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Holley TBI, anyone got it running right?

Discussion in 'The Garage' started by mtrdrms, Jun 15, 2005.

  1. mtrdrms

    mtrdrms 1/2 ton status

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    I have set the TPS to .65, I have set the idle correctly, I am not getting a "check engine" light, and I am still getting a terrible bog down low and lack of power everywhere. what is going on????
     
  2. Wingnutt

    Wingnutt 1/2 ton status

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    First off your TPS sensor should be set at .54v. You also need to set your min air setting for the IAC since you have a different setup that the factory unit. You can find out how to do this over at www.thirdgen.org. Although they are car folks aver there, they have some VERY knowledgable experts at TBI tuning and don't mind helping a truck person out.

    As for yer brand new Holley TBI, it uses Delphi injectors which flow a LOT more fuel than the farctory injectors, hence, you will be running very rich. This will foul you O2 sensor and plugs in short order. Long term concerns are a clogged or destroyed cat.

    If you do a search on my username, you can read all about my sorted adventures on how I finally managed to get mine to run right. A few people have had some success by simply turning thier fuel pressure down. This has it's drawbacks too, you can run into a lean condition at higher rpms...not a good thing. What you will have to do is in all probability, is to have you chip tuned for that Holley.

    The tuner will have to lean out the whole fuel curve, add a little tip-in and lean out the cold start cycle. I had Brian at www.tbichips.com burn me a chip that got me really close, but I still have a few tiny issues that I need to take care of as soon as my prominator arrives; but the .bin he burnt for my '88 should get you in the ballpark if that's the route you choose to take.
     
  3. mtrdrms

    mtrdrms 1/2 ton status

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    WHY would my TPS need to be set to .54v? The directions are for .65v. When I first hooked up my voltmeter it came out to .37v so I put to .65 and it didnt really help so I will go to .54v. I dont think I should have a big problem with the lean condition because my engine is not stock. I have an edelbrock intake, bigger cam, balanced assy, headers and dual flowmasters. But at this point I will try anything. Thanks for the input.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Why you would have fueling problems is that at low load conditions, the engine doesn't need as much fuel as the injectors are delivering. That's governed by the PROM, which is "calibrated" for stock injectors.

    To overly simplify injectors/pressure: you have a stock setup, runs fine. You put in injectors twice as large as stock. Now, the larger injectors are commanded to open just as long as the stock smaller ones, at the same pressure (remember, bigger injectors flow more, faster) which results in more fuel when you don't need it. So to combat that, you run a fuel pressure regulator, and turn it down so that not as much pressure is acting on the larger injector when it IS open. Which cuts down on fuel delivered, right? You really haven't solved the whole problem, which is that the injector is being opened too long, but you've solved the low load fueling issue more than likely.

    However, fuel pressure regulator setting is "global". What you do affects both high and low engine operation. You leaned it out at low load conditions, which is fine, but at high load conditions when your engine NEEDS that extra fuel, you end up with that restriction in fuel delivery perhaps causing the engine to run lean. That can/will destroy an engine in short order.

    Part of the proper way to solve the problem of larger injectors is (assuming same as TPI) to get into the PROM and change the injector constant, so the ECM can actually calculate things based on the actual injectors you have, not what it THINKS you have, which is wrong.

    This issue is dealt with on TPI as well. Ford injectors are a great swap, however, they are rated at a different (lower) pressure than GM. Since the GM fuel pressure is much higher than Ford, you end up running rich (open the injectors up same length of time regardless of size, but the higher pressure forces more fuel out) unless you get into the PROM and set the correct injector specs.
     
  5. Wingnutt

    Wingnutt 1/2 ton status

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    I know that the Holley instruction sheet says to set it at .64v, but that's way to high (btdt). Here's how the good folks at third gen explained it to me: since it's a direct factory replacement (both the IAC and TPS will interchange, but NOT the injectors), you need to run the the factory setting of .54-.58v in order for the computer not to have a hissy fit. :D

    This is because the PROM in the computer "sees" .54v as the default idle setting. This is also interconnected with the O2 sensor reading and the MAF readings to determine the correct fuel ratio at idle (in closed loop mode). The A/F ratio is based on the base pulse width (how long the injector stays open, usually measured in microseconds) which is set in the PROM, and modified/corrected (based on sensor readings) by the IAC.

    Once the TPS voltage goes up beyond what the IAC can handle, (if you are familar with carbs, think of this point as the transition from running on the idle circuit to running on the jets) the ECM modifies the length on time that the injectors stay open (a multiple of the base pulse width called the Binary Learning Multiple) based on air temp, engine temp, O2 readings, knock counts, and the MAF readings.

    Getting the idle A/F ratio correctly set at idle can be a absolutely hair pulling exercise in trial and error, BUT once it's correctly set, it makes tuning for midrange and cruse modes MUCH easier; WOT is another beast entirely.

    It sounds like it's time to get your chip tuned for the goodies that you have installed on your engine in order to make them work together and get the most power out of them that you can.

    One last thing, the overlap (in degrees) of your cam can also wreck havoc with your idle. This is because TBIs have a real healthy dislike for unsteady vaccum pulses which is caused by that nice sounding lope of a big cam.
     
  6. mtrdrms

    mtrdrms 1/2 ton status

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    This is a very helpful thread. I am going to print this and study it. I have already contacted TBICHIPS and mine will be sent out on Monday. Along with this chip is there anything else I need to upgrade (besides the Prominator and the equipment needed to burn my own chips)? He mentioned that the stage 2 chip is most likely to help my condition. I kept telling him that I had upgraded the motor and TBI. Is the stage 2 the best in your opinion wingnutt? He didnt pay much attention to my diagnosis and I am not doubting the man but I would like another opinion. Thanks.
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    So why are you buying a chip from these guys if you are ordering the stuff to make your own??

    Maybe I missed something, but anyone thats serious into PROM burning will tell you the only way to get it right is to spend a lot of time on your setup, and that can mean hundreds of burns.
     
  8. Wingnutt

    Wingnutt 1/2 ton status

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    I have to agree with dyeager535 at this point. If you are going to get into burning your own chips (or modifying the .bin in the prominator), why are you having Brian burn you a chip?

    Secondly, although Brian is a pretty good guy, but I been hearing that his "tuning" has slipped a little of late. I'm VERY surprised he sent you a chip without looking at you datalogs. I KNOW he has a .bin he burnt for my '88; but it had a stock engine and a free flowing exhaust. As far as the stage 2 chip, he didn't offer them when I purchased mine, so I'm afraid I can't help you to much there.

    I did the same thing when I started to get in to tuning. I purchased a chip from TBIchips, and after about 5 "re-burns", he seemed to lose interest, and didn't follow through by resolving a few small issues. As I learned more about tuning, I learned that he basically just throws more fuel and timing across the board and that's about it (this jives with rumors that I have heard); instead of closely looking at the datalogs of your ECM and giving you particular engine exactly what it needs. I guess this is OK for a general pick-me-up for a stock engine, but not for a modified one. Additionally, 90% of his chips are for cars, so don't be to surprised if your engine pings like crazy....even with a 170 degree t-stat and preminum fuel. It seems like our K-5s don't like all the initial and midrange timing that his chips contain.

    Brian's chips will get you into the ballpark, but expect to refine them for your particular engine yourself, by burning your own. About the best advice that i can offer is to wonder over to www.thirdgen.org and spend a couple of hours reading the DIY PROM board. Also don't be afraid to use thier search engine. There is a wealth of information there, along with some real tuning guru's.
     
    Last edited: Jun 20, 2005

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