1996 C1500WT 4.3L Vortec V6 engine RPM runs away
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1996 C1500WT 4.3L Vortec V6 engine RPM runs away
My Son purchased a used 1996 C1500WT with 4.3L Vortec V6 and 4L60E tranny. He is the third owner of the truck and it has approximately 56K miles that were verified by the title and registration. We have replaced the air cleaner, alternator and idler pulleys, tires, battery, engine oil cooler lines, both U joints (with grease fittings) and the water pump, hoses, thermostat and coolant.
I checked the throttle body and the throat was filthy. I cleaned it with TB Cleaner and a tooth brush. I had my Son start the engine and burn out the built up cleaner. I missed a few areas and had him open the throttle while I sprayed the TB cleaner. The engine started accelerating rapidly, he immediately removed his foot from the throttle and the rpms continued to climb. I told him to kill the ignition. We waited a few minutes and he restarted the engine and no issues. WE thought we might have a fuel pressure issue. We borrowed a pressure gauge from AutoZone and tested the system. We had 55-60 psi at idle and approximately 60-65 psi near full throttle. We tested the pressure after we changed the inline fuel filter on the frame. I removed the Mass Air Flow sensor and cleaned it with MAF spray on cleaner. The unit was a bit dirty and it looks much better following the cleaning. We decided tor replace the Throttle Position Sensor thinking it might be dirty/worn.
We finished replacing the water pump (significant leak at the weep hole) today. We flushed the cooling system with distilled water. We replaced the radiator hoses, heater hoses and bypass hose on the water pump and thermostat. We filled the system with the Orange Prestone as indicated on the label on the overflow tank and the owner's manual. We took the truck for a test drive. Gone were the noises from the failing water pump and the heater was working much better (I back flushed the lines and significant crap came out with the distilled water). We were nearly home and the engine rpm started increasing without warning. I asked my Son if he kicked it for the hell of it and he said NO. He indicated he lightly depressed the accelerator pedal and that was when the engine started accelerating. He removed his food from the pedal, braked and it settled down.
We are both stumped. No codes or pending codes from the scan tool. I considered removing and cleaning the Exhaust Gas Re-circulation valve, however the bolts did not want to budge and I was concerned I might twist one or both of the bolts off in the block. Water/antifreeze mixture had been dripping on the crank position sensor. No error codes from the sensor. One odd thing we noticed in park. The speedometer starts moving up to about 10 mph when RPM is 3k and 20 mph when RPM is 4K. Scanner Danner has a video concerning this and he suggests the alternator might be passing ac voltage. I check for ac voltage with my cheap sears multi meter and found zero volts ac. We removed the alternator and battery and had both tested at Autozone. Both tested 100% good. We occasionally loose sound from the am/fm AC Delco/GM radio. I don't know if we might have a bad ground. I need to locate the ground location under the dash.
My Son discovered an article indicating the original distributor is made of plastic and it is known to go south. We found an aluminum billet distributor and we may replace the plastic junk with the aluminum distributor. The work has been done over the last eight months.
This old man is about to pull out my remaining hair. I have been tinkering with cars from the time I was about 10. I watched Dad and learned from him. He did a majority of his own work. I look forward to any suggestions, comments or ideas what the issues are. It might be something simple that we overlooked.
Thank you in advance for your time and assistance.
Sincerely,
BS Du Bois
Evansville, IN
I checked the throttle body and the throat was filthy. I cleaned it with TB Cleaner and a tooth brush. I had my Son start the engine and burn out the built up cleaner. I missed a few areas and had him open the throttle while I sprayed the TB cleaner. The engine started accelerating rapidly, he immediately removed his foot from the throttle and the rpms continued to climb. I told him to kill the ignition. We waited a few minutes and he restarted the engine and no issues. WE thought we might have a fuel pressure issue. We borrowed a pressure gauge from AutoZone and tested the system. We had 55-60 psi at idle and approximately 60-65 psi near full throttle. We tested the pressure after we changed the inline fuel filter on the frame. I removed the Mass Air Flow sensor and cleaned it with MAF spray on cleaner. The unit was a bit dirty and it looks much better following the cleaning. We decided tor replace the Throttle Position Sensor thinking it might be dirty/worn.
We finished replacing the water pump (significant leak at the weep hole) today. We flushed the cooling system with distilled water. We replaced the radiator hoses, heater hoses and bypass hose on the water pump and thermostat. We filled the system with the Orange Prestone as indicated on the label on the overflow tank and the owner's manual. We took the truck for a test drive. Gone were the noises from the failing water pump and the heater was working much better (I back flushed the lines and significant crap came out with the distilled water). We were nearly home and the engine rpm started increasing without warning. I asked my Son if he kicked it for the hell of it and he said NO. He indicated he lightly depressed the accelerator pedal and that was when the engine started accelerating. He removed his food from the pedal, braked and it settled down.
We are both stumped. No codes or pending codes from the scan tool. I considered removing and cleaning the Exhaust Gas Re-circulation valve, however the bolts did not want to budge and I was concerned I might twist one or both of the bolts off in the block. Water/antifreeze mixture had been dripping on the crank position sensor. No error codes from the sensor. One odd thing we noticed in park. The speedometer starts moving up to about 10 mph when RPM is 3k and 20 mph when RPM is 4K. Scanner Danner has a video concerning this and he suggests the alternator might be passing ac voltage. I check for ac voltage with my cheap sears multi meter and found zero volts ac. We removed the alternator and battery and had both tested at Autozone. Both tested 100% good. We occasionally loose sound from the am/fm AC Delco/GM radio. I don't know if we might have a bad ground. I need to locate the ground location under the dash.
My Son discovered an article indicating the original distributor is made of plastic and it is known to go south. We found an aluminum billet distributor and we may replace the plastic junk with the aluminum distributor. The work has been done over the last eight months.
This old man is about to pull out my remaining hair. I have been tinkering with cars from the time I was about 10. I watched Dad and learned from him. He did a majority of his own work. I look forward to any suggestions, comments or ideas what the issues are. It might be something simple that we overlooked.
Thank you in advance for your time and assistance.
Sincerely,
BS Du Bois
Evansville, IN
