1990 Chevrolet Truck Runing Rich

I DON'T KNOW WHAT YOUR ORIGINAL PROBLEM WAS

I'M MORE OF A JEEP CJ KINDA GUY. AND OLDER CARBURETED STUFF

I AM UP ON SOME OF THE NEWER STUFF, I MAY BE ABLE TO GUIDE YOU ON SOME THINGS YOU MAY BE OVERLOOKING

CHECK OUT THE SECTION ON "HOW TO TIME YOUR VEHICLE" IN THE CHILTON. MAYBE YOU JUST VIEWED THE SPECS CHART AND MISSED THE ACTUAL PROCEDURE

ON MY JEEPS, YOU MUST DISCONNECT AND PLUG OFF THE VACUUM LINE TO THE DISTRIBUTOR TO PERFORM THE PROCEDURE (THEN HOOK IT BACK UP). YOU MUST ALSO INSURE YOU ARE AT THE PROPER IDLE SPEED WHEN YOU DO IT, OTHERWISE, THE MECHANICAL ADVANCE (IF YOU HAVE IT) WILL MESS YOU UP

YOURS MAY HAVE A VACUUM LINE OR A WIRE THAT YOU MUST TAKE LOOSE. LOOK IN YOUR BOOK!

ANOTHER MISTAKE IS USING A TIMING LIGHT WITH AN ADVANCE DIAL ON IT. FORGET THE DIAL, SET IT TO ZERO, WE'RE NOT IN NASCAR OR NUTHIN'. UNLESS YOU ARE SUPER COMPETENT ON USING THE DIAL.I USE A PLAIN JANE TIMING LIGHT, WORKS JUST LIKE THE ONES FROM THE 1940s

ANOTHER THING THAT MIGHT FOOL YOUR TIMING IS A "SLIPPED" HARMONIC BALANCER (ON OLDER STUFF ANYWAY).I'LL SEND AN EXPLANATION PIC

.I'M NOT TELLING YOU TO RUN OUT AND GET ON, JUST KEEP IT IN MIND, LOOK AT THE CONDITION OF YOURS

NOW THEN. THE SENSORS ON YOUR RIG MAY OR MAY NOT BE FUNCTIONING CORRECTLY OR MAY BE BADTHESE FEED INFO TO THE COMPUTERTHE COMPUTER TAKES THE INFO IT COLLECTS AND "MAKES DECISIONS" ----IT'S MISSION IS TO KEEP THE ENGINE RUNNING. WITH WHAT IT KNOWS. SORTA LIKE THIS.

THIS IS SORTA A QUICK EXPLANATION OF THE LOOPS

THERE ARE TWO "LOOPS"---"OPEN" AND "CLOSED"

OPEN MEANS THE SENSORS ARE GIVING THE COMPUTER "REAL TIME" INFO, EXAMPLE: O2 SENSOR IS TELLING THE COMPUTER THE OXYGEN CONTENT IN THE EXHAUST SO IT CAN ADJUST THE INJECTORS TO GET THE MOST EFFICIENT "BURN" POSSIBLE

BEING THAT IT TAKES A LITTLE WHILE FOR THE O2 TO WARM UP TO "TRANSMIT" INFO. HOW DOES THE ENGINE RUN?

SAME GOES FOR "TEMPERATURE SENSORS---IT MUST GET TO OPERATING TEMPERATURE BEFORE IT IS "SENSED" BY THE COMPUTER

THE ENGINE RUNS "CLOSED LOOP" DURING THE TIME IT AWAITS FOR SENSOR TO "COME ON LINE"---WHICH MEANS THE COMPUTER HAS "PRESET" VALUES PROGRAMMED INTO IT--IT RUNS OFF OF THEM, UNTIL ALL SENSORS COME ON-LINE. CLOSED LOOP SORTA MEANS, THE ENGINE COMPONENTS ARE "FED FALSE INFO", THAT WILL MAKE THE ENGINE RUN---THIS "LOOP" IS NOT EFFICIENT, USUALLY YOU WILL NOTICE IT ****RUNS REAL RICH****MPG GOES DOWN!

THIS IS NOT ONLY TRUE FOR THE O2 SENSORS, BUT OTHER SENSORS NOT WORKING WILL CAUSE THIS (STAYING IN CLOSED LOOP)---CLOSED LOOP IS BASICALLY "DEFAULT"

"OPEN LOOP" IS WHEN THE COMPUTER RUNS THE ENGINE OFF OF "RIGHT NOW!"--"REAL TIME" INFORMATION----BASICALLY THE PRESENT ENVIRONMENT IS BEING SENSED BY THE COMPUTER---BAROMETRIC PRESSURE/ OXYGEN CONTENT IN THE FUEL/ ENGINE TEMPERATURE/ AIR MOVEMENT INTO THE ENGINE/ ETC. ETC. WITH THIS INFO, THE COMPUTER DOES NOT RELY ON "PRESET/ DEFAULT" INFORMATION TO MAKE INEFFICIENT "FUEL DECISIONS"----IT CAN NOW USE THE "PRESENT ENVIRONMENTAL INFO" TO MAKE EFFICIENT FUEL DECISIONS GIVING YOUR VEHICLE PEAK PERFORMANCE

THERE ARE 2 TYPES OF SYSTEMS THAT I KNOW SOMETHING ABOUT

OBD I. SORTA THE 1ST GENERATION. THIS IS YOU!

OBD II. CAME ABOUT AROUND 1996

GET YOUR CODES READ. THIS WILL BE YOUR BEST INFO TO CONTINUE

IN MY AREA MOST AUTO PARTS STORES WILL READ YOUR CODES FOR FREE. BUT. MOST CAN ONLY SCAN THE OBD II

AROUND HERE."AUTOZONE" CAN READ BOTH OBD I AND OBD II FOR FREE !

MAYBE THIS WILL WORK FOR YOU!

THE SHOPS IN MY AREA WILL CAN/ WILL READ THEM TOO, THE CHEAPEST SHOP SCAN HERE IS ABOUT $55. SCAN ONLY AND MAYBE SOME FREE ADVICE

LEMME KNOW IF THIS HELPS YOU AT ALL

THE MEDIC