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Chevrolet Repair/1990 GMC Z71 4X4

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QUESTION: Tom, I went ahead and replaced the fuel pump in the tank. I also replaced the coil. I'm still having the problem with the truck stalling. I have taken the truck to 3 different shops & all 3 say there's nothing wrong with the truck. One of the shops did the dead head and said everything seems ok. I also pulled the fuel tank, washed it out, blew out the fuel lines, installed a new glass bulb fuel filter. If I would have know that owning a truck of this type, I would have never bought it. My other trucks are a 1975 gmc 3500 & a 1965 gmc 3/4 ton

ANSWER: HI KEN,,I KNOW THESE PROBLEMS WILL DRIVE YOU TO DRINK, BUT THERE IS A WAY TO ZERO IN ON IT..
I THINK IN MY PAST ANSWER TO YOU I TOLD YOU THAT WHEN THIS HAPPENS YOU HAVE GOT TO FIND OUT IF IT IS A FUEL OR IGNTION PROBLEM...WHEN WE HAVE A CAR LIKE THIS AT OUR SHOP WE DRIVE THIS WITH ALL OUR TOOLS WITH US TILL IT STOPS RUNNING..WE GET OUT OF THE CAR AND TEST FOR FUEL OR IGNITION...IT IS ONE OR THE OTHER THAT HAS FAILED..ONCE YOU ZERO IN ON THIS IT MAKES THE JOB MUCH EASIER...YOU COULD CARRY AROUND SOME STARTING FLUID AND WHEN IT HAPPENS SPRAY SOME DOWN THE THROTTLE BODY AND SEE IF IT STARTS UP...IF SO WE KNOW IT IS A FUEL PROBLEM. IF NOT MORE THEN LIKELY IGNITION FAILURE...THIS COULD ALSO HAVE A WIRE HARNESS ISSUES...THESE ARE THE WORSE PROBLEMS BECAUSE YOU DONT KNOW WHERE TO START LOOKING OTHER THEN REMOVING THE HARNESS AND CHECKING ALL THE WIRES INSIDE..THIS IS REALLY SOMETHING I WOULD NEED TO HAVE HANDS ON TO ZERO IN ON IT...I FEEL BAD THAT YOU REPLACED ALL THE ABOVE PARTS AND STILL HAVE THE SAME PROBLEM...THIS COULD ALSO HAVE COMPUTER PROBLEMS..HAVING A SCAN TOOL HOOKED UP TO THIS WHILE DRIVING WOULD HELP TO FIND OUT A FEW THINGS AS WELL...GOOD LUCK TO YOU ,,,TOM......

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QUESTION: Tom, I contacted a local college that I use to be part of the automotive staff & I know one of the automotive instructor. If I can get by till the first of the year, I can get some shop time to put the truck on the dyno and run the truck through with OBD1 PCM reader in place as well as an oscilloscope. I went ahead and replaced the fuel pump & ignition coil just because. I have a friend that's the manager at the Napa distribution center here in town & I can get parts at cost. I'll keep trying to figuring it out. I like the mileage I get with the truck compared to my other gmc trucks, (6 & 8 mpg) I drove the truck on the freeway almost 250 miles, kept my speed at 55 & didn't have a problem. After I got back home, the next day I drove the truck 65 - 75 mph and it stalled after about an hour. One other thing, I cant see where it would make a difference but when I bought the truck it had 245/75/16 wheels on it. 2 of the wheels were bent so I pulled a set of wheels off a 73 K5 blazer, drilled out the stud holes and mounted them on the gmc. they're about an inch and a half shorter than the stock wheels that were on the gmc. I just thought I'd put that in there because I didn't know if the gmc has some kind of speed sensor that could be causing the problem.

ANSWER: HI KEN..THE SIZE OF TIRES OR WHEELS WOULD MAKE NO DIFFRENCE ON THIS PROBLEM...LETS START OVER..
WHEN THIS STALLS DOES THIS START RIGHT BACK UP OR DOES IT TAKE A WHILE TO RESTART ???IF IT TAKES SOME TIME TO START FIND OUT IF THERE IS FUEL OR SPARK AND GET BACK TO ME...TOM...PS I AM GLAD YOU CAN GET PARTS AT COST..THIS HELPS YOU ALOT...

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QUESTION: When the truck stalls, it will start right back up most of the time but it cant be driven. If I put in into gear and try and drive it, it stalls out again but it has always started right back up. Also if I don't put it in gear I can rev the motor way up with no problems. To drive it I have to wait at least an hour. I've tried driving it at 15 minute intervals and its a no go till 60 minutes.

Answer
HI KEN,,THIS ALMOST SOUNDS TO ME LIKE THE IGNITION SYSTEM IS FAILING. THE REASON I AM SAYING IGN FAULT IS BECAUSE AFTER IT COOLS DOWN IT STARTS AND IS OK FOR A BIT... WITHOUT LOOKING AT THIS AND GETTING HANDS ON TIME ITS A GUESS. BUT I HAVE HAD PROBLEMS IN THE PAST ON THIS YEAR WITH BAD DISTRIBUTOR PARTS [MODULE, PICK UP COILS AND POLE PIECE.]IF I KNEW THAT THE IGN SYSTEM WAS SHUTTING DOWN I WOULD BE LOOKING INTO THIS REAL HEAVY. I DONT KNOW, THATS THE PROBLEM..IF YOU PUT A TIMING LIGHT ON THIS AND SEE IF THE SPARK FAILS BEFORE IT STALLS WE COULD ASSUME A IGN FAILURE...I HATE TO TELL YOU THIS BUT I WONDER IF YOU COULD GET A NEW OR USED DIST FOR THIS..THE OTHER REASON I AM GOING WITH THIS IS THIS YEAR DIST HAD A SPARK RETARD
SYSTEM IN THE DIST. [ELECTRONIC SPARK CONTROL]THIS COULD BE RETARDING THE TIMING SO MUCH THAT ONCE YOU PUT IT IN GEAR IT WONT MOVE.NO POWER WAY RETARED..IF NOT IN GEAR IT WILL REV UP...I WOULD GO WITH A DIST...DO YOU FEEL LUCKY ???? LET ME KNOW WHAT YOU DO WITH THIS...GOOD LUCK TO YOU,,,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.

Organizations
nys state auto repair industry and ase group.

Publications
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

Past/Present Clients
MANY CUSTOMERS IN OUR BUSY SHOP.

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