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Chevrolet Repair/1995 -c2500 Chevrolet 5.7 tbi stall hesitation rough

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QUESTION: A few weeks ago, my truck stalled a few times, once in a parking lot, once after coming off highway after a 25 minute drive - pulled over and it started, the parking lot incident took a few times as it would start and stall. Last week, I started truck at idle every minute or so rpm dips as though it's going to stall but doesn't. I drove it and it would not accelerate - Rpm go up but doesn't go more than 20-30 km - transmission fluid good - I decided to check fuel system- replaced fuel n air filter, sprayed tbi, checked fuses n relay - truck tuned up 6 mths ago - distributed cap, wires, plugs, rotor, fuel filter. A few days ago started it - went on highway and side streets - worked well - it was a warmer winter day - today - starts and stalls - I start it again and give it gas and it runs rough - not really rocking back and forth rough but dips in rpm.  Would love to isolate problem - can it be fuel pump?

ANSWER: MORN JOHN,,WELL THIS WILL TAKE SOME DIAGNOSTIC TIME TO GET TO THE BOTTOM OF THE PROBLEM..I THINK YOU MAY HAVE 2 PROBLEMS ONE BEING THAT WHEN YOU ACCELERATE AND THE RPM 'S GO UP BUT TRUCK DOES NOT MOVE AS IT SHOULD SOUNDS LIKE TRANSMISSION PROBLEMS FOR SURE..IF THE RPM'S DID NOT GO UP AND IT JUST STAYED AT ONE SPEED THIS WOULD SOUND LIKE FUEL PRESSURE PROBLEMS TO ME..
AS FAR AS WHEN YOU STARTED IT TODAY AND NOW IT RUNS ROUGH [ROCKING BACK AND FORTH THIS SOUNDS LIKE A IGNITION PROBLEM..YOU SAID IT WAS RECENTLY TUNED...LETS TRY TO GET THE ENG RUNNING GOOD FIRST,GET YOURSELF SOME FUEL INJ CLEANER OR CARBURETOR CLEANER AND OPEN THE THROTTLE PLATE ALL THE WAY AND SPRAY THE [BACK SIDE]OF THE THROTTLE PLATE OFF USE A RAG IF NEED BE TO GET IT CLEANED. THE NEXT THING AND VERY IMPORTANT IS CK THE FUEL PRESSURE. WILL NEED A GAUGE,BORROW OR RENT ONE..HOOK THE GAUGE UP THE THE FUEL LINE GOING TO THE THROTTLE BODY.YOU WILL SEE A CAP ON THE MAIN LINE REMOVE THE CAP AND HOOK THE GAUGE UP HERE.YOU WANT ABOUT 30 TO 35 LBS..DRIVE IT WITH THE GAUGE HOOKED UP AND TAPE THE GAUGE TO THE WINDOW WHEN DRIVING TO KEEP A EYE ON IT..THESE FUEL PUMPS WILL GO BAD AND DO THIS.IF FUEL PRESSURE IS LOW OR FLUCTUATING PUMP IS BAD OR SCREEN IS PLUGGED... SEE IF THIS HELPS WITH THE LOW IDLE AND SHAKE PROBLEM. [CLEANING THE TBI]IF NOT YOU ARE GOING TO HAVE TO GET THIS TRUCKED SCANNED AND CHECKED FOR DATA,SUCH AS OXYGEN SENSORS, MAP SENSOR AND ON AND ON...THIS MAY SHED ALOT OF LITE ON YOUR PROBLEM..THE STALLING PROBLEM COULD BE SOMETHING AS SIMPLE AS A BAD IAC MOTOR. [IDLE AIR CONTROL]THE LAG WHEN TAKING OFF IF NOT THE TRANSMISSION COULD BE A BAD TPS [THROTTLE POSTIONING SENSOR.] ALSO  LAST THOUGHT,,,CK FOR A GOOD SOURCE OF VACUUM TO THE MAP SENSOR. AGAIN THESE ARE ALL GUESSES. THIS SHOULD KEEP YOU BUSY FOR A WHILE GET BACK TO ME IF YOU NEED MORE INFO AND GOOD LUCK TO YOU,,,TOM..

---------- FOLLOW-UP ----------

QUESTION: I took a look at truck again. Just to clarify, the truck does not rock back and forth- it idles around 500 to 750 rpm and sometimes dips below 500 and tries to recover and often does. I pulled the air filter again and it makes a loud hissing sound. I sprayed it with throttle body cleaner. I put my finger in the carb and under the passenger side injector/pressure regulator and vehicle stalled and I felt gas being sprayed. I put my finger under the driver side port/injector/pressure regulator and felt no fuel going thru. I plugged passenger side with my finger and vehicle did not stall like it did when I block other side with my finger. At the moment vehicle has power and running normal!!! but vehicle has run normal before and then rough again. Any thoughts? should carb be making loud hissing sound. When I sprayed throttle body fluid in passenger side port, engine did little, but on drivers side, surge in rpm. Finally, on closer examination RPM do not go up significantly at 20 km so transmission may not be a problem. It seems like TBI was operating on 1 side/port only? what can cause that and this has been intermittent. Thanks for your help

Answer
HI JOHN, THE LOUD HISSING SOUND IS NORMAL THIS IS THE ENG SUCKING AS MUCH AIR AS IT CAN. OK YOU MIGHT OF JUST FOUND YOUR PROBLEM.YOU SAY THE ONE SIDE INJ WOKRS SOMETIMES..THIS IS NO GOOD IT MUST WORK ALL THE TIME..IF THIS IS JUST GETTING FUEL ON ONE SIDE THIS WILL CAUSE THE PROBLEM WITH IDLE, DRIVING, AND PERFORMANCE ISSUES..WHAT YOU WILL NEED TO DO IS GET YOURSELF A NOID LIGHT OR FUEL INJ LIGHT TESTER OR YOU CAN USE A LIGHT BULB #921 AND BEND THE PRONGS OF THE BULB UP AWAY FROM THE BULB AND PUT THE PRONGS IN THE INJ HARNESS OF THE INJ THAT IS NOT WORKING WHEN THE ENG IS RUNNING..IF THERE IS A PULSE MEANING LIGHT ON OFF ON OFF FLASHING FAST THE PCM AND WIRING ARE OK..THE ONLY THING LEFT IS THE INJ IS GOING BAD..IT IS NOT OPENING ALLOWING FUEL TO PASS OUT OF THE INJ..THAT WAS A GOOD FIND..WANT A JOB ??? ALSO THIS IS NOT CALLED A CARBURETOR IT IS JUST CALLED A THROTTLE BODY UNIT..JUST THOUGHT YOU WOULD WANT TO KNOW THIS..LET ME KNOW HOW THIS WORKS OUT FOR YOU..GOOD LUCK TOM....

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TOM SHEETS

Expertise

PLEASE READ ALL OF THIS BEFORE ASKING ANY QUESTIONS. IF THIS CHEVY SECTION IS MAXED OUT.YOU CAN REACH ME IN THE OLDS/BUICK SECTION. Will answer questions from 6:00am to 10:00pm all days [EST][[[ NO DIESEL OR PAINT QUESTIONS]]] will answer all 1965 to present QUESTIONS ON ALL GM'S on mechanics of these cars. Keep in mind i am not there in person i am going on what you are telling me !! PLEASE IF ASKING A QUESTION GIVE ME AS MUCH INFO AS POSSIBLE. THE MORE THE BETTER. SUCH AS YEAR,MAKE,MODEL,ENGINE SIZE. THIS WILL HELP ME HELP YOU. I will not be able to answer all questions because of some situations that i would really need to be there and see things for myself,such as electrical issues. In many cases i would need wiring diagrams. I can also give you an estimate on what the cost would be at our repair shop as an idea to help you. Keep in mind that my answer is ONLY MY ADVICE,ck with your mechanic as well.. >> THANK YOU, TOM..

Experience

I have been a ASE certified master mechanic for over 30 years and certified IN ALL 8 CATEGORIES,[engine repair,engine performance,auto trans,manual trans,clutches,steering and suspension,brakes,electrical systems,heating and air/cond. I am also a state CERTIFIED inspector for over 30 years. I do computer work [pcm]fault codes,pcm flashing,state inspection monitor readiness,repairs on exhaust,fuel service,[injection and carburetor,] charging system problems, running issues,alignments,frame problems,tire balance,struts and of course standard and anti-lock brakes.

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nys state auto repair industry and ase group.

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N/A

Education/Credentials
high school,4 years of tech school,and many many hours of auto training with many gm classes and aftermarket training classes..

Awards and Honors
ASE MASTER TECH CERTIFIED IN ALL 8 CATEGORIES.NYS INSP LICENSE AND A/C CERTIFIED

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MANY CUSTOMERS IN OUR BUSY SHOP.

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