Hey Fellas, read this site daily, rarely post unless I have something to add.

I have a 99 NBS ECSB Z-71. only mods are Ultimatepd Air Intake, PV Muffler Cat back exhaust, transgo shift kit , and an 02 PCM tuned by Nelson.

Been tryin to track down a loss in power for a while. THe last PCM livened the truck up for a couple days, then it went downhill again. For a few days after the pcm update, it ran great. It still runs ok, but is not as strong as it was.

No codes are being thrown. Truck has 80,000 miles. Plugs are good.

Any thoughts?

 

Cats could be clogged, but that's a long shot. Maybe the PCM is bad or being shorted out. Did you have all TM removed? If not I would try a retune with all TM removed and see how it reacts. It's possible that the PCM picked up spark knock and pulled back timing.
There are just so many factors to a decrease in power loss felt. You could have just gotten use to your truck. If not replace these items: Fuel filter, pcv valve, clean your air filter, pour a bottle or two of Berrymans fuel injection cleaner in tank with a full tank of 93 oct fuel.
Then replace O2 sensors. They are expensive though.
If none of that does it, then possibly your engine has excessive wear. Your compression ratio could be lower than it used to be. You can check this with a compression tester per cylinder. You may come up with something.
Valve springs could have weakened as well.
Like I said, there are many factors in power loss.

Jim

 

When you say it ran good for a couple of days, what type of driving were you refering to? Part throttle, or WOT? OBD2 PCM are always learning. In some cases they learn in the wrong direction. Can you gather a scan log of a typical drive cycle?

Richard

 

It ran good for a couple of days after the pcm upgrade. It was a combination of driving, wot runs, half-throttle runs etc..

Truck has less than 20000 miles on plugs, wires look good.
Fuel filter changed every 10,000 to 15000 miles. Trans routinely serviced.
No SES Codes present.

No pinging/rattling present.. PVC valve just replaced. TPS replaced.
The y-pipe and cats were replaced by GM about 25000 miles ago..

Thnaks for the responses.

 

Do you have any sort of scan tool that you can check fuel trims and ignition timing with?

Richard

 

All I have available is an old Predator Handheld..

No other toys. Looks like I may have to break down and buy hptuners or efi live.

 

The problem may have reared its ugly head today.

Lost first gear. Going down the road about thirty, truck popped, slammed, boomed, ffedhdfhdf???!!! .. Sounds terrible. No first gear..

 

Sorry to hear about the trans. woes. Sometimes disabling Torque Management causes the transmission to pack it in. Some can get away with it and some can't. I'm not exactly sure why that is though..........
Looks like your going to thow money at the trans. doctors for now..........

I wish you good luck sir,

Richard