Suburban99

Hi all,
Long story short i purchaced a suburban with a misfire that turned out to be a bad valve. I had the valve replaced but it still runs rough. It still misses and has multiple loud pops through the exhaust at idle and gets worse when you give it throttle. There is no check engine light, timing is correct, all new intake gaskets, plugs, wires, cap, rotor button and the injectors and distributor were upgraded some time before i bought it. Ive checked all over for vacuum leaks but cant find any. Fuel pressure is 60 when running and sits between 50 and 60 when not running and holds. Each injector gets pulse from the pcm. Each plug is sparking and compression is about 150 on each cylinder. When you first start it up it smells like gas strong when running. The stft on bank one is normal but bank 2 is about 25 give or take. Vacuum gauge fluctuates slowly between 15 and 17. The inside of the exhaust on the drivers side is coated in sticky black from that bad valve, the po drove it for a while like this. I was thinking the o2 sensor could be coated causing this issue. Also the crank sensor is covered in oil due to a timing cover leak so i need to address that. What do you guys think?

oilcanhenry

I think you are on to something with the folwed O2 sensor to be sure. I would repair the leak on the timing cover, but I've seen crank sensors covered in oil still working, but some simply do not, so there is that. Does it constantly misfire all the time?

Suburban99

I have the upstream sensors on the way so we'll see how that works out. Its a tune up item and the truck has 174000 on it so it needs done anyway. Yea its pretty consistant but every so often the short term fuel trim will drop close to 0 and it will idle great for a min. Then you give it gas then back to crazy trim at idle, popping in the exhaust and rough idle. St Fuel Trim goes as high as +50 on bank 2, bank 1 is normal. I may have found the issue last night though, i was poking around after dark and found the ignition coil is arcing. You can also see a glow of orange light from the top of the coil. Guessing its cracked causing a weak spark. Im getting a new one today and we'll see what happens.

oilcanhenry

That is some great diagnostic work that you have done, Suburban 99! Hoping it is just a bad coil too. Cheap fixes/repairs are always nice.