I've run across this problem recently in two cases, while reviewing LT1 data logs for members here. The engine is idling (TPP = 0%, VSS = 0) in Cell 5 or 8. It is not going to Cell 17 on decel. In both cases the PCM's have a custom tune, and in both cases the MAP at idle is borderline to setting a code (60-65kPa). In both cases, the engine is holding programmed idle RPM (800 or less), TPS volts are in the 0.60V range, no codes.

Not being a "programmer", what is causing this to happen? Is it an issue with the Cell boundaries?

 

I would like to know also...It seems no matter where i set my blm cell boundaries at it doesnt idle in cell 16. So i just put it back to the stock settings. Im stumped and would like more info into this as well.

 

Yours would be one of the two cases I'm asking about. The other is Chaos1187.

 

Right now it idles at cell 5 and sometimes cell 9 it goes to cell 10 at speed like on the freeway but never goes to the correct cell when decelerating.

Im starting to think there might be another setting in the pcm that controls when and where cells go.

 

Not directly the same symptoms, but I have read in a couple of posts (not personally experienced) that altering the emission settings incorrectly will cause incorrect BLM cell selection. In those cases it was sticking in cells16-18 and not using 0-15 after incorrectly setting EGR disable constant table entries. Which is completely opposite the symptoms in this post. But it does indicate there are other factors in the PCM software, in those cases, emission settings, that that effect BLM cell selection that are not published. Would be interesting to pin this down, but would be time consuming returning tune settings to stock till the problem cleared up, if it ever would. Also not to get to far off track the mystery of BLM cell 18 selection process and what TPS%, speed, MAP,etc the PCM uses to make that decision.

 

I've noticed the ...DAMN... log operating in Cell 1, with 40+kPA MAP readings, which would indicate the boundaries have been changed from stock. I assume when you have a cam that doesn't pull much vacuum, that it would make sense to realign the Cell boundaries to spread the Cells over the actual operating range of MAP/RPM, rather than assign part of it to low MAP operation, which never occurs.


....DAMN... - have you asked the tuner about this? As I recall, it's one of the name people that everyone here uses. I also believe you bough the car in this condition, and do not know the cam size. Someone told you it was "small", but the MAP is very high at idle. Maybe the tuner would have a record of the input sheet for the tune, showing the cam specs.

 

A little misunderstanding here lol ive owned the car for a couple years and when i had it tuned it still had a stock motor with a couple bolt on's. Only recently did i swap in this new motor which was in my friends car he said the cam was pretty small around a lt4 hotcam specs but he couldnt remember the exact specs.

And your right realigning the cell boundaries has no affect of how the cells change. I have been able to come across some "stock 95 a4" tunes i am going to try out to see if my cell's start working again.

 

I solved my cell problems...I loaded a stock 95 A4 bin and the car now idles in cell 16 and uses all the other cells as required! I am still unaware of what was causing the other tune to act in that manner.

Now i finally have a normal base to begin my own tune lol.

 

DAMN.. would you be willing to email me a copy of the defective tune, since it's from a tuner I'll treat it as proprietary and not share or copy it. I would like to see if I can identify what was changed to block the BLM's from working correctly. By the way I changed my BLM Cell MAP boundaries w/o any problems ... with my LT4 Hot Cam as I was never entering cells 0-3 (MAP < 32 Kpa) , jacked it up a little to 38 Kpa and the 50 to 54 to get a more even usage of all cells. For reference my hot cam 214/228 112 lsa .525 lift w/1.6 RR's idles at about 48-52 Kpa @ 850 RPM (neutral) if that helps identify what cam grind you have..

 

Pm me your address and i will send it on over. Let us know if you find anything out.

 

PM sent..

 

Your on the right track about the boundry being move to meet the operational range the cam now provides. I would suggest increasing ignition timing at idle until the vacuum increases and lowers the Kpa number as far as it will go. Sometimes I get a car that needs 32 degrees at idle and will still only get down to the low 40's high 30's. Its a process for damn sure.

Chris

 

I have noticed the same thing on powerdyne programms for the impala ss lt1 and some camaro applications. The programmer they used was from colorado and they were 4500 feet above sea level. I argued for a month that the tune was wrong. I found that when i would go into cell 16 the car wouldn't idle and stall out. On some of them one side of the engine would go full lean and the other side would go full rich and run like crap. The computer did not have the capabilities to make the amount of changes required. I did some tuning on their tune with the maf and got it to idle perfect. Just my 2 cents.

 

Thanks to injuneer i found this thread haha. So my input as far as adding to this is I do have the same problems with where the car idles at odd cells. I am willing to swap pcm or send it out for a factory tune and put in the size tires and gears Ill be running etc as I will need it anyways.

However I noticed byrons mentioned messing with setting on the MAF sensor in the pcm, my stock MAF sensor has been descreened by the previous owner dont know if this would be of concern. As well there is no thermostat....And I haven't found any other oddities (word?) that I know of. I would like to ask is there anyway that the cells may have gotten corrupted somehow a fault in the programming and it set to a different default because of it??

I know for a fact that the people who were messing with the car before me had no idea what they were doing. It has shown all over the car and well as we see continues to do so.

 

A miscalibrated MAF sensor will not cause the PCM to use the wrong Cell. It will not corrupt the files. The cell is defined by MAP and RPM. If the engine doesn't operate at the MAP and RPM used for the Cell 16 boundary, it can't use Cell 16. You have the same problem as .....DAMN.... - high MAP readings at idle.