Mk4 Golf Excess smoke at cold start

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
I have a 1998 Golf TDI Mk4 bought new and synthetic oil changed every 5000 miles. New air filter and fuel filter. Current done 64,000 miles and changed MAF at 52,000 (two years ago - not doing a big mileage).

Just checked pipes around the inlet manifold and everything looks OK. Last I looked inside the inlet manifold it had no more than a light coating and certainly not clogged up.

When MAF was last changed (genuine VW Part)there was a pronounced drop in performance, accelerating in particular. After changing it it drove like a new car.

Recently started pumping out excessive smoke from the rear exhaust when starting from cold, but clearing as it warmed up. Disconnected MAF and started from cold - no smoke at all. Reconnected MAF and still no smoke.

Reasonably confident fault lies with the MAF, or at least the signals it is giving to the Engine Management System. Have ordered a a new MAF.

Is this the right diagnosis?

On reflection it could be due entirely to a bad connection between the plug and socket of the leectrical connection, despite an electronic lubricant being used.
 
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jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
poor1 said:
On reflection it could be due entirely to a bad connection between the plug and socket of the leectrical connection, despite an electronic lubricant being used.
Very possible/logical conclusion. One more, of several, possible causes could be the fact that your TB has stretched a bit and retarded the injection timing. Cold starts are generally a bit better/quicker with the timing advanced, so if its a bit "late" and you crank a bit longer, it loads up a little extra fuel that when it fires up is expelled out the exhaust as smoke (unburnt fuel). Get it hooked up to the VCDS and graph the timing to see where its at. Has the TB been changed and what is current miles/km??
 

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
Many thanks for your considered response. Good to have confirmation on a line of thinking. Current mileage 65,000. Changed the timing belt at 40,000 (3 years ago)and made sure the dynamic timing was spot on. I'll hook up and check it again. The performance had been excellent since I changed the MAF for the first time at 52,000 (2 years ago).
 

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
You're right the dynamic timing has dropped back (retarded) a little to 48 t0 50.
Additionally a fault did show up on the MAF showing P1144 - 35.00 "open or short to ground". Fitted a new MAF and after clearing fault showed "no fault". I would appear that my theory of there being a bad connection might have been partially correct.
So I think the principle problem seemed to be the MAF, but I will take on board the retarded timing question and adjust it in due course.
The main thing for the time being is that the smoke problem seems to have gone away. If you have any observations regarding the faulty MAF readings I would be interested.
Many thanks too.
 

conate

Well-known member
Joined
Dec 5, 2003
Location
Norwich, CT
TDI
2000 Jetta TDI
I had the same problem a few months back and believe it or not I cleaned my snow screen and the smoke was drastically reduced.
 

fossill

Veteran Member
Joined
Mar 22, 2008
Location
Canada
TDI
Golf
Run a can of Lubro Moly Diesel Purge through it. Worked for me. Injectors probably a bit dirty and not giveng a proper spray pattern.
 

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
Thanks I will. Every little helps.

As regards the dynamic timing, from what I understand, so long as the timing point (on the vertical line)remains between the two top and bottom lines on the graph at a particular fuel temperature (shown along the horizontal line) the timing point is acceptable and there is no need for adjustment. As the timing point on my Golf is well within the graph lines there is no need for the timing to be changed.
 
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