idle air control valve (IAC) If this valve is gummed up with carbon deposits then you will certainly have power issues on takeoff as it helps to control the air supply.

You will also want to clean your mass airflow sensor (MAF) while you are at it. It is located in the air intake ducting and measures the airflow into the engine.
A dirty or faulty MAF can cause the engine to run rich and kill power as you've described. Be careful when you clean it as it is rather fragile.

Next would be to check for vacuum leaks including checking the PCV valve. It is a one way valve that should rattle noticeably and allow airflow in only one direction. If it is gummed up then it should be replaced or at least cleaned.

A plugged exhaust, specifically the catalytic converter can also cause this problem. Crawl underneath and give it a good shake. If it rattles then it is likely to need replacing and would be the cause of your issue.

You can test the coil with an OHM meter to make sure it is putting off a strong enough spark. The directions and specific readings for your make/model are located in any chiltons manual. The same goes for the specs and directions for testing the MAF sensor and the IAC valve motor.
Testing your throttle position sensor would not be a bad idea either. Incorrect readings from this sensor can also cause similar problems to what you described.

However if you pull one of the plugs and see that you are getting a nice bright blue spark then the coil is probably just fine.

You should pull each of the plugs anyways and inspect them as the condition of the spark plugs can tell you a great deal about what is going on inside your engine.

There are other possibilities of course such as checking the fuel delivery system, but these are the ones that I would check first. Remember to always test a suspected bad part before replacing it or you will end up making the parts stores very happy. A Chilton manual and a $10 volt/OHM meter can save you a boatload of cash down the road.

Let us know how it goes.