XJS ( X27 ) 1975 - 1996 3.6 4.0 5.3 6.0

Alternator & the Load Dump Module

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Old 10-11-2018, 11:14 AM
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Default Alternator & the Load Dump Module

Howdy all. I’ve got an 88xjs. The battery light has been blinking on/off. Whenever I hit accelerator it comes on. When I hit brakes, it goes off. That said, the battery gauge always stays at the high level

I’ve been told I need to replace the alternator & the load dump module. The module is hard to find and costs 2X the cost of the alternator.

Ive been reading many posts about bypassing the load dump module, but no one has said what the downside of doing this is. How does bypassing the module affect the alternator and/or battery? If I replace the alternator do I have to replace the module? How do I know whether I need to replace the alternator, the module or both?

Thank you very much
 

Last edited by VadimP; 10-11-2018 at 12:13 PM. Reason: Adding info
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Old 10-11-2018, 03:29 PM
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Firstly you need to determine if the problem is the alternator or battery, as the light will come on if either are bad.

Battery voltage with it disconnected should be at least 12.8v no less.

Re connect the battery and start the car measure voltage on the battery it should be about 13.8v, rev the car and the voltage should remain reasonably stable it may go up to 14v.

Next put your meter on AC volts and measure at the battery with the car running AC volts must be less than 0.5v
 
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Old 10-12-2018, 07:53 AM
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I'm sure I've read where others have bypassed/disconnected the dump module with no ill results....but I can't find or remember where.

It's supposed to protect against voltage spikes under xxx-circumstances; I think it was introduced along with Marelli igntion.

Cheers
DD
 
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Old 10-18-2018, 09:23 AM
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Originally Posted by warrjon
Firstly you need to determine if the problem is the alternator or battery, as the light will come on if either are bad.

Battery voltage with it disconnected should be at least 12.8v no less.

Re connect the battery and start the car measure voltage on the battery it should be about 13.8v, rev the car and the voltage should remain reasonably stable it may go up to 14v.

Next put your meter on AC volts and measure at the battery with the car running AC volts must be less than 0.5v
Hi Warrjon, did that with my mechanic. Battery was reading at 17v. Looks like I’ll be replacing alternator and load dump module. Finding alternator is not hard. The module is another story. Can you recommend any parts supplier or might you have an extra laying about 😉
 
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Old 10-18-2018, 09:27 AM
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Originally Posted by Doug
I'm sure I've read where others have bypassed/disconnected the dump module with no ill results....but I can't find or remember where.

It's supposed to protect against voltage spikes under xxx-circumstances; I think it was introduced along with Marelli igntion.

Cheers
DD
My mechanic, who knows he’s got a live one in me, says that letting the alternator run high (my battery is running 17v) can fry the main computer and a bunch of other stuff. Unfortunately my mechanical understanding of the car ends with my knowing where my credit card is, so I believe him 🤷*♂️
 
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Old 10-18-2018, 11:56 AM
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As you should. +50% is very very high.

 
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Old 10-18-2018, 12:55 PM
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Originally Posted by JigJag
As you should. +50% is very very high.

what do you mean +50% is very high? Battery is supposed to be around 13-14v. Are you referencing that?
 
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Old 10-18-2018, 08:35 PM
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Yes, 17V is very very high.
 
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Old 10-19-2018, 03:03 AM
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Originally Posted by VadimP


Hi Warrjon, did that with my mechanic. Battery was reading at 17v. Looks like I’ll be replacing alternator and load dump module. Finding alternator is not hard. The module is another story. Can you recommend any parts supplier or might you have an extra laying about ��

And the battery - 17v will boil the battery. Sounds to me like the voltage regulator has failed. Does the voltage change with RPM.

I would not worry about the load dump module, just disconnect it, the battery will act like a large capacitor to regulate voltage spikes.
 
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