Lb7 crank no start 6k rail pressure

[rmcelhany]

Hello have used this site in the past but first time poster. I’ve browsed for hours and can’t figure a next step to trouble shoot my truck( 04 lb7). Encountering a crank no start I have 6k rail pressure while cranking, used a test light to determine I’m getting injector pulse. All fuel related parts are newer around 20k miles. Head gaskets, head studs, new stock sized cp3, new 30% over injectors. Fuel related parts from LDS (heard about them from this site when I was going through my engine and I’m very pleased with their products). Anyways what direction do you think I should go in. Any tips are greatly appreciated thanks.

 

[2004LB7]

What test light are you using and how are you testing?

 

[rmcelhany]

Just a regular light bulb tester had the lead hooked to a ground on a battery terminal and unplugged the injector harness and put the prob on the pins. I have a multimeter I can use to see the volts that’s being sent to the injector if that’s a better idea.

 

[JoshH]

These injectors get constant voltage and have a switched ground. What you're describing isn't an accurate way to verify injector firing signal, and a normal multimeter won't react fast enough. You really need a lab scope to check voltage while cranking.

 

[2004LB7]

As JoshH said. That is why I asked the question as I did. The positive side of the injector line will give you a false reading. If anything, hook the test light across both injector lines and not to ground

 

[2004LB7]

Also, any codes?

 

[rmcelhany]

Only code I have is a P0540 air intake heater.
Any lab scope you can recommend?

 

[2004LB7]

I'm pretty sure @kidturbo has a smaller hand held one that is fairly cheap that might be up for the task. See if he chimes in on that one

 

[rmcelhany]

 

[rmcelhany]

Found this one might just go ahead and order it it’ll be here tomorrow. Any idea what reading should be to injectors?

 

[2004LB7]

I think your reading should look something like this. But at 96 volts peak. You might have more variations and kickback spikes but something similar

 

[rmcelhany]

Thanks for the help the guys I appreciate it. Lab scope should be in tomorrow I will get readings tomorrow afternoon or Saturday afternoon and will post my findings. I imagine I should measure all 8. What’s would be bad if this comes back bad? Ficm? What would my next steps be if the tests come back good across the board? Ran when parked then swapped trans bc it Burnt up on me (don’t know if that could play an issue). Just trying to give you all the info I have available. Again thanks to 2004lb7 and JoshH for your input.

 

[rmcelhany]

A few weeks ago when I hit it with a little starting fluid( I know less than ideal and dumb) it would sputter a little bit like it sounded like it wanted to start think this weekend do lab scope procedure on all 8 injectors and compression test to make sure I didn’t sear cam key being dumb. Thoughts?

 

[2004LB7]

Use gasoline over ether if you must use starting fluid. Much gentler. I've used a cap full on the air filter with good success

If you don't get a signal at the injectors, and we have verified you are testing it correctly then you'll want to test the control signals from the ecm to the ficm. And the crank signal to the ficm

If that is all good then it's timing, valves, compression and fuel pressure

 

[rmcelhany]

Ok I have a book infront of me that includes nothing to do with pin outs for ecm to ficm communication was hopping it would be in there but it’s more of an engine building/ engine spec book. I imagine it’s is electrical related have fuel out of a hp line to injector but I believe as you ( 2004lb7) have stated I was reading injector pulse incorrectly from the get go. And I think I have a ficm or ecm issue, the test with the lab scope will help track down issue

 

[rmcelhany]

Also would I just be best off just pulling upper valve covers and testing right on the solenoid studs on top of injectors or just how I did before and just unplugged injector harness and hooking up that way?