1995 Mk3 2.0 GTi cutting out

[JW590]

I am trying to fix my son's car - like dads do! I know this has been covered several times, and I have read loads of them. Unfortunately my story is the same as the others.... change loads of parts to no avail. It initially cut out after a 20 mile drive, but now it cuts out after about 7 miles. I wait and start it, then it only lasts half a mile a time. If I change something and go for a test drive starting with a 'cold' engine it will last between 3 and 8 miles. Then it's limp home a half mile at a time.... at least I've done it enough times to work out to go round in circles so I'm never too far away from home!

So far I have changed -

Crank angle sensor
Coil
Distributor cap
Rotor arm
Plugs
Leads
ECU relay
Fuel pump relay
Fuel filter
Fuel pump

After all this it still has the fault.

Any help or tips greatly appreciated.

Thank you

John.

[dragongreengolfgti]

Which engine is it?

Other things probably not the problem but
1. clean the throttle body
2.check all vacum hoses
3.if its abf check small hose to ecu
4.Check all earth points on engine and under battery tray
5. check battery it self
6. Try another coil if it was second hand or even new as some new ones are faulty 
7. a good service plugs,leads check distributor cap and rotor arm.
8. get a vag com test done
9. check your lambda sensor
10.check maf sensor

[JW590]

All parts except the fuel pump are new - but the fuel pump is fine. How do I tell which engine it is?

I am currently working on it and have worked out the following. If I unplug the fuel pump and put an external permanent feed on direct from the battery it seems to work fine - although driving around like that the other day it eventually did cut out (could have been the old relay). I have now replaced the permanent feed from the battery with a permanent feed from fuse 18 (fuel pump fuse), taking earth from the door hinge.

The 12v normally goes from the battery to the relay to the fuse and down the red+yellow wire to the pump.

It is now going from the battery to the relay to the fuse and down the external wire to the pump.

With the plug disconnected I have had 12v showing on the red/yellow wire - which is correct. However this is intermittent in that it is now showing 5v..... therefore the 12v is dropping somewhere along the red/yellow wire between the fuse and the plug.

I have also noticed on a wiring diagram on this forum that fuse 18 also feeds the Heated Oxygen Sensor Control Module - whatever that is. If I knew what and where it was I could disconnect it and see if the 12v comes back to the fuel pump plug.

Any ideas please?

Thank you

John.

[Seanl]

1.4/1.6/1.8/2.0 8v/2.0 16v??

[JW590]

2.0 8v - I've just put it in the title. I'm wondering if it's the Heated Oxygen Sensor.

Where is it so that I can temporarily disconnect it?

Thank you.

[Seanl]

Oxygen Sensor being the lambda sensor, located in the middle section of the exhaust, but not heard of this causing cutting out issues before. Other than what you've replaced, definately check your breather pipes as these are very common failures. At Idle, get someone to rev the car, whilst you watch the pipes. They get old and very soft, and collapse under load. Also clean the throttle body out, and maybe replace the MAF. You can disconnect the MAF to check it, but it will probably cut out as usual. Usual signs though are hesitation at 3k rpm, and diminished performance. Disconnect it and take it for a spin to see if you have noticable gains. They are quite fragile, but I have cleaned mine using electrical contact cleaner, and a cotton bud and it made the world of difference.

[JW590]

Thanks Sean, I'll do that tomorrow in the daylight.

I'm absolutely sure that I am on the right track now in that it's a 'spark' problem. Here is what I know....
 
Fuel pump unplugged with direct to battery 12v power on and it runs - however still cuts out after 7-8 miles.
Then cuts out at the same intervals of (say) half a mile. Same waiting time, same running time, therefore something is cooling down just enough for the engine to start again and as soon as it reaches temperature it cuts out.
Because the fuel pump has external power and is always running it cannot be a fuel problem but a spark problem, also think this because it just instantly cuts out rather than drops revs and cuts out.
Voltage across pump plug is 5v whether plugged in or not - which is strange because the red/yellow wire comes from fuse 18, and I have now linked into fuse 18 to get the permanent 12v supply (fuse is after the fuel pump relay) .... so somewhere along the red/yellow wire the voltage is dropping. i.e. the red/yellow wire and my external wire are coming from the same point, but the external wire has 12v on it, the red/yellow has 5v on it.
Fuse 18 also feeds the Lambda sensor control unit. Is the sensor control unit built into the ECU?
The plug earth wire is shorted to earth as it should be.
Stupidly I haven't yet checked the red/yellow wire against earth. Should be open circuit but may not be.
Something somewhere is dragging the fuel pump 12v feed down, and whatever it is is cutting out when it gets hot. It must be cutting the spark.
I disconnected the Lambda plug near the downpipe. The 12v did not re-appear at the pump. However all I have done is to isolate the sensor and not the wiring circuit / control unit.
I dropped the fuse/relay box down and the O2 sensor control module relay cannot be taken out, therefore I cannot isolate the wiring for it unless I can find the unit and unplug it.
The breather pipes on the top of the engine are split.
 
I've thought that tomorrow I will put battery 12v straight to fuse 18, ignition off, and check for 12v at the end of my new permanent wire and see what it is on the red/yellow wire. I'll then turn the ignition to first position and check again, then start the engine and check again. That should help to isolate where the problem is. If only I had a circuit diagram.... I'm good with circuit diagrams.

[Seanl]

Pretty sure the Lambda control is built in to the ECU although not 100%. Obviously controlling timing/ignition/fuelling so it would make sense. Split breather pipes will cause cutting out issues though, but you should have a rough idle as well, although you suspect spark/ignition to be the culprit go with what you think mate. You obviously know what your doing with regard to electrics/electronics etc, so I think you may be on the right track, just dont overlook the simple things is the only advise I can give. Good luck with finding the problem, and keep us updated with how your getting on. 

[madmanmart]

What engine code is the car? Also have you have any possible fault codes read?

I would not rule out an ECU problem too but that is very unlikely as they are usually pretty reliable.

[JW590]

Thanks for all the help so far.

Sean - the idle / tick over is fine despite the breather pipes being split.

Mart - no codes were showing up. I don't know where to find the engine code.

I will update as I go along tomorrow - it always annoys me when people don't put an end to their threads once they've repaired the car.

Thanks again.