4.8 Stage 1 Cam High Idle

[67Wagon]

Hi everyone,

I have a 67 Nova with a 4.8 LS engine w/ a Stage 1 cam from summit racing. Car has K&N air filter, headers, dual exhaust. The car is running very well, except for the idle. I cannot figure out how to get the idle to drop to the base set value. The desired idle rpm keeps increasing by approximately 125 rpm. If I set the base to 650 rpm the desired moves to 775rpm. I have tried changing VE, spark, idle ariflow tables with no change to this issue. The increased idle speed makes it really want to push through the brakes at idle. Any help would be appreciated.

Tune file and log attached

[gametech]

If you do a search you will find many people have had this issue with p59 computers. Fixes and success rates seem to vary.

[HATEHPTUNERS]

Your IDLE UNDERSPEED and OVERSPEED tables are JACKED!!!!!!!!!!!!!!!!!!!!!!!!!
Here's what you should do right now..... Go out, start the car, get it up to operating temperature... now while idling, go into CONTROLS on the scanner, and LOCK THE TIMING at something like 22 degrees. LOCK it so that it cannot fluctuate.. NOW... tell me what the IDLE rpm is doing, and if it has stabilized.... I'm going to guess that it will be MUCH closer to commanded, and much SMOOTHER with far less bouncing around.

Also, go look at Spark>advance>catalyst heating.. I would ZERO that table out if you do not have catalytic converters.. in fact, I'd zero it out even if you DO have them.. It's just one more thing affecting your idle spark (potentially) that you can remove to drill down on this problem.

If it is BETTER with the timing locked, then go into your UNDERSPEED and OVERSPEED idle spark tables and make it look like this;

[HATEHPTUNERS]

Also your VE table is going to need some work.. Look at the MASSIVE jump from the 1200 to the 1600 columns.... Look at the 3D image of your table and you will see the HUGE jump from 1200 to 1600, then it DIPS down from 1600 to the 2000 column... I don't think that's going to be your final VE table... Here, I've done some very basic smoothing to show you what a nice, smooth, VE table should look like when done... Please note these #'s were SOLELY for the purpose of demonstration-DO NOT use these #'s in your tune as I was only fudging the #'s to give you an idea of what yours should look like when YOU are done tuning it. Also note that you have many +100 #'s in the table.. That usually is indicative of a super charged engine, OR an offset issue when using a wide band O2 sensor to tune, or other erroneous data captured during a tuning session, OR..... most importantly-INCORRECT INJECTOR DATA----DATA DOES NOT MATCH THE ACTUAL INJECTORS, OR HOW THE INJECTORS ARE BEING REGULATED. Or, your injectors can't provide the fueling that the engine needs so the #'s in the VE table have to be FALSELY inflated in an attempt to get them to give the motor the fuel it needs. Weak fuel pump, too-small injectors, restriction in the fuel system somewhere... many things can give you +100's in the VE table.. Just know that it usually means something else is wrong.

[67Wagon]

Thanks for the replies! The VE table was actually from someone who tuned my car prior to me getting HP Tuner. He just pulled it from another customers file I believe. (I don’t really trust the tune). Does anyone have a better starting point for VE for a stock 4.8 w/ a small cam?

[HATEHPTUNERS]

Did you try locking the timing yet? What were your results?

In regards to the VE table, and the tune in general, you will be tuning ALL of it yourself to get it right.. Why not just start over with a completely stock tune from the repository? There is no telling what changes the previous "wonder tuner" did.. unless you download a completely stock tune and then do a "compare" and view the comparison log to see what all was changed. Then, once you can see the changes, you can figure out (hopefully?) why those changes were made, and then you can decide whether you want to keep those changes, or discard them. I'd start with an ALL STOCK VE table for your engine, and then begin VE tuning/Speed Density tuning from there.

Are you running the factory injectors? Have you changed any part of the fuel delivery/supply system?

[67Wagon]

When I locked it out, the idle slightly increased with 21 degrees and seemed to plateau from there with no change as I continued to increase timing. Desired idle is still reading 125 higher than set. Looks like another member is having this same problem. In regards to VE table, I will compare the stock tune. To tune, I essentially need to turn off MAF and compare LTFT. The deltas will be what fields need to be altered in the VE table correct?

[HATEHPTUNERS]

Lock the ignition timing at like 18 degrees, watch the idle rpm, if it's higher than your commanded, start lowering the locked timing until you get to a point that the idle stabilizes. Keep in mind it is NEVER going to be just flat lined at one rpm level. It is always going to rise and fall a little bit due to the switching of the O2 sensors. I'd like to see what else could be contributing to the idle swinging once the timing is removed from the equation. You know that raising the timing while it is locked will also raise your idle above commanded right? You can't expect it to idle at commanded when you lock the timing, and then begin raising it. The PCM is using timing to attempt to control rpm.. When you lock the timing-you have taken away the PCM's ability to adjust the idle rpm. Start with 18 degrees locked, then go lower until the RPM stabilizes at your commanded-then log that for review here. If something else is contributing to the erratic idle-locking the timing out makes it easier to drill down on what else could be causing it.

[HATEHPTUNERS]

Also, after finding where the idle stabilizes with locked timing, go out and lightly drive the vehicle and see if you are still having issues with the vehicle trying to stall when coming to a stop, or if it hesitates, or stutters, on acceleration from a stop, or when slowing down coming to a complete stop.

[bk2life]

Does anyone have a better starting point for VE for a stock 4.8 w/ a small cam?

use the stock tune.
what else have you changed?
headers? CAI?
post apicture of the engine?

[67Wagon]

Car felt sluggish when I put a stock tune in it. Cam, headers, dual exhaust, k&n air filter. Of course no smog equipment at all.

[bk2life]

felt sluggish

well duh..
of course it will.
that is why we tune.
but a mild combo with a small cam should start and run with a stock tune.
then the fun of tuning cmoes into play.
A small cam means more air/fuel/timing should be a pretty easy tune with MAF

[HATEHPTUNERS]

BK2LIFE nailed it... It is recommended to start with a STOCK tune as a baseline and then YOU must go in and tune the VE & MAF tables to work with your engines configuration. Too many times "wonder tuners" have hacked on a tune and it's FASTER and SAFER to just start over with an all stock tune, as opposed to chasing your tail attempting to fix a tune that has bad changes made to it by a previous hacker.. er, I mean "tuner". Sometimes, as we learn more and more, we look back and realize WE were the HACKER! OHs NOS! Ha ha ha

[67Wagon]

Thanks guys for the advice. What order do you recommend tuning VE>MAF>idle airflow?

[67Wagon]

Alright I have the LTFT down to +/- 1 % during cruise. Tuned my spark map, STIT is within .1 g/s. I am still having an issue where the rpm is increasing by 125 rpm 40 seconds or so after I start the car. It doesn’t matter if it’s in open/closed loop, adaptive set to zero. Any other ideas on what I can do to fix or band aid this?

One other thing to add is this is a 12606960 OS. Is there another OS that I can write onto this P59 ECU to remove? This is a 2004 DBW setup.

[gametech]

One of the few threads I read where someone resolved this issue involved swapping to a 2005 Sierra OS, but the guy did not post which OS number he used.

[67Wagon]

I have a 2005 Silverado with a 5.3 that’s is an identical setup minus the cam. I was thinking of reading and writing the calibration to this ECU. Since it is a P59 controller already, would there be a major issue with this I think the OS is 12592618. My ECU hardware is a 12586242.

[67Wagon]

All,

I just wanted to let the forum know that this flash with the 618 OS with a "write entire" solved my problem!! There is something in the 04 OS that causes this phenomenon. There are a couple things that I need to tweak now with the new OS, but it idles every time to the set rpm. With that said, I was wondering if you would be able to look at my latest tune and give any feedback of parameters that need to fine tuned that I may have missed. I finally see the finish line...

[gametech]

At least now when someone searches for this problem, an actual working OS # will show up in the results.