Auto Parts: ENGINE STUTTER, vacuum leak, vacuum line

Question
ON A 1991 SILVERADO 350 SFI V8 2 WHEEL DRIVE I HAVE REPLACED THE FOLLOWING DISTRIBITOR CAP AND ROTOR,SPARK PLUGS AND WIRES,GAS LINE FILTER, IGNITION MODULE (BURNT OUT), MOST OF THE ECM SENSORS MAP, THROTTLE POSITION, EXHAUST OXYGEN,PVC, EGR,ETC UNTIL THE SERVICE ENGINE LIGHT WENT OUT AND NO MORE CODES APPEARED ON THE ALDL DATA LINK.I HAVE ALSO SET THE TIMING PROPERLY.  THE ENGINE RUNS VERY STRONG AND EVEN IF YOU TAKE IT EASY WITH THE GAS PEDAL, BUT IF YOU TRY FOR TOO MUCH PEDAL IT BOGS DOWN LIKE ITS GETTING TOO MUCH OR NOT ENOUGH GAS. I MEAN YOU HAVE TO BABY IT OR YOU GET NO PICKUP. ONCE UP TO SPEED IT RUNS GREAT, ITS JUST GETTING THERE THATS THE PROBLEM . HAVE NOT TOUCHED THE THROTTLE BODY OR INJECTORS YET. HELP ?????????

Answer
Hi Dino,

Just a guess, but part-throttle (off-idle) engine shuddering is usually cause by an improperly routed port-vacuum line. Your EGR may be opening on part-throttle creating a huge vacuum leak and introducing too much recirculated gasses. Your fuel-rail regulator vacuum may be stopping at off-idle causing an increase in fuel pressure at the injectors which would cause a partial flooding event at lower engine speeds. I would say that vacuum would be the first, or in your case, the next thing I'd check. I can guess all day...

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Thanks for the question, I hope this information was helpful to you.
Fred
Knucklebusters Used Auto & Truck Parts, Inc.
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