JB_97ws6TA

iTrader: (6)

Doing a dyno pull to see where AFR is and it seems to stay in closed loop at 14.7 AFR. TPS voltage is 4.67 at WOT. The PE is set to 66% <2800 rpm and at 28% at >2800. It is a madtuner mail order so I called him to take another look at the tune and he said that everything looks correct. What are some reasons for the PCM to not go into PE? I don't have the foggiest idea when it comes to tuning but I really need to get this figured out. If it helps the rundown is as follows:

LT1 383 m6 with trickflow 21* heads
11:1 compression
BBK 58mm throttle body
longtubes with AIR/EGR

The motor and supporting mods have ~500 miles on them for break in before going to dyno. Almost everything is unproven as it was new when the motor was built. Any suggestions/info is appreciated!

Thanks,
JB

JB_97ws6TA

iTrader: (6)

also...fuel pressure is at 48 at WOT and it has freshly serviced and flowmatched 42# SVO green tops

joecar

Are the two delay tables set to zero seconds...?

Is the PE MAP Enabler set to low value (e.g. 15 kPa)...?

JB_97ws6TA

iTrader: (6)

I believe the enable is set to 15kpa but like I said I am by no means a tuner and have not looked at the tune itself personally. The technician at the dyno has a JET DST and looked everything over and he said everything looked fine and that it must be a mechanical problem but I am not sure what it could be. As for the delay tables I have no idea they had them on LT1 computers I had heard about them in trucks just in my crash course in tuning over the last 2 days trying to figure this out but I will definately bring that up to the technician. Is there anything other than the tune that could cause the computer to not enter PE? Could the computer itself be bad?

joecar

Oh, sorry, LT1, I did read rather quickly, forum section is "LS1-LS2-LS3-LS6-LS7" but you did specify LT1 in post #1, so my bad (I should slow down)... so IDK about LT1 PE delay...

PE is triggered by TPS... so check that TPS reads correctly.

Slowhawk

iTrader: (12)

Are you sure it's not going into PE? It could just be lean at WOT.

BLK02WS6

iTrader: (2)

^ what he said! You should also be able to see if it goes from Closed Loop to Open Loop when you go WOT on a scanner.

JB_97ws6TA

iTrader: (6)

at first that is what we thought was that it WAS that lean at WOT so the tech started adding fuel in the PE table and the AFR remained the same. After 3 or 4 adjustments and the AFR never changed we started to troubleshoot possible wideband issues so we swapped out the oxygen sensor on the dyno for another known good. WHen it read the same we then swappped banks to rule out possible exhaust leaks or misfires. When it also read that lean we then verified the dynos AFR with yet another oxygen sensor and a standalone innovate wideband. We then concluded that it must not be entering PE mode and that is why adjustments to PE have not effected AFR. We chacked TPS voltage and looked at the PE enable and everything checks out...WTF??? I don't know if this is the wrong section but I figured my best bet to get a GOOD answer was in here so if I am wrong I apologize but I really do appreciate the help

flame

iTrader: (13)

Still running a MAF? Is it dirty and not reading the airflow properly which in turn then the pcm doesn't give the correct amount of fuel?

ramairJP

iTrader: (3)

You need to log your commanded AFR to see if PE is doing its job.

WeathermanShawn

iTrader: (1)

I have had a similar experience once or twice on a 2002 LS1 at lower Rpms like you are describing. I could have swore it was not entering PE Mode..but it was.

Here is what I figured out. At lower Rpms a lot of time your Airflow (VE/MAF) are just too low for the Rpm. The PCM computes a fairly low CYLAIR and even though you hit PE Mode, there is just not enough fuel. I have seen that where Rpms are ~2400 and MAF Freq may be 6500 Hz..airflow ~100 g/s. In my case I was just simply bogging..and I could hear pinging and logged a little KR. Once I dropped a little Spark Advance in that region..no pinging or KR and on the next run the Airflow was much higher and PE Mode Commanded AFR matched actual.

The only thing I can think of PCM-wise is I wonder at low Rpms and depending on what FTC cell you are in, if EVAP interferes with PE or if there is an issue with the FTC matrix..you can not get into PE Mode. Of course logging can tell you all that.

The bottom line is this. Overall, you might have a harder time hitting Commanded AFR's at lower Rpms and airflow. You can chase it by calibrating for more airflow at those Rpms..but that can create problems at other Rpms and TPS %'s..I.E. you might be richer in PE Mode at part-throttle in another gear.

If you do another dyno run and cannot get into PE Mode at any Rpms, there is a real problem. Otherwise I would just slowly ramp up fueling below 2800 Rpms and get your Commanded AFR at peak TQ to match actual.

Sorry for the essay, but I fought over a similar issue recently. This is all personal theory. Can not really 'prove' it, but I did solve my PE problem using this method. Hope that helps..

JB_97ws6TA

iTrader: (6)

thanks for all the help guys, I guess it was going into PE but it needed quite a bit of fuel to get the AFR down. The tuner added a ton of fuel into PE then went back and adjusted the VE and it came in thankfully.