Well here is the story... I bought the car summer of last year from another board member. The dyno sheets with the car said the car put down 466.8 rwhp and 466.6 rwtq. However, these numbers were uncorrected. when I first got the car, there were no check engine lights.

Fast forward to last Thursday... I'm at the local dyno shop watching my buddy's LT1 car get tuned. I figure it would be cool to see the corrected numbers my car puts down, so we roll her up on the dyno. No tuning being done, just for ***** and giggles. The dyno operator/tuner asks me about the check engine light. I honestly don't know.

He proceeds with the first pull and I want to throw up. 406 rwhp, 395 rwtq. Holy ****. Car runs a little rich down low on this run.

He pulls out his scan tool and checks what my CEL is on for. O2 sensor and MAF. I don't know what to say considering that my car is tuned in speed density.

He proceeds to make another pull after turning off the CEL. This time a little better, 416 rwhp, 406 rwtq. The A/F was low 13s the whole pull, and timing was 28-30 degrees advanced the whole time.

The car has been getting worse gas mileage lately and it doesn't feel quite as fast. I thought that maybe the slower "feeling" was me getting used to the power, but I guess I was wrong.

I sent a PM to the former owner, and he seems to think the springs in the car are probably worn out by now (20k miles on the Manley duals w/ a 244/248, 612/615 cam).

I know it will be hard for someone to determine why my car has lost so much power, but is it due to corrected numbers, CELs, different climate w/ the SD tune, and/or the possible weak springs.

Any input will be greatly appreciated.

Thanks,
Alex

 

My pcv valve was shot and it was making the car run like ****.(vacuum leak making engine run lean and then pcm dumped a ton of fuel in to overcompensate...(fuel mileage took a dump too till I changed out pcv valve..(

Change out the 6 dollar pcv first..make sure its larger silver ring is not inside the black plastic cup that holds the pcv valve..(but rests against it)

If I told you how much my car took a dump till I replaced this little pcv valve you would not believe it...

It takes a minute to do..and 6 bucks for a pcv valve..

Try that first before anything else..

Then follow the previous owners suggestions on the valve springs..

least expensive and easiest meathods first ..IMO

Good luck and let us know if it helped.

JB

 

I would say the the previous owner is probably right. Im saying this to you personally. But some people just want a fast car and they don't know what it takes to have a car like that. Constant spring change for a big cammed street driven car is a must. Clutches are going to go sooner everything is. They don't make them like that from the factory for a reason longevity. I would have a tunner look at your tune but you said it had 28-30 advance and the A/F was dead on. You cant get much better than that. we had a Car go from 118-119 traps to 114-115. Just because of springs. Changed them out went back up to 118-119. You can have them checked to be sure. Just go over the car step by step you'll fine it then you'll be rolling agian.

 

Thanks for the help guys. I'll go ahead and do the PCV valve since it's only a few bucks, but my A/F was pretty good so I dunno how much that'll help.

I'm gonna do springs at some point, may wait till I decide on some heads.

How much would the climate/elevation changes possibly affected my car? From what research I've done, some people say it totally jacks everything up, some say it has no effect. Just not sure at this point.

Either way, I really appreciate the helps guys, I owe ya'll

If anyone else has input, feel free to throw it in here.

 

I wouldn't wait to long if you think its the springs...

I had a set take a dump at 23K miles on a mild cam 224/224 .563 lift w dual cranes and it was a bitch...

No damage but not fun..I got lucky...

I remember I was supposed to change them at 20K based off the tuner but they were booked ....

Don't wait too long...if you think its the springs..

Try the pcv first since its so cheap...but don't wait to long on the springs if you think thats it...

 

Ok, first things first. If your car is tuned in SD then I would hope you find a MAF code. You have to have the failure to enter SD. You can turn the SES light off for it. The O2 code once again, is your car tuned in Open Loop Speed Density or Closed Loop SD? If the latter which I would recommend if you don't have tuning tools then you should replace the offending sensor. If your car is tuned in OLSD then that code is irrelevant also. Down on power? Relative to what? The previous owner's claims on a different dyno with different standards? No proof in that. What about track times? Have you substantiated time slips to validate your claims or are we talking butt meter here?

 

The car is tuned in closed loop. I replaced the sensors yesterday w/ Bosch sensors so we should be okay there.

I know the power is hard to compare since it was on a different dyno in STD rwhp, but I wouldn't think the corrected numbers would be down 50 rwhp. I was expecting 15-20 rwhp less, but not this. Neither me or the previous owner have ran the car at the track, so I couldn't tell you that. The butt meter is saying slower. I know that this is also a very crude way to tell, but the car no longer chirps 3rd or 4th gear. Also the worse gas mileage was tipping me off as to something being wrong.

I'm going to get some new valve springs in it, 20k+ miles on these with a big lift cam so it makes sense, at least to me.

I will admit, I don't know a whole lot about SD, but am trying to learn.

 

470/470 cam only corrected is a very high number as is...as in "OMG i can't believe it" high lol whereas the numbers your putting out now seems more in line...but yes if you've already put 20k on those springs its time for a change, asap.

 

Climate conditions dont reraslly matter at all in SD since you are stull running closed loop. If you rean Open Loop then climate could be a concern.

 

? Dude, I understand you are just trying to learn...not to call you out or make you feel bad but the title of your post and your response to my questions are leaving me scratching my head. You just said you are in Closed Loop?

As far as the springs go, maybe a sponsor could chime in on the viability of the common "beehive type springs" life expectancy. 20k doesn't sound alarming too me.

A pure SD car left untuned thru a 6 month season change might have a perceptable "butt meter" type indication. 50-60hp, I would be pulling plugs, checking wires.

 

Do these engines ever want this much advance?

 

Alright guys, mistake on my part and I realize I'm dumbtarded

Car was tuned in OPEN loop. My apologies to those have been helping me.

Maybe this'll help diagnose the problem, and attibute some of the lost power to climate/elevation changes. The car was originally tuned in TX and it is now in KY.

 

some do

 

Ok it was tuned in open loop but do you run it in open loop? Some people tune in open loop just for tuning and when they finish enable closed loop again.

 

Yes the car is run in open loop exclusively.

 

O2 senors and maf are completely ruled out. Could possibly be your tune but i doubt if would be anywhere near that much of a difference. I would start by checking plugs/wires and then look for something mechanical.

 

I'm ordering valve springs, plugs, and wires tomorrow.

I'm considering putting the MAF back online at this point. SD seems like a hassle to me, especially since this isn't a FI application and it never will be.

Once again, thanks for all of your guys' help, I really appreciate it.

I will update ya'll throughout the process.

 

MAF's suck, i would leave it off.

 

From what I understand, unless I'm maxing out the MAF, there's really no good reason to go SD, but then again, I'm no expert at all this. Would you care to expand on your opinion?

 

Hey man, no problemo. Plugs, wires, plastic grocery bag sucked up against the filter. I really doubt the tune is the reason. (If it worked as advertised and no futher (significant) mods have taken place.) Parking break stuck on?
Anybody local willing to scan it? I would.