Good day. l hope l'm in the right section for this, maybe l should be in the scan/tune. Anyway l have an 03 Z06 with 168k on it. What started out as a simple long tube header/Dorman intake install turned into an almost complete eng rebuild in the car. l'm sure many of you have been there. Anyhow, l now have on it full length headers, 1.70 primaries 2.50 all the way through the resonators/x-pipe to the factory Ti cat back. Dorman/FAST LS1/6 intake with a LS2 silver blade 90mm t/b with Casper wire adapter. The heads are stage 1 CNC ported factory 243's with factory LS1/6 rockers with upgraded trunnions. New LS7 lifters and new factory pushrods. Still running stock cam. l will be upgrading this as funds allow which is why l went with the upgraded parts. l have both downstream 02's disconnected. l am getting the codes P0171 and P0174 which l know are lean codes. Research shows most likely unmetered air downstream of the MAF. Possibly from the intake connection or maybe even the intake manifold itself. l will check both of these in the am but l find either of those highly unlikely. My concern is l have ran this exact same setup a few years back, sans the ported factory heads. And if l remember correctly (its been several years) l did indeed then also get the same codes. The difference is, then the car, even before the tune, ran like a raped ape. l mean the torque/hp difference was HUGE. The car 1st through 3rd was uncontrollable if driven hard. Now, however, this car is soooooo sluggish it hardly can get out of its own way. Any thoughts? l should maybe mention that this 03 didnt feel as strong as my 01 on the bottom end even before l did any of this. So l guess there may be an underlying issue but l thought this would wake the car up. lt didnt

 

You’re in the right section !!...first off do you have a scan tool to look at fuel trims and some other data PIDS which can quickly diagnose this concern ??...if not you’ll only be guessing. Yes, a vacuum leak in the areas where you had mentioned or an exhaust leak upstream of the O2 sensor can cause these DTC’s. If the DTC set when the engine was under load it can be either a fuel delivery issue (fuel pump/ filter) or a dirty MAF sensor. With a loss of power which you are experiencing I would lean towards fuel delivery or MAF. You can rent a fuel pressure gauge at one of your auto part stores to help you troubleshoot.

 

Good day sir, sorry took so long to reply. How do l access my ' Auto saved' items? l just spent a good 20 min and a dozen or so lines replying to you only to be logged out when l hit send and then when logged back in it was ALL GONE.

 

Has happened to me too every once and awhile !!....I don’t think there is a way to access this but I may be wrong !!

 

Crap., Ok here goes again and will keep fingers crossed it doesnt happen again! l checked evey possible place for a vacuum leak, there were none present. l hooked up a fuel pressure gauge to the fuel rail and at idle it has 61psi and held steady all the way to 5k as l free revved it. lsnt this too high? l thought should be around 40-42psi? Anyway, l have decided to just put the cam in now so the eng will be coming apart again. Now with the videos l have seen with similar combo's, the cars yielded about 460RWHP. And these cars had the stock LS6 manifold with the stock t/b and factory 243 heads as well. Mine has the FAST with a LS2 90mm t/b and stage 1 CNC porting so mine should breathe much better so l think l can realistically expect somewhere around 480/490RWHP. Now my other question is this...l am fully aware the factory 28lb fuel injectors are woefully inadequate, and the standard go to seems to be 36lb injectors. l can get brand new Bosch direct plug in 42lb injectors from CorvetteMods for the great price of only $80! Since this car will be dyno tuned, can these injectors be tuned to work or do you believe they are too large? l have heard both and dont want to do this twice! Thank you so much for your help!

 

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A smoke machine is the usual way to chase down vacuum leaks. First, though, you need to know what is being reported for fuel trims and what the MAF is reporting. With that info you can decide whether it is mechanical, electrical or fuel delivery. The parts store code scanners will not help you with that. They are a free service to fleece you of money for parts you probably don’t need to replace.

Hard to find places for vacuum leaks are the connections on the back of the intake. The big line to the power brake booster, the tiny vacuum line to the vacuum accumulator, and the MAP sensor can all be leak sources. It is easy to bust any one of those 3 and ruin your day. Without a smoke machine you are guessing on those.

Dorman intakes have earned a mixed reputation. I NEVER use Dorman unless it is a total emergency. There is a reason their parts are less expensive

 

That is a good idea and l actually have a smoke machine that l have yet to use! Looks like the perfect opportunity to me. l just may do this. l have already sprayed around all those spots you mentioned with brake clean while the eng was at idle and never heard the idle change so l'm kinda doubting that l have a vacuum leak. l even as an experiment pulled back the HVAC vacuum line just a tiny tiny bit with the eng running and shot it with the brake clean and the idle jumped noticeably. But l may try the smoke machine anyhow. As far as the Dorman intake, l l personally have ran this exact same setup (sans the ported heads) on 2 of my other C5 Z06's and never had any issues whatsoever. And l sold the first one l did to a friend over 2 yrs ago and l still see him regularly and the Z is still running strong without issues. So, l can only speak from my own experience, but l'm 2 for 2 and if this one gets the bugs worked out of it and it also isnt the Dorman intake, l'll be 3 for 3! But thank you very much for your input, l always appreciate hearing as much as possible, good or bad!