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ok guys im sorry this is gona be a long post and i dont type great so please bear with me. first off i have a 2000 z28 LQ4 6.0 short block, LS1 241 heads bee hive springs, intake, bosch stock injectors, ect. i have a high duration comp cam but not sure of the specs real lopy ( good lopy not bad) a previous owner did all this work to it. and msd coils and wires. long tube headers and a few other things im likely forgetting. the PCM has been shop tuned in the past for a custom tune which i have no clue what they did. i was just told by the owner who did the build it was done to accomadate the larger displacement.
the problem
all was fine i had an engine light on since i had the car for a bad o2 sensor and never got to replaceing it. in the middle of driving on the highway all of a sudden this misfire started. it misses at idle and up to about 2200 RPM, it misses beyond that too its just nearly impossible to feel. so i get to working on it. check codes. 3 seperate o2 codes come up for the 2 o2 sensors ( the down stream 2 are removed and codes deleted out of PCM so no light for those) so i figure ill run a full tune up. first checked fuel pressure, running about 59 psi steady idle and under throttle ( i figured this was how they increased the fuel for the 6.0 ) took the coil spark tester to it and all coils sparked good. ( 40mm gap jumped it fine) so i got spark plugs, oil chage, fuel and air filters and 2 new o2 sensors. replaced all that ( i omited the wires cuz my MSD wires looked and fired fine ) got all this done and still no change. i did notice on the number 6 cyl old spark plug it was black and dry, like too rich carbon fouling, and cyl 2 was a little dark with mild deposits, all other plugs looked good.so it was time to break out the auto enginuity ( laptop based OBD II port diagnostic tool commonly used on ford diesel f series )
diagnostics results
i got some weird stuff from this while monitoring the o2 sensor voltages and trims. im getting that the passenger side bank is really really rich ( 160 miles to a tank of gas rich) its even noticable that the pass side engine compartment is remarkably hotter than the driver side just by leaning under the hood. my headers are running all stupid kind of hot on that side, but not the drivers. pass side o2 sensors is reading in the 0.8 -0.9 v range. while the driver side is 0.01 - 0.09 so i figured must be an injector stuck open. so i took cyl 6 and 2 injectors and swaped them to the driver side bank. figured with the spark plugs showing overfueling those should be the culprits. so swapped the injectors over and still had the same thing, pass bank is overfueling. so i figured maybe coils and wires. swapped the coil racks and all wires and still pass bank showed way rich when it should have moved to the driver side if any of those parts were bad. but from start to finish it stayed the same
summary
so with all the testing nothing i could do woulkd change the over fuel scenario in the pass side bank. i am now at a complete loss of what is going on. i pulled the valve cover to check for broken springs or anything and found none. all springs looked good but number 8 cylinder exhaust valve was halfway open. my impression has always been with hydraulic cams the valves should all close when oil pressure is removed. is this correct? could this be the issue? if so that valve could be bent and sticking open but im not sure. monday ill likely pull the valve cover again and manualy turn the engine to check it out dont know why i didnt while i was in there. there is no smoking no oil loss and no oil contamination either. ill post up still frames of the testing i did, some bar graphs and line graphs for the o2 sensors and the pics of the old plugs if i can figure the picture thing out. please help guys this thing is running like pure crap and its my families only vehicle right now so i cant afford to have it down for long. thanks in advance.
the problem
all was fine i had an engine light on since i had the car for a bad o2 sensor and never got to replaceing it. in the middle of driving on the highway all of a sudden this misfire started. it misses at idle and up to about 2200 RPM, it misses beyond that too its just nearly impossible to feel. so i get to working on it. check codes. 3 seperate o2 codes come up for the 2 o2 sensors ( the down stream 2 are removed and codes deleted out of PCM so no light for those) so i figure ill run a full tune up. first checked fuel pressure, running about 59 psi steady idle and under throttle ( i figured this was how they increased the fuel for the 6.0 ) took the coil spark tester to it and all coils sparked good. ( 40mm gap jumped it fine) so i got spark plugs, oil chage, fuel and air filters and 2 new o2 sensors. replaced all that ( i omited the wires cuz my MSD wires looked and fired fine ) got all this done and still no change. i did notice on the number 6 cyl old spark plug it was black and dry, like too rich carbon fouling, and cyl 2 was a little dark with mild deposits, all other plugs looked good.so it was time to break out the auto enginuity ( laptop based OBD II port diagnostic tool commonly used on ford diesel f series )
diagnostics results
i got some weird stuff from this while monitoring the o2 sensor voltages and trims. im getting that the passenger side bank is really really rich ( 160 miles to a tank of gas rich) its even noticable that the pass side engine compartment is remarkably hotter than the driver side just by leaning under the hood. my headers are running all stupid kind of hot on that side, but not the drivers. pass side o2 sensors is reading in the 0.8 -0.9 v range. while the driver side is 0.01 - 0.09 so i figured must be an injector stuck open. so i took cyl 6 and 2 injectors and swaped them to the driver side bank. figured with the spark plugs showing overfueling those should be the culprits. so swapped the injectors over and still had the same thing, pass bank is overfueling. so i figured maybe coils and wires. swapped the coil racks and all wires and still pass bank showed way rich when it should have moved to the driver side if any of those parts were bad. but from start to finish it stayed the same
summary
so with all the testing nothing i could do woulkd change the over fuel scenario in the pass side bank. i am now at a complete loss of what is going on. i pulled the valve cover to check for broken springs or anything and found none. all springs looked good but number 8 cylinder exhaust valve was halfway open. my impression has always been with hydraulic cams the valves should all close when oil pressure is removed. is this correct? could this be the issue? if so that valve could be bent and sticking open but im not sure. monday ill likely pull the valve cover again and manualy turn the engine to check it out dont know why i didnt while i was in there. there is no smoking no oil loss and no oil contamination either. ill post up still frames of the testing i did, some bar graphs and line graphs for the o2 sensors and the pics of the old plugs if i can figure the picture thing out. please help guys this thing is running like pure crap and its my families only vehicle right now so i cant afford to have it down for long. thanks in advance.
