96 3.8 random misfire
#1
05-14-2010, 01:38 PM
96 3.8 random misfire
Ok. I know this pops up alot in this forum, but here goes. I have a 96 Camaro RS. The motor was replaced with a 3.8 out of a 2000 Buick Lesabre. I have a random misfire code. Fuel pressure is a 45lbs before starting and 35lbs while running. New plugs and wires. 3 known good coil packs. ignition module tested good. Catalytic converter beat out. Now i have a new problem as well. The car will barely stay running unless you have it above about 3500rpm. and it misses like crazy. I also have a tps code. will this cause any of this? It also has used alot of gas, like a gallon and a half in 3 miles. any help would be appreciated.
#2
05-14-2010, 02:12 PM
check the data of the tps.
sounds like it might be saying the throotle is way open and flooding it.
also check the firing order and for spark at each plug
vacuum leaks , brake booster hose off ???
compression on all cylinders???
sounds like it might be saying the throotle is way open and flooding it.
also check the firing order and for spark at each plug
vacuum leaks , brake booster hose off ???
compression on all cylinders???
Last edited by 18436572; 05-14-2010 at 02:18 PM.
#5
05-17-2010, 05:29 PM
TPS was inexpensive and a quick fix with 2 screws on my '01 SS, not sure if it's similar on the 3.8L...
Do some easy quick checks, clean air filter? Run a few tanks of a quality fuel system cleaner. Next check all your sensor connectors as was mentioned, and get your fuel injectors tested.
What is the specific code(s) you get?
Do some easy quick checks, clean air filter? Run a few tanks of a quality fuel system cleaner. Next check all your sensor connectors as was mentioned, and get your fuel injectors tested.
What is the specific code(s) you get?
Last edited by libertyforall1776; 05-17-2010 at 05:43 PM.
#6
05-17-2010, 05:45 PM
If the misfire is random, inspect for the following conditions:
* Crankshaft Position System Variation. Refer to CKP System Variation Learn Procedure . The crankshaft position system variation compensating values are stored in the PCM non-volatile memory after a learn procedure has been performed. If the actual crankshaft position variation is not within the crankshaft position system variation compensating values stored in the PCM, DTC P0300 may set. The crankshaft position system variation learn procedure is required when any of the following service procedures have been performed:
o PCM replacement or reprogramming
o Engine replacement
o Crankshaft replacement
o Crankshaft balancer replacement
o Crankshaft position sensor replacement
o Any engine repairs which disturbs crankshaft/harmonic balancer to crankshaft position sensor relationship.
* System grounds. Ensure all connections are clean and properly tightened.
* Mass air flow sensor. A Mass air flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the fail records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the MAF sensor.
* Loss of EBCM/EBTCM Serial Data. If the PCM stops receiving data from the EBCM/EBTCM, DTC P0300 can set due to a loss of rough road data. Check for stored ABS/TCS DTCs, especially DTCs related to a serial data malfunction. Refer to Self-Diagnostics in ABS/TCS.
* Air Induction System. Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Inspect for disconnected or damaged vacuum hoses, incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, EGR valve, and intake manifold mounting surfaces.
* Fuel Pressure. Perform a fuel system pressure test. A malfunctioning fuel pump, plugged filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Pressure Test .
* Fuel injectors Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C (50-95 Degrees F) . Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside 10-35 Degrees C (50-95 Degrees F) .
* Contaminated Fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
* EGR System. Inspect for leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow.
* Extended Idle. Excessive open loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the freeze frame and fail records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures less than 80°C (176°F), the condition described above is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows more than 15 gm/s.
* Crankshaft Position System Variation. Refer to CKP System Variation Learn Procedure . The crankshaft position system variation compensating values are stored in the PCM non-volatile memory after a learn procedure has been performed. If the actual crankshaft position variation is not within the crankshaft position system variation compensating values stored in the PCM, DTC P0300 may set. The crankshaft position system variation learn procedure is required when any of the following service procedures have been performed:
o PCM replacement or reprogramming
o Engine replacement
o Crankshaft replacement
o Crankshaft balancer replacement
o Crankshaft position sensor replacement
o Any engine repairs which disturbs crankshaft/harmonic balancer to crankshaft position sensor relationship.
* System grounds. Ensure all connections are clean and properly tightened.
* Mass air flow sensor. A Mass air flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the fail records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the MAF sensor.
* Loss of EBCM/EBTCM Serial Data. If the PCM stops receiving data from the EBCM/EBTCM, DTC P0300 can set due to a loss of rough road data. Check for stored ABS/TCS DTCs, especially DTCs related to a serial data malfunction. Refer to Self-Diagnostics in ABS/TCS.
* Air Induction System. Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Inspect for disconnected or damaged vacuum hoses, incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, EGR valve, and intake manifold mounting surfaces.
* Fuel Pressure. Perform a fuel system pressure test. A malfunctioning fuel pump, plugged filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Pressure Test .
* Fuel injectors Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C (50-95 Degrees F) . Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside 10-35 Degrees C (50-95 Degrees F) .
* Contaminated Fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
* EGR System. Inspect for leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow.
* Extended Idle. Excessive open loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the freeze frame and fail records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures less than 80°C (176°F), the condition described above is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows more than 15 gm/s.
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