I just got my car dynoed and had a question. Every once and a while my car will stumble in the high rpm's (between 5500 and 6000), but not all time, it's basically random. The guy that tested the car felt it on the first run but not the others. The car put down good numbers but hp droped off around 5500. What could be causing it to stumble, ignition or fuel (lean in the high rpm's)? Fuel and ignition systems are stock, car has 35000 miles.

Thanks,
Eric

 

valve float. springs are weakening alittle, all stock right?

 

Yes, the engine is completely stock. If I let this go until I replace the heads, i.e. thousands of miles could I cause other damage to my engine? Aside from new heads, would it be expensive to upgrade the springs and pushrods, or for that matter worth it?

Thanks,
Eric

 

Hey Eric, I got the same "stumble" at high rpm in first gear only at random times. I have posted about this before but no one has convinced me it is internal drivetrain (just doesn't make sense b/c it is random and in my case only during one gear). I had a hiccup at about 5200 rpm in every gear when I had the SLP 'piece of s#!t'... when i finally took it off last year and replaced with the ASP UD and alt pullies it ran great in all gears up to the limiter...it took awhile before a got my first random "stumble" in first. I believe now this stumble is still pulley related but now is "better". Better balancing w/ ASP but obviously not quite there. It may may as simple as atmospheric conditions changing....but some exterior force is changing how the pcm is accepting the frequency of the engine created by the balancer. Not all people get this problem with their setup and mods. I do think every pulley acts and reacts a little different with each individual car.
One way to check this out would be to try running the stocker for awhile, but obviously don't want to go through the swap to prove something that I feel pretty confident about, and I like the increases with the pulley. So, when I do my cam swap I am going to put a new pulley in. I feel pretty certain ASP will work with me. I do think I am going to put the stock alt pulley back on....with all the accessories I am running the battery does not hold a good base charge and needs to be jumped if not started for 3 days (new battery installed already <img border="0" title="" alt="[Mad]" src="gr_images/icons/mad.gif" /> ). I am going to inquire to the hp advantage though...shouldn't be much.
Hopefully this analogy helps.
BTW, Could you imagine N2O burst when it happens. Thankgod I have never used it in first.

 

Thanks for your input, BLUBYU, I didn't think about the problem being pulley related. I see your logic behind it. I only have the ASP crank pulley and did the install myself. Maybe I screwed it up? I'am with you, I like the gains from the pulley and am not willing to go back to stock. I hope whatever the problem is, it doesn't get worse or cause other damage to my car.

Thanks,
Eric