2000 T/A , power fades under strong acceleration

I can't find anything wrong with my LS1 . No codes , 60 psi fuel pressure(in spec) , no misfire, no sensors damaged or wires broken . But when I accelerate under strong throttle it stumbles when I get to about 3500 rpm . When cruising along in 4th or 5th gear (manual) . I give it gas and it just moans like its sucking more air but it does not pull any stronger . new fuel filter , plugs TPS sensor . Cleaned MAF . All sensor seem to be working by the checks in my haynes manual . Any ideas ? Rob:banghead:

Hmm, It has to be something that the PCM does no moniter, do you ahve the after cat O2 sensors still on it? I would love to say it's a clogged cat but the sensors should catdh that, unless the restiction is elsewhere down stream?

Yes the O2 sensosors are still on . I did not know it would not throw a code for the post cat sensor. I was tempted to replace them for the hell of it . But $65 each changed my mind . I still have full throttle power most of the time unaffected by this symptom . Some days I don't even sense it . The exhaust does not have a muffled sound either . Tonight it drove like an LS1 should . I can't even pinpoint a weather condition to relate it to . I am going to replace the plug wires later this week . Eventually a full tune up . Changing the plugs too just to see if the Irridiums are causing it . Hate to think that I wasted $50 on them . Thanks . Rob

Yeah I was just tossing the idea around because I know they are expensive.

What is the exact spec for the fuel pressure? 60 seems a tad bit high althought I've seen an average mid 50's on most recent motors. Just curious.

Have you had the fuel gauge on the car when the problem occurs?

The haynes manual list 55-60 psi with key on , engine off . Not having any other source I don't know if it is considered too high. While running it should drop 3-10 psi, which it does . I bled off fuel thru the gauge while holding a high rev and it did not effect rpm or pressure. The only time it does the symptom is while driving . I can't get it to duplicate with the hood up by reving it . I can't put it in gear and torque brake it either since its manual . I am buying plug wires in the morn . It can't hurt , right. Rob

check out your coil packs. and make sure that all of your spark plug wires are fully seated and that the coil packs are plugged in fully. Might also want to make sure that all of your spark plugs are tight. I know its a pain on your car but it may be worth it.

hpfh. so when you accelerate and it 'moans' is it like..the engine doesnt rev up at all? like the tach just sort of stays there? i would say it sounds transmission-y but im sure the tach would pop all the way to redline if you floored it.. maybe its some vaccum advance thing... ._.;

no vacuum advance on the ls1 motors.

. I can't get it to duplicate with the hood up by reving it . I can't put it in gear and torque brake it either since its manual . I

Rob, Yeah like I said, I've seen mid 50's be the norm on newer systems so that (60 then slight fall off) would be ok. BUT, you really need to see where it is when the problem occur. What you need to do, is rig the gauge up securely to the windshield or post, preferrably with a passsenger to moniter it. Have them watch the gauge especially when you feel the problem begin.

I will try to make an extension hose since my gauge only has a one foot hose. Although I have new plugs in it , two months ago . They are the new Irridiums . So I bought a different kind and am going to change them with the wires tommorow . New MSD super red wires . Clutch is not slipping . I can still turn the tires in 3rd if I want . The moan I described was like the butterflies in the throttle body were openning with out additional fuel . This has been intermittent for over a year but recented it became a full time occurance . Rob

Also I am suspicous that my MAF sensor may be effected by the oil from my K&N filter ( have not re-oiled it) . But I tried cleaning the sensor but it made no difference . May try to find one in a junk yard . Rob

LS1 fuel pressure at idle and normal driving = 62 PSI

Sounds like heat soak. Bet when it is colder outside the problem goes away for the most part.

Update : I changed plugs and wires today and flushed my cooling system . Took it out for a road test and it ran perfect . I dogged it many times with NO hesitation or fade . I think the wires must have been breaking down when the engine was under a load . 60 k miles did not seem high but 6 years in the south may have done it . I hope this is it . Thanks for the help guys . Rob

Update : I changed plugs and wires today and flushed my cooling system . Took it out for a road test and it ran perfect . I dogged it many times with NO hesitation or fade . I think the wires must have been breaking down when the engine was under a load . 60 k miles did not seem high but 6 years in the south may have done it . I hope this is it . Thanks for the help guys . Rob
It was the iridium plugs.. sorry I didn't see this sooner but everyone who has posted a hesitation after installing iridium plugs have turned out to be them. Most people recommend NGK-TR55's for the Ls-1 Engines.