Ikarus

Okay, here goes. I'm building a 79 Stepside with an LY6 from an 08 Sierra and a 6L80 from a Pontiac G8. I'm finally trying to start her up, and all it does is crank all day long. I've checked every ground, every power wire, tried using every single wire in the ignition switch harness as my "Hot in ON and START" wire (I'm using a PSI Conversion harness), but no matter what, I get no spark. I've checked voltage at the coils, and all is well. I have fuel, and my PCM was just reformatted with a new tune to rule out any tuning issues (i.e., VATS). I don't see any recessed pins in the PCM connectors, and I don't see any obvious broken wires anywhere. I've checked voltage and resistance pretty much everywhere. I replaced the Crank Position Sensor because I wasn't getting RPM, and now I am. I haven't replaced the Cam Position Sensor, but it should start up regardless of that.

My wiring, as of right now (using this diagram):

Grounds:

Engine to chassis
Battery to chassis
Engine to body
Two PSI harness grounds to the back of the driver's side head

Positive:

Battery positive to starter battery positive post
Starter positive post has connections to Pin 2J on the firewall
Starter positive to junction block
Starter positive to two battery positive terminals from the PSI harness
Junction Block goes to alternator and Pin 2E on the firewall
Starter S post goes to Pin 6 on the firewall

The "hot during ON/START" has been tried on the cab side of Pins 3 and 25 (as well as almost every other one in the ignition harness)

I can't figure out what I'm missing. I had to re-run brand new wire and Type 56 terminals to the firewall because the original harness in this truck was completely trashed.

The weirdest part is, earlier this week, the truck started up for a couple of seconds, 5 or so times in a row. I had it connected to a laptop and an EFILive autocal so I could log whether or not it was even commanding spark, but it fired up instead. I've tried the same thing multiple times since, and I can't get anything from it.

Any help or direction you guys can give me would be appreciated. This is the first time I've ever built a vehicle, and until now it was going great.

I also posted this on the 73-87chevytruck forum, but LS1Tech gets more traffic.

Tuskyz28

I bet the computer is throwing the VATS....

Other words sound like it's locked in theft mode.

Ikarus

Pat Guerra, who made my new tune, specifically turned VATS off, since I thought that may have been one of the problems. Also, I thought it would fire up but shut off if VATS was enabled.

Tuskyz28

I'll definitely check back with Patrick. He knows his stuff on tuning.

Since you have check all the grounds... I'll make sure the motor have a decent amount of fuel pressure.....

Tuskyz28

A 79 fuel setup isn't enough to keep up with the newer LS motors. You may need a hotwire walbro kit......

Ikarus

Yeah, I didn't specify in the original post, but I have a Walbro 255 going to a Corvette regulator with -6AN all the way to the rail. I haven't checked with a gauge (I'll have to rent one from O'Reilly), but it definitely has pressure (don't ask me how I know).

I've pulled plugs and grounded them to the block but it's not putting out any spark. I'm just hoping there's a ground that I forgot or something like that. It's really weird that it fired up that one morning and then never did it again.

Ikarus

Pat is definitely great. He's done all but one of my tunes on the G8, and I've since gone back to his tunes on that car. That's why I went to him with the truck.

Rocknrace03

i also have a psi harness and had some issues at first. try taking some jumper wires and connect all the grounds together. The one on the back of the cylinder head must not have been grounding well. s soon as I tried that, it fired right up again. I have since extended them and brought them all to one spot instead of various places in the engine compartment.

Ikarus

I have them grounded to the same bolt on the back of the head, but I'll try moving them to the other side or jumping them to another ground. I'll try it after work and let you know how it turns out.

truckdoug

iTrader: (25)

no spark? I assume the psi harness has a separate relay for the coils. have you swapped relays around? double check the wiring on the relays.

are you getting fuel at the rail?

ls1_chevelle

iTrader: (9)

For ***** and giggles try grounding the computer body itself to the car.

1989GTA

Couple of things. It is recommended to have the ground in a "Y" configuration with the center of the Y being the engine block and all the other grounds spidering off from that. This helps prevents ground loops and funny electrical problems. So you would the ground wire (-) from the battery to the engine block and go from there to the other points.

I would not have all the battery power (+) going right to the starter. It draws the voltage down to low during the starting sequence and the ECM does not get the voltage it needs. You need a power cable/wire going straight from the battery to where your ECM gets its power. You can leave the power cable from the battery to the starter if you want. I used a robust junction block. This junction block is also where my alternator cable goes.

Ikarus

So I'm getting 12V at the ignition sequencers and individual coil plugs, but not the 5V for actual ignition (when cranking). In fact, the voltage on that pin goes negative during cranking. It's been ten years since I took an electronics class, but I know that's not right. I've put new relays in the fuse block as well. I'm looking at LT1swap.com for reference as to the PCM pinouts, and I'm going to check the Power Train Relay Coil Control pin. I can't think of where else to check.

I've reconfigured the grounds in the Y configuration, but that didn't really fix anything. I'll look at the power wires to see what I can do there, but the PSI instructions stated to send both positive blade terminals to the starter battery positive post. I'll try moving the wire that goes to Pin 2E directly to the battery as well, but I've tried directly wiring the "Hot in On/Start" wire to the battery and it didn't make any difference.

If any of you guys are in Little Rock, I've got 50 bucks and a case of beer if you feel like helping out!

Ikarus

If the PCM were bad, it wouldn't have taken the reprogram and then the full tune, right? It would at least pop codes, I'd think. I've consolidated the number of power wires down and I still can't get it to work. I'm about to hit a deadline. If I can't get this thing running this week, I'm going to have to start packing it up and pay to have it shipped back to Georgia. Original plan was to drive it back and tow the car, but I'm not going to be able to do that now. Ugh.

jimmyg

Make sure pcm has power while cranking . Mine was hot while key on but starter was robbing wire of power while cranking . U might want to put a meter on it and check it out

ls1_chevelle

iTrader: (9)

Did you try grounding the computer like I suggested?

Ikarus

I've even hooked the "hot in ON and START" wire directly to the battery. Nothing.

Tried this, too. Tried it to the chassis, frame, and battery itself. No dice.

Ikarus

Something just dawned on me that definitely isn't right. Since I've gotten so used to everything being weird and not responding correctly, I didn't even notice that as soon as I connect the battery, the throttle body, PCM, pedal, and fuel pump come alive. TB responds to pedal input with the ignition off. So there's a problem somewhere, and it's probably causing my voltage drop at the exciters.

This is, of course, basing it on the "TB doesn't do anything in my G8 with the ignition off" experience.

jimmyg

Some wires are battery, some are switched power .maybe your harness is mislabeled.

ijimmy

vats disables fuel delivery , not spark . Your computer is looking for crank signal, and cam signal , to start ignition spark , if both of those are fine , and working properly another thing , ground , can stop ignition spark . These ls engines require really good grounding to operate the way they should , from the factory all have atleast 3 ground wire to the engine , and I have seen 5 . If just one is not correct ,,, no spark