Is this normal glow plug behavior?

[dieseljunkie]

I had my glow plugs under manual control with a separate relay/solenoid but decided to go back to ECU control. I have a light bulb connected to the glow plugs so I can see whenever they are being powered.

This morning ambient temp was around 60F. I have VCDS monitoring group 012. All glow plugs are new and are good.

With ignition on:

glow plug status = 0101000 (all 1's=off)
light bulb = off
glow LED= off

After engine start:

glow plug status = 1011000
light bulb= on (glow plugs being powered)
glow LED = off

The light bulb remained on constantly for about 30 seconds as the coolant heated up and then shut off, then glow status = 11111111

My cluster temp gauge does work and VCDS does indicate correct coolant temp. I did put an ohmmeter to the dual temp sensors in the coolant flange on the head and verified that both sensors had the same resistance reading. I did not verify wiring continuity from the sensors to the cluster or ECU. I need to find a wiring diagram to do that.

Based on the above info. What's wrong with my glow plug system? Is the adaptation incorrect?

 

[Vince Waldon]

Are you wondering why the glow plugs come on after the engine has started, even if they weren't on for engine start?

If so... yes... completely normal behaviour... it's a drivability and emissions thing.

It's also why some folks get confused by glow plug error codes in the middle of the summer. ;-)

 

[dieseljunkie]

Are you wondering why the glow plugs come on after the engine has started, even if they weren't on for engine start?

If so... yes... completely normal behaviour... it's a drivability and emissions thing.

It's also why some folks get confused by glow plug error codes in the middle of the summer. ;-)

Yes, as I recall from what I've read in this forum that the glow plugs do not come on at all when it is above 40F, and when they do come on after engine start (@ below 40F), they would go on for a few seconds than off a few seconds and back on again, so I was surprised to see that they are on continuously for around 30 seconds in warm springtime weather.

 

[Vince Waldon]

I was surprised to see that they are on continuously for around 30 seconds in warm springtime weather.

Yup, they'll stay on continuously for several minutes after start, regardless of the weather... at least until a restart with hot coolant.

I have a dash LED on my plugs as well... the other thing I notice is that during this after-glow they will switch off when the engine revs above 2500... then back on again when the RPMs drop as you're shifting gears.

 

[TonyJetta]

dieseljunkie,
A few things to check:
1) Pull the coolant temp sensor and see how long the GP's stay on. If they stay on for a period of say >20 seconds.
2) Check the GP relay and fuse for deteriorated / melted connections. IF so, you may want to look at replacing the deteriorated / melted component(s) before continuing the restoration of the GP circuit.

Tony

 

[dieseljunkie]

dieseljunkie,
A few things to check:
1) Pull the coolant temp sensor and see how long the GP's stay on. If they stay on for a period of say >20 seconds.
2) Check the GP relay and fuse for deteriorated / melted connections. IF so, you may want to look at replacing the deteriorated / melted component(s) before continuing the restoration of the GP circuit.

Tony

I will do 1) in a few days.

2) The GP relay is fine. I had the cover off and the contacts are pristine.

Can you hook up a light bulb to your glow plugs and report back it's behavior?

 

[TonyJetta]

2) The GP relay is fine. I had the cover off and the contacts are pristine.

That's all well and good, however, the relay could have been replaced AFTER plastic was melted. You REALLY need to investigate the fuse holder, wires, and relay socket for evidence of melting.

Tony

 

[dieseljunkie]

That's all well and good, however, the relay could have been replaced AFTER plastic was melted. You REALLY need to investigate the fuse holder, wires, and relay socket for evidence of melting.

Tony

If there was any kind of melting on a prior glow plug relay, I should see evidence of heat at the glow plug relay socket, which also looks pristine. I have not checked the condition of the glow plug fuse because it is a PITA to get to. But I did upgrade the glow plug harness at the glow plugs to a custom one made from aircraft grade wires good to 40 amps and getting good voltage with low V drop at the glow plugs (11 volts). That tells me the entire circuit from the battery to the glow plugs is sound.

 

[Lug_Nut]

There is no pre-start glow operation at temperatures of about 40F and above.
There is a post-start glow operation until either the coolant temp is above about 160F, or the engine rpm is 2500 rpm or faster.
Drop the temp back down under 160 F (thermostat stuck open or something) and keep the rpm down and the glow plugs will operate all the time.

 

[TonyJetta]

OK...Just wanted to make sure you weren't resurrecting someone else's electrical problem(s).

Tony

 

[dieseljunkie]

This morning was 16C (60F) per VCDS on all 3 temps fuel, air, coolant.

Unplugged the temp sensor, turned key on and got a constant orange glow LED , light bulb across glow plugs on.

Plugged temp sensor back in, cycled key and glow LED was off, light bulb across glow plugs off.

Start enigine and stopwatch. light bulb came on immediately indicating power to glow plugs.

With engine idling light bulb went off at 3 minutes 10 seconds, coolant 36 C (97F)

These glow plugs are on for a lot longer than I thought and this explains why all 4 glow plugs were burned out when I bought the car. At every cold start in the morning, summer or winter, the glow plugs are on for 3 minutes!

 

[schultp]

At every cold start in the morning, summer or winter, the glow plugs are on for 3 minutes!

This sounds like normal afterglow but I'm sure other's with more knowledge will pipe in.