Hey, I'm brand new to this forum, never struggled so much with making an LS run lol

I just shoved a LM7 into a G-Body with a TH350. Chinese harness, P59 ECU, VATs off with HPtuners.

Fired up great, ran for 4 or 5 minutes, just to get the coolant into it. Shut it off, then turned it back on. No start. It'll crank well, but backfires like crazy and refuses to run, only sputters.

I checked spark at all 8 cylinders. Strong purple spark. Yanked the rails to check injector squirt, all doing what they do. Fuel pressure is 51psi ish at the Schrader.

Checked my grounds at the ECM, seem fine, less than .3 ohm, checked my 12v to crank and cam sensor. Fine. In HPtuners it says it's cranking at 150rpm. Checked coil grounds and injector 12V, both good. Out of desperation I tried the pinouts of the ECM, according to LSwiring (just the grounds and +12v though) but they seem fine too. No trans sensor to mess with things, throttle blade moves around. Brake cleaner does not start it. Doesn't even wanna run. Did a compression test, 150+ every cylinder. Even looked at the valvetrain, but all of them move. Swapped ECM to a different one, it doesn't matter, still same behavior.

Maf is the only sensor not connected, but I've never needed it to at least start the engine

I'm so lost, anyone got any ideas?
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"Maf is the only sensor not connected, but I've never needed it to at least start the engine".
Hooked up on first start?

 

No, never hooked the maf up. I tried throwing a truck intake on it this morning with a maf, no difference

 

Have you tried another crank sensor? Since HPTuners shows 150 RPM crank, we know the sensor is at least somewhat working, but maybe not well enough to synchronize the cylinder spark.
Since not even Brake-clean starts it, I'm thinking spark is at the wrong time.

 

That's what I'm thinking, I'm going to pick up a Delphi crank sensor at this very moment, and I'm going to get an extra cam sensor too just to be safe. Don't think I'm going to install it yet, but just in case the crank sensor doesn't work. The crank sensor that's in it is from Napa, so I don't doubt that's the issue. It's currently hailing, so I'll get this all done tomorrow,

 

Well I'm stumped. Tried new CPS, no luck. Same thing. Went and read codes again, and got a cam position sensor circuit code (342).

That's diagnosable, replaced the cam PS with the new one I got yesterday, no dice. Checked ground on middle wire, solid ground (0.01 ohm), checked C for 12V key on, 12.61 volts. (Gen 3, not gen 4, so I think it's 12V, not the 5 that x58 models would have right?)

​​​​​Am I correct in checking CPS wire A to pin 73 on the ECM? That wire checks fine from the sensor all the way to the ECM pin. That should be signal from what I see. I'm just...beyond confused what's happening at this point.

I've never had an LS swap fight me this hard lol
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SOLVED!

Appreciate all the ideas here guys, yall are awesome. I pulled the motor, turns out the reluctor wheel on the crank wasn't lined up correctly. I think it spun on it's mountings. yanked the sensors and intake, put em on another 5.3, threw it on the engine stand with the harness from the car, ran fine.

looks like this 5.3 is getting a ebay forged rotating assembly lol. Again, i appreciate all the ideas. Peace! until next time!

 

Ebay would NOT be my choice of sources for critical parts! Go to a reliable supplier,
Cry once, pay once.....

 

How does that happen? It's not like it comes into contact with anything (at least it shouldn't).

 

Yeah, glad you solved it, but how the heck would the reluctor go out of position. Even back when I said "spark is at the wrong time", I didn't consider a reluctor problem. (I was reluctant to do so.)

Like ​​​​​@G Atsma I would be careful about about major parts on ebay. Instead, consider something like a Summit brand kit for something lower cost.

 

i've actually used the evilbay Eagle forged rotating assembly before, it worked fine. It's a $200 5.3, i just use em till they blow up, then get another motor. usually last at least one season on the strip lol.

For cars i care about, i'll go summit

 

to you and Dixiebandit, I actually have no clue. the wheel on the crank was clearly off, but idk how that happened. spark was waaaayyyy off, but HPtuners was showing fine spark advance (14deg). IDK how this happens ngl. I've never seen this before.

ah well, you live and learn. I'm just glad its done, since i've been working on this car in the snow.

 

First I've heard of one coming loose without something hitting it..

 

Unlikely, but I had issue with start, barly run stumble want to stall, but would run with throttle, ended up being a sticking open Purge Valve...

 

[QUOTE=Thefox22448;20594918]SOLVED!

Appreciate all the ideas here guys, yall are awesome. I pulled the motor, turns out the reluctor wheel on the crank wasn't lined up correctly. I think it spun on it's mountings..
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You said the engine initially STARTED and ran several minutes while taking coolant. How did the reluctor MOVE at idle ? ( or move at ALL ? )

 

on my swap, I ran into the same problem. Gen IV w/Speartechhrmess, Once I put the MAF into a tube that’s mounted (vs hanging loose) to the TB mine started right up. FWIW.