installed bigger injectors.............had a ?
Thread Starter
Intermediate
Joined: Apr 2006
Posts: 43
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From: maumee ohio
installed bigger injectors.............had a ?
I went from the 28lb LT4 injectors to some 42lb racetronix injectors.The car started at first but barely idled at all.Then it shut off and wont start at all now.Is this what normally happens until the pcm is reprogramed correctly?Thanks...............
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Your going to need a re-tune. That could be the reason it will not idle or start now and it might be something else. It's a pretty straight forward process replacing injectors on a LTx car so I can't imagine anything not reconnected. The only thing that gets taken off is the injector covers and fuel rail. This is unless you have a different than stock intake.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
yes, it will need re-programming.
A change of the "injector flow rate"/constants/tables will be needed. That would be first, and depending on what else is done and how it looks in scans, the rest of tune should be looked over/tweaked.
A change of the "injector flow rate"/constants/tables will be needed. That would be first, and depending on what else is done and how it looks in scans, the rest of tune should be looked over/tweaked.
Last edited by mseven; Mar 8, 2008 at 07:04 AM.
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
You may cause damage to the rings if you keep running it that way. Your problem at the moment is that your injector constant is set up for the stock GM 28 Lbs injectors and now you have installed a 42 Lb injector. You are basically holding the injector open twice as long as it needs to be and my guess is you have the BLM's out of range for the O2's to compensate and keep in mind at WOT you have nothing to help as the O2's are not even used. You need two things to happen one get the injector constant correct and log data until your BLM's are in the 128 range then you need to log data at WOT to check your PE settings. For now you need to pull the 42's out and reinstall your stockers until you get the car tuned for the injectors.
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Racer
Joined: Dec 2007
Posts: 312
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From: San Antonio Texas
Look at his sign-on name.
Bet he has a 383ci with LT4 heads
.
LT4383........If your heads are extensively ported AND you have a fairly radical cam, then the larger injectors are be warranted.
But if you have stock LT4 heads and something like a HOT Cam, then the 28LB injectors will suffice.
IMHO, of course
.
KW
Bet he has a 383ci with LT4 heads
.LT4383........If your heads are extensively ported AND you have a fairly radical cam, then the larger injectors are be warranted.
But if you have stock LT4 heads and something like a HOT Cam, then the 28LB injectors will suffice.
IMHO, of course
.KW
Thread Starter
Intermediate
Joined: Apr 2006
Posts: 43
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From: maumee ohio
Sorry for the lack of info............
Ive had this car for a couple of years.Its a Scoggin Dickey 383 Lunati forged short block with Trick flow LT1 heads/LT4 hot cam(for now)And long tube 1.75 headers.It has the stock LT4 intake and injectors and Ive installed a Racetronix fuel pump kit and a Aeromotive FPR..Its always had a miss or what Ive narrowed down to running out of fuel at 5500rpm with the 28lb.It only makes 430hp at that rpm so Im hopeing for 475 or more with the swap but Im guessing the cam is going to hold it back.All I want is to pull hard all the way to 6300rpm rev limit that its set at right now.PCMS4less will be retuning it next week.Anyone know what power I can get out of the 383 W/ LT4 hot cam?......525/525 lift 218/228 duration at 112 if I remember correctly.. It actually makes more torque than the 2005 ZO6 LS7 that I drove surprisingly, up to 5500rpm anyways................Thanks
Safety Car
Joined: Dec 2002
Posts: 3,655
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From: Charleston SC
I am a little confused by your post. the 430 is it RWHP? If so that seems way high for your combo and there is no way 475RWHP is coming out of a HC 383, If it is CHP unless you plan on pulling the motor you will have to go off of RWHP. How did you narrow the miss down to a fuel problem? What was the injector duty cycle at that RPM and what was the A/F?
Thread Starter
Intermediate
Joined: Apr 2006
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From: maumee ohio
Continued..............
No,Im only makeing 367 rwhp acording to my G-TECH.I dont have a dyno around here so Im not sure what the A/F or anything is.I will eventually get it on the dyno and have it tuned correctly but for now Im just having pcms4less tune it and its been fine so far.I found a power chart that said the 28lb injectors are only good for 400hp at 80% and im just over that by about 30hp or so,somehow.Im guessing they are running at 100+% when I run out of fuel at the 5500rpm point.If I hold my foot in it the motor will go on past 5500rpm all the way to 6300rpm but with about a 1/2 second delay at that point.Ive actually had it pull all the way clean to 6300rpm one time after I installed a brand new f/pump but then it went right back to the same thing after that.Plus the 06 ls7 runs 42lbs and thats right around what power Im looking for out of my car.It does makes tons of torque down low.
Le Mans Master
Joined: Jul 1999
Posts: 8,683
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From: Phoenix AZ
Ive had this car for a couple of years.Its a Scoggin Dickey 383 Lunati forged short block with Trick flow LT1 heads/LT4 hot cam(for now)And long tube 1.75 headers.It has the stock LT4 intake and injectors and Ive installed a Racetronix fuel pump kit and a Aeromotive FPR..Its always had a miss or what Ive narrowed down to running out of fuel at 5500rpm with the 28lb.It only makes 430hp at that rpm so Im hopeing for 475 or more with the swap but Im guessing the cam is going to hold it back.All I want is to pull hard all the way to 6300rpm rev limit that its set at right now.PCMS4less will be retuning it next week.Anyone know what power I can get out of the 383 W/ LT4 hot cam?......525/525 lift 218/228 duration at 112 if I remember correctly.. It actually makes more torque than the 2005 ZO6 LS7 that I drove surprisingly, up to 5500rpm anyways................Thanks
Simply put though, those 42# injectors are WAY too big for your engine. I'm running 42# injectors in my 383, but I have a much larger cam and spin it up to 7200 RPM, and I still really don't need them, they were just recommended to me by my tuner...I could have gotten away with 36# injectors.
Also, how did you determine you were putting out more TQ that an LS7 Z06? I find that a bit hard to believe (383ci vs 427ci)!
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Ok, Now I have a better understanding. The 42's will work fine for your combo as long as the tune is done for them. Brian has a ton of experience with LT1's and nothing you have is way off the mark so they will be able to get the tune close just by mail order. The "rule of thumb" You read about for injectors has a wide margin of error, there are a couple of people on this forum that have run the stock 24#ers to the 10 second range so the stock 28s you have should work fine but so will the 42s, again depends on the tune. You will read a lot about what size injectors but the plain truth is you can use a wide range of injectors sizes just depends on what you feel comfortable with and the tune. As long as you are not at 100% DC the injectors are not maxed out. THere are some that believe go with the smallest injector possible and that will provide the best atomization, Me I like to keep my DC around 80% max and my 36's are right at 78-79% acording to my data logs, BTW had 42's on and returned for them the car ran just as well just lower DC's hope my never ending ramblings help
Thread Starter
Intermediate
Joined: Apr 2006
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From: maumee ohio
Hope I didnt but the wrong ones...........
My car just felt stronger down low in the 1500rpm to about 4000rpm range.Maybe because my compression is 11:8 versus the stock LS7s 10:8?.Im not sure but it just felt stronger between those ranges.That was at a autocross though and I had hoosiers on vs stock worn out tires of the Zo6.I was shocked as hell when I realized this and Im NOT knocking the Z at all.I was just VERY surprised and realized that my motor Could and hopefully will make some good power once I get this figured out with the miss.It will sometimes backfire at that 5500rpm point also????.I know what I really need is to take it to Livernois in Detroit and it have it properly tuned but as always it has to do with time and $$$$$$$$$$.The ECM is going out on Monday for a reprogram so I will keep you guys posted.........Thanks for the help.
Safety Car
Joined: May 2003
Posts: 4,283
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From: Houston Texas
Jayson at Motorsport Technologies Inc., down the street from me, once told me, that 24's will support up to 450 chp n/a hp. 30's should be way more than enough for you.
Racer
Joined: Dec 2007
Posts: 312
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From: San Antonio Texas
2. Stroker + HOT Cam + Trick Flow heads = approx 365 to 380 HP at the wheels in an Impala. Not sure what effect a Corvette's exhaust would have on this set-up.....you may come out a bit better.
3. Trick Flows have a large combustion chamber......64cc or so. So I'm betting that if your heads weren't decked a bit, that the relatively low (for a LTX engine) will cost you some HP. That's the only 'problem' I see.
Best of luck!
KW