No need for a new pcm, just get yours flashed, GM always has an update for their calibration and even though they don't list it in the update tabs, it magically fixes things, lol.

just a thought, it may not fix it, but that's the first thing i'd do.

good luck,

allen


btw, raising your iac counts above 60deg c. about 5pts will help with idle until you can get it flashed.

 

**don't change any VE tables

 

can you elaborate on that.. why shouldent they be changed???

 

I'd like to know why you said that too.

 

I agree with Ben, that cam shouldn't need tuning to run fine. Tuning is a bonus but not absolutely needed. I'd double check everything. Do you have any SES lights? Do you have misfires? It could be as simple as a bad plug or plug wire.

You could have the timing chain off by a tooth, which woud be like a BIG advance or retard. With that small of a cam, you shouldn't come into piston / valve contact issues unless it were off more than a couple of teeth. It would just not run quite right. Stumbling and idle issues could be explained by this.

 

BigTex
You been gone?When you get a chance please answer a couple of emails.

 

Sorry, I've been out of pocket. I'll get right to your mail.

 

The VE tables are actually fueling tables. Some try to scale the lower rpm cells down for easier cold starting (i.e. when the engine is initially running in open loop). However, changing even the cells in the Main VE table even just from 1200rpm and lower can cause problems with fueling under normal operating temperature (above 122*F the pcm goes to closed loop i.e. reads off O2s) because the VE is used in Both open and closed loop calibrations. If you want to know more, go to the PCM Tuning section and read the two sticky threads they have at the top about VE table -very good explinations. Cal, NoGo, and ChrisB are the smartest guys on this board I think.

To get you started, I would retune your IFR (injector flow rate tables) **NOTE: changing your VE tables will make this part nearly impossible to be accurate. So don't change the VEs

To tune your IFR with a new cam: (from a previous post)
"When you mod an engine, the Volumetric Efficiency changes. The VE tables affect L-trim readouts. For example, your l-trims could be perfect while in the VE cells of 5 and 21, but when you are in cell 7, it could have some wierd readout of -20 on the L-trims. What hohl was saying about the mapping out of the VE table is also right. Someone on this forum discovered which VE cells are PE (Power Enrichment) cells and which ones are at cruise.

When tunning you should use your L-trims to calculate what your IFR number should be. Take a long cruise and log all of your L-trim readout. Average them and multiply it as a percentage to your existing IFR numbers. For example: if your averages for Bank1 come out to +3.2 and averages for Bank2 come out to +3.0 -->avg. those = +3.1, so to richen up the mixture, multiply the IFR table by 96.9% (this will yield a smaller number in the IFR table than when you started) The lower the number in the IFR cells, the richer the engine will run.

If you have messed up VE cell values, then it will affect the L-trim readouts, affecting the IFR number, which will mess with engine performance. Use the stock settings on the VE tables! Even with my pretty big mods, only one cell is giving me troubles in the VE. I see this when I let off the throttle after giving it lots of gas, but not enough to jump into PE. The L-trims when I am in that VE cell go to something like +20. I disregard any L-trim readings in that VE cell if I am tuning for IFR."

 

If you have AutoTap this is the easiest way to tune IFR: (from a previous post)

Make sure you are in closed loop operation (if you are above 130*F you will be in closed loop) Go out and log l-trims for at least 10-15 miles of Normal driving -don't go into PE by giving more than 40% throttle. ***Take that file you just logged and while still having that file open in AutoTap click on File -> export to a coma deliniated file (sp?) I am pretty sure this function is under the File menu. if not just look for it on one of the top toolbar commands. This will put your entire log into Excel (download Excel off the net if you don't have it) Next, highlight one of the l-trim columns and select the entire column by holding down the mouse and scrolling down to the end of your log of l-trims in that column. With it still being highlighted, click on the "sum" symbol in Excel (a symbol that looks a black E at the top icons) This will add all of those l-trims logged in your run for that bank of the engine and put it into a new cell either at the top of the entire column of logs or beneith it. Divide that number by how many total readings you logged. i.e. you are averaging. Next do that to the other bank of l-trims. Average your averages and use that number as a percent to change your IFR table to.
Follow how I explained it with examples befor in a previous post if this is not super clear. I pretty much just wanted to let you know how to export a file and let Excel do all of the math for you.

Do a second log and confirm that your l-trims are more in check (somewhere between +4 to -3) You may want to export the file again and just average everything again. Are you around zero for your overall average? Good you are set.

 

All that sound good Ryan except for that last section. From what I have read you never want a positive l-trim. I always shoot for zero to slightly negative (0 to -8). Reason being, that if you ever hit PE with +l-trims, it will keep dumping fuel to make up for the lean condition and cause very inconsistant fueling.