dougx

How does one get a list of normal readings from another similar truck to compare with what I have on my truck to help locate a problem with a miss. I have a scanner that has a 50 item list on it. Another words looking for where the readings should be. 2003 2500HD 6.0L. Yes I know, if I can find another truck and scan it, but on line. THanks

tech2

service manual may have them but it may not be useful as the range can vary quite a lot depending on operating criteria.


without naming 50 PID's, what in particular sensor's are of interest?

dougx

looking for the fuel trims,map, oxygen sensors,02 sensors. The problem I'm working on is at

https://chevroletforum.com/forum/sil...ght=2003+po300

Thanks for any heads up..

tech2

when the engine is misfiring these 2 parameter id are inconclusive as they are skewed from the misfire.


if the engine is misfiring, fuel trim is meaningless. Fuel trim is a calculated value. (Normal fuel trims when in closed loop operation should be 0% +/- 10%. If it is adding or subtracting fuel more than 10% something is askew).




oxygen sensor voltages during misfire conditions will be skewed lean. Oxygen sensors sense the unconsumed air from no combustion event and will think the mixture is lean....so will add even more fuel.


if you have a misfire, isolate it to a particular cylinder. GM has the best misfire counters of any manufacturer. A high end scan tool will show live and history misfire counters. If your scan tool cannot do this, consider a powerbalance test. the code may show random misfire but the vehicle knows which cylinders are causing misfires.
if you do not have access to this type of equipment, consider a compression test to rule out mechanical problems. I have seen worn camshafts and lifters for this engine.


In short, IMO, rarely can vehicle live datastream help with misfire diagnosis.

dougx

after 719 seconds of run time here are the misfires. Also I have done a compression test all are about 140psi. cyl#1 11, #2 1035, #3 2769 #4 27255 #5 64 #6 6558 #7 37 #8 5933. Oddly enough it runs with power at above 1750 rpm. I swapped coils 1 and 4 it still had the most misfires and #1 the least. Can a crank position sensor or need of reprogram need cause this? Tried the lp gas over the manifold no effect. Over it's storage time the battery went dead several times and sometimes died while trying to start with low battery. PCM damage?

tech2

was the crank sensor replaced? If a new or different sensor is installed and a crank sensor variation procedure not learned, false misfire dtc will set...most likely at higher rpm.












are you saying it runs normal at 1700 rpm? Is it missing only at idle? So is the fuel trim adding fuel at idle and normal at 2000 rpm?

dougx

No, the crank sensor has not been replaced. It smooths out after about 1700 rpm. I can't tell if it is missing at that point but runs with plenty of power.
Short term fuel trim 1 -2.40, Short term 2 -27.40 Long term trim 1 -12.50, long term 2 - 12.50. Thanks for the help...

tech2

I need fuel trim at idle and 2500rpm, engine in closed loop operation

dougx

Thanks I'll provide those Sunday with new readings...

dougx

Fuel trims 2500 rpm Short term #1 -1.60 Short #2 -24.30
Long term #1 -6.30 Long #2 -18.80

Fuel trims at idle Short #1 -2.40 Short #2 -31.30 Long#1 -16.50 Long#2 -18.80


I noticed the ign timing at idle was 24 and at 2500 it was 41.50. On previous idle readings it was generally around 14.5....Thanks