need some confirmation on fueling issue

[trixdout]

So prior to changing my stock rusted fuel lines (which were not leaking at all), the car ran top notch shape. all scanmaster numbers were as they should. Specifically blm's. blm's at idle were 128. During light cruise the blm's would go from 128-138 max. Hit 17psi wiht 93 octane on an extender chip and no knock. Thecar was running great. Idle was steady, fluctuating more than .5 psi. The wideband was always between 14.1-14.8 at idle, which I deemed normal. This was all with a walbro 255lph.

Now my issue is this. After changing the lines to racetronix's fuel line kit (stainless braided teflon lined -8an feed and -6an return) and adding a vented gas cap while using the stock vent line. I left my fuel pressure regulator as it was. Once done with the install, I started the car and noticed my fuel pressure was 45 with vacuum on. Pulled off the vacuum and it rose almost to 50. I was baffled. Lowered it to 45psi vacuum off, as per extender chip instruction. Got the wideband going when I started the car and it was out of normal behavior. It was fluctuating between 13.8-16.1. Then I checked the blms and it was 120 pegged. This all happened yesterday.

Today I messed around with the fuel pressure because I read that adjusting that will tweak the blm's at idle. The more I increased fuel pressure the lower the blm. The lower I made the fuel pressure the higher blm.

I will be buying the 430lph pump that is e85 capable next year, no funds now.

My question is this. Because the feed line is larger, there will need to be more fuel needed to meet the same pressure that was before using smaller lines. So now that I have more volume in my lines going to the injectors, do I need to lower my fuel pressure in order to get the blm's to 128?

Side note, TurboBob or Eric can answer this question definitely, maybe others. When you guys set up the chips for a certain combo and in the instructions it says X psi of fuel pressure, is it to get the blm's exactly at 128 at idle because that is what is needed for stock fuel lines?

 

[baby6]

Dropping the fuel pressure will cause blms to rise. Lower the number, car is compensating for a rich condition, trying to lean it out. Vice Versa with high blms.

More fuel velocity/volume= higher pressure it looks like? Not sure about that one. But I am sure that is the reason your blms are low.

 

[earlbrown]

My question is this. Because the feed line is larger, there will need to be more fuel needed to meet the same pressure that was before using smaller lines. So now that I have more volume in my lines going to the injectors, do I need to lower my fuel pressure in order to get the blm's to 128?

Not true at all. Pressure is measured in pounds PER square inch. If you increase the square inches, the PSI is the PSI. If the pump makes "X" PSI, you can hook it to a fire hose and it'll still make that same numerical pressure reading.

Now when you changed your fuel lines (if you made no other changes) and your base pressure incresed.... that means one of TWO things (or both)...

Either your old feed line was a restriction and you got rid of it with the new lines... OR, you new return lines is restricted and causes the pressure to go up.

That one sounds a little more plausible. The voltage is a little lower at idle yet the pressure was higher. It would make sense when you're driving with the higher voltage the extra fuel flow would cause even more PSI due to overwhelming the return even more.

 

[trixdout]

Not true at all. Pressure is measured in pounds PER square inch. If you increase the square inches, the PSI is the PSI. If the pump makes "X" PSI, you can hook it to a fire hose and it'll still make that same numerical pressure reading.

Now when you changed your fuel lines (if you made no other changes) and your base pressure incresed.... that means one of TWO things (or both)...

Either your old feed line was a restriction and you got rid of it with the new lines... OR, you new return lines is restricted and causes the pressure to go up.

That one sounds a little more plausible. The voltage is a little lower at idle yet the pressure was higher. It would make sense when you're driving with the higher voltage the extra fuel flow would cause even more PSI due to overwhelming the return even more.

Would potentially having the feed and return twisted above the tank right where it connects to the fuel sender, after bolting back in the tank, cause the return to collapse and be a restriction? It's definitely after the regulator just not sure where.

 

[earlbrown]

Now idea how that's possible but, yes, twisting a line will cause it to constrict. If you're sure it's after the regulator (easy verification, take the return line loose so the fuel can dump into a bucket) it has to be return line, connections, or pump hangar.

Grab a straw and twist it. Same thing happens to hose.

 

[Raeban]

An easy way to think about the fuel pressure is that any excess fuel pumped by the pump past your desired pressure is sent back to the tank. If the pressure rises it has to be a restriction in the return or a malfunction in the regulator. As for the initial fuel pressure setting recommended by chip manufacturer's, my understanding is that is based on the advertised flow rating of the injectors which the chip burner uses to calculate fuel mass.

Fuel injector flows are typically rated at X volume @ Y pressure. Raising the pressure will increase the flow and lowering the pressure will decrease the flow. We are fortunate many manufacture's rate their injectors in #/hr @ 45 PSI base although the correction formula isn't very complex. Here is an example if it helps:

Flow 2 = (Pressure 2/Pressure 1)^(1/2) * Flow 1

If your fuel injector is rated at 65#/hr @ 45 PSI (Pressure 1) and you are running 40 PSI (Pressure 2) what is you new flow rate?

New Flow = (40 PSI/45 PSI)^(1/2) * 65 #/hr
New Flow = 61 #/hr

As you can see running slightly lower pressure would mean less fuel flow than originally programmed for and the computer would generally raise BLMs to add fuel during closed loop. It also worth noting that the reason for the manifold reference line on the regulator is to compensate for manifold pressure to try to maintain the 45 PSI pressure differential throughout the engine's operating range.

 

[trixdout]

Thank you guys for your help! I believe I may have fixed my problem. The return line was totally clear after running compressed air through it. Got the tank down and noticed the feed like was a little squished as well as the return line. They were twisted around each other like a bread bag wrapper thing. So I undid the twist and pulled whatever slack I had of the return towards the front of the car. This also made it much much easier to attack the return to the fpr. Going to be taking the car out today to see if everything is alright. Just to be safe I will unhook the orange wire to reset the adaptations the chip may have done in the past few days.