NEED HELP P0301 then P0300. Please help.

[joepro17]

Driving home a couple day ago mid drive SES light started flashing and reduction in vehicle power was noticeable. Had to drive it about 2 miles to get it home. It had a real rough idle at stops. Took a scanner to it, came back with p0301. Went to local parts store and got an ignition coil and 6 spark plugs (Acdelco) (needed them anyway. 108k miles). Changed ignition coil in cylinder 1 and all 6 spark plugs. Still runs like crap. Now getting code p0300.


Took it to independent shop they verified all the coils, spark plugs, injectors, compression was ok. They couldn’t figure out the problem. They think something could be wrong with the engine. Recommended I take it to a dealership. Before I do that any helpful advice would be much appreciated.


thanks

 

[Capote]

Did you get the 41-103 spark plugs?

 

[joepro17]

I did.

 

[mrrsm]

In the lexicon of "Fuel-Air-Spark"... Perhaps cleaning the MAF with the designated CRC Spray Cleaner and examining how tight the small Intake Manifold fasteners are if they move before reaching 89 " Lbs. The loose IM causes a very lean condition in the cylinders that has not been measured at the point of inhalation. the MAF and IAT measure air by weight that is monitored by the PCM... but unregistered vacuum leaks can throw a "Monkey in the Wrench".

 

[joepro17]

Any tips on tool combinations used for accessing the intake bolts? They seem difficult to get to.

I also noticed my muffler shaking a bit. That may be a result of the rough engine idle though.

 

[mrrsm]

Sure... Some other Members here offer their ideas and suggestions, too

http://gmtnation.com/forums/threads/intake-manifold-bolts.16460/#post-521954

 

[joepro17]

If anyone is interested, took it to the GMC dealership. There was no compression in cylinder 1. Had a broken valve spring. Had it replaced and is running smooth again.

 

[Sparky]

That would do it. At least it wasn't a cooked valve and could be fixed easier than yanking the whole head!

 

[joepro17]

Agreed. I'm considering this a win. Could have been much worse.

Also had them change the valve cover gasket and intake gasket since they were already there.

 

[mrrsm]

If you can remember what the driving and RPM elevation conditions where just before you noticed the drop off in power... would you describe any symptoms as to how soon the problem showed up afterwards? It will help others to know what to look for should they imagine other problems being the cause ...and never consider a Broken Valve Spring as a possibility. Glad you Dodged such a Big Bullet... ;>)

 

[joepro17]

Sure. I was going around 40mph on a street with rolling hills. It happened while going up in elevation. RPMs were most likely over 2k.

The loss in power was immediate as if someone flipped a switch. Vehicle went from driving perfectly fine to crap in less than a second. As soon as the spring broke the SES light came on flashing.

I would recommend rolling your windows down to listen for any unusual noise when the SES comes on flashing. I noticed a clicking noise coming from under the hood when it happened. I may not have heard it with the windows up. The clicking noise tempo was in line with the speed of the vehicle. As the vehicle speed increased/decreased the clicking speed increased/decreased. Obviously I didn't know what I was listening to at the time, but I'm thinking that clicking was the spring flopping around.

 

[mrrsm]

That "Big Bullet" you Dodged has just swollen up to the size of German Tiger Tank 88MM Artillary HE Projectile. How that Valve Stem failed to drop the Valve down inside of the cylinder and lunch your Engine at two grand of. RPM can only mean that you had God and His Angels following your progress uphill that day!

 

[NJTB]

The inner spring broke, outer spring held the keeper and stem in place.