Engine issue help

[Ron36]

Could be a thousand different things . Any sensor issue should through a code so u need to take it to a dealer . It's more money but they have the right tools . A common problem on those is clogged injectors . Fuel cleaners won't fix that . They will look at fuel trims to see if your car is running rich or lean. Also can check for 5 volt reference to all engine sensors . How's the idle at a stop , maybe spray some break clean on the motor to see if idle changes but that should set a code. A good scanner will show u pending codes ,witch are codes that the pcm is monitoring before it sets a light.hows your coolant level those car love to have leaking head gaskets.

[Ron36]

How did your old plugs look , any green tint or was the the end very white or the electrode burned off .GM's have a misfire counter u can check with a scan tool also . U will be able to see what cylinder is missing and if it's not enough times for the pcm it won't through a code yet.

[RoadWarrior]

If this car was in my shop the first thing I would check is fuel pressure. Install a pressure gauge that will not leak down overnight. Check the pressure to make sure its in spec, let it sit overnight and see how much it bleeds down, hit key and check the pressure first thing morning after ( do not start) . See how the pump acts. Then start it and watch the pressure gauge. If the pressure is slow to come up , then finally does and then the engine smooths out I would say you have a weak pump or clogged fuel filter or both.

Second thing I would check is if the fuel system is bleeding down via a leaky injector.

Third thing I would check is the coolant temp sensor reading on cold start. I have seen a lot of whacked out readings during cold starts on GM vehicles that cause a very lean or very rich condition. Keep in mind that a bad sensor does not always set a code especially if it only screws up for a short time. Catching these intermittent issues while they are happening is key to diagnosing them.

and one more idea , one more thing to check would be if you have a distinct smell of burning coolant coming out the tail pipe when you first start the car after it sits. Do you have any white smoke coming out the tail pipe ? Loosing coolant ? Not only do these 3.4's have a habit of a slow leaking head gasket but if I remember correctly they have a black plastic looking intake that burns a hole from the EGR passage to the coolant passage. When this happens it will have all the symtoms of a blown head gasket. I had one eat my breakfast, lunch and supper one time. Replaced the head gaskets twice thinking the machine shop missed a crack in a head the first time. Turned out to be a bad intake manifold which latter I found out was a very common issue. I might be wrong about yours having that type of intake BUT if someone else is reading this and you have a GM FWD v-6 and you have a black plastic intake then beware of this issue.

You could have a cylinder leakage test done and have a cooling system pressure check done . Just make sure you do them while the engine is cold because it sounds like that is when you are having your issue. ...............good luck and keep us updated.

[Karkov]

I sold the car

[RoadWarrior]

OK thanks for the update.

[newls1]

car sold... locked