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RPM'S Fluctuate

Tiny
HARRYCQ
  • MEMBER
  • 1988 OLDSMOBILE CUTLASS
  • 5.7L
  • V8
  • RWD
  • AUTOMATIC
  • 10,000 MILES
My engine is from Jegs and has been in the car for about three years. Everything is pretty much brand new under the hood. I just recently put a brand new fuel pump in about a month ago. I am driving to school this evening and my car is sputtering. The rpm's are going up/down while on the highway at about 50-60 mph. I did not want to go faster than that just in case. I look under the hood everything seems good.
I actually did run out of gas earlier this week, and that is when the rpm's began giving me a problem.
Not sure where to turn to, thank you in advance!
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Thursday, July 14th, 2016 AT 12:21 PM

3 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Is engine stock? Any modifications? Check for a vacuum leak and check fuel pressure with a gauge. Auto parts rent it. Is this carb or injection?
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Thursday, July 14th, 2016 AT 5:20 PM
Tiny
HARRYCQ
  • MEMBER
  • 2 POSTS
It is not stock. It is a rebuilt from Jegs motor 359 with a carb that is brand new. I checked all vacuum lines as well
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Saturday, July 16th, 2016 AT 4:51 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check under carb for vacuum leaking there and has this only happened since carb was installed? If it is then check the carb. Also see if the carb has an adjustment it may need that because of running to lean or rich. Finally check vacuum at intake with a gauge get back with reading at idle.
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Saturday, July 16th, 2016 AT 5:55 AM

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