Zac77K5

Hey yall I'm relatively new to the LS game and have done some extensive research and searching before trying to post what may seem like a redundant question. I already installed a 5.3 into a truck for a friend and did the wiring according to the instructions on lt1swap and had the computer flashed as well and it started right up when I tried it. However I installed a 2004 5.3 into my 77 k5 and it will not start. I checked for power at each coil and they checked out as 12v the ground and the computer controlled ground were good as well. (Not sure how to check the trigger wire though) I then check for 12v at crank sensor and that was good and the ground was good as well. I just can not figure out what the problem is. All grounds are connected to the engine block as they were in the donor truck. Also checked each ground wire at the computer and they were good as well. but from reading other swap no start problems I have tried the same solutions that got them results to start but I have had no success. Any help would be greatly appreciated as I'm needing to get this running so I will have a truck in college when I go back mid August. Thanks!!

Mike_hawk

What is your fuel setup? Have you verified that the fuel pump is priming? If you spray starting fluid in the intake and it starts that can indicate a fueling problem. You can take a spark plug out of the engine snap it back into the spark plug wire and hold the electrode to the frame/a ground and see if you're getting spark when someone cranks it(wear rubber gloves).

Zac77K5

I have got a walbro 255lph inline pump and I'm running the corvette regulator because my fuel rails are the returnless type. When I turn the ignition on the fuel pump turns on for 2 seconds then cuts off like it should. When cranking I can hear it kick back in and start pumping again. I've pulled a plug wire from one of the coils and then plugged a spark plug in it and grounded it to the engine and had someone crank it and had no spark.

Zac77K5

I haven't tried the starter fluid though cause I didn't see a spark.

33willys

iTrader: (1)

Always go back to basics. Do you have fuel? To check this you will need a gauge to connect to the test fitting. Just because the pump is running does not mean the fuel rail is getting the required pressure. Could have line blockage, lines hooked up backwards, faulty regulator, faulty off shore knockoff pump... Next, are the injectors firing? Need a noid light for this. Make sure they are firing during the start cycle. In some cases when the key is in the start position some circuits are cut out such as headlights...etc. Last is spark. Put a timing light on a plug wire to ensure you have spark. If each of the above checks out try starter fluid. If it will run then it points to clogged injectors. Let us know what you find.

Zac77K5

Ok so I put the fuel pressure gauge on at the rails and got 0psi i then went back to the pump and disconnected it from the regulator and it sprayed fuel everywhere. I turned the pump on manually to see if it was pumping fuel still and it definitely was. Could a brand new regulator not flow through it at all? I don't have an AN fitting adapter for the fuel pressure tester to check pressure coming right from the fuel pump

Zac77K5

I had the input and return switched on the regulator now I have 55lb according to the test gauge at the rails

Zac77K5

The noid light is not lighting up or flashing while cranking the engine.

trozfan

Check for voltage at coils/injectors during cranking. You may have them hooked to the wrong type of ignition power.

Zac77K5

Haven't tried it during cranking yet. Will try that here in a minute.

Zac77K5

Alright after getting the fuel up to 55psi I checked the voltage during cranking as suggested and she fired right up! Thank yall for all the help it is greatly appreciated!

33willys

iTrader: (1)

Thanks for getting back to us with the solution I'm sure it will help others. Hooking up the fuel lines backwards is VERY common, I did it on my first F.I. swap.