Glow plug time / coolant temperature sensor accuracy - PD engine

Having a bit of a cold start issue with the golf lately, its an 05 so it has the PD engine. In Calgary the glow plug light typically comes on for 3-5 seconds when it is below 10*C, working its way up to the full 8 seconds as the temperature dips.

Lately it is just flashing on/off (maybe 0.5 seconds) even when there is frost on everything in the morning. This seems drastically too short. When starting the car starts right away but stumbles/misses and smokes for 10 seconds or so.

I pulled out VAG-COM the other morning, and before starting the coolant temperature sensor reads 13-15*C even though it is 0-1*C outside and the car has sat overnight, HOWEVER, the pre-glow time shows as between 4.0 and 5.0 seconds, even though the light was NOT on that long. Once started the glow plug status shows the engine glow plugs remain on until the engine reaches 30*C.

Should the amount of time the light is on match the pre-glow time? And, how accurate should the temperature sensor be? It was changed last summer by the dealership due to a CEL triggered by it (too high / implausible - intermittent). Is it acceptable for it to be out by 10-15*C (don't think so, but I gotta ask...)??

My thoughts at this point are that by coolant temperature sensor is NFG, and that once replaced the glow time will be correct, but I am confused since vag-com shows the pre-glow time should be over 4 seconds, but it is clearly not.

sounds high to me.

ECT accuracy should be much better than that. After sitting overnight, it should match IAT pretty closely (within 3-5C I'd say). If it were me, I'd like to see if I could get someone to help me use a multi-meter to check for voltage to the glowplugs out of the harness during the whole process, to corroborate what VAG-com is getting from the ECM.

What's really getting me about this is that you're already dealing with frost the first week of September. I am not jealous.

Fred

I agree that it is too far off.

You might check out the connections and grounds. While they are known to go bad way to often, something else could be contributing to the issue.

I also agree that the light should stay on for the pre-glow period. Again poor grounds can cause ECU and relay issues. The one in the windshield wiper plenum would be a good one to clean.

DanG

Haha yeah, first week of september and we already had frost. After living in Vernon for 2 years I'm used to 20+*C days until november... this is an odd transition. 1*C this morning, going to go outside and check shortly.

I should have mentioned earlier, if I turn the key to 'on', and leave the glowplugs on (since the glowplug status in vag-com shows they are on, I assume they are) for 10 seconds or so, the car starts perfectly.

I'll note the pre-glow time this morning as well as other conditions so I have more data, and I'll try to test the glowplug harness and coolant temperature sensor connector tonight.

If the light should match the pre-glow period, then I am much much more worried since it makes all of this invalid since the ECU obviously knows the correct time and is for some reason, not able to provide it.

It could be as simple as a lamp or contact that is heating up, the metal is moving, and joint is opening. It can act almost as if it is a bimetallic switch.

Does the lamp go on and off properly during the VCDS output test?

Did you also check for codes?

DanG

Lamp works properly during VCDS output test, no stored codes.

I'm back inside from my testing, here are my results:
Coolant temperature sensor: 11.7*C
Fuel temperautre sensor: 11.7*C
Intake air temperature sensor: 13.5*C

So, it looks like my coolant temperature sensor is okay after all. Don't trust outside thermometers for an accurate temperature

Now, before starting, I turned the key to on, and received a pre-glow time of 4.83 seconds, but the lamp was only on for a second at the MOST.
Pulling the harness off, all glow plugs measured within 0.1 ohms of 1.0 ohms (cylinders 1-->4, 0.9, 1.0, 1.0, 1.0), however here is where I may see the problem??

When I turn the key to on, I get a very short 7.5V to the glow plug harness then it immediately drops off to 4.8-5.0 volts and remains there. This happens whenever the glow plug status shows 10110000 which I believe indicates that the glow plugs should be on. Shouldn't the PD glow plugs run at 7V, not 5?... Does this indicate a bad glow plug module / relay (since I don't know exactly what it is called on the PDs)?

The thing starts exactly the same without glow plugs plugged in as if I give it only the 1 second the light indicates I should. If I turn the key to on, let it sit for 5-10 seconds after the light goes out, then start it, the engine starts perfectly.

Once I unplug my coolant temperature sensor, so the glow plugs will come on (It is at least 90 deg F in my garage right now), the first half second is 6.8 volts, the remainder of about 15 seconds is 4.2 volts.

Hope this helps.

DanG

Z, I too have an 05 Golf GLS, and I recently had to change my coolant temp. sensor due to an erratic temperature gauge.
Yours may be on its way out if you haven't changed it already.
My GP light has always glowed for about 5 seconds and the plugs themselves stay on for about 20 sec. IIRC. I confirmed this with a Sears clamp-on amp meter, but I never checked the actual voltage of the plugs.

DanG, thanks for testing that for me. I was worried the glow plug module was on its way out on me. Looks like its good too.

Maybe I am just not used to how this car is aging, maybe everything is fine...?!
I just moved back to Calgary from somewhere MUCH warmer and lower elevation, so I am super paranoid about starting issues when it gets really cold. Every time I have come back here in the middle of the winter I have been stranded with a car that won't start (sometimes it's me forgetting the anti-gel since I filled up on the west coast where it was +10, sometimes its broken parts).

I guess both my wife and I don't need the car for daily use anymore. Since everything seems to check out as normal (aside from the pre-glow time mismatch) I'll leave it for now. I'll let you guys know if this issue crops up more seriously.

At 100300km now, so it's all on my head