This issue showed its ugly head yesterday while mapping, according to the laptop the batterys peak charge was 15.1v which is a bit high Russ (my mapper) said. Also when the car was revved the battery light on the dash came up.

Anyone experienced this before? The alternator was fine on my other engine and the loom is the same loon so im a bit bemused why its apparently gone a bit pete tong. Although ill happily accept it if thats the issue. One thing Russ did say was that it could be an earthing issue, as far as i can see the engine loom has 2 earths, i have them both attached to my inlet manifold?

Am i missing an earth or something?

 

I'd get the alternator checked out, it might have a dodgy regulator. That sort of voltage will quickly boil the water out of the battery

 

Ok mate, will do, i dont think the battery is up to much anyway so maybe a fresh battery along with a fresh alternator will do the trick

 

A duff battery (especially one with a shorted cell) can cause the alternator to raise the voltage due to excessive current demand being sucked up by a failing battery. Fully charge teh battery off the car and then load test it; As descirbed here: http://jgdarden.com/batteryfaq/carfaq4.htm


It also goes without saying after engine swaps to check the earth straps to the body and engine. And the main power lead connections to the battery and alternator (and the little sensing wire), any rust or corrosion on any connections or terminal need to be cleaned to fresh shiny metal.

If the battery is duff then try a new fully charged battery first (or swap with a known good one if need be; load tested and properly charged, of course). Correct charging info can be found here: http://jgdarden.com/batteryfaq/carfaq9.htm).

If the new battery is fully charged then the alternator should behave and give a more sensible voltage. It should be around 14.1 to 14.8v. If it still misbehaves replace the alternator (don't drive the car round until you do so or you'll cook the new battery too).

It is possible to replace the regulator on alternators, which is often combined with the brush box. ( I have done so a number of times in the past) this is far cheaper than a new alternator, but IIRC the Impreza/Mitsubushi alternator is a bit fiddly to disassemble (depending on model - needs de-soldering etc) and I'm not sure if new regulators are easily available. I know you can get them for Bosch units, but not sure about Mitsubushi, sorry.

 

Good answer from Ali.

 

Thats a cracking answer mate, ill get torn in tonight, much appreciated