Here we go again! LM7 crank but no start

[Paul Y]

Gentlemen,

After the euphoria of fixing my injectors not working on the passenger bank had passed, went out to the shed today to move the truck out so I could start work on another project and it wouldnt start.

Symptoms first.

Cranks but wont start
Fuel pump doesnt run.
No spark
Injectors not pulsing

What I have checked

All fuses - good with none blown
Ohmed pump relay 86 to earth - was negligible so thats good.
Jumped pin 30 -12v to 87 pump runs
Checked power to PCM at pin 20(?) - the orange one - 12V
Checked continuity between PCM - pin 2 - green and white wire - and the CPS plug - All good.
CPS was changed as part of the prior trouble shooting
Plugged in other known good PCM - still no start
There is no voltage on the CPS plug with ignition on - I was lead to believe that there should be 12 volts.
Battery voltage is 11.8v

The amount of frustration I am feeling towards this damn truck is beyond description. As it was running and now isn't I am hoping that it is something really simple and one of you clever souls will go "Ah Ha you Bald Twit its...."

Over to you Gentlemen, what have I missed.

Paul.

[WorldsCrappiestTruck]

Do any of your pink words have switched 12V from the ignition? The fact your fuel pump doesn’t prime, injectors don’t have power, etc makes me think your switch’s 12v from the ignition switch is missing.

[Paul Y]

I am beggining to think this could be the problem.

Strange why it was running 2 weeks ago and today.... nothing!

Just going through my wiring diagram to see what it what - its 9pm here and a bit cold so will check in the morning.

Thanks for the reply.

P.

[Paul Y]

Update.

After 8 hours of trouble shooting, testing the continuity of all lives, earths, triggers etc back to the computer, stripping the loom down and looking for any breaks etc I had that 'oh ****' moment when the pump started running as we started fixing everything back in place.

With #3 son on the key and my head on the passenger side where the computer, engine fuses and relays are positioned, wiggling the wires (technical) caused the pump to start and stop accompanied by an electical clicking. This was traced back to the Current Performance engine loom fuse box and eventually to the green and white trigger wire on the fuel pump relay.

Turn the key, pump runs, wiggle wires, pump stops. continue wiggling wire and pump kicks back on. The clicking sound was the relay energising.

Took the fuse and realy block back off the fire wall and the pump relay is not a great fit. Bent the pins and still not a great fit, but better.

Wiggled wires and same result.

This is where it gets weird.

Check the fuel pump fuse and there is no power across the fuse. Take the fuse out and test - its good - replace fuse, no current across fuse but power to back of fuse.

Wiiggle the wires, truck starts check power across fuse - nothing. Take fuse out whilst engine running pump and engine stops.

Put fuse back in and it starts. BUT THERE IS NO POWER ACROSS THE FUSE!!!!!!

What the actual F**********K!

I am not impressed with the quality of the Current Performance loom. The fuse/relay box is very poor quality so I am going to replace it with a better quality version as this seems to be where the problem lies. Whilst there is no actual 'Smoking Gun' the finger of guilt is pointing towards this cheap block.

Anyway, lets if this fixes the issue - cant help but think this could have been the underlying problem I have had all along.

A very frustrating weekend to say the least, will report back when I have upgraded the block and let you know what I have found.

P.

[leegreen]

Sucks it has been so much trouble. Do you still think the PCM was faulty in your thread for the P0200 code?
It may be worth treating the harness like a kit rather than a finished product, go through it, unpin each wire and check the crimp quality, fit of connector and ohm it out end-end

[Paul Y]

For $600+ dollars it damn well wants to be more than a kit!!!!!

I am beggining to think that you could be correct, I have had multiple issues over the past few ytears of getting the truck strted and running correctly ranging from, fuel pump not running, stopped dead and replacing the CPS, Bad starting - that actually was traced back to a broken wire, and then the PO200 fault which casued me no end of headaches, and cost!!

Looking for recomendations on a good quality 6 relay fuse box to swap out for the one thats in there if anyone has any?

Overall, taking a deep breath, this is so far removed from my day job that it is quite cathartic - well apart from all of the above! Learnt a lot and can now say that I have done everything on the truck. When it breaks down at the side of the road I will be able to fix it. Just as long as its not the engine wiring!!



P.

[WorldsCrappiestTruck]

Watch this video, then watch it again and again and take the images posted….and build your own with giblets from Amazon.

https://m.youtube.com/watch?v=aVyX33jYdoY


Crimp and solder everything. The relay holders click together like Legos and the fuse block attaches. I have this in my truck, 2 relays (one for the fuel pump, one for the Main power to things like coils injectors etc etc).

Very simple and cheap to make your own power-distribution system. Then, you’ll only have to worry about the connection quality of everything downstream. You’ll have good power. ☺️

[Paul Y]

Where was that video a year ago when I needed it!

Thank you, I am pretty confident with the wiring now but this gave me the extra little confidence boost to go it alone.

Thank you.

P.