LLY: How much psi is to much for a lift pump
- Thread starter TRUBBS
- Start date
I just finished doing a mild build. I by-passed the ficm and ran from ad straight to the cp3. At first start up my truck idled rough and sounded like it was running out if fuel. My airdog was set at 24psi. My actual rail pressure was damn near double the the commanded. I cranked it down to wear the actual and commanded was the same. That magic spot was 11psi. After that it idled perfect.
So my opinion is that once it raises rail pressure it is to much.
Also not worth running higher psi and reduce the life of your pump.
So my opinion is that once it raises rail pressure it is to much.
Also not worth running higher psi and reduce the life of your pump.
Well the CP3 gear spins at the same speed at idle, so the reason it was so high is that the lift pump was shoving more fuel past the regulator than it was set up to regulate at non-lift pump pressure. The same way a stuck or faulty reg will send actual to max. The CP3 will pump whatever fuel the reg gives it.
Hmm. We figured that was the issue.. He replaced all the return line seals, bolts and actually put new lines in it to. After all that it was still making oil.. He took that banjo bolt off, drilled it out and put an LBZ pump on it and it was golden. Didnt blow seal out of new pump and ran like a champ.
i used to run about 24psi with a fass260 and then a adII200. Truck loped like crazy. Now its on about 12psi with adII200. Only reason i ran it that high is because it would draw down to 10 psi at WOT. Now it might dip to 10psi at WOT.
I don't know, but once when I had a holley blue pump I put a tune in my truck that had a low idle speed, and in gear it loped so hard I could hardly hold it still with the brakes and it loped about three times and stalled.
You can eliminate the lope by altering the regulator current tables*.
My truck would lope a bit when I first put the AirDog on (at whatever default pressure). Rather than turn down the pressure, I adjusted the regulator tables. No more lope. While I was at it, I adjusted the tables across the board; now the actual rail pressure tracks the desired a lot better, especially on rapid throttle application or snapping off the throttle.
The down side: if you are not familiar with control systems and PID controllers, the tables will probably look like black magic.
*At least for reasonably small fuel pressures. I suspect high pressures can be handled too, but eventually the regulator will run out of travel and there will be nothing you can do.
My truck would lope a bit when I first put the AirDog on (at whatever default pressure). Rather than turn down the pressure, I adjusted the regulator tables. No more lope. While I was at it, I adjusted the tables across the board; now the actual rail pressure tracks the desired a lot better, especially on rapid throttle application or snapping off the throttle.
The down side: if you are not familiar with control systems and PID controllers, the tables will probably look like black magic.
*At least for reasonably small fuel pressures. I suspect high pressures can be handled too, but eventually the regulator will run out of travel and there will be nothing you can do.
I've messed with EFI live, and wrote the the tune that's in my truck now. But I don't really know anything about what your talking about.
What he said.
The only reason to run higher pressure is so at WOT your cp3 gets positive pressure to it. 5psi across the board at idle or WOT is enough to be a good maintained pressure (so long as it's steady pressure meaning the flow increases as needed to maintain 5 psi. I use 5 as a buffer to account for any sudden momentary drops in pressure. Positive pressure is the key word.)
If you have a steady 5 psi then your flowing more to the cp3 than is required and if your still losing rail, you need more cp3 plain and simple. Pressure is just a resistance to flow.
As previously mentioned, running higher pressure on an LB7/LLY will NOT affect how the FICM works. However, you can crack the circuit board, or blow the seals out. If you went high enough, you could probably blow up the case too. It's just aluminum and not originally designed to take ANY pressure.
What is affected is the FPR on the CP3. The spring and current flow at stock settings cannot regulate very well at higher pressure causing surging which results in a lopey idle. You can raise the current flow in the tables to compensate somewhat for this, but don't expect your FPR to last as long. It will run hotter and likely fail sooner. And this is inherent to all common rail trucks using electric flow control. (FPR)
dunno, you tell me. i ran 20psi to my FICM, i get a lope. bypass the fuel around the FICM and lope goes away. My truck is not the only this does this on as well. i dont think anyone has an exact reason as to why, like the posi-trac in the back of a dodge. nobody knows how it works, IT JUST DOES!
someone wanna explain this to me then?? maybe i should throw my spare FICM on and run fuel back through it to see
i got logs of it, all you see is rail change. undo the flow into the FICM or back the PSI down and rail goes consistant.
Just a hose. My factory fuel filter is deleted. After and before the banjo bolts the hose just clamps to a steel tube. So I just jumped around the ficm
That hose you used probably wasn't much longer than normal either I imagine.
It just doesn't make sense what you say you found. If you have ever seen the inside of a FICM, there is absolutely nothing in it that should be affected by pressure. It's just a circuit board. Lots of guys relocate them and don't even run anything for cooling liquid through them with no issues.
How long did you run it bypassed?
Lol I know!!! I've seen pics from way back when guys were first bypassing it. It's still bypassed, been that way for about a year. Left the ficm on the valve cover though as I don't feel like extending wires nor is there anywhere that I think looks clean to mount it.
Guess ill throw my spare on and plumb it back in and see what happens.
Guess ill throw my spare on and plumb it back in and see what happens.