Chevrolet Repair/1990 GMC Z71 4X4
QUESTION: I have a 1990 gmc z71 4x4 with a 305ci motor, 5 speed transmission. the problem I have is I was accelerating up an onramp to get on the freeway in 3rd gear, about 200ft up the onramp the engine sputtered and died. It started right back up but couldnt put it into gear and drive. once I tried to accelerate in first gear it would sputter and die. If I didn't try and drive it would idle fine, I can accelerate the motor with no problems. I had the truck towed home. my neighbor came out and asked if I checked the ECM codes, I said no & that I didnt know what he was talking about. He put a jumper in the connector under the dash and told me to write down the codes as he preforms the test. He said there were no error codes that everything was fine. the next day I drove the truck about 60 miles with no issues of stalling or dieing, the only thing was a strong exhaust smell while idling. Once I started driving the truck the smell went away. there are no sounds of an exhaust leak, just the strong order coming from under the hood. other than these issues the truck idles and runs great with no loss of power. the engine has 90,000 miles and this is the first issue I've had with the truck
ANSWER: HI KEN,THIS IS A VERY HARD QUESTION TO ANSWER OVER THE WEB..I CAN GIVE YOU A FEW IDEA'S BUT THEY ARE JUST A GUESS. YOU SAY NOW THIS IS RUNNING GOOD AND NO ISSUE AS OF WRITING THIS...IF THIS WERE MINE I WOULD SUSPECT THE FUEL PUMP IS STARTING TO FAIL,IT IDLES OK BUT AS SOON AS YOU GO TO TAKE OFF IT WOULD NOT PERFORM.[UNDER LOAD].THIS COULD BE FROM LOW FUEL PRESSURE. GET THE FUEL PRESSURE CHECKED AND TELL THE TECH TO DEAD HEAD THE PUMP AND SEE WHAT THE MAX PRESSURE IS..HE WILL KNOW WHAT DEAD HEADING IS..FUEL PUMPS WILL DO THIS WHEN THEY ARE STARTING TO FAIL...THE FACT THERE IS NO CODES IN THE SYSTEM ON A PRE OBD2 PCM DOES NOT TELL ME ALOT..THE OTHER POSSIBLE CAUSE IS A FAULTY IGNITION COIL,SOMETIMES WHEN THEY START TO GET HOT THEY WILL ALSO FAIL,LACK OF SPARK OR THERE IS SPARK BUT VERY WEAK..I WISH I COULD HELP YOU MORE THEN THIS BUT THIS WOULD TAKE SOME HANDS ON DIAGNOSTIC TIME...IF YOU NEED MORE HELP LET ME KNOW GOOD LUCK TO YOU,,,TOM...
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QUESTION: Thank you, The other part of the question is what about the exhaust leak, could/can the EGR give an exhaust leak? Also I don't feel any vacuum to the EGR. Since my first message I've been driving the truck everyday with no problems other than the intermittent exhaust leak. The only time I have the problem is when I take the truck on the freeway
ANSWER: HI AGAIN KEN,,SO YOU ARE SAYING THE ONLY TIME YOU HAVE THE PROBLEM [ORIGINAL PROBLEM] WITH THE TRUCK IS WHEN IT IS ON THE FREEWAY..DID YOU EVER GET THE FUEL PRESSURE CHECKED OR NOT ?? BECAUSE THIS IS WHEN A FUEL PUMP WOULD ACT UP THE MOST UNDER MAX VOLUME...OK MOVING ALONG TO YOUR NEXT QUESTION,EGR AND EXHAUST LEAK,THIS WOULD ONLY LEAK IF THE GASKET UNDER THE EGR VALVE WAS BAD OR THE 2 BOLTS THAT HOLD IT IN PLACE WERE BROKEN OFF OR VERY LOOSE.VERY RARE..AT IDLE THERE WILL BE NO VACUUM TO THIS EGR VALVE AT ALL..THIS VALVE NEEDS TO BE CLOSED AT IDLE OR THERE WILL BE A STALLING CONDITION..THIS EGR VALVE IS CONTROLLED BY EITHER A TIMED PORT,MEANING UNDER THROTTLE THERE WILL BE VACUUM TO THIS TO OPEN IT. IF THIS EGR VALVE IS CONTROLLED BY A ELECTRICAL SOLENOID THE PCM WILL TELL THIS VALVE WHEN TO OPEN,AGAIN UNDER LOAD....SO NOT TO WORRY ABOUT THIS..AS FAR AS A EXHAUST LEAK GOES I HAVE SEEN MANY EXHAUST MANIFOLDS CRACK OR WHERE THE CROSSOVER PIPE BOLTS UP TO THEM, THE BOLTS MAY LOOSEN AND CAUSE A LEAK..SOME OF THE CROSSOVER PIPES WHERE IT BOLTS TO THE MANIFOLD WILL HAVE A GASKET BETWEEN THEM THAT BLOW OUT..YOU HAVE TO FIND WHERE ABOUT IT IS LEAKING AND GO FROM THERE..TO PINPOINT THE EXH LEAK GET YOURSELF A 2 TO 3 FEET HEATER HOSE OR GARDEN HOSE WITH BOTH ENDS OPENED UP,START THE ENG AND PUT THIS HOSE WHERE YOU THINK IT IS LEAKING,[DONT KINK THE HOSE] AND THE OTHER END UP TO YOUR EAR..YOU WILL PINPOINT THE LEAK REAL FAST LIKE THIS..YOU WILL BE SURPRISED HOW FAST YOU CAN ZERO IN ON A LEAK...LET ME KNOW HOW THIS GOES AND GOOD LUCK TO YOU,,,TOM..
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QUESTION: on the fuel pump issue. Do I have to use the fuel pump thats in the tank or can I use an external Holley fuel pump with a Holley regulator. Also I noticed that the coil is mounted externally to next to the distributor. Again do I have to use the factory coil or can I use an accel coil.
HI KEN,,YOU HAVE TO USE A INTANK FUEL PUMP..IF YOU TRIED TO USE A EXTERNAL PUMP THE NEW PUMP WOULD NOT BE ABLE TO PICK UP THE FUEL IN THE TANK BECAUSE IT WOULD HAVE TO COME TRHOUGH THE PUMP IN THE TANK.TO USE A PUMP LIKE THIS IT WOULD HAVE TO BE A DUAL PURPOSE PUMP[[[SUCK AND PUSH FOR PRESSURE]]].HOWEVER THIS WOULD HAVE MAJOR RESTRICTION...DROP THE TANK AND INSTALL A NEW INTANK PUMP...AS FAR AS THE COIL GOES YOU COULD USE ANOTHER KIND OF COIL. THIS SHOULD HAVE NO PROBLEM AT ALL...GOOD LUCK TO YOU,,,TOM...