My Vette- '93 LT1 with the LT4 conversion. Meziere water pump, BBK 52mm TB, LT4 intake, LT4 heads, HotCam kit including the 1.6 roller rockers, Exotic Muscle long tube headers, No catz, stock resonator and mufflers. chip from a company that makes for this conversion.

My problem- I ran her on a dyno and it runs lean after around 3,500 rpms.

rpms a/f
2.3 = 14.49 3.1 = 13.10 3.9 = 13.30 4.7 = 14.18 5.5 = 15.43
2.4 = 13.88 3.2 = 13.11 4.0 = 13.32 4.8 = 14.45 5.6 = 15.59
2.5 = 13.86 3.3 = 13.20 4.1 = 13.26 4.9 = 14.56 5.7 = 15.73
2.6 = 13.27 3.4 = 13.18 4.2 = 13.33 5.0 = 14.74 5.8 = 15.57
2.7 = 12.84 3.5 = 13.20 4.3 = 13.35 5.1 = 14.83 5.9 = 15.30
2.8 = 12.97 3.6 = 13.22 4.4 = 13.52 5.2 = 14.94 6.0 = 15.14
2.9 = 13.10 3.7 = 13.22 4.5 = 13.69 5.3 = 15.13 6.1 = 15.10
3.0 = 13.09 3.8 = 13.27 4.6 = 13.88 5.4 = 15.26 6.2 = 15.04

I am not very savy when it comes to this kind of stuff and need help to understand these numbers and how to solve my problem. I have checked fuel pressure and my fuel filter has been replaced. i have the stock LT1 injectors (24 #) could I need larger injectors? Or can the chip need to be re-done? Any help in the right direction would be appreciated. Thanks

 

What was the running fuel pressure after 3500 RPM? If its around 43 to 45 then the pressure is OK. Typically the fueling in the ECM is rich stock which surpises me as to how lean you are. Have you done any tuning in the PE tables, if not that is what I would have done next.

 

You could just be sucking air at the headers - I'd check for leaks.

 

They read 43 psi with regulater connected at high vaccume and 48 psi regulater disconnected or low vaccume.
What are PE tables, The chip maker asked me for fuel pressures and the shop gave me those numbers. I don't think he actually drove the car with the pressure gauge connected under acceleration. I know that I have a new fuel pump and a new fuel filter when I replaced my fuel sending unit. I have read that the stock LT1 injectors may be squeaking by with the mods I have.

 

No, I did the dyno run before the headers where installed. I went back a couple of weeks later to install the headers. I didn't want to dyno again without knowing why she was lean. Thanks.

 

I'd put the original tune back in it just to be sure - I saw the headers and assumed that was the most likely cause; but a header leak isn't the only cause - always best to rule out mechanical problems first; tune second.

 

Here is a funny thing. I was getting some info together to send for a chip and when I took out the chip it says on it "LT1/HOTcam". I was wondering since I have LT4 heads and LT4 intake, would this make it lean. I figure if the LT4 set up flows more air than an LT1 and the chip says LT1 could this be my problem? Unless this isn't that big a difference and the computer adjusts for the increased flow....

 

Hi,
I may have missed befor , Did you say that sombody varified that your fuel system in not droping in presure as your RPM increases. This must be done in a Tall gear to test properly, and pressure Must be maintained to the RPM that you intend to run this thing.

You are running WAY lean so you need to make some changes B4 you continue testing. You will need an adjustable regulator, and crank the fuel pressure up to about 60 (No Vaccuume) Testing the pressure up like this temporarly add some fuel, and will show if you have a week fuel pump. IE: It will be harder for the pump to maintain 60PSI than 45.

You could Pull the 24#ers out and put in 36 or so but if you have no fuel pressuer, neither one will squirt no matter how big.

My car, on the dyno, in 3rd gear, with a stock in-tank pump.
Went from 50PSI fuel at 3000 RPM to 32PSI at 4300.
You can't tune a car that is running out of gas.
I changed the pump to a Wilden 255 and solved my problem.

By the way, I had no fuel pressure drop in second gear because the RPM curve was to fast.

What's Left:
You have Injector size and pulse width (from the chip map)
You need to find out if the chip you have was tuned for. what injectors,and the combination should be at least close to yours.

You need to determin how much power you combo should make. Size the injectors to match, and then you will need a new tuned chip.

I believe that the 24#ers at 60PSI will support 450HP, but will not live long at that high of fuel pressure and duty cycle required for it.


Hope this helps,

Chad
BLWN BUX

 

Well. I ordered another chip from a different maker. The SOTP feels better and the fuel oder at idle is improved. The fuel economy seems better (to soon to tell how much better) When I get a chance I will get another dyno run to compare the graphs. Overall driving seems improved also.

 

Did you get a chip from us? If so let us know how it works out for you and if you have a chance to dyno it let us know what the AFR was so we can tune it up better if need be.