Haynes Forums  

Go Back   Haynes Forums > Haynes Roadster Forums > Electrics
FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
  #1  
Old 29th June 2016, 07:58 PM
RichardH RichardH is offline
Senior Member
 
Join Date: May 2015
Location: fife scotland
Posts: 177
Default mx5 alternator testing

my 1.8 mx5 engine 1999 is not charging, i suspect the alternator is faulty but there isnt much about testing them , i have 12v on the heavy cable which comes from the battery via main fuse, i would expect this to rise to 14v ish on startup but it doesnt.
the plug onto the alternator has two wires a grey and a grey/red, i have 5v on the grey and nothing on the grey/red, from the web i reckon the grey/red should have 3 v AC ???? as a signal to the ecu. before i cough up for another alternator anyone any ideas
Reply With Quote
  #2  
Old 30th June 2016, 09:57 AM
Ianr Ianr is offline
Senior Member
 
Join Date: Sep 2014
Posts: 216
Default

My alternator was ecu controlled and would not charge. I traced it to a broken wire somewhere in the loom by checking continuity from the ecu to the alternator. Wire replaced and off it went!
__________________
My build blog here http://ianhaynes20.wordpress.com
Reply With Quote
  #3  
Old 30th June 2016, 11:25 AM
flyerncle flyerncle is offline
Senior Member
 
Join Date: Mar 2008
Location: gateshead,near cobbly bit of A1 North
Posts: 3,188
Default

Ford/Jag have smart charge too,usually broken wire in harness causes non charge.
__________________
Cost : Little as possible.
Thanks : To those who by their generosity my build has progressed.
Its a handmade sports car not a flaming kit car !!!


If at first you dont succeed,avoid skydiving...

No parachute require to freefall,only if you want to do it twice.
Reply With Quote
  #4  
Old 30th June 2016, 12:26 PM
RichardH RichardH is offline
Senior Member
 
Join Date: May 2015
Location: fife scotland
Posts: 177
Default

thanks guys the plot thickens. spent hours trawling the net last night about this, the mev forum had a bit about non charging and i found two things, there is a sensor in the airbox that measures temp before the air reaches the maf sensor i hadnt plugged that in as i have no airbox, plugging that in made the charge light go out when running. but still no charge, another post mentioned a plug that lives in the boot of mx5 that needs to be plugged in, found that this is the grey/red from the alternator, i runs from the alternator up the drivers side to the boot, then plugs into the lighting loom and comes all the way back to the front to the ecu. plugging that in now gives me a small charge, battery increases by about 0.5 volts, with the car running i am getting 12.9v of it drops to 12.3 ish.
still not sure if the alternator is gubbed or the ecu is still telling it not to charge as much.
i have continuity from the alternator to the ecu on both wires but there is feeds off them doing other things not in the wiring diagrams
Reply With Quote
  #5  
Old 30th June 2016, 03:53 PM
RichardH RichardH is offline
Senior Member
 
Join Date: May 2015
Location: fife scotland
Posts: 177
Default

so after further testing i am wondering if something isnt switching on the charging of the alternator or alternator istself , i have checked continuity again from alternator to ecu all ok, i have 5 v on the grey and nothing on the grey red, if i link the wires together so there is 5v on both wires the alternator charges high 14volts, if i feed the red/grey 12volts the alternator charges up 16v.
my thinking is the 5v to the alternator should come back on the other wire as a signal/voltage to regulate the charging, therefore new alternator?
Reply With Quote
  #6  
Old 1st July 2016, 01:16 PM
flyerncle flyerncle is offline
Senior Member
 
Join Date: Mar 2008
Location: gateshead,near cobbly bit of A1 North
Posts: 3,188
Default

They do "overcharge" on Ford/Jag due to temp and high discharge on starting etc and ecu controls this and you will see 14/15 1/2 volts when cold,also needs silver calcium battery or voltage will fry normal battery.
__________________
Cost : Little as possible.
Thanks : To those who by their generosity my build has progressed.
Its a handmade sports car not a flaming kit car !!!


If at first you dont succeed,avoid skydiving...

No parachute require to freefall,only if you want to do it twice.
Reply With Quote
  #7  
Old 8th July 2016, 06:53 PM
RichardH RichardH is offline
Senior Member
 
Join Date: May 2015
Location: fife scotland
Posts: 177
Default

so another alternator arrived from ebay today, problem solved. the last gauranteed one is knackered, hopefully i can get the regulator part and swap it in the duff alternator and keep as a spare
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT +1. The time now is 08:34 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.