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Discussion Starter · #1 ·
Hello - I'm encountering a periodic fuse blowing issue that I can't resolve. Has anyone encountered the similar situation and isolated the problem?

My 10 amp F7 fuse for the Ignition Coil / Injectors on my 2007 Exige S periodically burns out. When it does the car won't turn over and it sounds as though the multi function relay is pulsing. I've replaced the engine harness itself as well as the multi function relay recently. The engine starts & runs fine when the fuse is replaced...but...why is it burning out?

I put a blinker bulb in the fuse in an attempt to understand if I had a broken wire or short to ground. You can see the light 'blink' and hear the multi-function relay (?) cycle in the video. The blinking light throws me b/c it indicates a grounded circuit. Is that what's burning my fuse out?

Any help would be hugely appreciated - "Bummed Out in Boston". - BL
 

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Does the car allow more fuel, when the 2nd cam is engaged?
Are you going around a right or left hand corner, hitting a bump etc or what is happening when the fuse blows?
Did the harness include new power block?
Is there a chance the bottom of F7 fuse terminals are touching, as I believe you can test from the bottom?
 

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Have you done a visual check of the ignition coil wires under the engine cover? One of those wires may be pinched and abraded, and shorting out against the cam cover.
 

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Discussion Starter · #5 · (Edited)
Does the car allow more fuel, when the 2nd cam is engaged?
Are you going around a right or left hand corner, hitting a bump etc or what is happening when the fuse blows?
Did the harness include new power block?
Is there a chance the bottom of F7 fuse terminals are touching, as I believe you can test from the bottom?
Thanks so much H20Ham - I checked the fuse terminals as you suggest and am proud to report they ARE NOT touching.

The car does allow more fuel on the 2nd cam - however - there is a 1000 rpm flat spot that was never there before. The car is running the ITG cold air intake, which I will remove as KrugSpeed says it’s not ideal.

The fuse blows while sitting in the garage and has happened when removing / reinstalling the ECU. The car is a race car and has a master kill switch. The ECU removal/install is done with the switch in the ”OFF” position.

I’ve also tested the coil packs with a multi-meter and they all test fine. Working on a multi-meter test of the MFRU next Using these instructions. So far, I’m struggling with the test as I’m finding that only the Main ECU relay (L18) responds to being supplied with power. The other THREE do not. Does that seem right?

Any further ideas would be warmly welcomed. Thx! - B

1285012


1285013
 

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Discussion Starter · #6 ·
Have you done a visual check of the ignition coil wires under the engine cover? One of those wires may be pinched and abraded, and shorting out against the cam cover.
Great thought AustinP - the engine harness is brand new OEM replacement and looks great on a visual inspection. Maybe I should ohm it out? Thoughts? - B
 

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Hi GDBB - uh, I think so. It was cold (i.e. 40 degrees Fahrenheit) when the video was shot but maybe your observation is beyond that?
Just sounds quite lopey. 40 isn’t too cold. Just sounds like it’s not running correctly. I have a MFRU if you want to swap it out. I don’t need it.
 

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Thanks so much H20Ham - I checked the fuse terminals as you suggest and am proud to report they ARE NOT touching.

The car does allow more fuel on the 2nd cam - however - there is a 1000 rpm flat spot that was never there before. The car is running the ITG cold air intake, which I will remove as KrugSpeed says it’s not ideal.

The fuse blows while sitting in the garage and has happened when removing / reinstalling the ECU. The car is a race car and has a master kill switch. The ECU removal/install is done with the switch in the ”OFF” position.

I’ve also tested the coil packs with a multi-meter and they all test fine. Working on a multi-meter test of the MFRU next Using these instructions. So far, I’m struggling with the test as I’m finding that only the Main ECU relay (L18) responds to being supplied with power. The other THREE do not. Does that seem right?

Any further ideas would be warmly welcomed. Thx! - B

View attachment 1285012

View attachment 1285013
Curious did the flat spot start after the ITG CAI install? I ask because BOE states that it requires a tune.
 

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Curious did the flat spot start after the ITG CAI install? I ask because BOE states that it requires a tune.
Looks like in the video it’s stock air box not ITG but I’m curious as well as you do need a tune for the ITG as the flow rate is different for MAF sensor
 

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Discussion Starter · #11 ·
Just sounds quite lopey. 40 isn’t too cold. Just sounds like it’s not running correctly. I have a MFRU if you want to swap it out. I don’t need it.
Thank you GDBB - I’ve tested both of the MRFU units that I have and they both ohnm out correctly, so I think I’m ok on that front.

Now that I've ohm'd out the coil packs & mutlifunction relay we took apart together and everything checks out on my Lotus. The bottom line is that I've found no problems. My next best guess is to re-assemble and run it until the fuse blows again - and - if it does, move up from 10a to 15a and see if that solves it. Thoughts - B
 

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Thank you GDBB - I’ve tested both of the MRFU units that I have and they both ohnm out correctly, so I think I’m ok on that front.

Now that I've ohm'd out the coil packs & mutlifunction relay we took apart together and everything checks out on my Lotus. The bottom line is that I've found no problems. My next best guess is to re-assemble and run it until the fuse blows again - and - if it does, move up from 10a to 15a and see if that solves it. Thoughts - B
Is there a certain set of conditions that it fails? Like certain rpm, speed, road conditions, atmospheric conditions? Can you reproduce or get close to reproduceable conditions that you could looks at everything in the wiring with thermal gun or camera? Maybe with higher amperage fuse it will show better?
 

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Thank you GDBB - I’ve tested both of the MRFU units that I have and they both ohnm out correctly, so I think I’m ok on that front.

Now that I've ohm'd out the coil packs & mutlifunction relay we took apart together and everything checks out on my Lotus. The bottom line is that I've found no problems. My next best guess is to re-assemble and run it until the fuse blows again - and - if it does, move up from 10a to 15a and see if that solves it. Thoughts - B
Just out of curiosity, did this start AFTER you swapped to the new engine harness? Reason being is I just installed a new factory engine harness as well and it threw a code for awhile and also had a TERRIBLE electric burning smell. I thought something was wrong, but I couldn’t find anything. What the smell was, is the offgassing of all the tape glue and or plastic wrap on the new harness itself. It took about 5 separate drives about 30 mins each until it was off gassed enough and ironically, about halfway thru that smell, my code went away. This code was for a “misfire/coil” even tho there wasn’t one. Strange.
 

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Discussion Starter · #14 ·
Looks like in the video it’s stock air box not ITG but I’m curious as well as you do need a tune for the ITG as the flow rate is different for MAF sensor
The ITG MAF tube is bigger than the OEM air box on but uses the same MAF sensor. It would make sense that a tune is needed for the bigger volume. I’ve swapped back to OEM and stuck the Rev300 kit on the shelf. It’s WAY too much for a stock motor in race conditions, heat is a major problem.
 

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Discussion Starter · #15 ·
Just out of curiosity, did this start AFTER you swapped to the new engine harness? Reason being is I just installed a new factory engine harness as well and it threw a code for awhile and also had a TERRIBLE electric burning smell. I thought something was wrong, but I couldn’t find anything. What the smell was, is the offgassing of all the tape glue and or plastic wrap on the new harness itself. It took about 5 separate drives about 30 mins each until it was off gassed enough and ironically, about halfway thru that smell, my code went away. This code was for a “misfire/coil” even tho there wasn’t one. Strange.
That is super interesting, thank you for sharing. We’ve run about 30 miles with the new harness but have no codes so far. The fuses must have blown on starting efforts. I’m back together now and going to the track to shake down on 4.30. I’ll report more details after the shake down.
 
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