480 horse Ls3 first start problems
 

Finally started my 480/376 LS3 and it will fire, but almost dies immediately. Twice it continued to run when we disconnected the maf sensor, but hunted. It continued to run when we connected the sensor. Using the gm computer and harness. No codes read. Help!

Re: 480 horse Ls3 first start problems
 

Maybe sensor and tube diameter not the same as stock. Anything other than stock makes it run poorly without retune.

Re: 480 horse Ls3 first start problems
 

Thank you, I'm using the GM tube designated for the LS3. Perhaps it's facing backwards. Will check this weekend.

Re: 480 horse Ls3 first start problems
 

The MAF was facing backwards. Now it starts and runs well.

Re: 480 horse Ls3 first start problems
 

Having put a couple miles on it I've got a few observations. First, it's really fast, like scare me fast. Anybody who tells you 480 plus horsepower is no big deal has bigger huevos than I do. Secondly, I need to move the throttle pedal up higher on the firewall and away from me. My leg is at a strange angle and it's very uncomfortable. We'll have to bleed the brakes again or get a vacuum reservoir for the power brakes. They are a little spongey and there is too much pedal before the brakes really grab. Finally, a hydraulic clutch is the way to go with a swap like this. No squeaks or groans. A nice linear engagement. Truck fires instantly and settles into a lopey idle almost immediately. It's a lot of fun to cruise around in.

Re: 480 horse Ls3 first start problems
 

Good deal....what do ya have it in?

Re: 480 horse Ls3 first start problems
 

I second Mongo's question -- what's the ls3 mounted in?

Is it an engine from a donor car, or a GM performance crate engine?

Do you have a clutch pedal position sensor connected? What sensor? How's it mounted? Any pics?

Re: 480 horse Ls3 first start problems
 

GMC crate engine with captainfab's hydraulic clutch setup. McLeod hydraulic throwout bearing on a tremec tko.

Re: 480 horse Ls3 first start problems
 

Just after 1st fire.

Re: 480 horse Ls3 first start problems
 

Looks like a nice truck. Too bad it's hanging from the roof...

Do you have a clutch pedal sensor wired into the engine computer? If so, do you have any pics of how you mounted that sensor to the pedal?

Re: 480 horse Ls3 first start problems
 

No clutch pedal sensor. Why is one necessary? Engine is wired up using GMPP ecu.

Re: 480 horse Ls3 first start problems
 

The LS3 used a clutch pedal sensor in the Camaro's. I assume the Corvette was similar. This sensor would disable the starter(controlled by the ECM in factory applications) if the clutch is not depressed. It would also disable the cruise if you hit the clutch pedal. The third reason is partially speculation. I'm told the Deceleration Fuel Cutoff tables were modified if you had the clutch pedal depressed. Folks have expressed some problem with clutching to a rolling stop, and having the engine hesitate and die. Supposedly, if they had a clutch sensor installed, it would fix that problem.

Being your ECM is from GMPP, they may have adjusted the tune to eliminate the need for a clutch sensor.