My ‘99 LS1 has about 170K on the odometer. It runs well, no noise, leaks, doesn’t burn anything but fuel. Still running the stock exhaust.

I recently had a PCMForless tune that really made a nice difference. Along with their usual performance settings, I had them tune out the torque management shifting, EGR and A.I.R. I also told them I was about to install an LS6 intake manifold and to set the fans for on at 160 degrees. Prior to the intake install, these new settings were great and the car ran very very good. I’m certain they tuned it for the LS6 mainfold.

Today, I installed the LS6 manifold. While I was in there, I swapped in new knock sensors. I also removed the EGR system and installed new GM PCV piping. The TB was pretty gunky and it got a good cleaning. I even had a new OPSU on hand in case I broke the original, which I did not.

The install went well, and everything looks good. The car runs good, fires right up, no leaks, hissing, drama or otherwise.

It runs good with good power at lower RPM and from a standing start, it chirps the 315's a little more than before. However, as it spools up, it seems to have less power than before. It spins up to 5,500 RPM but it slowly gets there with little power. I expected it to have more power, not less than before.

If I was diagnosing a car like this, I’d say it was fuel starved like the filter was clogged or the pump was bad. But this coincided with the work I just did and it was better before.

I was thinking that the LS6 has bigger injectors to match the bigger airflow but it appears that LS1 and LS6 engines got the same injectors.

I’m gonna put a fuel pressure gauge on it and see if it tells me a story.

Should I be looking at something else? I’ve already triple checked everything, nothing is out of place, twisted, crushed, unplugged, etc.

I realize that my engine is hampered by the stock exhaust but I do think I should see at least the same power production, not less.

 

I would try changing the fuel filter and check the fuel pressure. How old is your fuel pump?

 

The fuel pump was changed by a previous owner but it probably has 100K on it. The fuel filter was changed a few weeks ago.

I checked the pressure last night. 60PSI at idle and it holds when gunning it.

 

Are you driving the car while checking the fuel pressure or just reving the engine in park?

 

Good question - blipping the throttle with no load won't show much of a drop in fuel pressure. If you are observing little to no pressure drop under load (WOT run at a pretty good rate of speed so you can actually see what's going on), then most likely you are not fuel starved.

If you've recently replaced the fuel filter (which you say you have), I'd have no reason to suspect a fault in the fuel system. The tune being off sounds like the most likely culprit here.

 

There’s good news but first:

No, I have not checked the fuel pressure while driving, my gauge’s hose is not that long.

I did this work on Sunday morning. I starting driving the car by about 1PM Sunday afternoon. During the job, I had the battery disconnected. This first day, I drove about sixty miles in various traffic including highways with several re-starts

The car is now running great. At this point, I’ll assume the PCM had to learn the sensors and fuel/timing maps over again and it just took a long time to do so.

I’m puzzled why it took so long. The last time I reset the PCM, after a short drive of about an hour and two re-starts it was fully learned.

The PCMforless tune is definitely spot on. Honestly, I never thought a high milage stock engine would run so strong-despite having the original exhaust system. I’m very happy with the car at this time.

Thanks for the help guys!

 

edit: I just re-read the post and realized you're experiencing the exact opposite as what I originally thought. You should definitely feel more power in the upper rpms

 

As I understand it, the 98-99 cars had slightly bigger camshafts than the 2000 and up cars. A LS6 intake manifold would do slightly better on a earlier engine.

The car runs great. I guess I was a little paranoid about my work. The last time the PCM reset it was pretty quick. This time, it took two days and much more driving. This is what tripped me up.

I’m still gonna check the fuel pressure while driving and I think the TPS may have a dead spot, surely it’s the original. A new one is on it’s way.

 

Usually just cleaning the TPS will fix a TPS issue FWIW....

 

Hey SOMbitch!

As the TPS is a potentiometer, like a volume control in a stereo or mixing console, it would have a plastic film resistor with a metallic wiper. I would consider this a wear item. And as cheap as they can be had, I’d rather a new one under my foot. Sometimes, rarely tho, the car surges a little bit, before and after the tuning. I suspect the TPS.

I saw a red non-WS6 TA just like yours today, stock wheels. Sweet! Two old white guys in blue & red Trans Ams on the highway....

 

Hey watch that old guy stuff, there are more of us than you think...LOL

BTW Paul, your setup and mine are almost identical, 99's mostly stock, stock exhaust, ls6 intakes...I did my intake swap back in the end of april and dont drive my car much, maybe 150 miles since then but mine runs good too for what it is. I hear some say after headers that actually lost low end response which is what I like the most, I have a hypertec tune in mine but sending my pcm out to frost or maybe a full dyno tune soon too. FWIW.

 

Glad you got it figured out If you decide to check the fuel pressure do it on a good pull (3rd or 4th gear) a hard load on the engine will tell you how the pump is doing?

 

HAHA Yeah one of those old guys could have been me if you wre in NC but your only as old as you feel and act and my GF tells me I am very immature.... At my age I take it as a compliment


Back to the point Paul you are correct but when mine threw a TPS code I just pulled it out and cleaned it real good with some MAF cleaner I had laying around. It was really carboned up but going on year now with no issues.... Next time it acts up though I will prolly just get a new one and be done with it....

Glad you got it figured out and those cheap fixes always make you feel good

Oh and don't use big words like potentiof@cker that the rest of us don't understand.............

 

I was thinking about this today. Isn't the TPS external that rides the throttle shaft? If you cleaned off carbon, wouldn't it had been on the IAC which is an internal componant in the intake stream?

 

LS1 fuel pressure is 58 psi btw bnot 60 psi.... Your stock injectors are fine for what little mods are on your car.

I did injectors on my car when I changed my cam.. You need to hood your car up a HP tuners and see what Duty Cycle you're running. Like I said when I did the cam, my Duty Cycle was 98%.. That means my injectors were spraying pretty much all the time. 108% is all the way open. I bought FORD 42# injectors, tuned them and now my DC is 54%

Try to seafoam your motor.. and pour 1 entire can of seafoam in your gas tank..

Good luck

 

Update: I finally got around to installing the TPS. While I was at it, I pulled the IAC and hit it and it's bore in the throttle body with carb cleaner and a rag.

The surging is gone. I guess the TPS had a dead spot.

 

fuel filter trans might be slipping