I am swapping my 92 Camaro RS V6/T5 with a 95 Camaro Z28 LT1/T56. I have rewired the harness and installed the engine and trans. i have connect all vacuum lines, fuel lines and sensors but haven't added coolant or Y-pipe (oxygen sensors are connected on headers). i wanted to verify the VATS and fuel enable circuits were correct so i attempted to start the engine. The car cranks, starts then dies immediately. I've checked the computer fuel enable signal to the FP relay. 12v during fuel prime and 12v during crank and start. The 12v remain for a second or two after the car stall then goes to 0v. I feel like the computer/fuel signal circuit is working. I hooked up a FP gauge and during the first fuel prime (KOEO) the pressure goes up to about 20 psi. On the second, fuel prime the pressure goes up to about 40 psi. The pressure will start to drop about 5-8 psi after the pump stops. The engine will crank and start with about 40 psi but die immediately. I was able to get the car to run twice using the WOT method. While it was running the fuel pressure started at 42 psi then dropped to 32 psi but the car continue to run. i was able to rev the engine multiple times. It idled at about 1K rpms but i shut it off after 40 seconds because it had no coolant. After it cooled down, i tried to start it one more time and it started then stalled immediately. The ignition coil, fuel pump, fuel pressure regulator and filter were changed a month or two ago as precaution. The filter was installed in the correct direction. Any thoughts on why the car stalls? BTW, the engine ran in the donor car. I was able to drive it up on a trailer, off the trailer and into the garage.

 

I haven't dealt with LT engines, but have done enough work / swaps on many SBC / LS combos to give an observation that may help you-

if you are able to keep it running using the throttle pedal as you say and rev it, etc you have already verified that you are getting fuel, air, spark... otherwise it wouldn't run. however it sounds like you don't have the right combination of that available for just idling on its own and why it doesn't stay running unless you have your foot on the throttle

i would make sure your IAC (idle air control that is on the throttle body) and other air intake are set up and plugged in correctly. is the MAF plugged in. what changes have you made to the air intake versus the donor car. it takes very little air to idle... however if that is not correct it is very easy to stall

 

Alan91z28 thanks for replying. I basically pulled the engine from the donor car, rebuilt it (slipped crankshaft bearing, new OEM crank, OEM cam, rebuild kit, fuel pump, fuel press reg, ignition coil, fuel filter and fuel/PS hoses). I did attempt to clean the throttle body while it was disassembled (the donor car and engine was really oily/dirty). I didn't remove the IAC or the TPS. Perhaps i damaged it, I will take a look at that today. My buddy suggested that as i was typing up the post last night. This social distancing is really putting a damper on buddies help.

 

I have been down this road before with the LT1/T56 swap.I love mine,it has been three years since I finished my swap.
What kind of fuel pump did you use? I do not think the pressure should drop that much that fast.
If you have a scanner or software,I suggest checking coolant temp,tps voltage,and fault codes.
Clean and inspect the MAF and you can also try to run it with the MAF unplugged.
I recommend putting coolant in and trying to run it for a while.

 

So I checked out the IAC and it checked out good according to Chilton. ~50 ohms on c/d and ~50 on a/b. I cleaned it and the TB up then reinstalled. tried starting the engine but had same results, it was slow to start then when it did, immediately shut down. Alan91z28 thanks for the suggestion. at the least, the IAC is cleaner now.

LT1/TA, I replaced the pump with another OEM pump (MFI V6 pump). I read that they both V6 MFI (~44 psi) and LT1 (41-47 psi) use high pressure to feed the injectors. so when I hooked up the pressure gauge, I zeroed it by bleeding the gauge line. On the first KOEO, the pressure goes up to 41 psi, between KOEO cycles, the pressure will drop to about 5 psi in less than 2 minutes. Weak new fuel pump? Wrong fuel pump? Is there a check valve that prevents the pressure from dropping on the feed line side once the pump stops?

I don't have an OBD1 scan tool with OBD2 connector or software, yet.