I am working on fixing a high rpm miss, but i found something very interesting when I was logging some WOT passes. Keep in mind my rev limiter is set at 6950 rpm. Every time i accelerate from a stop, it pulls right up to exactly 6375 rpm, then starts missing like its hitting the rev limiter. 6375 is flat out as high as it will go. Whats up with that? I can't figure it out....If the rev limiter is set at 6950, it should pull right up to the rev limiter just fine. It doesn't seem like an ignition issue to me, b/c its just weird that it stops pulling at 6375 EVERY time. Sounds like something in the programming is preventing me from going over 6375. My log goes like this:
RPM:
6000
6055
6185
6245
6300
6375
6375
6250
6200 <---still WOT, even though revs are falling...

Every time it just stops pulling at 6375 exactly. Anyone have any ideas?

 

The stock PCM uses an 8-bit data field for RPM. Each "number" represents 25rpm, so the max RPM that will fit in the data field is 255 X 25 = 6,375. It will support RPM higher than that, it just can't indicate it on a scanner.

 

So its actually going above 6375 rpm, it just won't show it on a scanner. Damn it, sounds like an ignition issue still

 

How did you adjust the lash on those Comp R's? Anything more than an 1/8 turn is too much. If you went near 1/2 turn...you just found your problem.

 

The new version of TTS DataMaster is supposto poll a different field in the pcm (a 16 bit value) so can read higher values (it's on their site as a beta product).


Sounds like you are having some other issue - it is probably higher than 6375 - that value in just an artifact of the pcm scaling method, as outlined above.


Chris

 

Would that lash adjustment apply for Hotcam kit roller rockers as well? I'm having a miss starting around 5500 that I am trying to figure out as well, I think I may have them adjusted too tight. I thought I was supposed to go 1/4 - 1/2 turn past zero lash?

Thanks.

 

The Comp R's come with a bit of pre-load. All they need is between a 1/16th - 1/8th of preload. I know from experience that if they're too tight, you'll rev to a point, and then it will feel like you've hit a wall.

I have mine a tad bit less than an 1/8th turn. Now revs freely...

 

Cool, I'll re-lash them then. I have them at 1/2 turn past zero lash. Thanks

 

rpm 16 is the value you want to look at in datamaster.

 

Thanks for the info bro, thats exactly what it was I gave it about 1/16-1/8 turn past 0 lash, and it now revs to 7000 no problem. I originally had it at 1/2 turn past 0 lash, which was obviously way too tight.

 

I heard a roumor that they make the Comp R' lifters again. Is it true? If true, where can you get them?
Thanks guys!

 

Combination Motorsports carries them.

http://www.cmotorsports.com

Great guys, great prices, great service. Flat out, GREAT!

 

i do not understand how it could cause that problem, not saying anybody is wrong, just don't understand

 

ltlhomer,
Thanks for the info! I heard good things about those guys, too.

 

Glad I could help...enjoy!!