To data link connection - and possible cylinder head gasket problem: where to start?

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Orchid70

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Transporter Syncro 1999
2,5i petrol
Engine code AET
315 000 km
VIN: ZZZ70ZXH090784

Wish to have some advice before pulling the cylinder head.

I have no contact with OBD. So no Auto-scan.
I have no Manual for fuses, but I think the fuse number 21 is for data link connector. That fuse has only 1,2V, if I remember right.
No interior lights or radio.
The radio is after market, and the connector does not have the pin 3.
According to the owner, the radio worked sometimes after he bought the car in beginning of the year.
Also the drivers door window did the same - but doesnt work anymore. The cables through the door has been professionally changed.
The clock and the trip meter zeros its self at start.
The climactronic blinks 25 times, when ignition is turned on, then works as normal. I thought it used to turn on directly, when the engines is running before - but now it turns on only after those 25 blinks. But not 100% on that.

I wanted to make sure first, that the engine would run properly. It has had problems with leaking coolant for at least 3 years prior (from reading the bills that followed with the car).
They filled in Bar's leak stop, in early 2018 and changed thermostat and thermostat housing.
5 months later, they changed coolant pump and cam belt, due to a coolant leak.
In 2019 doing some other work, they wrote "white smoke starting cold - keep an eye on coolant".
In December 2019 - there was a leak on manifold gasket and the 5 gaskets were changed - today we could see that the valve cover has been lifted (when we checked for cylinder leaks, we lifted the cover to easily find top dead centre on every cylinder). Is it even possible to change manifold gaskets without lifting the cylinder head??
When we picked up the car, the low coolant alarm came on, half way home. The owner then told that they had filled in coolant several times.
The coolant looked like brown/red poop in colour. There is quite large leak at the coolant pump again. There is a pool of coolant on the ground.
The owner had also taken this car to a vacation with the family and "the car ran like bag of beans sometimes" - guess when it was cold.
We started by changing the radiator and the extra coolant pump (it sounded really bad). Taking out the thermostat and flushing the system.
Changed spark plugs and ignition cables (they had been changed 15 months ago, but there was corrosion on one of the cables, due to not been fitted on properly), I have tested with a new ignition coil just to be sure.
The distributor cover and rotor had been changed together with the spark plugs and cables - there was water and coolant (from the reservoir above) inside, but otherwise ok.
BUT THE ENGINE STILL DOESNT RUN ON ALL 5 CYLINDERS - specially when cold. Its better when the engine is warm.
It feels worse after the coolant flush.
This is what I have checked:
Exhaust in the coolant water with combustion leak tester (the fluid) = nothing.
Checked compression = within specs.
I bought OTC cylinder leak down tester and there was 20-25% leak on two of the middle cylinders, the rest were perfect, under 5%. Never listened, in order to try to find closer where the leak was, because the car is outdoors.

So my question: where is the best place to go next:
Lift the cylinder head to see if something has happened with the gasket?
Or search the electrical issue - is there ANY chance that the engine would not run on all cylinder, from the - is it K line - electric problem??

Thank you
 
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Uwe

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So no contact to any control modules? Instruments? ABS? Central locking? I'm trying to think of what else would be in a 1999 T4.

The cylinder head gasket issue really belongs in General VW/Audi Repair, but I'm leaving this here for the OBD connection problem.

-Uwe-
 
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Orchid70

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Pulled out the multi again:

At DLC:
Pin 4 and 5 = 3,5 ohm resistance to chassis
Pin 4 and 5 = 118 mV KOEO (between battery negative and DLC)
Pin 7 = battery voltage
Pin 16 = the voltage fluctuates between 334-390 mV KOEO

Oh and fuse 21 is intact

And - when I wanted to check if the pin 16 had different voltage with engine running - I opened the door and closed it with multi in my hand.....
With door closed: 6 Volts.
Door lock open, door still closed: 6 V.
With the door all the way open - back to millivolts.
Guess the problem with wiring is located in the door loom after all. Yikes....
 
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Orchid70

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No contact with any control modules.
So better move to the correct group =) Sorry about that.
 
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Uwe

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Pin 16 on the DLC should have constant 12V power, no matter whether the key is on or off, or whether the engine is running.

-Uwe-
 
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Orchid70

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Narrowed it down to the interior light switch on the door pillar. When I push it in - the voltage goes up 13V briefly (battery voltage 12,5) and straight to 7V.
When I release the push button - the voltage goes down.
Cant see anything out of the ordinary behind the fuse box.
I did check before, behind the glove box if the light had shorted - nothing there either.
 
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Orchid70

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OK - I missrememeberd - fuse 21 has battery voltage!
Pin 16 has not.
 
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Uwe

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I think you should fix that because I don't know of any scan-tool that will work without power from Pin 16. ;)

-Uwe-
 
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Orchid70

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Nope - I know =)
Just dont know where to search next.....
Not sure the wiring diagram I have, is correct - it seems to be a bit different car this Syncro, looks like having late models fuses fitted on it (dont have the manual to know what fuse is what).
I have found info about fuse 9 being for the rear wiper in some cars (this has it - not working) and in Elsa win: from september 2000, it going to "Control unit with display in dash panel insert - J285" - that sounds just about that it could be correct. But the car is from 1998.
 
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Orchid70

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We pulled the head and could see that head gasket and the inlet and exhaust manifold gaskets had been change not long ago. The exhaust manifold had been welded (10 months ago according to the bill) but already cracked in the weldings.
The engine was covered in coolant and coolant leak CEMENT - on the coolant pump side.
We changed head and exhaust manifold. Both coolant pumps, engine oil pump, thermostat, fixed the electrics and so on and so on. The distributor wire connector was glued together, screws on inlett manifold werent tightened, different size nuts on the exhaust pipe on the manifold (those took me hours to get out).
Car is running now and the owner had forgotton he said that we were to fix it - at ANY cost...... so he still havent paid it all.
It ended with me putting in an extra wire from battery positive to pin 16 at DLC - fused of course. I had to, because the immo kicked in when we had put the engine back together again - after some weeks wait for parts (VAG have stopped selling gaskets for this engine in 2018!).
Some pics from what we found.... the coolant pump and cam belt was changed less than a year ago and was now dripping out coolant. I dont know which of Bar's Coolant Leak remedy they used - but this is what it did:







 
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