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#11 | |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,697
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Maybe Todd can tell us where the Prop Gain tables are for the $AFA, $AF Mask ID. If you're getting a surge, it may be due to too high a Prop Gain. That could also explain the popping exhaust on decel. You'll want to start by lowering the Prop Gain in the <16gm/sec cell. I'd agree with Todd that you'll want to check the #of steps at DFCO and not drop the IAC steps too quickly. Had same issue with my old 84. At some rpm points in DFCO, I'd push in clutch and motor would go dead. Whadya think Todd, would that help? |
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#12 | |
![]() Join Date: Jul 2005
Location: Atlanta, GA
Posts: 81
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My IAC counts are well into the double digits at idle (15 or so). I honestly can't remember what they are during the surge. I'm assuming they run pretty low when it surges. Question: Why does it only do it until the speed goes below a certain MPH? It seems to settle down around 5 MPH and if I blip the throttle when I'm not moving, the idle drops like a rock right to the set idle RPM and doesn't dip at all.
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#13 | |
![]() Join Date: Jul 2005
Location: Atlanta, GA
Posts: 81
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I have the DFCO completely disabled. I don't see any Prop Gain table, is it one of the ones that never made it into the masks?
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![]() 1991 Chevrolet Corvette ZR-1 |
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#14 | |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,697
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#15 | |
Join Date: Aug 2005
Location: Fishers, IN
Posts: 812
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While it is tempting to go in and start changing the calibration, such as has been suggested here, I honestly don't think that is the solution. GM didn't miss the tune on 6000 cars, and they all don't surge. Some things to check... 1) if the condition exists only with the modified cal, is the spark advance smooth in the region of low load, low rpm? Has the closed throttle advance been increased? 2) check the MAP hose for contamination. When I had this condition, the MAP reading at coast down was fluctuating wildly, and causing the surge. 3) if you still suspect the IAC movement is responsible, try to reset the IAC motor as outlined in the service manual. Todd |
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#16 |
![]() Join Date: Jan 2004
Location: Alex VA
Posts: 1,087
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Hi todd,
I have a question, I had the secondaries removed and unfortunately VA has cut the HC standard down to 48. it's made it impossible to pass. car does have cats (random ss, probably not nearly as good as stock) and I haven't yet had a wideband to see how rich the car is running but it seems WAY rich at light throttle. I need some help to tune the car to pass emissions. marc is a bit too far away in chicago. I do have EASE, and I could install a wideband or take the car to a shop with a dyno. the car is an LPE 390 and has the big 234 cams. do you think there is ANY way I can get this car to pass??? I tried doctoring the gas with alchy a few years back when I had the LPE chip in the car (open loop). it was even more rich and I could get the HC down to about 97 running 2/3 alchy, but I don't think that will work anymore, when I last tried the "cocktail" it still was up to 150 HC and I couldn't get the car to run with as much alchy in the gas. I love the ZR-1, but this is a problem any ideas (besides moving) ![]()
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95 390 LPE ZR1 (505 rwhp) LSV = Lingenfelter Super Vette Twin Turbo 2003 Z06 (800 RWHP) |
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#17 |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,697
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Shawn,
I did a search on ThirdGen regarding surging decel. This was in a thread that deals with another ECM, the EBL. I won't go into what ot is but I used it for almost 2 years. Outstanding piece of work by RBob. That ECM in combination with Moates OStrich and Tunerpro RT really changed tuning. So here's RBob's advice: "'Option word 3 - bit 5 - OpDcl' is probably set. This will put the ECM in open loop fueling during decel. Once un-set, you may experience surging during decel. If so it may be either the proportional gain at the gms/sec airflow is too high. Or the ECM is switching in and out of async fuel mode. DFCO, to enter this the vehicle speed needs to be above the MPH parameters, and the RPM above the RPM parameters. This is usually for highway speeds on a thottle lift. Keeps the CAT(s) from melting. RBob." Here's the link to that thread. http://www.thirdgen.org/techboard/di...=surging+decel Granted EBL code is not the same as our LT-5 stuff but I think you'll find that the controls do pretty much the same thing. Its just that RBob has provided an .xdf which makes all those paramters available to the tuner along with a bunch of tuning aids. I agree with Todd that first and foremost you make sure everything is "mechanically" correct before turning to the tune. As a side note, if any of you don't know RBob, he is one of the more highly knowledgeable sources over at 3rd Gen. Heck of a nice guy too. I keep begging him to build a version of EBL for our LT5s. ![]() |
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#18 | |
Join Date: Oct 2007
Location: lone pine and mammoth lakes ca.
Posts: 544
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#19 | |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,697
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RK, I would definitely put a WB on it. Is the issue you're having at idle or all through the rpm band? |
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#20 | |
![]() Join Date: Jul 2005
Location: Atlanta, GA
Posts: 81
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