DatsunV8

Hi,
I have a '78 Datsun 280z that I put a 5.3 from a 2003 Sierra in. I installed LS1 intake and accessories, with an aftermarket LS standalone harness. This setup is DBW.
My issue is, the engine turns over but no start. Simple right? Well not so much. I bought two different ECMs that had vats and emissions disabled. Both have this issue of turning over, but no start. I can spray starter fluid and get it to start sometimes, once it starts it'll idle for minutes at a time. Easy, fuel issue...
maybe not... I install the original ECM that came with the engine that still has vats enabled and it fires right up every turn of the key, until vats turns the engine back off. I'm lost at this point. Why would that ECM fire up no issue, but the other two that have vats deleted will not? Could this be a DBW/ECM compatibly issue possibly? That's the only idea I have left... Thanks for any suggestions

bobcratch

could be a lot of issues. without knowing if those other ECMs have the proper tune on them or not, its tough to say.
first thing to do is hook up a scanner and check for codes. even the cheap bluetooth dongle with android torque app should be enough to read any codes from the ECM.

DatsunV8

No codes on any of the ECMs. The only thing that will change the starting issue is putting the original ECM that still has vats enabled. It will fire up a second then turn off when vats kicks in.
if I have vats removed from the original ECM would it change anything else that could make it not start like the other two?

bobcratch

it shouldn't. i have done this several times with engines - bring them home, put on the test stand, delete vats, and they have all fired up straight away. Admittedly, i also used the factory wiring harness and fuse panel with all 3, so it was "easy" in the sense that i knew everything was hooked up properly.

LS1 TJ

With the ECM with the vats removed does the fuel pump come on when you turn the key to start? When you turn the key to "on" you should hear the pump start and if it ECM doesn't see crank rotation it will shut down the fuel pump. I would check fuel pressure at the rail. I got a cheap Harbor Freight fuel pressure gauge. Pressure should be around 58 PSI.

DatsunV8

I ran the fuel pump through It's own circuit and relay not through the ECM just to check that no go. I'm stumped.. I thought possibly the first ECM I got the guy programmed it wrong so I bought another one from someone else and the same thing. At this point I'm going to just send off the original ECM and have vats removed.. not sure why that's the only one that will actually start

bobcratch

unfortunately you dont have enough posts to PM you - send me an email at bobcratchet555@gmail.com - thanks

DatsunV8

email sent.

Thanks