B4 Cold Weather Hard Starting/Smoke - Coolant Temp. Sensor??

Well, we're getting our requisite 4 weeks of winter in Georgia and my Passat has developed a hard start problem in the cold. At first I suspected bad glow plugs or harness, but now I'm suspecting the coolant temp sensor.

The symptoms, hard starting(unheated garage - cranks about 10 seconds before starting on one or two cylinders and about another 10 seconds before the other cylinders start), lots of white smoke(unburned fuel) and slow warm up. No CEL and the glow plug light only illuminates for a couple seconds regardless ambient temperature. Once warmed up, it starts easily. With these symptoms and no CEL, must be the coolant sender - or am I all wet??

In the Bentley, I see reference to G2 and G62. Are these two circuits in the same sender?? In ETKA, it appears that there's one unit with multiple choices(I understand the color thing - I need to check and see which I have now).

Right now I'm planning to pick one up on the way home - any other ideas?

Thanks!
Patrick

Having gone through a bad sensor and it's replacement just this month, I will say it didn't have a starting problem at all. It started just like new without TDIHeater plugged in on 26* morning.

You may have a fuel problem due to sudden colder then normal weather. But you have a B4 and we have A4, so there could be big differance I guess and could be a bad sensor.

The sensor has two parts. One drives the glow plug circuit. The other drives the temp gauge.

If you think it is the sender, try diconnecting it and see how long the GP light stays lit. Should be several (+12) seconds.

You could also have a timing problem. Timing is to be advanced when cold. Your base timing may be retarded or the cold-start thingy on the pump may be faulty.

Originally posted by Old Navy:
You may have a fuel problem due to sudden colder then normal weather.

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<font size="2" face="Verdana, Helvetica, sans-serif">Thanks ON, but the problem has persisted across several tanks of fuel from two different stations.

Originally posted by weedeater:
If you think it is the sender, try diconnecting it and see how long the GP light stays lit. Should be several (+12) seconds.

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<font size="2" face="Verdana, Helvetica, sans-serif">That's one reason I suspect the sender. GP light only stays on for 2-3 seconds max. That doesn't seem adequate when the garage is ~25degF.

Actually, if I unplug the sender and my problem goes away, that should clinch it, right??

You could also have a timing problem. Timing is to be advanced when cold. Your base timing may be retarded or the cold-start thingy on the pump may be faulty.

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<font size="2" face="Verdana, Helvetica, sans-serif">Definitely need to check base timing - will do tomorrow.

Thanks Weedeater!
Patrick

If your glow plug light is going out after only 3 seconds at that temp, it is TOO SHORT a glow period. I have the same trouble between 25-35F. The solution is "multiple glows in sequence" before engaging the starter. Turn switch to "on" and when glow light goes out, quickly turn ignition switch off then on and glow again. When glow light goes out, repeat for a third glow. This should give you 9 seconds of total glow. After third glow, engage starter, and your engine will start smooth as silk! Trust me! Been there, done that!

Mike,
That's exactly how I have to start my A4 Golf on cold mornings. What's going wrong? Temp Sensor? Warp core breach?

My "take" on this (strictly unscientific, I might add ....) is the sensor's calibration table is not entirely accurate. If the outside temp goes into the teens or below, the glow plug light will stay on somewhere between 12 and 15 seconds, and the car will start right up without stumbling on only one glow cycle. But, let the overnight temp "warm up" to 25-35F, and the glow plug light will not stay on long ..... indicating that there is inadequate glow plug heat to allow the engine to start without stumbling and lots of smoke. I think this is a "feature" of the coolant sensor calibration table, and I just live with it and adjust to it. (Besides .... It's cheaper than buying a new sensor that likely will behave the same way!) Just an IMO ....

Well, I tried unplugging the sensor and let the glow plugs go about 15 seconds before starting. The car started right up - still some smoke, but not nearly as bad. I guess I'll try a new sensor and see if it helps. I didn't have this problem last winter

Patrick

This problem has been recently reported in the A3/B4 "General Maintenance" forum. See the following thread, and the several remarks.
http://forums.tdiclub.com/NonCGI/ultimatebb.php?ubb=get_topic;f=42;t=000090

Originally posted by Mike in Oshkosh, WI:
This problem has been recently reported in the A3/B4 "General Maintenance" forum. See the following thread, and the several remarks.
http://forums.tdiclub.com/NonCGI/ultimatebb.php?ubb=get_topic;f=42;t=000090

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<font size="2" face="Verdana, Helvetica, sans-serif">That would be THIS thread...

Picking up a new coolant temp sensor this afternoon.

Patrick

Originally posted by weedeater:
You could also have a timing problem. Timing is to be advanced when cold. Your base timing may be retarded or the cold-start thingy on the pump may be faulty.

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<font size="2" face="Verdana, Helvetica, sans-serif">Good call weedeater! It appears that retarding base timing is at least part of the problem.

My favorite local dealer is out of the yellow/black sensors. On order, but should be in by Wednesday.

Patrick

You are correct GM! I tried to post the link to ANOTHER thread in order to point to THIS thread and got things backwards! Oh well, at my age, I'm allowed a few liberties ...... <G> You guys are bringing back some very old memories. My very first diesel auto, a '63 MB 190D had a manual injection pump advance knob ... Had to pull it out, glow for 1 minute, and then start the engine ..... So, yes .... the injection pump advance could be part of GM's original problem.

An update - replacing the temp sensor did improve cold starting, but didn't alleviate smoke. Resetting base timing up to "52" from "10" did the trick. Cranks immediately now in 30 degree weather(this weekend predicted to be in the 20's overnight) with only a wisp of smoke when cold.

Thanks again for the lead weedeater! You da man!

Patrick