Mk4 Golf compatability? and intermittent running

[SRHeer]

I have a 1999.5 Golf TDI and may buy a 2000 Golf TDI - now the 2000 runs fine for about 15min and then shuts down - wait a few minutes - starts back up and rund fine until shuts down again - now I was wondering what might be the cause - thinking maybe ECU or as Bentley manual calls it ECM - but can I try my 1999.5 ECU in the 2000 and run it and how can I tell if it is compatable - or what else does one suggest to look for? - maybe poor grounds or maybe weak injection pump - Is there some way to check for weak injection pump? What might it be - something that warms up or is in use for a while shuts down but then after rest it works - ah - what to look for or what might others have expreineced here on this and or what might be good to check or test and how?? hey thanks for your advice!

[chittychittybangbang]

sounds like classic relay 109 issue. Look under steering wheel panel at relay panel, if relay 109 is black replace with newer gray.

If you replace it and it's fixed, can you send me the bad relay 109 so I can test it and share what I learn?

[SRHeer]

this is a Mk4 - no relay 109 here on mine anyway - sounds like what came in Mk3 Jettas etc - but not sure - ok - thanks though always need to remember those quirks - I wonder what relay takes the place of the 109 in the Mk4s???

[SRHeer]

do you know what relay 109 ran? thanks

[SRHeer]

Ok I found relay 109 - on mine was not on the relay block - off to the side - will have to investigate - thanks!!!

[Seatman]

109 is the main power relay for the ecu, they start to play up and cause things like no start, car conking out for no reason etc.

[SRHeer]

The problem did turn out to be relay 109 - the 2000 Golf TDI finally quite alltogether - fortunatly it died while I had it up on ramps in my driveway to inspect how I was going to go about changing out the AC compressor - after it would not start after cranking over for some time I checked - not finding 12+ volts at injection pump shut-off valve. I replaced R109 with a known good one and it cranked and started right away and then put falty R109 in 1999.5 Golf and it would not start - so I now have 4 on order from idparts for less than $10 each - thanks to all those who helped with getting this sweet Golf on the road! I got the AC compressor to change out but it does not look like that much of a job - ChittyChittyBangBang I can open realy and investigate what might have been probable cause and report back and or if you really want to take a look at relay I can mail to you what is your address?
Later
Stephen