1.6TD hates starting when warm

[vwbusman66]

I bought a 1984 Jetta 1.6TD GL today (my first watercooled VW) with one perplexing issue:
The car starts great when cold. Like, three cranks and it lights right up. However, when it is warm (thoroughly warm, run for an hour) and then shut off, it really need partial/full throttle and the cold start lever to give it a chance to fire up. Furthermore, it doesnt really start great when it does fire- it takes a couple seconds to fire in all four cylinders. Once it is running, it runs great again.

Any ideas why this is? It seems like the polar opposite of a worn out diesel. The pump timing is set correctly (recent timing belt). True mileage is unknown but the body and engine are both far too good to match the 390k reading on the odometer.

My one theory is that the glow plugs aren't running when it is warm. I noticed this today when trying to get it to not start. From cold, the light comes on and stays on for a little bit, and then goes off. When warm/hot however, the light never comes on! Could this be the culprit? (read here??: http://www.vwcaddy.com/showthread.php?50377-Engine-Temp-Sensor-Glow-Plugs-out-when-warm)

Is it as simple as this, or could it be something to do with the ignition switch or wiring?

James

[ToddA1]

If the coolant is warm enough, it won’t trigger the GP relay to fire. Disconnect the GP trigger wire at the head flange and see if it makes a difference.

-Todd

[rabbid79]

If the coolant is warm enough, it won’t trigger the GP relay to fire. Disconnect the GP trigger wire at the head flange and see if it makes a difference.

-Todd

I second that.  Makes all the difference.

[ORCoaster]

Some folks run a manual switch to the GP's to flip them on when the engine is in need of a little pre-glow if the engine is slightly warm or cooling down after a short run.  You might consider that, put a light on it so you know to turn it off and not run with them on for the rest of the trip.

[rabbid79]

A normally-closed pushbutton switch on the temperature sensor wire also works nicely.  The GP relay behaves as normal unless you push the button, which opens the circuit, and makes the relay think the temperature is very cold, causing it to heat the GPs.

[fatmobile]

Yeah ,just unplug the wire from the glow plug sensor as a patch.
 But you probably need a new starter or better connections. Crank for awhile and feel for warm spots in the cable connectors..
 It's probably not turning over fast enough when the engine is warm/tight.