drperformance

iTrader: (5)

My 95 LT1 engine surges when in closed loop and I can not figure out what is causing it. I have checked near every thing a couple of times now and I stillo can not find what is causing it. When it surges my wideband says that it is bouncing lean, but when I unplug the O2s and force open loop the the car runs great. So what sensor could cause this in closed loop?

I have already:
replaced opti with complete MSD
replaced both O2s
replaced map
checked plugs and wires
checked for vacuum leaks
checked for exaust leaks
replaced icm
checked the coil

drperformance

iTrader: (5)

Any Ideas?

AMigs87IROCz

First stop throwing parts at it....save yourself from the poor house!! K.I.S.S. the situation...how about the following:
-Closed/Open loop happens by the thermostat heating up and opening in junction with your temp. sensors...that info is fed to the computer.
-What is your temp gauge reading?
-What is the scan tool( if u got one) reading for engine temp?
-Have you tuned/flashed the ecu lately?
-Will this surging happen after car is fully warmed up or after some hours of driving?

...when you say "surge" what exactly happens...idle get rough....car stumbles like a dead cylinder....rpm hunting??
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check engine light...pending codes??

drperformance

iTrader: (5)

The car was tuned by PCMforless and it starts rpm hunting the second it hits closed loop. I can watch the tach bounce a couple hundred of rpm, and when driving it wants to die at stop lights, when shifting gears, and I can feel it when driving at a steady speed. My Wide band says that it bouncing lean when it surges. This does not seem to be temperature related, it does it cold or hot the second it hits closed loop. And from monitoring my scanner and temp gage my car consistently runs at 180 with a 160 thermostat but I am unsure at what temp it goes into closed loop.

And like I said if I keep the car in open loop it runs great.

AMigs87IROCz

EGR valve? My camaro did that...I couldn't differentiate if only on closed loop but my surging and stalling at idle was my EGR valve not doin' its job...have you tested it?

drperformance

iTrader: (5)

The EGR has been deleted and programmed out, at least PCMforless should have.

drperformance

iTrader: (5)

Some other guys VSS post remined my of something about my car. After I stroked my LT1 to a 383 and had the computer reprogrammed by PCMforless it gave me code 97 (VSS ouput low)? I tried a new VSS and still the same problem? The only other thing that I could think that would effect this was the output shaft, since I just rebuilt the tranny and cryoed the output shaft. But everyone assured me that it would not effect the VSS. So I ended up sending my computer back to PCMforless and having them delete code 97 from my computer.

Could this be causing my hunting or surging in closed loop?