'95 LT1 tip-in Stumble in SD mode?

[EagleMark]

What are cam specs @.050 ?

Need WAY more timing and higher idle. 96 MAP is nuts.

Do need to disable EGR...

HTH!

[sherlock9c1]

From LS1 tech's website: stock B-car cam: 191/196 0.418/0.430 lift 111 LSA. (don't know for sure but assume durations are at 0.050" measurements).

This car has a 2005-vintage pcm for less tune in it. It was always punchy off idle but never had the stumble until I disabled the MAF and whatnot.

[EagleMark]

MAF was adjusting fueling. SD your VE is way off.

2. Zero degrees seems low but I suppose at that rpm (400-600) and MAP (96kPa) that's expected?

zero degree timing and 96 MAP at idle?????? come on? Seriously?

I haven't looked at the log, will do so in AM. Is there any DTC/Error codes?

[RobertISaar]

that sounds like the "stumble" coming off of idle...

also, the ONLY tuning you do with EGR enabled is EGR fuel compensation and EGR added spark. having it on at any other time will skew everything else.

[sherlock9c1]

zero degree timing and 96 MAP at idle?????? come on? Seriously?

As Robert pointed out, this is during the tip-in event itself. Throttle opens, engine RPM goes down, then MAP goes way up. Normal idle is around 30-ish kPa.

I haven't looked at the log, will do so in AM. Is there any DTC/Error codes?

None of any significance. This car never locks the TCC for some reason (haven't hunted that down yet) so I wired in a manual TCC override switch that occasionally triggers a TCC Stuck On code.

[sherlock9c1]

Update - based on what the short term fuel trims (STFTs) were doing during the stumble, I added 13% fuel across the board to 400-1000rpm and 45-100kPa and then smoothed the 1200rpm line 45-100kPA into the 1400rpm line. I also changed the EGR min/max rpms from 600/2400 to 900/2500. The stumble has gone away although I did discover the car has a cold misfire under load that was masking the solution. Gotta go chase that now too. But.. once warmed up, the stumble appears to be gone.

[EagleMark]

Have to clear that MALF 85, it says the TCC is stuck on, also a bit is set that says Trans MALF has occured, never know what PCM is going to do differantly for each error/MALF code?

Also saw a bit set for TCC temp, it came on and off a couple times, as does low oil bit when you take off. But these are nor errors, just indicators.

If TCC is stuck on... well it will cause a stumble off idle, no slip, or partial slip.

Your STFT and LTFT look great. O2 look fine. I can't see anything to cause the stumble, but I did see the stumble.

1995 has a PWM TCC, so direct on switch is not a good idea...

[sherlock9c1]

I should clarify - I built the transmission in this car, and I installed a TransGo HD2 kit and physically disabled the PWM control of TCC lockup in the valvebody while I was in it. I put the switch in because at the time I was not aware of how much you coul do via programming. The TCC never automatically locked on this car ever since the day I bought it. Maybe I should start another thread on that?

On a side note, honestly, if I had to do it all over again, I'd put the Sonnax fix in and re-enable PWM control as the part-throttle TCC apply can get pretty harsh. The other thing I found out is that the stock TCC regulator valve limits TCC internal pressure to 80psi, but when you lock it open like the common redneck fix was, you let full line pressure hit this 12" diameter converter - that's a lot of surface area for that pressure to act on and push between the transmission and the engine.

[bobdec]

Sherlock9c1, looks like when you hit the throttle at record 5361 you basically stalled for fraction of a second MAP shot up and drove you onto the upper right of main timing table to very low or negative timing settings. Your VE main table looks stock at 400-599 RPM row but then goes 8-10% on the lean side (high settings) starting at 600 RPM row. EG: at 40 Kpa 600 RPM you VE cell is 70.7 efficient when stock is 62.1 so you are (70.7-62.1)/70.7= 12.1% leaner than stock in that cell. Since adding fuel helped looks like you got this fixed. As far as EGR emission test is 15 and 25 MPH on dyno. Just figure out what gear and RPM you will be in and make sure EGR is enabled at that RPM. Otherwise it may fail the NO test. I set mine around 1200 RPM enable (back in the days when required). Usually EGR disables at low vac (high MAP) your was engaged at 87.5 Kpa, that's abnormal.