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Thread: Thanks OLD SCHOOL EFi!!

  1. #1
    Carb and Points!
    Join Date
    Oct 2013

    Thanks OLD SCHOOL EFi!!

    After a while....I just couldn't stand how underpowered Dad's 1995 K2500 was! I decided to do some engine upgrades.
    In the past I had used a small comp cam and with a lot of screwing around, got it to work OK with the TBI.
    In case you don't know, GM TBI is a speed density system and is extremely sensitive to engine vacuum...which any aftermarket cam will mess with!

    I ended up using the smallest Lunati cam in their voodoo series.
    This 8600GVW LO5 is supposedly a little different than the the 1/2 ton LO5's in the it has 8.75 or 8.3:1 compression depending on what info source you use. It supposedly uses the old school GM 929 cam instead of the TBI peanut cam.
    The install was pretty straight forward. The AC condenser will flip out of the way without disconnecting it and the cam is just too long to come out without removing the entire grill, dang it! And with the big floppy one piece oilpan gasket....I had to trim more of the "lip" edge off the timing chain cover than normal to get it back on.

    Since it was a flat tappet cam I had to "run it in". With an oil pan full of Comp Cam break-in oil, we lit it off. Man I hate the pucker factor of firing something up and going straight to 2000/2500rpm for 20 minutes!!! (I saw after I pulled the intake this block was drilled for a roller cam.....I should have stopped what I was doing and found the parts for a conversion)
    Like a rookie....I had the timing severely retarded....and the exhaust manifolds were glowing cherry red, but we got through it!

    After I got everything running well, I added a throttle body spacer so I could use a flat bottom open element air cleaner and remove the "choke collar" under the stock TBI unit. I also set the fuel pressure to 13.75psi.

    The last part of the story is....tuning! As I mentioned earlier, this speed density TBI will not tolerate ANY changes in manifold vacuum. The cam I use was listed as TBI compatible. It should be listed as TBI compatible WITH TUNING! It ran just fine without tuning, but there was no power increase over stock.
    I stumbled on to and got busy learning about TBI tuning! For a relatively small amount of money, you can datalog GM TBI with TunerPro RT and get A LOT of useful data!
    This process isn't exactly plug and play.... You have to do some leg work. Silly things can foul you up. You need to get a ALDL cable, get the correct drivers for the cable then set the com port in your lap top for the cable. Its not as hard as it sounds and there is a ton of info on how to do it.
    Next you're going to need to find your "BIN." file by reading the code of the chip in your ECM/PCM

    This is where I ran into a snag.... The truck I was working on is an oddball because of the stick so there was no BIN. listed in any database I could find.
    Enter Old School EFi. If you look around you will find a user DaveW that answers a TON of questions. David runs Old School EFi and took on my tuning project.
    I sent my chip to him so he could read the bin and then I could start the datalogging process.

    David required about 100 miles of clean error code free datalogging to start the tuning process. (through my initial datalogging I discovered the O2 sensor was failing even though it wasn't setting a code)
    David had the chip dialed in on the second try and the truck runs GREAT!! It is a night and day difference from the stock chip. It now pretty easily pulls 4th gear to 4K redline! Now, it not a rocket by any means, hell its still slower than a stock 5.3, but it feels soooo much better than before!
    I will go out on a limb and say that 70% of the performance increase was from tuning alone. I really wish I had tried tuning it stock first to see what it felt like.
    By looking at the stock BIN in tunerpro, the stock tuning had VERY limited timing advance. David fixed all that. And unlike off the shelf chips, the timing is only added where needed and not across the board.
    I was really impressed with his customer service!
    Dad is very pleased with the new found performance! Although....Its not just all for him....this is now a nice tow vehicle for take the Shelby the drags!

  2. #2
    Carb and Points!
    Join Date
    Mar 2015
    Hi andyk1500! I'm new to this GM EFI stuff as well and willing to learn. I think DaveW will be a huge help when I get all stuff I need to proceed. I recently bought a 1995 K2500 (8600 GVW) 5.7 that I want to keep "relatively" stock , but get the most from my TBI. Really enjoyed your write up!!! Regards, Randall

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