Alright, I tried this on the EFIlive forums, but I'm desperate for an answer and nothing I've tried has done worked has done much at all.

Heres the problem...I just put in a cam(232/240 112+4) and I've been having horrible bucking issues since then. The car drives fine above 2000rpm, but once the rpms drop while I'm in gear, it starts bucking, it gets pretty bad around 1800rpm and at 1500rpm the car is shaking so violently it feels like its going to snap in half. The more throttle I give it, the better it is, with throttle completely closed it is horrible. I've tried everything with fuel and spark, but its pretty obvious it just wants more air.

The last few days I have spent the majority of my waking hours reading and trying to solve this, and this is what I've tired/found out so far...

Regardless of what I set my throttle cracker and follower to, they both drop to 0 the second I let off the gas...I have put the decay rates to 0, put the delays to max value, played with the activate/deactivate parameters, put the values of the cracker and follower up to 5+g/s each in every cell....no matter what I do, they drop to 0 right away...It also has trouble returning to idle because there is no throttle cracker/follower.

I have tried a complete reflash of the stock tune, only changing the fuel and spark tables.

I was originally using a 2000 ls1 pcm, flashed with a 02 operating system, that I reflashed to and efilive custom operating system hopeing it would do something - nada.

Details - 3000lbs car, 2000 ls1/t56, 4.1 final drive, all bolt ons, 232/240 112 cam, using efilive to tune, open loop/speed density.

Right now I'm thinking about trying to find another PCM to try...just because I'm completely out of ideas. Please I'm desperate for an answer, if anyone can tell me whats wrong, I will paypal that person $20...if a sponsor figures it out, I'll print out a sign with their name and tape it too my car for the next week

Thanks!

 

We got this...I'm confident.

**Edit** Maybe not.

 

To some extent your going to have to deal with the cam surging. How much of it you can cure with a cam that size is the real question. My first bit of advice is to go ahead and kill throttle crack based on road speed entirely. My next step would be to work on throttle follower steps to keep the stalling to a minimum. the last step is to go ahead and play with min throttle setup and Iac counts. then maybe play with timming by going down to take torque out of the problem area.

 

I looked at your tune and it's so whacked out from stock, it's no wonder you're having problems. I used to try lots of wild stuff on my car. Then I got the Road Runner. The more I put my tables back to stock, the better the car ran. Basic things first. Drill your TB or crack the blade until you get 30-60 IAC counts at hot idle with AC off. Next, get your RAFIG higher than it is now. With that cam, you should at least be in the 7-8 g/sec range when warm. Don't mess with the IAC effective area table (at least not until you've absolutely exhausted everything else). Your IAC is running out of room because your RAFIG is too low and it's going to zero. If you have a hole in your TB, make sure it's not too big. Again, make sure your IAC counts never fall below 30 when fully warmed up with AC off. If they do, close the TB blade more.

I've tuned 6 cars recently and all had cams with lots more overlap than yours. All ran perfect. I'd be happy to send you some files if you'd like. Remember, the closer to stock, the better you'll run.

 

I have no doubt that the car won't be able to archive near stock drivability...with only 12 degrees of overlap, its not exactly huge compared to what a lot of people on here are running.

I feel like the answer is pretty obvious - the throttle cracker and follower tables are not doing their jobs. I'm not a tuning expert by any means, but I feel like if I could get these tables decaying out as they should, instead of dropping to 0 right away, I'd be in a lot better shape.

Right now I have just flashed an EFIlive custom operating system hopping that maybe trying something else with the operating system might work...it didn't. I had been using a 02 operating system on my 00 pcm from the beginning, I just got a stock 00 tune and stuck my fueling, spark, and desired airflow tables in it and left pretty much everything else stock....tomorrow I'm going to flash it on, with the 00 operating system, and see if my throttle cracker and follower work *fingers crossed*

 

When your car is idling and fully warmed up, what are your IAC counts with ac off? Have you changed/moved around the IAC effective area table?

 

Be sure the cracker follows road speed and, importantly,
tapers to zero smoothly. Stock tables on some years have
spikes and holes which challenge the idle control loop to
keep up, and if motor response is "soggy" it can't. You
are trying to make a "smooth landing", is all. The rest of
the problems are not about the cracker, but idle base tune
(airflow, air/fuel/spark). You can kind of determine what
makes the motor happy by spending some time with the
bidirectional controls, messing around the IAC, the AFR
commanded and the spark until it idles at the right RPM
and as smooth as possible. Going back to closed loop
will be tricky because of overlap effects etc., there you
have only O2 switchpoints to play with (may just elect to
run full time open loop). Mixture plays a really big role in
stabilizing idle (or making the motor happy enough, that
it responds in time to airflow/IAC and IAC/RPM loops).

Anybody playing with the PID params to fix it from a
control loop stability angle? I'm pretty sure there's a
handle there but I haven't gotten hep to that jive,
yet.

I also think there is a problem with low end fueling,
misfueling against MAP dimension puts you very prone
to fuel-loop surging. Even with everything locked (IAC,
spark, AFR) I can still see surge on a low-overlap 224
range cam, MAP is still "busy" and RPM, IPW follow.
Don't have a good idea of how to model the ideal, and
haven't been thorough / methodical enough to try the
different VE:MAP tapers but my gut says this is where
you will find idle stability at the root of it, in open loop
at least.

 

IAC counts are ~50-60 with no load...throttle body is drilled and RAFIG was done properly. IAC table has been stock 95% of the time I had been messing with this.

I seem to have got it working, although only with the stock OS, heres what I posted on the EFIlive forum about it.

http://forum.efilive.com/showpost.ph...4&postcount=39

If anyone still has any ideas what could have been wrong with the 02 OS's I was using, I'm all ears!

Thanks.

 

Another thing contributing to your problems have to do with your Commanded Fuel in Open Loop (B3605). Your table has you at 1.13 A/F ratio from 75kPa up which is right off idle with the cam you have. You should put in a better looking table than that.

 

Is you throttle body an aftermarket or stock throttle body?