car cuts out at 4000 rpms on 1995 Buick Riviera

replaced fuelpump. and the car is not showing a check engine light. what could it be

Asked by for the 1995 Buick Riviera
I would check the fuel pressure first as it is critcal. Many things could cause this, too numerous to mention and without driving the car it's almost impossible to tell you. Why did you replace the fuel pump? Was there some other fault or was this what you were trying to fix? Scanning the system might still show something out of range, even without a check engine light coming on.
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ignition synchronizer