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

  1. #1
    Fuel Injected! babywag's Avatar
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    TBI Fuel volume delivery? are 5/16" and 1/4" fuel lines too small?

    I have 2 Jeeps, both are AMC 360 engines w/ 16197427 TBI systems.

    #1-('88 Grand Wagoneer) I have a stock chevy truck in tank fuel pump installed in the tank & 3/8" supply line / 5/16" return line.
    FP is ~13psi and the truck has been running very well for a few years now.
    It was originally a 1227747 that I re-pinned the harness and swapped to the 16197427.

    #2-('90 Grand Wagoneer) has been a real PITA, lots of issues.
    Every time I find an issue and fix that something else seems to pop up.
    (Exhaust leak, vacuum leak, different throttle body, new injectors, IAC)
    Also started w/ a 1227747, but swapped over to a 16197427 because I had one, and I like them better.

    This one the fuel lines are the stock Jeep sizes 5/16" supply and 1/4" return.
    Fuel pump is an Airtex# 2182 mounted to the frame rail.
    FP is ~15psi right now, and the truck runs well, but seems like the fuel system is inadequate?
    @13psi the VE tables were getting maxed out.
    I have monitored fuel pressure while driving w/ 2 different gauges and the pressure is steady.
    I have monitored the fuel pump voltage while driving, and it's battery voltage ~14.2 and never decreases.
    AFAIK the engine is stock, but for 177k it has great compression and will spin the tires easier than my other one so ?

    So back to my original question, can you have adequate constant fuel pressure and still have a volume/delivery issue?
    Could the smaller lines be an issue?
    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.

  2. #2
    Super Moderator Six_Shooter's Avatar
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    I've never tried to run 5/16" and 1/4" fuel lines.

    I'ave always used 3/8 and 5/16" to avoid any supply or return issues.

    In my Datsun, I added the 3/8" supply, and use the factory feed that is 8mm (5/16") for the return.
    The man who says something is impossible, is usually interrupted by the man doing it.

  3. #3
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by babywag View Post
    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.

    Quote Originally Posted by babywag View Post
    Could the smaller lines be an issue?
    Yes.

    Quote Originally Posted by babywag View Post
    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%?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  4. #4
    Fuel Injected! JeepsAndGuns's Avatar
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    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.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  5. #5
    Fuel Injected! babywag's Avatar
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    Quote Originally Posted by EagleMark View Post
    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?

  6. #6
    Fuel Injected! shimniok's Avatar
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    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. :)
    1986 Jeep Grand Wagoneer - stock AMC 360 V8, 3" exhaust - 1227747 ECM - $42 ASDU - tc.wagoneer.org - www.bot-thoughts.com

  7. #7
    Fuel Injected! babywag's Avatar
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    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
    Tony
    Looking to buy TunerCat OBDII
    '88 Jeep Grand Wagoneer (aka Babywag) and '90 Jeep Grand Wagoneer (aka JUNKbucket) both fuel injected
    '94 Caprice Wagon

  8. #8
    EFI GearHead ! EagleMark's Avatar
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    There's another quick way to fix BLMs! Change Stoich AFR to what E fuel is, 14.13...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  9. #9
    Fuel Injected! babywag's Avatar
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    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.
    Tony
    Looking to buy TunerCat OBDII
    '88 Jeep Grand Wagoneer (aka Babywag) and '90 Jeep Grand Wagoneer (aka JUNKbucket) both fuel injected
    '94 Caprice Wagon

  10. #10
    EFI GearHead ! EagleMark's Avatar
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    I wasn't disagreeing, you had found the problem and fixed it right. Thanks for sharing mistakes, it's how we all learn.

    But changing Stoich is just that, no need to change all other AFR tables. Stoich setting is the start of all the other AFR tables.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  11. #11
    Fuel Injected! babywag's Avatar
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    So, yesterday got an email from Mr. Injector regarding the old injectors that were installed in this thing.
    (I replaced them with new ones a while back)
    Sent them in to cleaning/testing mostly out of curiosity.

    After cleaning @15psi they only flow ~62lb/hr ~3% less BEFORE cleaning.
    According to GM they should be ~61lb/hr @ 11psi.
    @ 15psi they should flow more like 71lb/hr
    sqrt(15/11)*61=71.23

    So with .bin set to calculate VE based on 61lb/hr = injectors weren't even close to delivering that.
    According to rough math since I don't have the actual pre cleaning numbers yet...
    The injectors were only flowing ~56-57lb/hr @ 13psi.
    Would explain why I had to add so much to VE tables, and why I was maxing out.
    Would also explain why bumping my pressure to 15psi helped somewhat.

    So lesson learned...just because the pressure is good/steady/etc. doesn't mean the flow is
    Tony
    Looking to buy TunerCat OBDII
    '88 Jeep Grand Wagoneer (aka Babywag) and '90 Jeep Grand Wagoneer (aka JUNKbucket) both fuel injected
    '94 Caprice Wagon

  12. #12
    EFI GearHead ! EagleMark's Avatar
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    3% difference if on both injectors is not bad! I've had increase up to 9% on one injector and 4% on the other, in the end they were the same. That is a big difference.

    There's a lot of discrepancy in this area. In the end having both injectors flow max because of cleaning and being the same is key.

    First is what GM rated them at, I've seen 11 to 13 and I have no idea which is correct? Since every TBI stock I've tested since 1987 seems to be at 12? A stock 5.7L engine at 12PSI and WOT runs over 100% injector duty cycle and some VE tables are over 100%, so there's barely enough fuel to handle a stock motor.

    There is a fact of TBI injectors having a 10% varible do to production machining. Greg machined one apart and we can see why. I think this is where flow matched injectors came from.

    Fuel pressure gauges have a HUGE difference. The cheap ones from summit that go under hood and the cheap harbor freight are horrible even if you can read them shaking. The under hood oil filled gauge is only accurate when cold, if it was accurate, they all seem to drop when hot. Even good quality gauges can have a sweep from 0-60 makes it not as accurate as one 0-15 or 20. I finally bought an expensive oil filled race gauge for my temp tuning fuel pressure setup and it matches three Snap On fuel pressure gauges at TBI pressures and MPFI pressures, it has a 0-60 gauge.

    Then what fluid was used by GM for this testing? Is it same fuel as injector cleaning service? I know the fluid Mr Injector uses mimicks gasoline! I've spent a lot of time with him to get these dialed in because most machines are not designed for this low TBI pressure, they use a higher pressure for cleaning. That said we had this setup to where 5.0L, 5.7L and 7.4L injectors all came out just a little higher then what GM rated, so it is consistent.

    Looking at all my injector reports from Mr Injector they have 2 results, 20 PSI dynamic and 13 PSI static. If yours were only 56-57 at 13 PSI that is almost the entire 10% and the worst I have ever seen! The worst I have even seen before were 5% short, most are a little over.

    When I do a tune I do start with serviced injectors with results given. But if I am running out or room in VE? Pressure goes up!
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    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  13. #13
    Fuel Injected! babywag's Avatar
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    Yep, lots of conflicting info out there.
    I contacted the manufacturer of my "new" injectors.
    Specs state testing @11psi = 61lb/hr +/-
    Also contacted a friend that is a GM tech and he gave me the same info.
    So my injectors are/were low compared to spec.

    I specifically asked Mr. Injector to test @ 15psi well above stock and 12psi I've seen.
    They only flowed @ 62lb/hr = below spec etc.
    This would put them @ ~57lb/hr and well below spec @ stock pressure.

    So would explain some of the issues I've had w/ this POS.
    Tony
    Looking to buy TunerCat OBDII
    '88 Jeep Grand Wagoneer (aka Babywag) and '90 Jeep Grand Wagoneer (aka JUNKbucket) both fuel injected
    '94 Caprice Wagon

  14. #14
    EFI GearHead ! EagleMark's Avatar
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    Yup, that's a lot of missing fuel at WOT or high load...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  15. #15
    Fuel Injected! gregs78cam's Avatar
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    Ya know, long ago when I had the injectors for the camaro cleaned, the numbers that he gave me were a bit confusing. Then last week when I picked up the pair of 4.3L injectors, the receipt showed 85, but no units. So I went back in for clarification, and he did something on his calculator, and came up with 680cc/min @20psi. That converts to 52lb/hr @13psi. That is a BIG difference from the 46 in the 4.3L .bins that I have. IDK. Now if he actually tested them at 25psi, then that works out exactly. I guess I will see what happens with the other pair that I take in tomorrow.
    Last edited by gregs78cam; 05-23-2013 at 07:42 PM.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

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