And externals need to be mounted below the tank to gravity feed. The pumps are pushers not suckers

Lowered the fuel pump got it to run for a sec then back fires think the valves are maybe too tight

Should have the mods change subject just to avoid any wirdness for psi conversion s

Jay, did you have the engine apart? Maybe a cam change? I've seen many people put too much preload on the lifters of a SBC, and it will back fire and not run every time, but I'm not sure it's possible to accomplish this with an LS platform, to that extent...having said that...you said earlier in the thread that you weren't getting spark. Can you verify spark and fuel?

Ls3 rockers are not adjustable. If a cam swap was done then measuring pushrod for proper length would be the prudent thing to do.

These are hydraulic rollers so unless they are way off it would not keep the motor from running

I'm trying

may just have to roll down to Cali

Ya that's true. Cam was never taken out. It's a crate engine with the 480 cam

I'll get back on it tomorrow.
Thanks for all the helpful hints

Car starts up found out why the car backfires. The rockers were off the valves all he way on a few cylinders.

Think we got it figured out

Dang, Hecho en where?

Two rocker arms have bad bearing so in going to buy a new set and replace them all.

Anyone run roller rockers? Or should I stay with the stock style rocker arms with the Trunion kit?

Trunnion kit. we swap em on all ls

I would stay with the stock rockers in your case. We've seen failures with those too.

So a brand new unfired GMPP crate engine had bad rocker arms right out of the box? That doesn't sound very encouraging..

Don

The engine had 25-50 miles on it long story the engine was in a car that had a small fire. 1960 Chevy it was in caught fire but they got to it within a min or two so just the intake and other plastic parts were melted. The engine did have water in it for some time. Thinking now two lifters may be bad.

I'll order the Trunion kit anyway just to cross that out

could lifters feel spongy? Think they just need to build up pressure maybe from cranking the engine over and not starting all this time could of drained the oil?

Should I replace them dont really want to pull the heads

:confused59:

The fire would have been helpful info to pass on when looking for help diagnosing the start up issue:headspin:

:innocent: :ohsnap: :ohsnap:

You should make sure you have good oil pressure before starting. LS motors can be difficult to prime. Remove the plugs, disable the ignition and fuel and crank til you have good oil pressure. This is quite important.

Don

Damn fix one this then another thing goes wrong.

My fuel pump wire lost power. Fuse is good relay is good. what the..............

PSI Harness. Fuel Pump relay gets 12V from the ECM when Ign is turned on.

So are you saying you don't have 12 on the wire that goes from the relay to the pump?

No Power so its mailed back out to Gary @ PSI

He said he would get it fixed and set back to me. Ill get there soon

Before you send it back to PSI, just be aware that the ECU shuts off the power to the fuel pump after 5 s (I think) if the engine is not running. Not sure if you know that or not.

It use to do that now it does t have any power coming from the ECU.

Back at it....

ECU Re Programmed everything seems like it should run. It wants to start but just wont fire.

My fuel pressure is only at 50 PSI could that be too low?

It should start and run just fine with 50 PSI

Make sure you have 12v going to red ignition wire with "key on & cranking".

The wire I fed it with had power with key key on only, but nothing when cranking. It would turn over, but not fire up. It's a fairly common issue (sorry if you have already checked this).

So my new Vaporworks tanks in. I hooked up a scanner to the car and its throwing a P0135 code. The scanner says Crank sensor but I changed it. Online forums says o2 sensor. Hmmmm

Does it start and run now?

Car will still run with the P0135 code. In fact it should start and run even if the O2 sensors are not installed.

No start it wants to start it sounds like but nothing

po135 is the heater circuit....ASD relay controlled.

Have you called PSI again yet?

J,

Did you check for this?

We add a relay to provide 12v to the ignition circuit during cranking. Also double check your power and ground circuits. Something ain't right.

I am going to check to check the injectors with a NOID light. It will fire for a split second. I think the ignition switch could be bad? Maybe its dropping too much while cranking?

If it is the factory style switch in the dash it will provide zero voltage while cranking. This system ran 12v cranking voltage from the resistor bypass on the starter.

You can run a relay with a diode to use the purple starter wire as a signal to send 12v to the ignition circuit.


Vince

Thanks Vince,

I have been thinking about this a lot. I am going to try this tonight or tomorrow.

You don't need any additional relays or diodes.

I've done 5 LS swaps on 1st Gens all with factory ign switches. 3 GM Perf Harness, 1 Psi and 1 reworked GM take out harness.

LS ECM

You need 12v switched power to the PSI fuse box.

The ECM is powered up with ign 12v. When you turn the key on the ignition and fuel pump relays close.

When you hit start the purple wire provides 12v to the starter.

From PSI

NO-START
1. Red Ignition Wire (From back of Fuse/Relay Center) has 12-volts with the Key in the ON
position and CRANKING position. This cannot be stressed enough, most NO-START
conditions can be traced to this wiring issue.
2. Check that 2 Large Ring Terminals by Crank Sensor are connected to CONSTANT POWER.

Batt. Battery Positive (2 LARGE RING TERMINALS COVERED IN BLACK HEAT
SHRINK), These are often mistaken for ground wires because of the black heat shrink

Thanks for all the help. Soooo I think I know what's wrong the car will start for a second if it's been sitting for an hour or so. I think the injectors are clogged or not working. They were new injectors they were from a friend that works at Magnuson Superchargers. I think the were sitting for some time as the car smells like stale fuel. Either the injectors aren't getting power or the injectors are clogged. Testing that tomorrow. If all else fails I got a guy coming to look at it this Sunday.

are talking about the PSI harness or the factory GM fuse panel?

I was thinking he might have those mixed up but the PCM is powering up from his description.

Jay, pull a spark plug. If it's wet, the injectors are firing. The noid light will help you in seeing if they are firing. You'll be amazed at how simple your problem was, once the car starts.

He said he has the PSI harness. Maybe injectors are clogged but to have all clogged would be a surprise to me.

Car had a engine fire which could have damaged them however as I read it he has different injectors in it now.

As always it's probably something simple like a loose ground.

A friend of mine had a problem with his LS and PSI setup cranking and not starting. Turned out where the 2 grounds bolt to the rear of the head the bolt was a touch too long and bottoming in the threads. The bolt was tight but the grounds were loose.