RedIrocZ-28

Doin some data scanning the other day and I have been experiencing some light (lower speed) cruise shudder. I pinpointed the problem, and for me it happens when I take my foot off the accelerator enough to hold a constant speed (after accelerating), the TPS reads about 5-6% open depending on speed. The car will instantly drop from BLM cell 10 to 6. (Which brings up another interesting point... I have bever seen BLM cell 7-9... ever show up.) So in BLM cell 6 it will cruise for a few seconds... probably about 5-10 seconds and then the shudder will happen. Its pretty violent sometimes so I have to let off and press the gas again to get back into cell 10.

In my readings, I've tracked down a few possibilities.

#1 Could be a lean miss at low RPM and I might need to add or subtract timing, fuel should be ok because the BLM's are about 128.

#2 Fuel vaporization may npt be up to par with the new bigger cc (ports not chamber) heads. I may need to crank up the pressure.

#3 The problem is probably related to cylinder temp falling. Somthing that I read a long time ago by Grumpy said that there is a large difference between a Nascar motor and a street motor. The Nascar motor needs to be able to dissipate heat that builds up obviously very fast and this heat on the pistons and rest of the chamber have a certain name. On street cars we don't need to dissipate heat as fast but with out modded motors we change the characteristics of the dynamics.

So, I am thinking that #1 my plug range is wrong, not sure if I need to go hotter or colder... I have 1 range colder than stock currently with an AFR 195 headed 355 with a Stealth Ram and a custom grind 228* 234* cam.

Also, I'm going to the dyno tomorrow and am gonna try to tune this beast a little bit. Wish I knew what I was supposed to do for that besides use AFR tuner.

Anyone wanna give me a real quick crash course on WOT dyno tuning? As in Change X and X values and see what you get for gains/losses.

TIA!

eric305TPI

Do you have highway fuel enabled in the bin. If so it could be leaning out too much and cause a shudder. Also having the torque conver clutch engage too early could cause a shudder.

kane91z

i'm having the exact same problem in my 91 after 5-10 secs she really starts suddering bad as if she was really lean

i was going to try and lower the A/F ratio to 14.5 and see if that helps any