Ignition Fuse Blowing on Dyno - LotusTalk - The Lotus Cars Community
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post #1 of 11 (permalink) Old 07-13-2019, 07:56 AM Thread Starter
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Ignition Fuse Blowing on Dyno

Hey Guys,

Question for the masses: Finally took my car to get Dyno'ed. The tuner said when it "torques back real hard" the car dies and it's always the 10A ignition Fuse that's popped. You can drive the car fine on the streets, but anytime the car is under a high load the it pops the fuse. If it were a grounding issue I would think it would happen all the time, but since it's only under high torque does anyone else know what it might be? Thanks in advance for suggestions.
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post #2 of 11 (permalink) Old 07-13-2019, 08:01 AM
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Are you logging voltage during the run? If you have an issue that's causing voltage to dip (alternator slipping?), current has to go up as a result. Heat can also cause this by raising resistance.

No specific experience here, this is just general electrical system behavior.
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post #3 of 11 (permalink) Old 07-13-2019, 08:12 AM
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I don't have any idea. I'll throw this out though, the amount of energy needed for a spark to jump a gap goes up when the pressure goes up meaning the coil has to put out a higher voltage to the plugs. Perhaps when on the dyno the cylinder pressures got high to the point that the coils are drawing too much current and causing the fuse to blow. In over 40 years of wrenching on cars I've never seen this happen, but it is possible I guess. Personally, I'd do a good resistance check on all the coils to see if they are in spec and near uniform with each other. Check the wiring in the system for good connections, especially the grounds (95% of strange wiring problems are caused by bad grounds).
It's possible you're seeing this only on a dyno because the cylinder pressures are getting higher there, or it might be because with no movement through the air the engine bay is getting more heat soaked than when you're driving down the road. Keep us updated on what you find.
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post #4 of 11 (permalink) Old 07-13-2019, 09:31 AM Thread Starter
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Quote:
Originally Posted by Jetblast View Post
I don't have any idea. I'll throw this out though, the amount of energy needed for a spark to jump a gap goes up when the pressure goes up meaning the coil has to put out a higher voltage to the plugs. Perhaps when on the dyno the cylinder pressures got high to the point that the coils are drawing too much current and causing the fuse to blow. In over 40 years of wrenching on cars I've never seen this happen, but it is possible I guess. Personally, I'd do a good resistance check on all the coils to see if they are in spec and near uniform with each other. Check the wiring in the system for good connections, especially the grounds (95% of strange wiring problems are caused by bad grounds).
It's possible you're seeing this only on a dyno because the cylinder pressures are getting higher there, or it might be because with no movement through the air the engine bay is getting more heat soaked than when you're driving down the road. Keep us updated on what you find.
Rob
Gents, thanks for the suggestions. I'm currently using the factory engine ground location for a few different components: surge tank fuel pump, A2W IC fan, a circuit panel I added for my cabin gauges. Is it possible to overload a grounding point?
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post #5 of 11 (permalink) Old 07-13-2019, 10:45 AM
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Originally Posted by Rizzydee View Post
Gents, thanks for the suggestions. I'm currently using the factory engine ground location for a few different components: surge tank fuel pump, A2W IC fan, a circuit panel I added for my cabin gauges. Is it possible to overload a grounding point?
No, you cannot overload a ground since it is down stream of the fuses. What you can do is have a bad ground point that has the current increases, the voltage drop at this ground point increases. This is usually detected by the point getting warm/hot to the touch. If a bad connect is left long enough, you can actually burn the wires off of the connection point. Normally, this only occurs with large current sources.

Later,
Eldon
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post #6 of 11 (permalink) Old 07-13-2019, 10:47 AM
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Originally Posted by Rizzydee View Post
Gents, thanks for the suggestions. I'm currently using the factory engine ground location for a few different components: surge tank fuel pump, A2W IC fan, a circuit panel I added for my cabin gauges. Is it possible to overload a grounding point?
If the contact is a good low resistance connection then no you can't overload a grounding point (within reason). That being said, I was an aircraft maintainer in the military for over twenty years and the electricians there always limited it to three connections per grounding point on the aircraft. I've seen hundreds of electrical ground problems on cars through the years but I've never seen a ground connection with too many ground wires.
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post #7 of 11 (permalink) Old 07-15-2019, 10:18 AM Thread Starter
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Tuner was able to fix the problem. I'll post the fix shortly. To confirm as well, factory Exige s shift light is 7500 and redline is 8000k?
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post #8 of 11 (permalink) Old 07-15-2019, 12:38 PM
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Tuner was able to fix the problem. I'll post the fix shortly. To confirm as well, factory Exige s shift light is 7500 and redline is 8000k?
Redline is not 8000, its something like 8500 for 1 second then it drops down to 8000 (double check this but I believe it's correct) Not sure when the shift lights come on stock.

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post #9 of 11 (permalink) Old 07-15-2019, 02:09 PM
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Redline is not 8000, its something like 8500 for 1 second then it drops down to 8000 (double check this but I believe it's correct) Not sure when the shift lights come on stock.
I think the constant redline is 8200 but close enough. Also, not sure if the shift light comes on at that point or before.
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post #10 of 11 (permalink) Old 07-20-2019, 05:38 PM Thread Starter
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Fixed the ground issue. Ended up that the cable bunch going into my engine bay fuse box had come loose over the years and as the engine moved shifting through the gears on the dyno they were pulling slightly on the pins and grounding the ignition Fuse out. We re-pinned and extended the harness and there have been no more issues. Ended up with 272hp and torque was 186 on the Dyno.

Thanks to everyone for the input and advice. There are some big minds on this forum!

Last edited by Rizzydee; 07-20-2019 at 05:47 PM.
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post #11 of 11 (permalink) Old 07-20-2019, 05:45 PM Thread Starter
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Also on the Dyno after 8300rpm the power dropped significantly. On my car there weren't any indications of power drop as the torque and power were pretty constant until it fell off.
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