TBI Fuel volume delivery? are 5/16" and 1/4" fuel lines too small?

[EagleMark]

So back to my original question, can you have adequate constant fuel pressure and still have a volume/delivery issue?

Yes. Smaller line less volume.

Could the smaller lines be an issue?

Yes.

I've read several places that the small lines work just fine, but I'm wondering why 2 virtually identical vehicles have such different VE.

It will work on low HP engines, but you have obviously found there is a difference! If you ever swap to bigger lines I'd like to here results of test.

12-13 PSI, stock pressure on factory stock engine comes with maxed out VE table. Actually some are more then 100%?

[JeepsAndGuns]

Guess I'm the exception. I have 5/16 feed and 1/4 return on my AMC 401 MPFI system. I have not had any fuel delivery issues. I have a late model XJ fuel tank I mounted in the rear and modded the in tank pump assembly with a combo of XJ and WJ parts. Also ran all new hard lines when I switched to that tank.
Before that I had the stock tank with a frame mounted pump.

[babywag]

Yes. Smaller line less volume.

Yes.

It will work on low HP engines, but you have obviously found there is a difference! If you ever swap to bigger lines I'd like to here results of test.

12-13 PSI, stock pressure on factory stock engine comes with maxed out VE table. Actually some are more then 100%?

I would have done it already, but dropping the tank is a real pain on these things, and the fuel sender needs modification for the larger sizes.
I may up the return line to 5/16" since I could use a stock supply line I have laying around.
Modifying the return tube of the sender isn't bad.

I did make some progress today, I can FINALLY run it in closed loop without it yanking fuel/throwing fits and going lean as H*LL.
Through comparison of the WB gauge to AFR displayed in TunerPro I noticed that stoich wasn't being reported as 14.7
Tunerpro was reporting 15.5 AFR when WB gauge was showing 1.0 WTH?!?
I've been fighting with this thing forever, and was ready to light it on fire and roll it down a hill.
Open loop it would run great, every time I would re enable closed loop it would have a fit.
Even on the 7747 it was doing the same thing, and with no way to get the AFR into the datastream I NEVER would have seen this.
I've been driving this thing around in open loop for months, kind of defeats one of the main benefits of FI.

So I messed with the WB analog outputs.
I changed them gradually until 1.0 on the WB display was = 14.7 reported AFR displayed in Tunerpro.
Enabled closed loop, fired it up and BAM it runs like it should.

Now the previous analog settings worked my other truck and it was running fantastic and very easy to tune w/ the WB.
That truck has virtually the same set-up, but runs a lower FP and the VE tables aren't maxed out as much.
Why I would have to change the analog outputs that worked fine on the other truck to accommodate this truck I have NO IDEA.

I'm soooo sick of this truck, but we'll see if I'm finally the blind squirrel who found his nut?

[shimniok]

FWIW, and I am late to the party, but I am running the stock feed/return hard lines. I've had no problem dialing in the VE tables and in fact have a bit of fueling to spare (max VE1+VE2 is probably 95 or so).

So, looks like I will be coming back to this thread among others when I get arond to running a WB. Whee. :)

[babywag]

Hoping I finally figured this out.
Tried a stock bin and started from scratch vs. the bin from my '88.
My BLM numbers were pretty low 110-120.
Seemed odd to me, and still not agreeing with how it felt when I drove it, and what the wideband was telling me.
Removing fuel was only going to make it run worse, because it wasn't running that rich, and actually lean in some places according to the wideband.

So, thinking to myself I'm missing something simple? but what.
Well, I'm running 15psi fuel pressure...duh!!!
I never adjusted the injector flow rates in the bin.

Changed them to reflect I'm running 15psi, and bam BLM#'s magically telling me what I already knew.
Showing more realistic BLM#'s now 126-135

I feel soooo stoopid now

[EagleMark]

There's another quick way to fix BLMs! Change Stoich AFR to what E fuel is, 14.13...

[babywag]

I don't think that would have done it in this case.

I had previously changed the bin stoich AFR value to 14.13, and was having the exact same issue.
Closed loop BLM#'s saying richer than stoich(contrary to wideband), PCM pulling fuel and going lean.
I could force open loop and get it to run fine and maintain whatever AFR commanded in tables.
Anywho tried that in March. http://www.gearhead-efi.com/Fuel-Inj...oich-14-13-AFR

Stock injectors ~61lb/hr, but increase the pressure to 15psi and they're more like ~71lb/hr.
61*sqrt(15/11) = 71.23
So changing the injector flow rate from 61 to 71 was it. One little setting.

Changing stoich AFR in the bin is a PITA, have to change all the other values/tables too.
Easier to just leave it @ 14.7 and just calculate using stoich.
Pretty sure that's how the code works behind the scenes?

I may say or type 14.7, but my brain is thinking 1.0.

All I know is this thing runs the way it's supposed to now, and the PCM is friends with the BLM#'s.