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Thread: Tuning cold start/raising "cranking" RPM.

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    I was reading your initial complaint about the high idle after a cold start, and since you're "direct drive" with the jet, I have a thought. I'd play at the IAC Parked Position at the cooler temperatures as well as the After Start Decay Rate. Just for a test, I'd try and lower your IAC Parked Position significantly in the "cold start" areas. It'll probably take longer to light-off, but it shouldn't kick as hard when it does. Also, try lowering the After Start Decay Rate by a few seconds. Again, this will let the engine return to a normal idle quicker. I'm by no means an expert on EFI tuning, but these are the things that make sense for me as a test to try and combat your run-away scenario on cold start.

  2. #12

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    I'll be really interested in how this thread goes. I have the same delayed start issue. With my old TBI system starts were an instantaneous 1/4 second turn of the key at right a idle at any temperature. That system had a dedicated starter connection so the ECU never had to guess if the engine was cranking. The TBI system was also fully functional down to 8 volts, so battery dip during cranking wasn't an issue either.

    In additional to some of the parameters above, I've also been working with the Fuel Prime Percent & Multiplier as well to help the engine get over the hump. To me the one quick key stroke, fire to the correct idle is the mark of a high quality engine and fuel system. I sorely miss it from before.

  3. #13
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    Quote Originally Posted by Floobydust View Post
    To me the one quick key stroke, fire to the correct idle is the mark of a high quality engine and fuel system. I sorely miss it from before.
    To achieve close to this statement is up to the end user to take an entry level, universal TBI unit, and make it specific to their need. Most modern built EFI systems will never fire as fast as the units from the '80s (or a carb), as many of those units did not wait for a crank or cam sync to happen. They immediately fired the plugs at the first signal from the pickup. The more modern units will wait for a proper sync of the cam and or crank sensor, which does take a rotation or two along with processor speed to start the ignition sequence. Having the engine start in less than one second is about all you can ask for with this unit.

    For many years now, the modern vehicles' ECU keeps the starter spinning even after you let off the key or button to attempt to finish the start sequence all on it's own, whether you want it to or not.

  4. #14

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    Quote Originally Posted by 63 bomb ohc View Post
    I was reading your initial complaint about the high idle after a cold start, and since you're "direct drive" with the jet, I have a thought. I'd play at the IAC Parked Position at the cooler temperatures as well as the After Start Decay Rate. Just for a test, I'd try and lower your IAC Parked Position significantly in the "cold start" areas. It'll probably take longer to light-off, but it shouldn't kick as hard when it does. Also, try lowering the After Start Decay Rate by a few seconds. Again, this will let the engine return to a normal idle quicker. I'm by no means an expert on EFI tuning, but these are the things that make sense for me as a test to try and combat your run-away scenario on cold start.
    Yeah, that's the plan. At first I was stuck because it seemed to be an un-winnable balance between "more fuel & air" to get it to start quickly, and then "less fuel & air" to make it less aggressive once it started. Now that I know that something funky is going on with my ignition, I should be able to figure it out, and can then reduce my IAC and cranking fuel (hopefully significantly) to get it to start a bit better.

    To me the one quick key stroke, fire to the correct idle is the mark of a high quality engine and fuel system.
    I agree - that's the goal! It doesn't need to be instant, but within one second, and without causing such a fuss when it finally lights off, would be great!

  5. #15

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    @abc: Yes, that's totally correct. Indeed, ECU starter control gives the impression of a one click start, even though there's a delay while sync is achieved (mostly for startup emissions control).

    But the Sniper is essentially 1980s technology reincarnated, so it should be possible to achieve something close to instant start. The current 3-5 seconds (and sometimes more) is not making the grade for me, so I'll keep working on it. I'm sure information from this thread will be helpful.

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    After reading this article: https://www.efisystempro.com/efi-pro...ator-x-stealth, I was able to get mine to start on the first revolution every time. It's a great read.

  7. #17

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    Excellent read, thank you! One thing that stuck out to me is that the Sniper does not run the fuel pump during cranking? Mercedes pumps start running at the very first crank rotation event and GM TBI pumps run when the starter solenoid is engaged. Why doesn't the Sniper want to have a steady, predictable fuel flow during cranking (there's no safety hazard here)? Fuel pressure decay will vary wildly depending on the installation particulars, hence the need for complicated startup fueling that may or may not be consistent.

    I have a manual fuel pump override switch (momentary for safety reasons). I tried an experiment today. I had a friend hold the switch in the run position so that full, regulated fuel pressure was available for cranking. And sure enough, all starts were sub one second. Based on this, I'm going to add a relay to force pump run during cranking, essentially mimicking the TBI pump run during cranking function. We'll see how it goes, but variably sinking fuel pressure during cranking seems absurd to me.

  8. #18
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    Quote Originally Posted by Floobydust View Post
    One thing that stuck out to me is that the Sniper does not run the fuel pump during cranking?
    Yes, of course it does! Anytime the ECU detects an RPM signal, the fuel pump runs.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, 36-1 crank trigger, 1x cam sync, 200A 3G alternator, Optima Red battery, R134a A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM converter, B&M Hammer shifter, Stifflers trans crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  9. #19

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    Hmm. Conflicting information. I'll have to put the VOM on the pump feed and see which is correct.

  10. #20
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    Where did you read the ECU doesn't run the fuel pump while cranking?
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, 36-1 crank trigger, 1x cam sync, 200A 3G alternator, Optima Red battery, R134a A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM converter, B&M Hammer shifter, Stifflers trans crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

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