P0300 multi cylinder misfire

Well after spending a lot of money and making some uneeded repairs, I got the 99 LTZ running. Insured, tag, and smog test.

I have been driving it all weekend. No issues. I noticed the throttle cable sticking on hard acceleration and low coolant sensor (but not running hot and coolant is full as is overflow tank). One it cooled off, I pulled engine cover to see if accelerator cable was damage in some way. I worked it back an forth and seemed fine. I then depressed the accelerator pedal numerous times. Seemed OK. Started car. very rough. Engine light. Grabbed scanner and #6 misfire. Cleared code. Started car accelerated a bit and then ran very rough, died, wont stat at all. Now multiple cylinder misfire.

This is where I was when I parked the car in the garage three years ago after the shop told me the coil packs and ignition module were fried. That was all replaced.

I can't believe I caused this just by moving the accelerator cable back and forth. Heck you have to do that to reset the change oil reminder.

Man o man

Edited. Now to add insult to injury, I went out and tried to start. The engine is locked and will not turn. Other than a coolant leak, or worse (no knocking when running), could it have pumped a cylinder full of fuel and hydro-locked? I will have to pull the plugs later and see if it will turn over later.

I love the car but when it decided to die, I guess it really wanted to die.

Corndog...

It's fried apparently. No coolant in tank or radiator. It never ran hot on temp gauge. Pulled front plugs very oily. Will pull the backs and see if it is still locked. If not locked I may fool with it, if so, anybody interested in a 99 Black LTZ?

Edit: pulled all the plug and it spins. I guess that's a good sign. Number 4 full of coolant. All the new plugs looked awful and smelled of coolant. The bad thing is I put new head gaskets and upper intake manifold gaskets on it.


Corndog...

After a lot of reading on this board and other 3800 sites, I think this problem is corrected. The EGR pipe burned a small hole in the Upper Intake Manifold Plenum and I just didn't see it. Coolant leaked in and hydro locked the engine in the number 4 cylinder. Lesson learned. If you are replacing the UIM gaskets think about replacing the UIM as well. I bought the Dorman UIM with the smaller stovepipe. A lot of aggravated owners with GM over these UIMs.

Anyone know if one of the parts stores can tell you if the coil packs and ignition module are bad? That was the original diagnosis and I believe I wasted money on that. The shop I had done business with said that was what was wrong. Apparently, they haven't worked on many 3800 engines as this is a common problem with coolant leaks in the UIM cause misfires, coolant loss and hydro locking after the car sits.

After a lot of reading on this board and other 3800 sites, I think this problem is corrected. The EGR pipe burned a small hole in the Upper Intake Manifold Plenum and I just didn't see it. Coolant leaked in and hydro locked the engine in the number 4 cylinder. Lesson learned. If you are replacing the UIM gaskets think about replacing the UIM as well. I bought the Dorman UIM with the smaller stovepipe. A lot of aggravated owners with GM over these UIMs.

Anyone know if one of the parts stores can tell you if the coil packs and ignition module are bad? That was the original diagnosis and I believe I wasted money on that. The shop I had done business with said that was what was wrong. Apparently, they haven't worked on many 3800 engines as this is a common problem with coolant leaks in the UIM cause misfires, coolant loss and hydro locking after the car sits.

yeah upper intakes on the 3800's is'nt new,goes back quite a few years
sorry you found out the hard way,i think a recall should have been sent out.gm does'nt want to confess up!!