No start issue

[mongocanfly]

I'm going to abandon the po452 thread..I'm pretty sure it's not my issue
Still cant get engine to run on it's on
Me and PSI have been trying to rule a wiring issue and solve this and I've come to the conclusion that's it's not a PSI harness issue..
What I've done so far
Verified I have 12v key on and crank and have 12v outgoing from the ignition relay
Verified fuel rail pressure, 58psi
Verified 12v at the injectors
Verified harness grounds
Checked fuses
Only code on scanner is po452
Cleaned injectors and verified good spray pattern
Checked injector firing with a noid light..(no fire)
The engine will run if I pour some gas in the throttle
What I've noticed is when I start a crank sequence ,the injectors will fire 1 time..
Then they dont fire again during the crank cycle..
I couldn't see the noid at 1st so I turned the shop lights out, when it does fire the 1 time, it is a very dim light...nothing like how bright they show in the video..but it just fires once during cranking
Gary at psi is thinking it may be in the ecm tune..
The guy I use is hard to get on the phone,,very busy man,, may have to call 50x before he answers..
Just wanting to pick y'alls brains and see if I'm missing something before I call him

Little background
I have changed the intake to the Holley 300-136, mounted the throttle on it with a adapter, the map sensor is integrated in the adapter plate, the maf is mounted on top of the throttle, the cam has been swapped to a btr stage 1
Engine will run, just not on its own

[Joyridin]

Did you test the crank and cam sensors? I would start there.

[mongocanfly]

No I havnt...and not sure how...will do some research..
I pulled this engine from a wrecked ,running truck,so I know it was good when i got it

[Joyridin]

Originally Posted by mongocanfly

No I havnt...and not sure how...will do some research..
I pulled this engine from a wrecked ,running truck,so I know it was good when i got it

I would definitely start there. I don't know what they cost, but it might be worth just replacing them altogether.

[ls1nova71]

I would get it tuned. I've only swapped one cam and that engine wouldn't run for anything before it was tuned. Also changing the intake along with the cam only adds to the problem. Find a good tuner, they should be able to fix it I would think.

[mongocanfly]

Thanks guys.. I'll try to get the tuner on the phone this week and see if he can look at the ecm ..
He was aware of the cam/intake swap when he did the unlock and base tune..but something could have got missed..he does hundreds of these unlocks a yr and runs a LS swap garage and a dyno, along with a fab shop..so I trust him..

[AussieinNC]

Make sure VATS is totally turned off. There are some versions where this requires two different actions to make sure its shut off...

[mongocanfly]

Got with my tuner guy today.. he looked thru his files where he did the ecm unlock.. he said it should be good.. and to double make sure, he hooked up and checked the ecm itself to make sure everything was there..it was .. he already had his suspicions as to what it might be.. crank sensor not reading.
He says you get the initial injector pulse, then the ecm needs to see engine rpm to continue firing the injectors...that's why I see the 1 time injector fire when cranking... since this was a running engine when I did the swap, he said I need to check the crank sensor wiring.. he said hes seen 3or4 harnesses that were pinned wrong in the past yr or so..and just to rule out the ecm ,were gonna put it in another truck tomorrow and make sure it runs..
Joyridin mentioned the crank sensor above...Still not sure how to check the crank sensor..but he did say if I had a hand tuner I could check the crank sensor signal with it...gonna check wiring 1st..

[biketopia]

If you end up replacing the sensor, go with a genuine delco part to save you more headache later.

[mongocanfly]

So I pulled the canker sensor..set up a multimeter test like shown on video..
got no reading from the signal wire..
So I got a new crank sensor.. installed it..still nothing..
HG suggested checking with a scanner.. so I hooked it up set it on live mode..
It shows 0 rpm while cranking....
Biketopia..I asked for acdelco at parts store but they didnt have one. So I took store brand to try..
Plan was if that fixed it I would get the acdelco and swap it out.
But I'm still searching for what's wrong..
Electronics dont bother me when they work..but when they dont work, it gripes me to no end..
I'm not a good electrical troubleshooter and its frustrating

[mongocanfly]

Did some late night testing..
I back pinned the ecm plug on pin #2 ,light green wire..turned key on and I have 12v there..
Then I back pinned #12, dark blue wire..and started bumping the engine over..
it cycles 12v-0v-12v-0v-12v-0v...
So I'm assuming it's getting a crank signal..
Then went back and redid the multimeter test on my old sensor..and it is working..not sure what I did wrong the 1st time.. but it pulses correctly..
I really hate wiring..haha

[mongocanfly]

Stuck my ecm in a buddys truck...cranked and ran perfect..
So that rules out the ecm and programming as the issue..
Crank sensor shows to be working..
Grasping at straws now.

[RustyPile]

I've been retired for several years but I worked over 30 years as a auto mechanic.
when sequential FI came out, I did a lot of driveability and no-run repairs.. It's been a long time since I've been under the hood of a sequential FI vehicle, so I may be wrong on some of this..

As you know, it takes two revolutions to complete the 4 "cycles" of an engine.. The computer has to determine a few things when you first "hit the key".. The crank sensor takes care of telling the computer the engine RPM.. The cam sensor tells the computer where in progression of the 4 "cycles" each piston is.. Only then can it fire the correct injector. During the start sequence, the ECM will fire all injectors simultaneously only to give a little "richness" to the incoming charge. To continue to feed fuel, the ECM needs to know which injector to fire first..

I said all that to say this: Check the cam sensor and its related wiring.. I'm betting that's your problem....

[mongocanfly]

Thanks Rusty..that's what I'm checking now.. I have ohmed the wiring from the cam sensor to the ECM..that part is good.. been trying to figure out which wire on the cam sensor is the signal wire..
I googled it and have seen multiple wire colors shown..
Been trying to search on ls1tech, but cant find what I'm looking for

[Accelo]

What if their is 12v at the injectors and it's the computer grounding of the injectors that is the issue? The dim noid points in that direction. I would reconfirm my computer grounds including the one that attaches to the back of the block.

[mongocanfly]

Its got 12v at the injectors..
Tuner said the dimmish light from noid I'm seeing is normal..
I've double checked all the grounds, and just for funzzies, I ran extra grounds from the neg side of battery to each harness ground..
Its getting the 1st signal pulse to the Injectors, but it's not giving the signal to keep firing the Injectors..
I was told this is the function of the crank sensor..but from what I've checked, its working..
I was also told it will run without the cam sensor.
When I check it with the scanner in live mode, it shows no crank rpm..
But it's getting the crank sensor pulse signal at the ecm plug

[biketopia]

What year and vehicle is the harness and ECM out of? I'll see if I can get you the alldata print out.

[mongocanfly]

It's a 03 5.3 from a Silverado

[RustyPile]

You said something about the engine can run without the cam sensor.. That's not completely true. The engine needs a functioning cam sensor in order to start. If the cam sensor fails while the engine is running (this is the case for most failures), it will continue to run.. But once the engine is turned off, it will not restart.

If I remember correctly, the "common" or ground wire for all the engine sensors is the same color, sometimes with a trace. Look for that on the cam and crank sensors.. The other wire at the sensor carries the signal.. Remember, these two sensors generate the signal and send it back to the computer, not the other way around. In order to trace the wiring you really need an accurate wiring diagram.. It's common knowledge that some of the aftermarket service manuals contain inaccurate information. If possible, obtain a genuine GM service manual.

A "quick search" for "2003 Silverado Wiring Diagrams" turned up this site: You'll need to register to gain access...

https://portal-diagnostov.com/en/roo...ring-diagrams/

[Accelo]

You might try this site as they have the best help around on the computerized LS motors.
https://ls1tech.com/forums/pcm-diagnostics-tuning-7/
Also have listings on the wiring diagnostics and diagrams.

[mongocanfly]

The harness is a psi.. they have been very involved in helping me with this..
Here are some parts of our emails back and forth
--------
Har-1015 harness. Even with the cam sensor un plugged it will still start.
--------
Crank rpm comes from the crank sensor the PCM must see an rpm during cranking, then the cam sensor locates the #1 cyl. to commence the firing. In the event there is no cam signal. The PCM defaults to back up fuel mode and the vehicle still starts. If you have no crank RPM it will not start.
-------
No crank rpm = no start, cam sensor does not affect the crank rpm.
--------
I spent several hrs last night cruising ls1tech.. but couldnt narrow down what my issue is..
I'll check that link out and dig some more..

[RustyPile]

Originally Posted by mongocanfly

The harness is a psi.. they have been very involved in helping me with this..
Here are some parts of our emails back and forth
--------
Har-1015 harness. Even with the cam sensor un plugged it will still start.
--------
Crank rpm comes from the crank sensor the PCM must see an rpm during cranking, then the cam sensor locates the #1 cyl. to commence the firing. In the event there is no cam signal. The PCM defaults to back up fuel mode and the vehicle still starts. If you have no crank RPM it will not start.
-------
No crank rpm = no start, cam sensor does not affect the crank rpm.
--------
I spent several hrs last night cruising ls1tech.. but couldnt narrow down what my issue is..
I'll check that link out and dig some more..

The 5.3 had just been introduced when I retired so I didn't get the chance to work on it.. However, the 3800 and it's "little brother" 3300 FWD had been around a while.. The early additions of those engines were famous for their cam sensor failures.. Almost 100%, when the engine failed to start, the cam sensor had failed. I kept a new cam sensor in my toll box, and without any trouble shooting, I'd put that new sensor on the engine and most of the time it would fire right up.. If it didn't start (I don't remember one that didn't) I'd re-install the original and I'd begin legitimate troubleshooting. I honestly don't remember an engine with a failed cam sensor that would start..

I don't believe in just throwing parts at a problem, but I'm almost tempted to suggest that you arbitrarily replace the cam sensor without proof that it has failed..

[mongocanfly]

Yeah ,that's why I was trying to trace down which wire and pin location is the signal wire from the cam sensor..
When I did a Google search, I'm seeing diagrams showing different wire colors and pin locations for this. ..nothing like misinformation of the internet when trying to troubleshoot
But I'm about ready to just start throwing parts..I already changed crank sensor, guess il throw a cam sensor on it and see what happens
It still puzzles me though, this was a running engine prior to the swap

[RustyPile]

Unless the wire color changes before it gets back to the computer, you should be able to determine wire color at the sensor end of it.. PSI should be able to provide the pin location and wire color information...

The following is a bit of a stretch but will provide a positive way of getting the signal back to the computer, and also will determine whether or not problem is in the harness... Make up a long jumper test lead with the proper sensor plug on one end and computer connector pins on the other end.. When you have the pin location info in hand, simply remove the sensor pins/wires from the computer plug and install the jumpers..

[Accelo]

You may be to the point of needed profession help. Access to a scope with current and voltage reading capabilities may be required.

When mine would not start I eventually called in the guy that built my harness.
Turned out I may have caught it if my eyes were younger.
The wires were pined in incorrect locations. (The pin location depends on the view, from the back or the front of the plug) The vendor pined it 4-3-2-1 instead of 1-2-3-4.
If I have better eyes maybe I would have seen the numbers as they were right on the plug, abet behind the silicon sealing ring.

I am not indicating my issue is yours but another set of eyes is always better. Especially if they have some training and tools.
You will find it the last place you look!
Cheers, as you may need some before this is running.