Hey guys, I am looking for some info or insight into my issues. I've got a 99 sierra w/ an LS6 in it that I built several years ago. It's got Patriot performance stage 3 heads (cathedral port), .650 springs, cheatr cam (.601 intake lift, .578 exhaust lift, 118 lsa) Edelbrock efi intake, 90* elbow, 90mm edelbrock t-body, ls2 injectors and truck fuel rail. Here's my issue, at first I had the truck intake and associated fueling components on the engine, it ran great, I tuned it w/ hp tuners, no problems. Then in the quest for more, I put the edelbrock intake and t-body and LS2 injectors on it, I don't remember having this problem to start with, but now at about 2700-3000 rpms, if I go full throttle it just feels like I've got a restrictor plate on the engine, and it stays that way up past 5,000 or better, and it occasionally pops or backfires in the exhaust like detonation or pre-ignition. Part throttle accerleration is awesome, I've had a fuel pump going out on it for awhile, and thought that was part of my issue, that I was getting adequate pressure under load, and was having extended cranking time. I replaced the fuel pump, and my starting issue was immediately resolved, and power feels slightly better but still doing basically the same thing. I believe I am having a tune issue or combination of issues. I've recently heard the edelbrock t-bodies are junk. I think its a timing problem or fuel issue, any comments greatly appreciated.

 

post up your tune and a log or two. do you have a wideband?

 

It will be late this evening before I can post my tune, I have it on my laptop at home.

 

When you installed the LS2 injectors did you just copy the flow rate over? If the injector values are a sloped value (the value changes with intake kPa change) and you are running the stock return style system it will not run properly.

 

If I remember correctly, I pulled up a stock tune file from the repository, to see what the flow rates and values were, for an ls2 application, and modified mine accordingly. But I have modified this program for this truck so much during everything I have done to it, it all runs together.

 

The problem you are more than likely experiencing is due to the injector values. The stock 99 silverado fuel system was designed to be a return system. The return system uses the intake vacuum referenced to the fuel pressure making the injector value in the tune a constant number. The LS2 injector tune is used on what is called a non return system therfore it can not reference the intake vacuum in the tune. If you look at a stock 99 Silverado tune the injector value is a constant flow number. If you look at a tune for the vehicle the LS2 engine and injectors were removed from the flow is in a slope. Unless you changed the fuel system, and there is no need so it is still the return style referencing intake vacuum. You need to determine the flow rate for the injectors, and make it a constant number in your tune. What are the injectors out of?

Basically this works like a straw in a soft drink. When you suck on the straw it is like intake vacuum.

 

I believe your right. I just pulled my tune to look at it, I believe that is what is going on, here's my tune, hopefully you tuning guru's won't laugh too hard when looking at it. While your viewing it, if you see anything else that looks off, point it out to me. 99 GMC WHATS UP.hpt

 

You need to get a wideband on it to see what the fueling is looking like... without one, you are shooting in the dark. Sounds like it is lean, and as said above, your injector flowrate table probably has a lot to do with it...

 

Thanks guys for the help, sometimes it hard to see the forest for the trees. Somehow my power enrichment table got all screwed up, and the injector flow rate was off somewhat. Now it runs like a scud missile.