Glow plug problem?

[meatball]

Evening all, got a small annoying problem,
When I start my car, I wait for the glow plug squiggle to go out, fire the truck up, but after firing, the light comes back on for a second or two, which is the query I'm asking about.
Any ideas? Maybe change glow plugs, be my first idea but any help, suggestions welcome.
Ps now running on 50/50 svo/ diesel, 103k no knowledge of plug change.

Thanks in advance
Craig:thumbs

 

[solarman216]

sounds more like a hiccup on the timer module that controls the glow plug relay, but rayf3262 I am sure will have a better idea, Rick

 

[meatball]

Cheers rick, can't believe how many modules, and sensors these bloody things have got, but thanks for that, I'll look into that at weekend:thumbs

 

[rayf3262]

On the assumption your vehicle is a TDi with ECU control:
Both the glow plug relay and the glow plug dash indicator are independently controlled by the ECU.
The dash indicator is NOT an indication that the glow plugs are on or off, it simply illuminates for a period of time (10-40 secs) dependent on engine coolant temp and switches off when the glow plugs have been on long enough for you to start the engine.
The glow plugs will actually remain on until the engine reaches operating temp or you exceed something over 4000 rpm. (all done in the name of emission control)

As your engine appears to start ok, I would assume the GP's (or some of them at least) are working ok.
The ECU will have no concept of whether the glow plugs are actually working or not it simply switches them on/off based on engine temp.
If they are not working then starting issues from cold in this weather should be obvious.

The real puzzle here is why the GP light comes back on again.
I can't think of a reason that the ECU would switch the GP lamp on again without an ignition off/on cycle.

One side of the indicator is connected to +12V while the other is connected to ground by the ECU to turn the light on.
I am inclined to think that the cable from the indicator to the ECU could be damaged and being grounded somehow, possibly exacerbated by the vibrations from the engine once started??

 

[R1cho]

On the assumption your vehicle is a TDi with ECU control:
Both the glow plug relay and the glow plug dash indicator are independently controlled by the ECU.
The dash indicator is NOT an indication that the glow plugs are on or off, it simply illuminates for a period of time (10-40 secs) dependent on engine coolant temp and switches off when the glow plugs have been on long enough for you to start the engine.
The glow plugs will actually remain on until the engine reaches operating temp or you exceed something over 4000 rpm. (all done in the name of emission control)

As your engine appears to start ok, I would assume the GP's (or some of them at least) are working ok.
The ECU will have no concept of whether the glow plugs are actually working or not it simply switches them on/off based on engine temp.
If they are not working then starting issues from cold in this weather should be obvious.

The real puzzle here is why the GP light comes back on again.
I can't think of a reason that the ECU would switch the GP lamp on again without an ignition off/on cycle.

One side of the indicator is connected to +12V while the other is connected to ground by the ECU to turn the light on.
I am inclined to think that the cable from the indicator to the ECU could be damaged and being grounded somehow, possibly exacerbated by the vibrations from the engine once started??

I was going to say could it be an earthing problem but yours sounds far more impressive :lol

 

[ssteve]

i know that on the "n"reg sprinter i used to drive the glow plug indicator light came back on after starting engine, found this to be indicating that a glow plug was u/s, and it was!!!

ssteve

 

[rayf3262]

i know that on the "n"reg sprinter i used to drive the glow plug indicator light came back on after starting engine, found this to be indicating that a glow plug was u/s, and it was!!!

ssteve

These Nissans are old school, there's no way the ECU could sense one or more failed GP's.
It can though sense a faulty GP relay, but on the assumption the thing starts ok from cold it's unlikely be that.
In any event it would have a DTC logged and the MIL light on.

 

[solarman216]

Cheers rick, can't believe how many modules, and sensors these bloody things have got, but thanks for that, I'll look into that at weekend:thumbs

Knew rayf would have the intimate knowledge, I can only guess as not had a TDi long, Rick

 

[rustic]

I can't think of a reason that the ECU would switch the GP lamp on again without an ignition off/on cycle.

A bit of lateral thinking... maybe this is the actual fault, it is doing an ignition off/on cycle.:nenau

There have been issues of problems with the ignition switch, and maybe this has a bad connection within the switch, and re-triggers the glow plug module.

Worth thinking about:nenau.

best regards,
Rustic

 

[rayf3262]

A bit of lateral thinking... maybe this is the actual fault, it is doing an ignition off/on cycle.:nenau

There have been issues of problems with the ignition switch, and maybe this has a bad connection within the switch, and re-triggers the glow plug module.

Worth thinking about:nenau.

best regards,
Rustic

Very good point,... loads more to check then.
Offending part of circuit diag. for perusal: