I don't know how to fully tune with VE, but...

VE is dealing with the efficiency of your motor. The camshaft has a direct impact on how efficient the motor is at different rpms and conditions. It is physically altering airflow. The VE tables are mapped to the stock cams powerband, which provides proper fueling under those specific conditions. Going to a differnet cam should shift the VE of the given motor some, causing improper fueling under different conditions. Every cam has its optimal range where it operates at its best (read that as peak efficency). Think about it, a large cam sacrifices low end power for upper rpm power (shifting its efficent range).

That being said, if there was a good way to correctly remap the VE table to a specific engines needs and mods (cam, intake, headers, etc...) then the trim values would be right at 0 for every cell. But every engine combo is different and each mod you do alters the way an engine operates. I'd think the middle rpms would have the closest ratio for VE between the stock cam and a larger aftermarket one. It would be the low and high rpms that have the greatest difference between the stock cam (strong down low but dies hard later) and aftermarket cam (weak down low that builds up to strong at the end).

Anyway, my point here is that fueling is going to be off after a cam swap. Thats why you'll see different ltrim values for the cells in the low rpms than in the mid and upper rpms. Just changing the injector flow rate would alter fueling for all cells at once and in only one direction (richer / leaner) when it really needs to be fattened up in certain areas and leaned out in certain spots. Those specific fueling changes could be handled by altering the VE tables.

 

I just dont understand why it runs like it is. It ran great the night after the install and 3 days after. I had an SES light the day after I installed the cam. But it went away. I made dam sure my gears were aligned right. Even had 2 people check on it. I just figured this 99 PCM with no updates whatsoever was causing my problems. Even if I dont have an SES light, could the PCM be picking up misfires and fowling things up?

 

BigTex,
You are absolutely correct!
You are correct again. A perfect tune would show nothing but 0 for l-trims.
Good point BigKID. I guess this fact should be included...shoot for ltrims 0 or negative as negative ltrims will not subtract fueling, but positive ltrims will add fuel. -good point BigKID

Hey how about this one for 99Silver5.3's situation. The cam is giving him misfires (which is happening with that size cam and low rpms/idle) This makes the converter act funky. ...not locking correctly? Wouldn't this feel like a loading when the truck was given a little throttle from idle?

I know it is not something you want to cruise around on forever like, but could you just disable the misfire code from the pcm and drive for a while and see if that may solve something. If it does not, then make sure to turn that code back on.

 

I would try to put a few more miles on it without getting in to too hard. I have heard some engines take a while to learn new cams. Maybe yours is one of those.

 

Maybe thats the wierd jerking I feel when im driving. Ill disable that code or increase the misfire tolerances in the Diagnostis tab in Edit. I got some tuning to do tomorrow.

 

does it feel like you are pulling a trailor at speeds?...kind of a going smooth and then it feels like someone pulls on your bumper? If so, that is definitely a transmission torque converter locking and unlocking characteristic. I remember my converter doing this to me on a trip back from California and my thermostat broke in the open position. My radiator (RonDavis racing) is so good it made the engine run too cool 144*F This cooled the trans so much from the trans cooler being in the radiator also that the converter kept unlocking itself to try and warm the tranny fluid up. It felt like I was towing a trailer when it would lock and unlock.
Anyway..good luck man

 

Thats exactlly what it feels like!!

 

Look at the Edit document or some of the tuning threads about turning off misfire detection at low rpms. That will make the truck ignore misfires that are due to a cam swap but keep the detection enabled for real misfires. That should stop it from turning on the SES and messing with your converter lockup functions.

Also, add some timing to the extreme low end of your idle timing table and hi/low octane timing tables. Get the timing to about 20-22* in the 0-1200 columns and first 4 rows. That should help to smooth out idle some. You may need to alter VE in that same range, but lets just hold off on that for now. That cam should be fine without many tuning changes.

 

Where can I get these GM updates for our pcm's you guys are talking about?

 

Any GMC or Chevrolet dealer should be able to update the pcm for you. A word of warning though, if you update at a dealer and you have previously installed edit on your pcm, the next time you try to run edit it will not recognize the pcm. I think Flyer had this problem.