99 gmc 4x4, truck is mechanicly taken care of, problem is if i trump on the gas the truck will hesitate, motor sounds muffled, pinging noise like bad gas, shifting is held back. If I ease into to it, to go faster, it works fine. Great accelleration, smooth, shifts nice. I have changed: plugs, wires, TPS, MAP, MASS, intake gasket, fuel filter, air filter, had the injectors cleaned and tested, fuel pressure is good, changed all O2 sensors. What could this be????
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The code is a cylinder misfire in cylinder #4-it could be a bad coil, bad sparkplug wire, bad sparkplug, a problem with the fuel injector, or a mechanical internal problem like a valve in #4 not seating properly. With that cylinder not running at optimum, you will experience hesitation.
If not taken care of, yes, it will cause further problems. Gas mileage will suffer, unburnt gas may wash into your oil sump, emissions will be high, the catalytic converter may get damaged through contamination, oxygen sensors may become contaminated and need replacing- the list goes on. Do have it checked-it might be a simple fix, but it should be taken care of.
sometimes the plugs for the selonoids under the truck get wet and voids connections, you can check power at fuses and switch then down on actuators for the 4x4. My 90 has a floor shifter and if this is yours also then i'd check the linkage under truck for proper operation and shifting. My 03 yukon xl has the push button type on dash and everytime i get the truck washed at the car wash my 4x4 wont work for a day or two, as the plugs under truck get wet and shorts connections. I"m to lazy and it really doesnt bother me at the moment to climb under and dry and seal them so they are water tight.
i read about this in popular mechanics, because of the thinning air the map sensor doesn't read enough vacuum and leans the fuel mixture back, one of the solutions is to run higher octane fuel, try contacting popular mechanics automotive dept, to see if there is any other cure
hope this helps
i know the camp verde hill of which you speak , last vehicle in the shop with that same scenario , after doing everything possible including a catalyst check , as we could not duplicate the problem , we replaced fuel pump at owners request and next trip he confirmed it was a fix .