Hard starting, was Glowplug relay location

[T5TDI]

Originally posted by B3Syncro:
I am assuming that the glow plug relay is defective, and is not reading the ECT sensor correctly, but would like to hear some other opinions first.

<font size="2" face="Verdana, Helvetica, sans-serif">I don't think it works that way round. The ECU reads the ETC and actuates the glow plug relay depending on the coolant temp recorded. It sounds like either there could be a problem with the wire between the ECT and the ECU or with the ECU itself. You could check the ECT/ECU wire & mulitiplug for continuity (with the ECU disconnected) If you find that ok and want to get really serious you will need access to a break out box so you can check the ECU output to the glow plug relay.

Check any ECU grounds too, I think the ECU grounds the glow plug relay to actuate it.

 

[B3Syncro]

I thought the same as you, but then arrived with the following conclusions:

If the wire from the ECU to Glowplug relay was defective, the output check wouldn't work correctly since the ECU controls the Relay.

If the wire from the ECT sensor to the ECU was at fault, then unplugging the ECT wouldn't change anything either.

I do agree that one of these wires could have an intermittent fault, but I have been able to repeat my tests numerous times under different circumstances with the same results, so I am reasonably sure that they are OK.

I will do a thourough check of these wires tommorrow.

To save me some headache, where is the ECU located?

Any other ideas?

 

[Don Splaun]

Here is where I found the broker wire. Don Glow Plug Circuit

The ECT is the radiator hose flange next to the head. It sounds to me that yours is ok.

 

[T5TDI]

On the earlier Golf TDIs the ECU is under the dash just off centre (slightly towards the passangers side on left hand drive cars) Not sure if later ones are the same.

It's odd that the glow plug output tests work every time... Perhaps there is a break in the wire very close to the CTS (or the CTS multiplug itself) and the action of pulling it off re-makes the connection in the wire? Don's wiring diagram is helpful, remember to give the wires a good wiggle when you are checking for continuity and look out for any wiring chaffing because it's not in its proper clip.

I remember I saw somewhere (I think it was here) a way of checking the glow plug relay with Vag-Com can anyone remember and help us out?

I'm sure you already know but the glowplug status is in group 13.

In "block" 1 11111111= glowing off (not sure what numbers = glowing on, but I can find out if you need to know).

00010000= pre-glow
01110000= start of glow
11110000= interim glow
10110000 = post glow

block 2= pre glow period
block 3 =supply voltage
block 4 =coolant temp

 

[T5TDI]

Originally posted by Brodie:
[QB]
In "block" 1 11111111= glowing off (not sure what numbers = glowing on, but I can find out if you need to know).

But I'll hazard a guess at 00000000 Dooohhhh

 

[spoilsport]

Originally posted by Brodie:

I remember I saw somewhere (I think it was here) a way of checking the glow plug relay with Vag-Com can anyone remember and help us out?

<font size="2" face="Verdana, Helvetica, sans-serif">That would be the output test function. VAG-COM tests the GP relay. Presumably, it's diagnosed as OK if you hear a click under that test.

Apparently B3Syncro has already done the output test.

 

[B3Syncro]

2000 Golf TDI with 80,000 kms.

I'm having cold starting dificulties and haven't yet found the solution. The car starts rough when weather drops below freezing.

Here is what I know so far:
Glow plug light only comes on briefly for approx 1 second with no power to glowplugs. Engine cranks longer than normal and when it starts up, it misfires for a few seconds then smooths out.
On a cold morning when the ECT is unplugged, light comes on for approx 10-12 seconds and there is power at glowplugs. The car starts as it should with minimal cranking and no roughness.

This problem is occasionally intermittent. I tried to diagnose it this morning and the glowplug system worked normally.

Most of the time it acts up though.

Here is what has been done so far without any success in solving the problem.

- 1 week ago I checked for DTCs with VAG COM & found a faulty ECT sensor.
- Replaced ECT with correct Green sensor & cleared all DTCs.
- Checked Glowplugs and found all to be OK with same resistance.
- Performed Output check and all related systems are working OK.

I am assuming that the glow plug relay is defective, and is not reading the ECT sensor correctly, but would like to hear some other opinions first.

Any ideas?

Thanks,
Les Burt

 

[T5TDI]

I know it doesn't really matter because you can check it with a meter, but it wasn't the output test. Still I supppose block 13 does the job well enough anyway.

 

[VelvetFoot]

I would think if there is an open or shorted circuit you would get an error code. How about using the vag-com to look at the coolant temp in the morning when this problem happens to see if it equals ambient temperature? Perhaps you got a bad ect sensor.

 

[B3Syncro]

Thanks!

I'm going out to spend the day with the car to try to locate the problem. I'll let you allknow what I find.

Les

 

[B3Syncro]

Here is what I did today in an effort to identify the sorce of my problems.

With engine cold and outside temp reading just below freezing (-1 C)
Tested the glowplug harness for open circuit
Checked the fuses
Checked various ground connections
Ran VAG COM and did an output test
Verified that ECT sensor read outside temp accurately(Value was -3.6 C)
Disconnected VAG COM and with a test light, montored glow plug power during start-up.

Here is what I found.

The system is working as it should with respect to the wiring and components, it just appears as though it is not providing suffient preheat time when it is just around freezing.

When ignition is turned on to heat the glowplugs, the dash light comes on precisely as long as is indicated in VAG COM measuring block 12 (actual was 5.2 seconds). I also noticed that the glowplugs remain on for several seconds after the indicator light goes out. You can hear the relay click when it finally cuts poer to the plugs.

I started the engine and warmed it up until VAG COM indicated a coolant temp of +5 C. I shut the engine down and checked Block 12 again. Now the glow plug preheat time was reduced to 1.2 seconds. I verified this by turning on the ignition and timing the indicator light. It came on for a second and went off as it should, but the glow plugs stil remained on for a few seconds longer before the relay gave an audible click.

I again warmed up the engine to +10 C and repeated the above steps. Now Block 12 showed 0 preheat time and this was confirmed by the lack of power at the glowplugs when ignition was turned on.

The car appears to not be getting suffient preheat time since it starts rough when around the freezing point. If it gets well below freezing, it starts fine!

MY big questions are:

Is it normal to not have glowplug preheat when the ECT is reading anywhere above 7-8 deg C?

Is it also normal for the glowplugs to continue heating even after the indicator light goes out?

I guess I'm just to used to the old 1.6 and it's habits!

Any ideas or suggestions?

Thanks,
Les

 

[weedeater]

Is it normal to not have glowplug preheat when the ECT is reading anywhere above 7-8 deg C?

Is it also normal for the glowplugs to continue heating even after the indicator light goes out?

<font size="2" face="Verdana, Helvetica, sans-serif">1. yes.

2. yes. At least, it doesn't surprise me.

 

[T5TDI]

The 5.2 seconds glow time sounds about right, for just above freezing. Mine is about that long. Is it possible you simply have have a bad glow plug? I know you already checked them but what reading did you get? Less than 1 ohm? Also it would be good to know how much current is being drawn by them. Worth carefully checking the heavy duty cable connections for tightness (and heat) all the way back to the glow plug fuse too.

It may be that the reason it starts better when you pull off the CTS wires is that the fixed value the ECU uses allows a longer glow time. That would explain why it starts ok when it's a lot colder, the bad glow plugs/current loss in the wiring means the glow plugs need a longer to get to the required temp.

It would be interesting to know what value the ECU uses when the CTS is pulled off. (I haven't checked mine) My manual just says ...simulates a "cold" condition.

I agree about the light going out but the glowplugs staying on. When the light goes out that just means it's ok to start, the label file for Vag-Com (above) says there is a 'post glow' usually this is at a lesser current than the full glow for starting. If this is the case it does seem a bit odd to me that the ECU manages to do this without a another relay/resistor somewhere.

You could watch the numbers change in the blocks during warm up and see if you can shed any light on this.

I'm only speculating now

 

[B3Syncro]

I checked the resistance of the glowplugs and got .6 ohms on all 4. I haven't checked the glowplug wiring for excess resistance yet, Nor have I done a current draw check.

I did watch VAG COM for the post glow operation and it does work and at an outside temp of -1 C, the post glow worked for at least 45 seconds.

The post glow system has me wondering how it works. The wiring diagram indicates that the 4 GPs are wired together and then split into 2 wires which go to the relay. It has been posted several times in the past that there are actually only 2 GP per wire at the main harness. Is it possible that the post glow system puts these glowplugs in series to reduce the heat output during post glow? If this is the case, then it is also possible for the relay to be stuck in the post glow mode. I'll be doing a voltage drop test along the harness to help locate any weak points. I will also try to figure out the post glow circuit to see how it actually works.

I will be investigating this further, but won't have time for atleast a week or so.

Thanks for the help and keep the suggestions comming!

 

[T5TDI]

I only have the basic ECU pin diagram, but I agree that there must be more to the glow plug system. Your theory of the glowpugs in series sounds good.

Can you see from your diagram what switches the high current? The glow plug relay appears to be a standard relay in the fuse box (like relay 109) so surely there must be another somewhere to carry the 6o amps or so (as in the case of most other diesels?)

I quite fancy buying a laptop based oscilloscope for work but I'm meeting severe marital resistance

The model I have in mind (@ 750 UK pounds) has a few extras like hi amp inductive current clamps. Just what you need now! Here's a typical waveform for diesel glowplugs in case it helps

http://www.picotech.com/auto/glowplug.htm

Note the 'pulsed in sets of two' comment...

[ November 04, 2002, 14:06: Message edited by: Brodie ]

 

[B3Syncro]

A laptop based oscilloscope? sound VERY interesting!

I'll have to investigate further!

Thanks,
Les Burt