mannythechamp

Yup as mindblowing as that sounds to anyone that knows anything about cars.

Story, Car is a 49 chevy pickup that I have swapped a 5.3 lm7 off of an 04 avalanche. I scooped up engine, tranny, pcm, and wires off the original car, and it ran perfectly fine.

Now Vats has been removed and I have reworked the harness, I have solid power coming into all the coils, injectors, and all the other pink wires at all times!

If I try to start the car I dont get any spark, the second I unplug any injector, any of the 8 wala i have spark and the car will try and start, it sputters hard but if i open up the throttle i can keep it alive for a bit, then plug in the unplugged injector and she smoothens up nicely! I am completely stumped with this

any insight or ideas would be appreciated greatly!

I am assuming it might be a grounding issue but I have no clue as to what else might need ground, The whole rework section has one ground that came off the c2 block, the engine has 2 ground in the back of the block and the one that goes from the frame to the block.

Thanks!!!

LS1-450

iTrader: (33)

Should be 3 grounds to back of block. Check an Avalanche wiring schematic to find the missing ground.

mannythechamp

According to this. http://www.justanswer.com/chevy/0sa52-need-locate-grounds-truck.html

There are only 2? Is this wrong? Or am i just confused?

LS1-450

iTrader: (33)

IDK, all the LS1's I know of have three. Try comparing that schematic w/ an 04 F-body or Vette schematic & see if anything jumps out @ you. Looks like either a short to ground or a missing ground. There is an issue w/ a circuit related to starting the car. I'd look @ all start related circuits.

mannythechamp

Everywhere i read everyone says the engine harness has 3 grounds to the block, i know for sure i only have 2 at the back right now bolted up so i will look for another one, it has to be a ground issue i cant come up with anything else that would cause this

ls1nova71

iTrader: (4)

The third ground is on the driver's side down low behind the power steering pump. Maybe check that.

mannythechamp

So i took apart the grounds cleaned them good and i can get it to start, takes a litttle while to start, and i have to give it gas ,and runs a bit rough but that might be due to not having a fuel oressure regulator on, ima go get one, a rad so i can keep her on for a while and then report back as I monitor the live data.

ls1nova71

iTrader: (4)

So you found all three grounds? The one on the lower driver's side is the ground for the ignition so without it you wont get any fire, odd that it would work with one injector unplugged though. Did you find that out by accident?

mannythechamp

Yea complete accident lol, but she fires right up now gonna monitor her now and make sure everything is working properly. You guys still run dexcool on swaps right?

ls1nova71

iTrader: (4)

I ran Dexcool once until I found out the hard way your cooling system needs to be totally sealed. If not when the radiator cools down it pulls in air and Dexcool and air make baby **** looking mud. I flushed it and now only run the green stuff.

ijimmy

I dont know how any ls baised engine would run at all without a fuel presure regulator

bczee

iTrader: (12)

I don't use Dexcool on any of my swaps. I do a complete flush of my systems and use the normal green stuff.

If i can't flush the engine before taking it. I will start it up with water. Flush it a few time and the use tge green stuff. Never had a problem if junk building up due to the Dex being in there before.

mannythechamp

I guess the green stuff is what i will put in! thanks guys!


I learned this the hard way! lol these engines are finicky with their fuel pressure

Something interesting is going on, I go to fire her up and i notice that she cranks and runs for a quick second shuts off i crank her a bit more and then unless i throttle her for a bit and wait till she gets used to running she wont stay on..

As far as codes I have 6 codes none of which i think are associated,

Maf code since its not in yet,

engine temp using a different sensor,

fuel level,

engine oil pressure low voltage, no idea why?

Malfunction indicator lamp, no CEL light yet

and engine rpm output, i have no tach yet..

she runs great after a while idle is even with what ecu is asking for no misfires nothing

Thanks again

LS1-450

iTrader: (33)

Are you kidding me? Come back after the MAF & temp sensor are in & working.

mannythechamp

got the maf on and plugged in..

as far as the temp sensor? would it cause a difference?

after a few more hard starts and replugging in the fuel gauge, it now starts instantly

has me a bit worried! but its hopefully gone

ls1nova71

iTrader: (4)

Without the temp sensor plugged in the PCM thinks it's -40 degrees out, so yeah, it can make a difference!

ls1_chevelle

iTrader: (9)

Like said above... You are very wrong on your assumption.

get the MAF in

use the factory GM coolant sensor.

If you have aftermarket gauges, put that sensor in another location!!!

mannythechamp

You guys were absolutely right, I decided to keep the oem sensor the pcm reads actual temps now instead of -38 lol!

Thanks for all the help and insight!

LS1-450

iTrader: (33)

Yah, thanks for wasting our time. Should have told us no MAF or temp sensor up front.

Old Geezer

iTrader: (3)

Sounds to me like the cart is before the horse...Let' try it, even tho the system[s] are not hooked up.