New 5.3 LM7 low on power
 

Ok guys, looking for a little guidance. I rebuilt a 5.3 lm7 with all stock bottom end, new bearings throughout. New 4.8l pistons, ls6 cam, intake, tb and injectors. I fired the car for the first time the other day and drove it for the first time today. The problem is, it is extremely low on power and has virtually no throttle response. Engine rpm barely increases even at 3/4 throttle or more. Iam stumped here. Any ideas as to why it would seem to be so low on power? When the car is in park or neutral it will rev up fine though the RPM range and sounds to be fairly healthy.....

any insight or help is greatly appreciated.

Sounds like its going into limp mode. Check fuel pressure at rail for starters, could be a bunch of things, need more details. Is it drive by wire, what's your trans, what is exhaust setup. Are you running a MAF or speed density tune.......... :headscratch:

T,

Its not drive by wire, we are running a 4L60E. ITs MAF and headers with dual exhaust. I think the trans is low on fluid though, would this cause the engine to feel like this? I know as for transferring power it would effect it but the engine itself seems very sluggish. Also Im pretty sure I have a miss on cylinder 7 that I can seem to track down.

Random misfires? Whats the code number?

Also troubleshoot your TPS.

Could also be a trans deal - if stuck in second gear. Just throwin that out there for thought because SOMETIMES my truck will not downshift to first from second after. It only does it once a great while and its never permanent.

Check your O2's or possibly replace them. One of mine went bad on me.

ok, i was thinking it could be the trans since the fluid was so low. I appreciate the ideas. Ill keep all this in mind while troubleshooting

well I checked a few things the other night, I couldnt find any obvious issues, cylinder 7 is definintely missing though. Also the transmission was really low. I guess I didnt put enough fluid in when I initially filled it. It took a good 2.5 quarts. I guess that would explain it not wanting to go anywhere when I tried to accelerate. But I still dont get why the engime didnt want to rev...:willy:

A little update, I think I narrowed it down to the trans being in "limp mode". All the research I did points to this. The engine seems to being running fine but the trans is stuck in third gear (will go into 2nd if done manually) I do have reverse though. So I did a little testing and made sure there is 12v going to the trans and that the VSS is operating (I even swapped it out with a new VSS, no change) From here Im not sure what to do. How do I clear the PCM from limp mode? What else would cause this? Anything else I should check? Any additional help is greatly appreciated.

A good start would be to see what the ECM is telling you by reading the codes. With out the codes you are shooting in the dark.. Roger

I bought a bluetooth adapter so I can read the codes on my phone, should be here wed. Wish I bought this earlier