'04 C5Z, KB supercharger @17psi, 317 heads (ported and polished), BTR dual valve springs, 15gph meth injection, green top injectors, SD tune by Shortuning, long tube headers, dual 3" exhaust and no cats (4 3" bullet mufflers). I know the KB is generally considered a turd of a s/c but the meth injection helps a lot with the IAT that plagues these units. So even if it's holding back my max hp potential, something else is going on. Here's my problem, something just isn't right. My car is SLOW! I'm talking slower than stock slow! Something isn't right, there has to be something mechanically wrong but there is no obvious indication that there is. I still have the stock clutch (and have a SPEC ready to put in), but it doesn't feel like the clutch is slipping nor do I smell burning clutch. There is no smoke from the exhaust and the idle and acceleration is smooth (a slight stumble sometimes when I accelerate). It just seems like it's working against itself, almost how a truck feels when you try to accelerate hard pulling a trailer, like there is a great resistance somewhere. Maybe it's not running on all cylinders, but wouldn't that throw a code? I plan to pull the spark plugs and look at them, and will also do a compression check but if those were the issues wouldn't there be signs other than reduced power?
What else could be my problem?

I thought maybe the meth was making me run rich, but I put on a larger pulley to reduce boost to 10psi and disconnected the meth but it ran the same. A little less power but still was slow to rev and build power.

FWIW, it wasn't always like this. When I first put on the KB it would spin the tires 1st-4th gear. Now I can barely break them loose in first. The car sat for a couple years, and something may have happened before I parked it.


Colby

 

Could be a million things. Spinning tires is not always indicative of power. Too many conditions factor into traction.

Get it to a competent tuner and run it on the dyno. That stock clutch is definitely not doing you any favors.

 

Do you have CATS?? Is the exhaust system congested? Bent, clogged ect.. What exhaust system do you have??

That's what pops into my head as I was reading your post.

But, like ArtClassShank stated, it could be a number of things. If it were me, I would drop the exhaust at the header/manifold flanges and see what an open exhaust does to the performance. If that doesn't change things, you really need to data log the engine/PCM to see what going on.

Bill

 

Long tube headers, dual 3" exhaust, no cats. 4 3" bullet mufflers. Yes, that would make sense but exhaust definitely isn't the problem. I also thought on the other end of the spectrum; a clogged air filter choking it. But I thoroughly cleaned it and still the same.

Colby

 

Do you still use a MAF? Or you Speed Density Tuned?

 

SD tune, MAF is gone.

Colby

 

Anytime I see..... "The car sat for a couple years, and something may have happened before I parked it"....I think FUEL INJECTORS !!...I'd look at that...these injectors get clogged up sitting around for a long time !!...if you can get your hands on scan tool I'd be looking at O2 sensors and fuel trims under load...then consider getting them professionally cleaned.

 

Good idea. I hadn’t thought about that. I will definitely check the injectors. I believe I can check those with my DashCommand app. If not, I’ve been meaning to invest in HPTuners.

With the same amount of air and less fuel wouldn’t it run lean and send a code?

Colby

 

YES !!...it will set a DTC (P0171/0174) BUT the long term fuel trims have to be about 23%....if your long terms are at 22%...no DTC !!...when that fuel evaporates it leaves all kinds of gum and varnish....drain the tank and get some FRESH fuel in there !!

 

It has fresh fuel. I’ve been driving it daily. It runs fine, it just seems way down on power..

Colby

 

Along with that,, see what fuel pressure is when you go into a boosted application.

 

I have a fuel pressure gauge. I have a stock pump (plan to put in a C6Z pump when I do the clutch) and KB BAP w/ Racetronix harness. Fuel pressure sits at 60psi but will drop to about 58psi under full boost.

Colby

 

Colby,
Fuel pressure should not drop under load !!...you may have a pump/fuel filter getting ready to go...along with some maybe clogged injectors !!...now after the car sat it was running OK for awhile THEN started acting up ??

 

Yeah, I've known my stock fuel pump was struggling to keep up. My injectors (Ford green top, 42lb I believe they are) are nearly maxed out as well. Dyno tuner told me that when he was dialing it in. That's why I need a better pump in there.

Colby

 

I messed around with it this evening and discovered a few things.

First, my injection nozzle was clogged so I wasn’t running any water/meth injection. Without it my IAT’s are crazy high so I’m sure timing was being pulled way back.

Second, once that was fixed I took it out on a long open stretch so I could watch my #’s. My fuel pressure is dropping badly. It starts dropping almost immediately and we’ll before redline I was under 50psi and dropping so I backed off. Clearly, I need a larger fuel pump but I am sure my 42lb injectors are nearly maxed as well. I know this could cause me to run lean and destroy my motor, but could it also cause a reduction in power or would the injectors compensate by staying open longer (assuming they weren’t maxed out)?

So this weekend I am going to tear it apart and 1) install my Spec Stage 2 clutch, 2) install a larger fuel pump (I have an Aeromotive Stealth pump but have read bad things about them so I will probably just install a C6Z pump) and larger injectors (60lb), and 3) schedule a dyno tune. After that I’ll see how it runs.

Colby

 

Colby

I have some lessons learned for you with that SPEC Clutch install. Please call me.. PM Sent.

 

fuel pressure dropping is not good however if your car was tuned with the pressure drop in mind then you may be ok but the safest route is to stay out of boost until you get it sorted out... do you have a wideband in the car?... if so keep an eye on the afr's when you see the pressure dropping and see what it is vs your commanded afr in your tune if you have access to that... how about hptuners or a datalogger?

 

I figured out my problem. I am relieved but also a bit embarrassed. I was checking my fuel trims in my Torque app, thinking it may alert me if there is an air or fuel delivery problem, and I noticed something quite bizarre. My throttle response was peaking at about 72%. I thought it was the app but the app just reports what the ECU is seeing. So I investigated further. When I replaced my carpet I forgot to bolt down the plastic stop behind the pedal. As a result the carpet was pushing it up and was stopping my pedal from having full travel. So I bolted it down and my throttle response went to back to 100%. Took it for a spin and she’s back to normal! Makes sense, WOT was really only about 2/3 throttle which is why it felt “slow” as if I was towing something!

Colby

 

No offense meant C, but thank you for the explanation! It busted me out in guffaws; my first thought was, I din't work on that car... that's something I would do. Amazin' how much a blower helps when ya press the pedal down all the way!

 

I love the easy fixes