Alternator or CIM

[johnnyallen]

Hello everyone, this morning on school run, my car went berserk, when I started it up, I noticed the dash and display dimming slightly more than usual, but put it down to being a cold morning, then 10 mins away from home jammed in traffic, the dash, info display and all lights started flashing on and off, but only when I reved the engine up to drive, when idling everything was fine. Also the overload relay behind the glovebox was clicking on and off
First thought was oh my god, the CIM has gone, but when I got home, I checked the voltage on the battery and got the following :

Engine Off in Sleep mode : 12.7v
Engine idling : 13.8v
Engine reved to constant 1000rpm : 11.2v to 16.9v (hunting up and down)

To me it sounds like the voltage regulator has gone on the alternator and the spike in voltage is causing the overload relay to trip, what do you guys think please?

Thanks John

[lee gsi]

Your diagnostic sounds correct.

The alternator shouldn't be putting that much voltage out no matter what.

[johnnyallen]

Phew thank god for that... now a trip to fleabay!. Out of interest, does any veccy C alternator fit or ire they all specific to enging besides the amp output?

[rushy]

It could be a 100 or 120 amp mate. Do the two halfs interlock or just line up next to each other, I take it you have s 1.8 or 2.2 petrol?

[johnnyallen]

Its a 2.2 mate, and is the 100amp version, just wondering if just replacing the voltage regulator would be best, or just gamble on a complete 2nd hand unit.

[yysnet]

Did you measure the voltage by DIREDTLY probed to the battery electrode?
Or to the connector nearby?

It's not normal for a battery voltage rised to 17V and dropped to 11v.

Your diagnostic is sound right, but i would check the battery and connection first.

[johnnyallen]

OMG just tried to get the alternator out, all fine until the last bottom centre bracket bolt, cant get a spanner or socket onto it because of the flippin air con pipes in the way, whoever designed this engine needs my breaker bar wrapping around his neck. Checked all the connections around it, everything sound, Anyway, grazed nuckles and a bad back later I put it all back together and started it up, all seemed fine until about 10 mins later then it went nuts again. I'm gonna go and cry in the corner now.

[johnnyallen]

Did you measure the voltage by DIREDTLY probed to the battery electrode?
Or to the connector nearby?

It's not normal for a battery voltage rised to 17V and dropped to 11v.

Your diagnostic is sound right, but i would check the battery and connection first.

Yes mate on the battery itself, connected op-com too to watch the system voltage, and that shows similar fluctuations, plus fault code for overload relay and no communication to CIM.

[yysnet]

Bless, GM is really a bad design. you have to go down the car like a rat for a oil filter change.

[rushy]

you have to go down the car like a rat for a oil filter change.

Eh? The filter change is probably the easiest I've come across on any car. Pop the hud, and there it is facing upwards towards you.