Solo

Hey Guys,

I am about at my wits end here and need your help. I bought a basket case, (1999 Chevy Silverado Silverado 2500 with a 6.0 Liter Engine), and after working through a laundry list of codes that I have tracked down and repaired I still have one code that I am unable to correct.

In going through the previous codes and other issues that were showing when I bought the truck I have replaced the following...

1. Bank 1 O2 sensors (upstream and down stream)
2. Bank 2 O2 sensors (upstream and down stream)
3. TPS
4. MAFS
5. EGR Valve
6. Crank Shaft Position Sensor

I also installed a new/reman Jasper motor last week since the milling on the original motor hadnt been done correctly when I rebuilt it fifteen months ago.


The freeze frame data is as follows....

Fuel Sys 1.............CL
Fuel Sys 2.............CL
Calc Load(%).........15.3
ECT(*F)................161.6
STFT B1(%)...........-0.8
LIFT B1(%)............17.2
STFT B2 (%)..........0.0
LIFT B2 (%)...........13.3
MAP(inHg)..............11.2
Eng RPM.................2013
Veh Speed(mph)......39
MAF(lb/min).............4.5
TPS(%)..................19.6


I'm not one to just throw money at a problem and hope that it gets fixed by the luck of the draw so I would really like to get this issue found, isolated and then repaired. Any and all ideas you all have would be GREATLY appreciated!

Thank you in advance.

Solo

UPDATE: 11/07/2013

I found two vacuum leaks on the intake manifold and changed out the four suspect fuel injector plugs/wires, (all on the driver's side). No change on the P0300 Random Misfire OBD Code though....

tech2

since the motor is new, I assume everything is good mechanically with the engine. old engines had cam lobe life wear.

even though its a random misfire code you can still isolate it to a particular cylinder. good scan tools will display misfire counters for each cylinder. view this data to determine which cylinder to focus on.

power balance test is another way

once you know which cylinder is the problem cylinder, swap the spark plug, if problem doesn't follow the plug, swap the ignition coil.

if the misfires are all on one bank, check for bad 02 sensors or clogged cat

Solo

UPDATE: 11/08/2013

I installed new fuel injectors on the #1, #5, #6 & #7 cylinders... found out that the re-manufactured injectors I bought on the original rebuild aren't worth the box that they arrived in. I changed these four out when I discovered that the Teflon boots that goes over the tip of the injector were missing, (all I can surmise is that the dispersal pattern caused it to get hot enough to burn it off). I also cleaned out the EGR valve...


Still getting the P0300 code on the reader... so here are the questions that I have:

1. I am not getting a failure code on the Camshaft Position Sensor. Could it still be bad? And if so, could this be a cause of the P0300 code?
2. Could the catalytic converters be bad even though I'm not getting a failure code?
3. I have heard that the iridium plugs could cause this in this year of Silverado. Would platinum plugs work better?

Any thoughts or ideas you guys have would be most welcomed, I'm shooting from the hip here.

Solo

Thanks tech2 for the advise! Will check on that in the morning.

Tech

Well based off your freeze frame data I don't like the long term fuel trim numbers that high. I'd prefer to see long term at max around 10%. make sure you have good fuel pressure. Also I prefer to use GM ACDelco plugs for all the LS series of engine families. My one question is when does the p0300 set? Cold start? At operating temp? At idle? Under load? Etc......

Solo

UPDATE: 11/09/2013

The P0300 code shows up right around 50 mph... the plugs that are in it are new AC Delco iridium plugs. Should I change them out for the platinum plugs?

Here is the new Freeze Frame Date since installing the new fuel injectors and cleaning the EGR Valve...

Fuel Sys 1.............OL
Fuel Sys 2.............OL
Calc Load(%).........16.9
ECT(*F)................129.2
STFT B1(%)...........-0.8
LIFT B1(%).............8.6
STFT B2 (%)..........-4.7
LIFT B2 (%)............5.5
MAP(inHg)..............13.9
Eng RPM.................1904
Veh Speed(mph)......48
MAF(lb/min).............5.1
TPS(%)..................22.7

One question I have is if the catalytic converters could be plugged and be causing this? I'm not getting a failure code on that or the O2 sensors...?

tech2

the ecm will not run certain monitors when misfires are occurring...if it did you would get numerous false dtc setting.

unscrew the front 02 sensors on both banks to bypass the cats. test drive; is the misfire gone? if yes, you have plugged cats.

Solo

UPDATE: 11/13/2013

I pulled the upstream O2 Sensors and drove it for a little over 30 miles and the misfire still showed up. It seems to show up only after 45-55 mph... so I am at a loss as to what could possibly be wrong. Like as said earlier the fuel pump, fuel filter, fuel relay and pressure regulator are all new... I will put the fuel pressure gauge on it tonight and let you know what I find on that. Any other ideas?

tech2

what all was changed over in the engine replacement?

you still need to find out which cylinders are misfiring