2003 Buick Lesabre Misfire and Engine Light

I have a 2003 Buick Lesabre 3.8L, I am getting a code P0300 and P0302 code from Autozone. I have changed out the spark plugs and wires and the 3 coil packs. The car is running a little rough but not dying. It is still getting the same codes? Someone suggested checking the #2 injector, so i did it with a screw driver while running, and i can hear it ticking. Any suggestions??

I couldn’t tell you if it’s getting the same code since I’m not there with a scanner, but if it still misfiring I would assume you still have the same problem on cylinder number 2. Since the plugs, wires, and coils have been replaced, it really only leaves an injector problem or a mechanical engine issue.

Sorry, It was rescanned at Autozone and had the same P0302 code. I guess i could just replace the one injector, as its only a $100 bucks. What do you mean by mechanical engine issue? As in “put it in the shop”?

I would not recommend replacing the injector unless you know for sure it’s bad. That is just wasting money that could be better spent in truly diagnosing the car. As for the mechanical engine problems, I mean like a lack of compression on that particular cylinder, a burned valve, etc.

Even a vacuum leak could be causing your problem, so I wouldn’t jump at replacing parts.

I am barely a parts changer at best. Checking compression, burnt valves…wow. I don’t know that i have ever seen a valve before. How can I check for vacuum leaks?

You can check for vacuum leaks with a vacuum gauge and watch for fluctuations, or you can also spray around the intake area with some brake clean and listen for RPM changes. But be VERY careful, it ss highly flammable. Stay away from ignition components.

I am normally a put it in the shop kind of guy, but due to wife’s unemployment over the last year I have began down the fix it yourself road. In the last 6 months i have changed the alternator, tensioner pulley, serpentine belt, 2 rear air shocks, upper & lower manifold gaskets, thermostat, radiator, plugs, wires, and coil packs. 2 weeks ago it was running in top shape, now this??

Yeah things seem to happen like that.

I don’t know how to use the vacuum gauge, nor do i have one. I will try and spray the brake cleaner around the intake(throttle body)?

Mainly around the intake ports, concentrating around the cylinders that have problems. And that is just a check. If you find a problem, more diagnosis will be needed. If you don’t find a vacuum leak, you’ll have to keep trying to diagnose whether it’s an injector or engine problem.

By intake ports, you mean the upper air plenum?


This may sound really stupid, but I just changed the gasket around the upper air plenum. Since i torqued it to the required amount, then how will brake cleaner be able to get into the intakes?

It shouldn’t be able to, that’s the point of checking. If it can, then you have a problem.

I had to go and buy my first torque wrench just for it. Ok i got you. Well it sound like i can do some more trouble shooting with the tips that you gave me. Thank you for all of your help.

No problem at all, good luck!

Picture of the GM 3.8L 3800 V6 EngineGM ignition coil with one corroded tower.

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4 comments to 2003 Buick Lesabre Misfire and Engine Light

  • Shawn

    I have a 2003 buick lesabre I am getting lean fuel code (p0171) and P0300 , I went to a shoppe they said it was misfiring because of lean fuel and catalytic was clogged. The cat would get glowing red. It also is running like crap, so I replaced the cat, intermediate pipe and muffler and both o2 sensors. I also replaced the plugs a week before this the plugs did not look bad. The 03 buick has lack of power when starting and is still running rough and getting codes,
    I did disconnect the battery for 30 mins to reset the computer but still after new plugs, new cat, new o2 sensors, new intermidate pipe and new muffler Same codes p0300 and also p0171 but the p0171 after i erased code would sometimes come on but always the p0300 code. I also here a slight rattle when u slowly hit the gas. The rattle does not sound like a rod though it’s a more thumping type noise then stops

    Any pointers??
    Where could I look to find vacuum hoses diagram?
    Could that be the issue?


  • Shawn

    And lack of power before and after repairs when starting to step on the gas

  • Admin

    The catalytic converter failed because it was running so bad. Check fuel pressure and check for a vacuum leak.

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