P0300 in 5.3 swapped OBS
02-03-2022, 12:34 PM
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P0300 in 5.3 swapped OBS Got me a new Home Depot Hauler with a 5.3 swap. Need help diagnosing a P0300. The motor is a 2002 lm7 out of a Sierra. It was running really rough when I bought it with the first scans being a p0332 and p0300 so i figured the knock sensors were causing the issues. Also, the previous owner capped the front steam vent so I fabricated a new steam vent line to the radiator, changed the knock sensors, plugs and wires and fuel filter. Put it all back together and then began getting a P307. Changed the coil pack on cylinder 7 and it went back to a P0300. It ran much better after those fixes but not 100%. It idles perfectly, no lifter noise and the injectors all sound good with a stethoscope. I only feel the misfire under acceleration.
FTB1S1 and FTB2S2 aren't receiving any input according to my OBD2 scanner so that will be another thing i look at, but I'm not confident those would cause the P0300.
I believe it could also be the cam position sensor based on what I've read on forums. I haven't done a compression or leak down test yet and I know I should, but I was hoping for a simple solution before going out and buying more tools. For my LS mechanics out there, what would you recommend doing next? Any input on the issue would be greatly appreciated.
FTB1S1 and FTB2S2 aren't receiving any input according to my OBD2 scanner so that will be another thing i look at, but I'm not confident those would cause the P0300.
I believe it could also be the cam position sensor based on what I've read on forums. I haven't done a compression or leak down test yet and I know I should, but I was hoping for a simple solution before going out and buying more tools. For my LS mechanics out there, what would you recommend doing next? Any input on the issue would be greatly appreciated.
02-03-2022, 01:01 PM
#2
TECH Fanatic
P0300 is a general multiple misfire code right? So, let's do the cheap stuff first.
Check all the plug wires to make they're seated properly and none are loose or burned in any way.
Check the intake manifold and associated vacuum hoses for leaks, as well as the intake manifold gaskets themselves. (have new gaskets on hand, they're cheap, and are probably due for a change, the o-rings get brittle over time.
Check the plugs, make sure they're all the same manufacturer, general condition, and gapped correctly. If not, replace.
Check all the fuel injector orings for leaks at the intake and at the fuel rails. (definitely check super close on #7 since it already threw P0307.
If at all possible, check the fuel pressure at the rail via the shrader valve (YouTube has lots of videos) .
Unplug and replug any injector harnesses to verify that they are seated properly too. Those are the basic major low cost options.
If any of that easy stuff doesn't solve the problem, you should definitely do a comp/leak test and go from there.
Check all the plug wires to make they're seated properly and none are loose or burned in any way.
Check the intake manifold and associated vacuum hoses for leaks, as well as the intake manifold gaskets themselves. (have new gaskets on hand, they're cheap, and are probably due for a change, the o-rings get brittle over time.
Check the plugs, make sure they're all the same manufacturer, general condition, and gapped correctly. If not, replace.
Check all the fuel injector orings for leaks at the intake and at the fuel rails. (definitely check super close on #7 since it already threw P0307.
If at all possible, check the fuel pressure at the rail via the shrader valve (YouTube has lots of videos) .
Unplug and replug any injector harnesses to verify that they are seated properly too. Those are the basic major low cost options.
If any of that easy stuff doesn't solve the problem, you should definitely do a comp/leak test and go from there.
