So i'm trying to get my car dialed in finally after the new cam setup and for some reason i have a shakey RPM graph on Datamaster. The RPMs will climb real fast, real steep, then flatten out for just a second. Then another steep climb then it flattens out for second then climbs on up. It does this from 4500-6100 when i stop. Looking at my old datalogs from my past combo the problem was there too. I'm now running a different cam with different springs so i don't think its valve float, and it starts at 4500 which seems kind of low for valve float. I assume if the RPM's are doing this it has to be a miss correct? is there any way to find out if its ignition or something else? I could really use some help guys. Here is a datalog for anyone that has the capability to look at it.

http://www-personal.ksu.edu/~bperkins/rpm.zip

 

I would suspect the opti if you still have one. I know that when I had mine still the car would sometimes act like you are describing in the higher RPM range as well as idle sometimes. Delteq DIS fixed that issue for me. Does the car run strong or does it feel like it's holding back on ya?

 

I can speak for him on this issue.

The car runs strong but its not 100%. I suppose it could be the opti but there are no other signs to point to it just yet.

I almost wonder if somehow the spark timing isnt staying constant eventhough it says it is on the log. A variance of 5 degrees could probably do just whats happening here but I dont know of any way to test the theory.

 

Any false knock readings?

 

Oh not so much really... few degrees here and there but if you look at the .cvs file its not a factor.

The problem stems from really only a handful of things since much of whats on his car now has been replaced recently trying to resolve a low hp problem... still not all there way resolved but we're getting close.

Really the only parts left from the first dyno a couple yrs ago are all the ignition componants, the injectors and the shortblock. I guess we didnt touch the heads except for new valvesprings but I dont see that being an issue.

 

I'm at work and can't download anything from the internet

But it sounds like it may be an ignition problem. Is the opti the stock unit or has it been replaced already? From what I can make out it's definitely not anything to do with the engine internals or heads. The opti would cause all these problems if it were failing.

If your friend hasn't toutched his ignition components yet it may be a good idea to start with the spark plugs, then replace the coil, wires, and finally opti, though I would highly recommend going to a DIS like Delteq or LTCC.

 

The opti has been replaced but not since the rebuild... maybe 15k on it. The wires are MSDs and are the same wires are the first dyno run so they are a possibility. Hes going to replace the ICM and coil with one that we have laying around.

I can tell you the problem is not a misfire. A misfire would show up on that log but I do wonder if the timing is fluctuating a few degrees for some reason. Hell, I dunno if thats even possible.

 

Thanks for answering his questions for me Brad. Why do you think its not a missfire?

 

Because a misfire is going to throw fresh oxygen down the the O2 sensors and they will show lean. Plus if its a random misfire then youd feel it and the motor would vibrate.

 

you have pm.