Code P0305 check light on

Maybe the injectors dead. I don't really know where to begin as I've had the car several years and never had to do anything but put gas in it. My scan tool shows it's logging misfires on #5. It runs funny just for one injector to be bad as if it is going to fall apart. I hope nothing more sinister is going on like the engine itself is failing.

If I need to change plugs the manual talks about rotating the engine forward. It makes sense I think other than the prying part. I don't know what to pry on and guess I need to go buy a ratchet strap to hold it in place once its rotated.

Maybe the injectors dead. I don't really know where to begin as I've had the car several years and never had to do anything but put gas in it. My scan tool shows it's logging misfires on #5. It runs funny just for one injector to be bad as if it is going to fall apart. I hope nothing more sinister is going on like the engine itself is failing.


It also had code P0300 random and multiple misfires detected

If it's a 3.1L you don't need to rotate the engine. The rear plugs are a challenge, but I've always done them without moving the engine at all.

I think I need to clean the injector system before anything else. Maybe 5 is just gummed up.

I just ordered one of those air pressure cleaners on ebay for $110. It may not fix this problem but figure I'll use it
at least once a year from now on. Has anyone used one of them? I don't know what brand of cleaner to buy to run through
the system.

could very well be a sticking lifter or valve. #5/#6 is at the rear of the engine and gets the hottest. When I rebuilt the top end of my engine earlier this year, the back was HORRIBLE could barely move the lifters.

why don't you seafoam the gas and seafoam the crankcase to see if there is any change? At different times if you can so you know what fix caused improvement.

I'd start with a can of gunk engine flush, new oil, and can of seafoam.

If you can live without the car for a week, take out the injectors and have them restored by someone like Mr Injector which is about $100 for all 6.

Yes have the car in the garage and driving my spare. My spare car is a 75 Buick Century. The car never has any problems just sits faithfully waiting for the day when one of my newer vehicles takes a dive. This valve issue sounds dire. How do you Sea-foam this engine? I used Sea-foam on my 87 Plymouth once but it is a single injector and you just poor down the throttle body. I've got this gizmo coming in tomorrow that you fill up with injector cleaner and pressurize it with air and the engine runs off of it until the thing is empty. You feed the cleaner into the service port on the fuel rail. Are you familiar with this method? Will an engine run on straight Seafoam? Maybe this treatment will help the valves as well. I like your thinking on getting all the injectors refurbished but would like to try simple things before taking it apart.

If it's a 3.1L you don't need to rotate the engine. The rear plugs are a challenge, but I've always done them without moving the engine at all.

Got the engine to rotate enough to get to them but what a major pain in the ars. Sorry attitude but my other cars are much older and so easy to work on. I think I fumbled around with the plug job for almost 2 hours. Sadly the #5 misfire is still there. The plug did have a lot of brown crud on it whereas the others looked good. So next step will be the pressure injector cleaner which I will be amazed if it fixes it. I'll probably have to get the injectors out and have them refurbished. I'm impressed that anyone can do those back plugs without moving the engine.

I've done quite a few. As I said, it's a challenge, and takes a good variety of sockets and extensions, and those under the coils are really toughest, but it can be done.

The "brown crud" on the #5 plug could be from oil, coolant contamination, a slightly rich mixture along with weak ignition, or poor compression and a cold cylinder. An injector flowing too little would tend to create a fairly white plug and too rich would tend to create a dark brown or black soot on the plug.

keep eye on your crankcase oil, unless you have already dealt with the leaky lower intake gasket defect... that could be dexcool on the plugs. do any of the plugs smell like dexcool?

seafoam.... 1 can in the tank, a 1/2 a can into the oil

i would get a quart of gunk (or similar) oil flush, which you add to dirty oil and idle the engine for a few minutes. Then you do an oil change. Then you add new oil and 1/2 can of seafoam to the new oil.

I would not ride out that new oil change for 5000/7000 miles, but when the oil looks dirty which will probably be sooner than the recommended interval.

The sludge I found in the engine, and inside the lifters, was not hardened up, but still soft and easy to clean out when i did the rebuild... so I think engine flush + a can of seafoam might do a good job at freeing up the lifters and valves

The fuel level in the car was low at the time of the misfire. Under the 1/8 mark so I added a can of injector cleaner which would be a high percentage compared to a full tank. Anyway was watching the analyzer (Autotap) and observing parameters and clearing the code but then it didn't come back. The flashing check engine light and the code had been coming on all week immediately after clearing it. I threw up a misfire gauge on Autotap which had always been maxed on cylinder 5 and nothing. No counts. Was it the injector and the idling with the cleaner cleared it maybe. The pressurized injector cleaner I bought on Amazon (OTC) requires an adapter for the GM fuel test port so had to buy that and it will arrive later this week and I can blast the real cleaner through the injectors. I may change the plug wires while I'm at it. I'm the second owner of this car and the prior had the lower manifold gaskets replaced around 60K. The car has 125K now. The number 5 plug actually has a little bit of gray material on the electrode and dry. The Hg reading in Autotap is stable at 10.3in-hg which at sea level would be around 15in-hg. I'm at 5000 ft.