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Bonneville GXP/ Northstar Powered Cars Discuss your Bonneville GXP and/or any other Northstar powered Olds or Cadillac... Including the 3.5L Twin Cam V6 (Short Star ) 4.0L and 4.6L Northstar V8's. Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 05-06-2008, 02:28 AM   #1
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Default 4.0l 98 Aurora surging

My new to me 98 Aurora 4.0l works great except for one thing I've found. Sometimes, when you are cruising at 70mph -ish, the car rpm'* will shoot up for no apparent reason. It is obviously downshifting and I don't know why. It will do a few short "vroom vroom'*" up around 3500rpm then go back to where it is supposed to be. And when this happens, the cruise kicks off too. And it is sporadic. I've had it happen to me once, and my girl drove on a 180mi trip and there was about a 5min period where it was acting up as such. She said "I think the injectors need to be cleaned." I politely said "Maybe." What are your thoughts- some sort of speed sensor needing replacement maybe? It only occurs at 70mph.
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Old 05-06-2008, 02:30 AM   #2
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No clue, I would drive 75 then. LOL

Not familiar with those engines, but when was the last tune up?
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Old 05-06-2008, 11:07 PM   #3
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Seems to have a hard time staying in TC lockup.
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Old 05-08-2008, 02:30 AM   #4
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Thanks for the responses.

One other thing that I forgot to mention- when the rpm'* surge, the speedometer swings down. So when the rpm'* go from cruising at 1600rpm to 3500rpm, the speedometer goes from 65mph down to 30mph for short spikes. Also, it happened at around 35mph today. I'm thinking it is something electrical- hopefully a simple sensor? I dunno, any other thoughts would be appreciated.
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Old 05-12-2008, 08:49 AM   #5
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Default Speed Sensor

It sounds exactly like what was happening in my GXP. Mine was caused by a bad speed sensor. I had it replaced and everything was fine again. You might want to check for that. Good luck!
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