Fueling issues trouble starting
Thread Starter
Teching In
Joined: Dec 2024
Posts: 4
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Fueling issues trouble starting Over the last 4 years I've been putting my truck back together and it won't start. Ran through all parameters I can think of and have narrowed it down to fueling
Lm7 gen 3 computer
96lb injectors
2 340lph pumps wired parallel
I believe I scaled the injectors correctly...will crank and try to fire off but won't.
Ran vcm hp tuners scanner during startup to try and figure it out.
Here is where I'm at:
During the prime cycle pressure pegs out the gauge the falls back to about 45 psi.
during cranking the gauge pegs out.
If I prime the truck and then shut off the fuel pumps it will in fact start with the fuel in the rail but as soon as I turn them back on the truck dies.
I'm at a loss....and ready to through in the towel...please help before I loose my mind
Lm7 gen 3 computer
96lb injectors
2 340lph pumps wired parallel
I believe I scaled the injectors correctly...will crank and try to fire off but won't.
Ran vcm hp tuners scanner during startup to try and figure it out.
Here is where I'm at:
During the prime cycle pressure pegs out the gauge the falls back to about 45 psi.
during cranking the gauge pegs out.
If I prime the truck and then shut off the fuel pumps it will in fact start with the fuel in the rail but as soon as I turn them back on the truck dies.
I'm at a loss....and ready to through in the towel...please help before I loose my mind
Thread Starter
Teching In
Joined: Dec 2024
Posts: 4
Likes: 1
Thought about that....I will have to figure that out if it becomes a possible solution. It is my understanding that pumps run parallel do not affect the pressure but does double the flow providing both pumps are equal. Is it possible that the higher flow rate (640lph---2 340lph parallel) would push through the stock vacuum controlled regulator ? Factory regulator is at 58 psi and my pumps are only rated at 43 psi.
One of those pumps is hit or miss on overpowering the stock regulator. With 2 in parallel there is absolutely no chance it will work. The "rated at 43psi" is meaningless in this situation. That is merely the pressure they will hold at the full rated 340lph. With any luck the pressure was so high it locked your injectors closed. Otherwise, you probably flooded the engine bad enough to have a lot of gas in your oil already.
Thread Starter
Teching In
Joined: Dec 2024
Posts: 4
Likes: 1
Good to know....
guess my next steps will be to disable one of the pumps and replace the plugs. Check the oil and if anything looks off change that too.
If needed would it be possible to run an aftermarket regulator back on the rail....before the factory? Not looking forward to re-plumbing the whole system
guess my next steps will be to disable one of the pumps and replace the plugs. Check the oil and if anything looks off change that too.
If needed would it be possible to run an aftermarket regulator back on the rail....before the factory? Not looking forward to re-plumbing the whole system
If I am reading this correctly, you have the older FPR on rail vacuum referenced truck setup. If that is the case, the easiest route would be to get aftermarket rails and regulator, and use adapter fittings to plumb those to your existing feed and return lines. That being said, it would still be a good idea to power your second pump on a boost pressure or rpm based switch to avoid having both running constantly. There is also the possibility that with the pumps staged in this manner, one of them will not overpower the factory FPR. In that case, you would not have to replumb anything, except maybe a check valve on the second pump. A search of this forum will reveal a myriad of ways people have handled their fuel supply.
Thread Starter
Teching In
Joined: Dec 2024
Posts: 4
Likes: 1
Thanks for the info! Been looking at the fuel rail option...it would give me more control. Running the second fuel pump on boost or rpm wouldn't be a bad i dea either...hell I'm in it this far I may just do both.
Who would've thought in my first post id get real answers and not a bunch of people telling me ive done it all wrong.
Thanks again!
Who would've thought in my first post id get real answers and not a bunch of people telling me ive done it all wrong.
Thanks again!
