Well it happened again. This time I knew exactly what the problem was before opening the engine up. I even used Autotap to help.

The car was running perfectly normal. Stopped at a Taco Bell for a bite, came out fired up the car and "lumpity, lumpity, lumpity".

I thought maybe the AC being on, might have been related, so I turned it off and restarted. Same thing. Car had very low power and I limped it home.

I sensed early that it was a valve spring, because when it cranked over it was had an occasional higher sound during cranking at different intervals (can't create the sound, but you probably know what it sounds like with a spark plug missing).

Anyway, So I put Autotap on and it was flaggin cylinder #6 as misfiring.

I could smell fuel coming out the tail pipe. I also pulled the connector to the fuel injector (#6) and virtually no difference in power. Hmmm.

I told the mechanic that I thought it was a broken valve spring on the exhaust valve to cylinder #6. He just called and confirmed that my guess was 100% correct.

That was the third valve spring busted in the last 3 years. I didn't rev it, nor was it cold or anything conducive to breaking steel. This time in less than 6 months. I have 1.6RRs and a mild cc-304 cam.

Arrgh. This is not fun.

 

What brand and part number? Installed height? Max lift?

Do you let the motor get up to operating temp before you beat on it?

 

Hopefully not not running the stock springs; if yes, your lucky you haven't broken any push rods.

 

One of our 383 Lt1 blower motors has this issue too. It's a LT4 in a '97 SS with a procharger. Fully built motor with callies and manley bottom end, the heads are set up with Manley Nextek springs at 1.770" for 125 closed and 325# open, plenty to coil bind. This motor has broken 3 valvesprings in 3 years also, different cylinders each time. Guy doesnt beat on it when cold or anything like that. My only idea is that he is creating some weird harmonic that is killing the valvesprings when he commutes at 70mph everyday for 70 miles.

So other than the obvious, which I now see that you said you warm it up each time, I am clueless too as to why this is happening.

 

Why dont you just opt for strong beehive valvesprings. Problem solved.

 

You said that "Autotap" can flag misfires in a particular cylinder?
How does it do this?

Can my Datamaster or freescan do this?
This would be very useful tto find my possible misfire.

 

OBDII cars ('96+ f-bodies) have a crankshaft position sensor, can detect missfires, and pinpoint the cylinder that is the culprit. OBDI ('95 and earlier) cars cannot do this.