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1Likes
02-28-2021, 09:13 AM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Why is it dying?
My Dart 351W has developed a new trick. It happens when for instance I pull out of a driveway and see a red light ahead. I accelerate moderately hard in first gear, then just drop my foot off the gas to coast to the red light. As soon as I drop my foot off the gas, the engine dies. Just stops dead, like I turned the ignition key off. No stumble, just dead. If I put it in neutral, it starts right back up, but occasionally with a bit of a stumble on startup before it idles smoothly again. If I accelerate through the gears, slow or really pushing it, it doesn't die. Only under the sort of situation I described above. My first thought is some sort of ignition problem, but I'm not sure where to look. I have an MSD distributor, and the rotor and cap look good. MSD 6 box. I have a Crane coil (installed by the PO) but don't know if I should just replace that to see what happens, or keep looking elsewhere. I have noticed at cruise, that I think I feel an occasional stutter, like a very intermittent miss, but it might be nothing more than road bumps I'm feeling. If any of you have any suggestions, I'd sure appreciate hearing them. This is at the least embarrassing, and at the worst, potentially deadly.
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02-28-2021, 01:59 PM
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CC Member
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Join Date: Feb 2002
Location: Dadeville,
AL
Cobra Make, Engine: Sold my EM.
Posts: 2,459
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Not Ranked
Has anything similar happened under hard braking? And do you have mechanical or vacuum secondaries? And what is your idle RPM?
__________________
Tommy
Cheetah tribute completed 2021 (TommysCars.Weebly.com)
Previously owned EM Cobra
"Never attribute to malice that which is adequately explained by stupidity." - Hanlon's Razor
Last edited by Tommy; 02-28-2021 at 02:52 PM..
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02-28-2021, 06:37 PM
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CC Member
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Join Date: Feb 2007
Location: Savannah,
Ga
Cobra Make, Engine: Unique FIA
Posts: 57
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Not Ranked
I had something similar, engine might die when I let off the throttle. Then crank right back up as if nothing ever happened. I got lucky and spotted a small crack in the MSD mag pick up module in the distributor. The mounting of the sensor with caulk kept it together pretty well, I guess, and made the fault difficult to see. Odd why it seemed to happen on engine deceleration. Anyway, worth a quick look! MSD - may suddenly die
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02-28-2021, 09:16 PM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Quote:
Originally Posted by Tommy
Has anything similar happened under hard braking? And do you have mechanical or vacuum secondaries? And what is your idle RPM?
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No, I had a hard braking situation a couple days ago, and no stalling issues. Carb is a Quickfuel 650 with mechanical secondaries, idle is right around 900.
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02-28-2021, 09:18 PM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Quote:
Originally Posted by 8litercobra
I had something similar, engine might die when I let off the throttle. Then crank right back up as if nothing ever happened. I got lucky and spotted a small crack in the MSD mag pick up module in the distributor. The mounting of the sensor with caulk kept it together pretty well, I guess, and made the fault difficult to see. Odd why it seemed to happen on engine deceleration. Anyway, worth a quick look! MSD - may suddenly die
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I'll dive a little deeper into the distributor to see if I can see anything like that. he really odd part is that it only happens on decel after a quick hard accel. Normal deceleration, or winding back down through the gears produces no drama at all.
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03-01-2021, 02:05 AM
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CC Member
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Join Date: May 2008
Location: Brisbane,
QLD
Cobra Make, Engine:
Posts: 2,797
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Not Ranked
Sounds like a harness moving around.
With the engine idling, move your distributor pickup wiring all the way up towards your 6AL, and also and wiring that can move under g force.
I would also like to know if the car accelerates well continuously, at least for 3 gears.
__________________
Gary
Gold Certified Holden Technician
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03-01-2021, 04:18 AM
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CC Member/Contributor
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Join Date: Feb 2000
Location: Greenville,
SC
Cobra Make, Engine: 70 Shelby convertible, ERA-289 FIA, 65 Sunbeam Tiger, mystery Ford powered 2dr convertible
Posts: 12,701
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Not Ranked
While everyone else is focusing on spark, perhaps a look at your fuel pump/fuel system and a further search for a vacuum leak may be in order. Had a similar issue a year and a half ago, mysteriously went away, only to rear it's ugly head on a weekend cruise when the fuel pump finally gave out 125 miles from home. With Covid regulations in place, the car got a nice ride home on a flatbed, with wheel bonnets, we got stuck in an Uber
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03-01-2021, 05:24 AM
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CC Member
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Join Date: Feb 2002
Location: Dadeville,
AL
Cobra Make, Engine: Sold my EM.
Posts: 2,459
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Not Ranked
My next move would be to reset the warm idle to 11-1200 RPM just for diagnosis. Repeat the action that caused the engine to die before and see what happens. If the engine dies again, I'd focus more on electrical causes. If it keeps running, I'd focus on the fuel system. .... My thinking is that the rapid acceleration/deccleration may inded be causing something electrical to move; but it is also possible that going from near wide open throttle to fully closed butterflies may be causing an air fuel ratio problem. ... For the record, I'm far from an expert on this topic. If someone better informed comes along, take their advice over mine.
__________________
Tommy
Cheetah tribute completed 2021 (TommysCars.Weebly.com)
Previously owned EM Cobra
"Never attribute to malice that which is adequately explained by stupidity." - Hanlon's Razor
Last edited by Tommy; 03-01-2021 at 05:26 AM..
Reason: Typo
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03-01-2021, 06:22 AM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
All good suggestions so far, and I'll give them a try one by one. I really appreciate the efforts to help, welcome any additional thoughts, and will report back with any updates and hopefully a resolution.
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03-01-2021, 06:25 AM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Quote:
Originally Posted by Gaz64
Sounds like a harness moving around.
With the engine idling, move your distributor pickup wiring all the way up towards your 6AL, and also and wiring that can move under g force.
I would also like to know if the car accelerates well continuously, at least for 3 gears.
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I'll spend some time tomorrow with wiring to see if I can find anything obvious.
Running through the gears, it pulls hard...real hard...first through fifth. It's definitely not a fuel starvation due to fuel bowl slosh issue.
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03-01-2021, 06:29 AM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Quote:
Originally Posted by mrmustang
While everyone else is focusing on spark, perhaps a look at your fuel pump/fuel system and a further search for a vacuum leak may be in order. Had a similar issue a year and a half ago, mysteriously went away, only to rear it's ugly head on a weekend cruise when the fuel pump finally gave out 125 miles from home. With Covid regulations in place, the car got a nice ride home on a flatbed, with wheel bonnets, we got stuck in an Uber
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Pressure gauge shows a steady 6.5 pounds of fuel pressure at idle, but it's under the hood so I have no idea if it drops under acceleration. I can run it up with a blip of the throttle lever and it stays steady, so I'm assuming at this point, that the pump is good. The filter however, is another idea I hadn't considered. PO put an inline filter in it also easily located under the hood, so I think I'll change that and see if it makes a difference.
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03-01-2021, 06:34 AM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Quote:
Originally Posted by Tommy
My next move would be to reset the warm idle to 11-1200 RPM just for diagnosis. Repeat the action that caused the engine to die before and see what happens.
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Good idea...hadn't thought of that.
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03-01-2021, 07:31 AM
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CC Member
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Join Date: Jul 2005
Location: Bartlett,
Ill
Cobra Make, Engine: Everett-Morrison LS1
Posts: 2,448
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Not Ranked
Anybody near you that you can borrow another carb from??????
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03-01-2021, 07:40 AM
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Average Guy
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Join Date: Sep 2002
Location: Rushville,
IN
Cobra Make, Engine: red Shell Valley, white stripes
Posts: 579
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Not Ranked
With the engine running, wiggle the wires on the back of the ignition switch. See if the engine cuts out. It's a long shot, but worth 90 seconds to try it.
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03-01-2021, 08:47 AM
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CC Member
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Join Date: Feb 2018
Location: Lodi,
CA
Cobra Make, Engine: 427 manowar forged crank roller rockers . BIG CAM.
Posts: 785
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Believe it or not I actually had a internal battery short that caused me all kinds of trouble Not saying this is your problem very unlikely but it does happen.
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03-01-2021, 04:02 PM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Quote:
Originally Posted by Jerry Clayton
Anybody near you that you can borrow another carb from??????
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Actually, yes. I think I'll give that a try this weekend.
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03-01-2021, 04:04 PM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Quote:
Originally Posted by hauss
Believe it or not I actually had a internal battery short that caused me all kinds of trouble Not saying this is your problem very unlikely but it does happen.
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Battery is an Optima Red Top and only about six months old, but Murphy's Law being what it is, it's certainly not impossible.
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03-01-2021, 04:24 PM
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CC Member
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Join Date: May 2008
Location: Brisbane,
QLD
Cobra Make, Engine:
Posts: 2,797
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How about the rear float level a fraction high, and flooding the engine on decel?
Drop the level by 2 flats at a time, and retest.
__________________
Gary
Gold Certified Holden Technician
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03-01-2021, 04:27 PM
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CC Member
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Join Date: Nov 2018
Location: Priceville,
al
Cobra Make, Engine: Unique FIA
Posts: 334
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Not Ranked
Mine does the same thing. I can brake faster than the floats can keep up with. I just deal with it. I've never ran out of fuel on acceleration.
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03-01-2021, 09:40 PM
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CC Member
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Join Date: Jan 2020
Cobra Make, Engine: Superformance, Dart aluminum block, AFR aluminum heads.
Posts: 28
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Not Ranked
Quote:
Originally Posted by Gaz64
How about the rear float level a fraction high, and flooding the engine on decel?
Drop the level by 2 flats at a time, and retest.
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Good idea. I'll try that before switching to the loaner carb.
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