Let me first say thank you all for still being here to help all Blazer owners. All of my hobby's and work have kept me from contributing here of late and it is great that I can still come here for help.

Monday night our 2001 Blazer suddenly started to run terrible. It was running fine when shut off then the next time the wife started it it could barely idle, had poor power and trouble getting it to go more than 50 mph. Rotten egg smell from rich exhaust also. She drove it home about 20 miles that way.

When first checked it had a Po302 code. I started with a new cap and rotor and plugs which made no change. I then installed a known good coil and ignition module,still no help. I don't own a spark viewer so I used a timing light and found that I was getting spark ok and ruled out the ignition system.

At this point I decided it was just getting too much fuel and removed the upper intake cover. The area at the back under the pressure regulator was washed clean. I had normal fuel pressure that did not leak off and no leaks visible at any of the injector tubes. I decided the pressure regulator had been leaking and replaced it. Still no improvement.

At this point I decided to not buy any more parts till I did a compression test. Should have done it sooner. Found good compression on all the cylinders but #2. It had no compression at all. A look with a small camera showed the top of the piston looks good. I could not see the valves with the camera. After thinking about it I realized a valve spring must have broke and pulled the valve cover. Here is the #2 exhaust valve spring.



If I did this kinda stuff everyday I would have know sooner to suspect something like this. The vacuum gauge showed I had poor vacuum that was jumping around badly. Couldn't find a vacuum leak anywhere though so I dismissed it at first. Oh well I only wasted about $130 so far. New springs and seals on the way. Gonna see if she will live a little longer, only 211,00 on her so far.

Sorry for the long post thought it might help others.

Blazeme

 

Nice job diagnosing! Unsteady vacuum at idle and no compression is a dead give away for a broken spring or burned valve. I sure hope you didn't remove the cylinder head. The job can be done with the head installed. Let us know how it goes.

 

I've had loads of fun on my 2001 with 207,000 miles with the P0304 for several months. Like you, I tried ignition and fuel changes to no avail. If your interested, you can read the details on my P0304 post I just updated.

https://blazerforum.com/forum/2nd-ge...ttempts-85473/

I finally checked the compression, and, like you, wished I'd done so sooner. However, I only check #2 (supposedly good) to #4. I got 170 and 130 lbs. respectively. I did the wet test and psi raised to 135-140 lbs., so it may be my rings, however, there is no visible oil smoke or smell at the exhaust. I need to do a cylinder leakdown test as suggested by members here and also pull off the valve cover and take a look. I'm getting 130 psi, could a spring be broke, or valve stuck cause the 130 psi reading?

My does not have an erratic vacuum like you are getting, and it runs fairly well, just a miss at idle.

Glad you found the culprit. I'm on day 15 of driving on expired registration because it can't pass ATL emissions.

 

Left the cylinder head in place. Already own the air fitting and spring compressor.

I put air pressure on the cyl today and it looks like the valve still seats and seals good and no air blowing through the piston. I was pretty sure the valve had not touched the piston. I am also thinking since there was no compression at all on the cylinder it would not be firing good enough to burn the valve that was hanging open? I hope.

Got the 12 new springs and seals, now gotta find time to do the work. Anniversary today so out to dinner first.

 

Well I got all 12 springs and seals replaced. Now she starts up and runs normal. Looks like we got real lucky and the drive home didn't hurt it. If that valve had come loose and dropped into the cylinder I would be shopping for a different vehicle.

 

Good job. Glad you got her going. Thanks for posting back.

 

There is one thing I can't understand. When I removed the broken spring a very small stretched out spring came out with it. It wasn't tangled up in the valve spring, just fell out loose at the same time I removed the bad spring.

I know it is the spring from the valve stem seal as the top of this seal was torn loose from the rest of the seal and the spring was missing. The other 11 seals all had their springs in tact.

The loose seal spring surely didn't play a factor in the main valve spring braking did it? I don't think the main spring would compress tight enough for the small seal spring to cause that kind of interference.

The seal spring is mashed 3-5 times it's normal size. Seems like it got smashed between something.