Engine running 70c Excessive Fuel consumption and dangerous when cold

[spud72UK]

Hi,
I have got a 93 Mk3 1.4 Golf with ABD engine for my son ( single point FI ) which had been sitting for 6 months ( not sure if important or not ).

A bit of history of what has happened so far :
The previous owner had problems with the car stalling and sometimes not restarting, once the car was MOT'd we had that problem too, investigation with the help of the Forum found it was the Hall Effect Sender in the dizzy so replaced the dizzy problem solved and happy days I thought, how wrong could I be.

Problems now
Misfire at low revs - changed plugs and coil fixed that.
The temp gauge when driving never exceeds 70c ( even after 30 mins ) and I get 20 mpg or less out of the car. The gauge seems to be accurate as when it is stationary it will eventually get to 90c and the rad fan ( now that I have fixed that - new wiring needed ) comes on.
Signs were typical of a stuck open thermostat, tested that but it was ok. A week or so later still with the same problem changed the thermostat and still runs exactly the same at 70c.
I am on coolant sensor number 3.
I think that the cool running is causing the excessive fuel consumption.

When starting from cold it revs to just over 1000 rpm and revs nicely but once I start driving it ( son doesn't want to drive it at the moment as dangerous ) within a few hundred yards when you pull out at a junction it can loose all power ( does not stall ) revs go right down and you may get 5mph out of it. If you push the clutch down and be gentle with the accelerator you can gradually build the revs up enough to rev it hard to carry on, after about 1.5 miles the problem seems to clear its self and drives fairly ok.

Timing has been done and checked several times 6 BTDC at 800 rpm.
Vacuum hoses on the FI until & to the evap valve have been replaced.
VAG COM no faults.

Misfire keeps coming back as plugs are too black - running far too rich.

When warm drives ok but still very very poor mpg.

I think that this is everything.

Any ideas would be appreciated

thanks
Simon

[tony-1977]

Did you put an OEM thermostat in? The cheap alternatives aren't always the best


---Sent from my iPhone 6 using Tapatalk

[spud72UK]

It came from Euro Car Parts for about £13 so not a cheapy - do you think that it is worth trying another. Not having a lot of luck with parts first coolant sensor & oil pressure switch from GSF were faulty.

[niall campbell]

go to VW and get the parts

I would change both thermostat and coolant sensor

If you want, or should as good practice ............................... boil the new and old thermostat to make sure they are both fully closed when cold & both open at the same time FULLY OPEN

[spud72UK]

The 3rd coolant sensor is from TPS so hopefully ok - will test the thermostat tomorrow, thanks

[spud72UK]

Tested old and new Thermostat. Found the spec should be start opening at 84c and be fully open at 98c

Old one ( original ) started to open before 80c

New one ( ECP ) I found markings on it of 82c and found it was fully open at 80c not ideal at all.

The thermostat is discontinued by VW and Heritage are out of stock, ECP told me that they had another one which opened at 87c when to swap it to find that it would not fit as it was the plastic cylinder sort. Only option to swap the one from ECP in case it was faulty.

The power loss problem when cold I am going to try to remove the Lambda sensor from the exhaust and run it in fresh air to see if that make a difference.

[wildbeeste]

The revving problems and the high fuel economy are not going to be anything to do with the thermostat.
Many years ago I had an original Audi 100 which had very similar revving problems - revved ok at standstill but lost all power shortly after moving off - it was a collapsed catalytic converter. -
looked fine from the outside but rotten inside. If you knock the outside of catalytic box you will soon hear if it is ok or not - lots of rattling and sounds of metallic bits moving around is bad - sounding like a slightly muffled oil drum is good.

[spud72UK]

Many thanks for the info, gave the cat a knock and sounded very solid despite looking like the original one ( car hasn't done a lot of miles ). Decide to take the lambda sensor out and it was covered in thick soot. Cleaned it and found a damaged wire ( hanging on by a thread ) to the probe in the engine bay.

Currently running with the Lambda not in the exhaust and hole blanked to see what happens, it ran ok last night but was slightly warm so will take it for a spin again today. If it works will then have to work out if the is a current problem or old problem.

Replacement thermostat from ECP seems to be better but need to go on a good run to warm up.

thanks everyone for their help

[spud72UK]

Took for test drive when stone cold - still the same as it was day light could see lots of black smoke from the exhaust - running far too rich.

[spud72UK]

Disconnect Lambda sensor so that it runs in default mode still the same so not sensor, seems like it is running on 2 cylinders so resistance test on the plug leads next and a compression test.