Golf 1.6 Mk4 - engine cutting out while driving...

Hi everyone :sadwavey: .... I hope I can get some advice ..I have been searching for a Golf owners club website so I get to the bottom of this trouble that I am having with my dad's car...

I bought a MK4 Golf 1.6 ...1998 reg. model (Auto with AC) for my retired mom & dad. It has done around 40K miles.
When I got the car around 2 months ago, I had a full major service done on it along with cambelts.
Its had:

new spark plugs
new battery
new oil / oil filter
air / pollen filter
fuel filter
new belts / tensioner
new waterpump

The mechanic pointed out that it seemed a new alternator had been installed on the car... as it looked more clean and shiny compared to the other engine parts.

All was running smoothly for nearly a 1000 miles until last week.. when my parents are driving along.. and suddenly the airbag + ABS light (that's what dad told me) came on.. and the car started beeping...a minute or so later the engine cuts out and the car cannot be started. When you try to crank it.. you just get a clicking sound... (as if the battery was dead). Leaving the car overnight .. it starts up fine again...

The problem reoccurred again.. this time they were quite far from home... so I had the RAC recover the car to my house.

I did this test on the car the following morning:

test the battery voltage while engine is off: 12.5 v

I then start the car (car starts right away without any hesitation), and with the engine at 2000rpm and with all the electrics running in the car (wipers, fan, ac, headlights, radio, window demister, etc. etc...) I test the voltage across the battery and i get: 14.1V. Then I switch of all the electrics and with the engine still running at 2000rpm.. I get: 14.4V

So I guess the charging is ok and the battery is ok.... so why is it that the battery seems to get drained...(if that's what is happening). Is the alternator giving up intermittently ?

I can't reproduce the fault consistently ... so I can't really demo it to a mechanic to get the source of the problem...

Has anyone encountered something like this before... ?.. or any ideas as to what to do / how to diagnose further ?....
I am very hesitant to give the car back to my parents.. as I don't want them to get stranded somewhere... :dunno:

regards,
- seth.

ok.. I've made some progress... as to reproducing the fault...

I start the car up...with some of the electrics on... lights, demister..radio..etc.. and all seems normal.. (i.e. alternator is kicking out around 13.5-14V... ) .. leave the car idling like this and watching the multimeter..... and around 7-10 mins later....i see the voltage dropping !... revving the engine.. causes the voltage to drop further...
....
so suddenly it seems the alternator has given up... soon the ABS, airbag light , warning light (the circular one with the exclamation mark in the middle)...come on.... now if i keep blipping the throttle... sometimes.. the voltage jumps back upto 13.5V ... and all seems normal again...
but sometimes.. it doesn't .. and goes right down and the engine dies...

now its not possible to start the car .. as the battery has been drained... wait a few hours or jump start the car.....all seems fine.. and the process repeats itself...

based on this ... it is accurate to assume a new alternator is needed..?? . i thought either it would work.. or it wouldn't... this intermittent behaviour is a bit suspicious...and makes me wonder if it is something else...

guys ....ANY help much appreciated...:Screem:...

BTW...is it easy to replace the alternator...?.. how long will it take ?.. do I have to remove the belt completely....?

You must rule out the wiring circuit from the alternator to the battery and check for resistance of the wiring disconnected from consumers and dont forget to check the security of the battery terminals and alternator bolted contact and multiplug for the alternator along with the engine earth at the gearbox.Also carry out alternator out put test via amperage,on the alternator there will be a sticker and it will tell you your amperage rating ie 90amps

Hi...
thanks for info...based on the tests.....I think the alternator is suspect.. I have pulled it out...
it is a Lucas alternator (number: LRB00486)
I can't see an amp rating anywhere...
any good suppliers where I can get an original new part (rather than a refurb one)....?
what would be the amp rating on this ? .. the car is S reg 1.6 Auto with air con. Fully standard... no updated stereo / accessories, etc...