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Thread: AFR ?

  1. #1
    Fuel Injected!
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    AFR ?

    I have a 1993 Chevy Truck 3500 4 door ramp truck that I just acquired, it has a 7.4 4l80e 16147060 BAMP

    The previous owner said it had always, since day1, had problems with turning the exhaust manifolds cherry red while pulling.....

    Well sure enough it does, just sitting here idling the manifolds are at 635* deg on my infrared temp checker....isnt normal like 300to 400?

    My question is what can cause it to do that? He said its had 4 sets of manifolds on it over the years, and has pretty much done this since it was new.

    My thought was originally that it was too rich and the unburned fuel was causing the overheated manifolds.

    But I just got a new AEM Wideband,and it shows under wot 15.8/16.5,and cruise 15.3/15.5 to 1,which is pretty lean right?

    Have been thru all the tune up stuff, and timing settings its at 8 degrees now with connector unplugged, and I tried it at 2 and 4 degrees and it still did it but was down on power a little,
    'seems to run best and not ping at 8.

    Exhaust is new 2 1/2 back to 2 brand new flow masters,no converters, so everything there seems to be ok, no restrictions.


    Fuel pressure is a little low at 11 psi.....

    I'm getting ready to work on getting that up to 15 or 16?

    And to do some logs, over the weekend.

    any thoughts ? or anyone else ran into this?

    I know I've heard about this year motorhomes doing it
    Last edited by mike454; 04-12-2020 at 04:04 AM.

  2. #2
    Fuel Injected!
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    check injector part numbers, perhaps they're the wrong ones.

  3. #3
    Fuel Injected! PJG1173's Avatar
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    I have seen this before. my tbi 4.3 used to do this under a load for extended periods of time (chewing through the mud). manifolds would glow read hot. had a buddy tell me that this is typical of tbi's. I turned up fuel pressure and no more glowing manifold problems but was a little rich in other areas.
    87 4Runner, 15" spring lift, 3" body, chevy vortec 355, 5.29 gears, 38.5x15.5x15" Boggers, 280hr, 16168625 running $0D
    93 S10, 36x12.5x15 TSL's, custom turbo headers, 266HR cam, p&p vortec heads, $0D Marine MPFI with 8psi boost.
    05 Silverado, 2' lift, 4" exhaust, Bully Dog programmer,

  4. #4
    Fuel Injected!
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    If your fuel pressure gauge is accurate, shim that regulator till psi is 13, huge difference in fueling with a couple lbs of fuel pressure on a low pressure TBI system. Note, there is a 70 second power enrichment delay in the BAMP program. That's not doing you any favors either.
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  5. #5
    Fuel Injected!
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    yes I had ran into that before on the fuel pressure too. I will get it up to 13 and double ck my gauge, its an older Mac but on low pressure a lb or 2 either way wouldn't help.

    I talked to the guy that bought the truck new and he says its had this issue since before the warranty was out and the dealer couldn't straighten it out after swapping everything....engine and all.

    so we'll see.
    on that pe delay set it to 0 correct?

    mike

  6. #6
    Fuel Injected!
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    During tuning I usually set the delay to 0, then after finished I like to add a short delay as it helps fuel economy when driving around town and lot's of transients that might trip un-needed PE.
    -Carl

  7. #7
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    ok, i modified the FPR to make it adjustable... got the fuel pressure set to 14 psi,it will go to 16 max with the screw i used.
    that brought the afr down some overall,and runs better... I havnt checked the manifold temps yet,but ill bet they are lower,with more fuel available now.
    I did 2 short logs (attached) if maybe someone could take a quick glance at them and offer areas of improvement i appreciate it....( i'm new to all this but eager to learn)
    Next i need to figure out how to be able to log the wideband readings in with the tunerpro logs.
    i did change the wot delay to 2.0 as in-tech suggested
    Any other kinda universal changes thats common on all these bins?
    Thanks mike
    Last edited by mike454; 04-16-2020 at 06:01 PM.

  8. #8
    Fuel Injected! donf's Avatar
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    Quote Originally Posted by mike454 View Post
    ok, i modified the FPR to make it adjustable... got the fuel pressure set to 14 psi,it will go to 16 max with the screw i used.
    I am very curious what the dead head pressure and volume on your pump is. I replaced my pump before even starting a tune. Most now are not up to the task volume and pressure wise after so many years. Don't tune around a low volume, low pressure pump. I used a 30 psi big block pump in my 5.7 van, just to make sure the regulator is what is setting the pressure.

  9. #9
    Fuel Injected!
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    its a new (has 5000mi on it) airtex for the 93 truck
    if i'd been in on that i wouldve had them get the 94/95 model to get the higher pressure
    i will deadhead it while ive got the gauge hooked up
    Last edited by mike454; 04-16-2020 at 08:59 PM.

  10. #10
    Fuel Injected! PlayingWithTBI's Avatar
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    Another avenue is the AC Delco EP381 pump from the Vortec. Plenty of pressure and volume on my 5.7L TBI.

  11. #11
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    dead headed at 16 psi.
    Volume 2.35 quarts per min.
    pump seems to check out good.

    raising the fuel pressure helped it some

  12. #12
    Fuel Injected!
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    ok,
    the fuel pressure increase helped the overall lean condition,WBO now doesn't get into the 16.00 AFR now stays around hi 15's
    going by the logs what is the easiest/safest way to richen the fuel mixture??,for a complete rookie.
    I've been a shop owner/mastertech for 25yrs but mostly on oem,drivability ect,troubleshooting the difficult stuff for the rookies.
    So I understand the basic issues,and what the engine needs,
    if someone could take a look at my logs and point me in the right direction.
    id like to hook up my aem Wideband so it will be on the logs as well.....but if I read it right it is difficult on the 16147060

    Thank you
    mike454

  13. #13
    Fuel Injected! donf's Avatar
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    The fuel pump at 16 and a regulator pressure at 14 would be a no go if the truck was mine. Way too close together. I would be curious what your injector numbers are. To be running so lean with no motor work done makes me wonder.

  14. #14
    Fuel Injected! dktool's Avatar
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    Have you confirmed that there are no exhaust leaks up stream from the wide band ? That will screw up the reading.

    With the 7060 you cannot integrate data from the WB.
    I went around on that subject with my 7060.
    Also, I have 12 psi fuel and no problem maintaining 14.7 cruise and 12.0 on p.e.
    Last edited by dktool; 04-18-2020 at 08:00 AM.
    Dean

  15. #15
    Fuel Injected!
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    every tbi vehicle i have owned or worked on for a friend we have upgraded to the TPI pump (ac delco only!!). made a world of difference on my caprice even before i replaced injectors and played around fuel pressure. never used vortec pump but if its cheaper than TPI pump, it's a no brainer.


    EDIT: if you watch your fuel pressure gauge and flick the throttle to WOT and the needle moves, replace pump. if you can monitor it @ WOT underload even better.
    Last edited by tayto; 04-18-2020 at 06:27 AM.

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