Hey guys. In my first attempt to modify a bin file with tunercat, I'm trying to eliminate the flat spot I see at close to 4000 RPM on the tach. What happens is when I get close to 4000 RPM in third gear at WOT the RPMs drop a few hundred RPM then they start creeping back up. Could it be going lean or not have enough spark ? My Diacom doesnt show ANYTHING unusual at that spot except of course the RPM drop and a slight leaning out like a drop of about 50 mv... What do you guys think I should play with in the bin ? Thanx

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92 Z28 L98 350
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Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

Blade,

That is the Mandatory Torque converter lockup point. No matter what ... the ECM commands TC lockup at that MPH. If you plot your Vehicle Speed you'll notice that the speed still increases even though your RPMs drop.

The newest TC calibration file has a setting in the ECM Constants section called "TCC Unlock Prevention Speed Threshhold". That should be the mph that you see your RPMs dropping. Only problem is ... even if you bump up this setting it doesn't seem to work I verified that TC is using the correct BIN addresses. They are 100% correct ... but, I think that I am still seeing lock. Modify this parameter to a higher mph ... like 115mph. Burn a new chip and then try again. Let me know if it works for you.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.587 @ 107.97mph (1.710 60ftr) on the long runner setup.
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels. Stock Wheels. No Weight Reduction.
Gunning for NA 11's with the MiniRam II and Hooker LT Headers.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

I had the same problem but found a "hardware" solution to it. A friend and I confirmed with a scan tool that the TCC is (as Tim said) locking up at WOT. I installed a TCC lock-up harness that keeps the TCC from locking up in any gear but 4th. Poof! Problem gone! The harness installs between the 4-pin harness going to the tranny and the corresponding connector on the left side of the tranny. You can find one for about $35-40 at Summit or Jegs...

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Greg Westphal
'87 IROC 305TPI/A4

 

AHA! So that's what that is! LOL Maybe I should install a switch and just lock it anyway while I'm racing....

 

I bet if you defeat the tcc your times will get slower......heeehe. Read the hard rock camaro articles, they lock up the converter in 2nd gear and et is reduced and that car is pretty dam impressive to me.

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87z 383. mini ram tremec 5spd, funny gas, 1,3/4"headers. other stealth goodies.

 

Actually, my IROC got faster, as in better trap speeds, since my engine could rev higher going through the traps. Plus, my Precision Industries 2200-stall (more like 2400) converter is pretty efficient, so I wouldn't gain too much. Just MHO...

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Greg Westphal
'87 IROC 305TPI/A4

 

That's what I think too. I watched mine on diacom and the speedo and NO the mph is NOT climbing and it only seems logical since the RPMs of the engine are not either. LOL