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Thread: REALLY Bad Fuel Mileage

  1. #1

    Default REALLY Bad Fuel Mileage

    I drove my Sniper powered Wagoneer (AMC 360) the other day in some extreme (97°F +) heat and it got REALLY bad fuel mileage. I drove it about 40 miles on the highway, and it drank up 10 gallons of fuel. It wasn't even that bad with the carb. I had a datalog running, but I accidentally turned the vehicle off before I closed the datalog out. (If there's a way to fix this, I'm all ears.) Anyway, I have attached my current GCF to this message. If anyone would help, I would appreciate it.

  2. #2
    Join Date
    Dec 2009
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    Connecticut
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    Default

    Holley's base calibrations are not designed for good fuel economy.
    Good fuel economy is a direct result of the fine-tuning performed on the EFI system.
    NOTE - I've found the following EFI tables to be the most significant areas for improving fuel economy:
    Target Air/Fuel Ratio Table (too rich in cruising area).
    Ignition Timing Table (not enough advance in cruising area & light acceleration area).
    Acceleration Enrichment Tables (way too rich once Fuel Table is self-tuned).
    Coolant Temperature Enrichment & A/F Ratio Offset Tables (base calibrations too rich).
    https://forums.holley.com/showthread...8640#post88640 (AFR & Timing Information)

    Here's one good example:
    http://www.carsandparts.com/en/exper...-simple-1.html (Read "Dyno and Drive" segment - 16.5 MPG with an 860HP/742TQ 555" BBC)
    WOT power and cruising economy, are two separate segments of the Target A/F Ratio Table, so you can optimize both.
    https://forums.holley.com/showthread...9736#post89736 (Air Temperature Enrichment % Table Tuning)
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  3. #3

    Default

    Okay, I'm messing with it today. I did a little tuning in the Air Temp Enrichment curves. I moved the values between 120°F & 200°F down to about 95%. Is this the right direction to move with these curve points? Is there a way to take every point in the Base Fuel Table and move it down by 10%?

  4. #4
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    Quote Originally Posted by FrozenCajun View Post
    I moved the values between 120°F & 200°F down to about 95%. Is this the right direction to move with these curve points?
    You tell us: http://forums.holley.com/showthread....7913#post67913 (Air Temperature Enrichment % Table Tuning)

    Is there a way to take every point in the Base Fuel Table and move it down by 10%?
    Of course there is, with the Sniper EFI software. Read last sentence below.
    If you'd like to manually tune the Base Fuel Table (even while the engine is running), read below:
    Left click & drag to select a group of cells, then use the CTRL & Arrow keys (▲►▼◄) to change the highlighted cell values.
    The ▲ & ▼ arrow keys adjust the Base Fuel Table slowly (one tenth at a time). The ◄ & ► arrow keys adjust it rapidly.
    Or you can left click & drag a group of highlighted cells, and right click "Offset Selected" to adjust the entire cell group.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  5. #5

    Default

    Now I'm not a happy camper. I was running it on the road for some Learning time, and it just quit at a stop light. No warning, no sputtering, it just quit. I'm getting fuel, but no spark. If I ground out the points wire from my MSD 6AL, the coil fires. No spark at all. It's almost like Sniper just decided to quit firing the ignition. What gives here?

  6. #6
    Join Date
    Dec 2009
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    Connecticut
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    Well what does your ignition system consist of?
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  7. #7

    Default

    All brand new parts. AMC type Duraspark distributor (not new, but the pickup is new), advance all locked out. MSD 6AL box hooked to Sniper with the points wire. Setup in Sniper as MAGNETIC and Sniper controls the spark. It was running really nicely. I got to a stop light and it just quit.
    Last edited by FrozenCajun; 07-03-2017 at 12:06 AM.

  8. #8
    Join Date
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    Connecticut
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    Quote Originally Posted by FrozenCajun View Post
    Setup in Sniper as MAGNETIC and Sniper controls the spark. It was running really nicely. I got to a stop light and it just quit.
    Search the Sniper EFI forum about the magnetic pickup problems.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  9. #9

    Default

    I just set the Minimum Signal Voltage to 0.5 volts like was said in another thread. I really hope that works. Everything else is wired correctly & working. The Sniper cycles the fuel pump if I touch the magnetic pickup leads together, so I'm assuming Sniper is working properly. There's something between there and the MSD that isn't allowing it to fire the ignition.

    I just tried it with the Minimum Signal Voltage at 0.5V. Nothing. I put a meter on the white wire coming off Sniper to check if it was providing ground to the MSD box...nope. Here's my current GCF. Please have a look to see if I have screwed something up.

  10. Default

    Quote Originally Posted by Danny Cabral View Post
    Search the Sniper EFI forum about the magnetic pickup problems.
    I'm thinking that the problem is my Texas engineered Duraspark distributor. Today, I ordered an AMC model GM large cap for it, just to get it running until we get moved to Louisiana, and I can afford the MSD distributor for it. I know Sniper won't be able to control the timing. However, I do have to say that I did at one point have a junkyard GM TBI (speed density, ECM 1228746, $61 code mask) running on an AMC 360, with a GM HEI module used to control the timing. It was a mess of wires, but it worked. It was certainly Franken Jeep, but that engine was a beast! I may try the same thing (re: ignition control) with this engine just as an experiment. A GM HEI module is just a set of glorified points in a box. I sure do wish Holley would make a Dual Sync distributor for the AMC V8s. That sure would make this process MUCH easier. I would buy one for sure!

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