Glow Plugs Burning Out - 3rd Set in 12 Months

[Shaunous]

Hi Guys,
As I said, im onto my 3rd set of glow plugs now (installing them this arvo) in less than 12months. I would have tried to diagnose earlier, but i've been working oversea's and it was easier just to replace and worry about it later at the time.

I've got a 98 GU RD28t, I've read there is a glow timer relay that is temperature regulated, so the plugs stay on untill the engine gets up to 50degree's and then switches off.

I've tested that once or twice in the past and it seems to work, but that doesnt mean it gets sticky or stays on every other time, as I drive the car daily.

Anyway, my question, Where is this relay, is it a simple relay to replace, or should I look elsewhere for the problem as it could be something else.

I've searched around here on the forum but cant seem to find anything, so maybe its not a common problem.

Thankyou in Advance

Shaun

[Yendor]

Are you using good quality glow plugs? What is wrong with the old ones?

Check the earth to the head and also make sure there are no bad connections in the wiring from the glow plug fuse to glow plug relay and busbar.

The GU doesn't have a separate glow plug timer, the glow plugs are control by the ECU. The ECU determines how long the glow plugs stay on for by information it receives from the engine coolant temp sensor and engine rpm.

The ECU switches a relay on and off, this relay supplies power to the glow plugs.

The relay is mounted on the inner guard near the firewall on the driver side.

When relays play up they don't normally intermittently stick on, so I don't think this will be your problem.

I would also check the engine coolant temp sensor.

It could also be very helpful in diagnosing the problem to set up a temporary warning light inside the vehicle. Connect one side of the test light to earth and the other side directly to the glow plug busbar. This will show you exactly how long the glow plugs are on for.

Once you have the new glow plug installed check the voltage at the busbar when they are on, again make sure the return earth via the head is ok.

[Shaunous]

Hey Yendor,
The plugs are open circuiting, burning out, (zero resistance). I've used a different brand plug each time. I'll try the test light in the circuit method, thats probably the best way to figure it out. The wiring to and from the busbar is physically clean and OK including joins, but whats hidden under the harness protecter may be a different story.

If the engine coolant temp sensor was out, wouldnt my temp gauge in the cab show an incorrect reading, it seems to work fine, and sits in the one spot, around half, once its up to normal temp.

Anyway i'll get the multimeter out and check a few things, I may have been dreaming when I checked the plugs were off after it reached 50degree's to be honest.


Are you using good quality glow plugs? What is wrong with the old ones?

Check the earth to the head and also make sure there are no bad connections in the wiring from the glow plug fuse to glow plug relay and busbar.

The GU doesn't have a separate glow plug timer, the glow plugs are control by the ECU. The ECU determines how long the glow plugs stay on for by information it receives from the engine coolant temp sensor and engine rpm.

The ECU switches a relay on and off, this relay supplies power to the glow plugs.

The relay is mounted on the inner guard near the firewall on the driver side.

When relays play up they don't normally intermittently stick on, so I don't think this will be your problem.

I would also check the engine coolant temp sensor.

It could also be very helpful in diagnosing the problem to set up a temporary warning light inside the vehicle. Connect one side of the test light to earth and the other side directly to the glow plug busbar. This will show you exactly how long the glow plugs are on for.

Once you have the new glow plug installed check the voltage at the busbar when they are on, again make sure the return earth via the head is ok.

[Yendor]

The gauge runs of a different temperature sender unit to the ECU.

To be honest, I don't think this will be your problem anyway but it's still worth doing a visual inspection of the connector at the coolant temperature sender.

If the glow plugs were staying on for excessive periods of time you should be able to see physical signs of damage on the glow plugs, such as distortion in the end or the tips missing or badly burnt.

You are fitting the correct 12 volt plugs?

Double check there is no voltage drop to the glow plugs, it should be roughly the same reading as across the battery when the glow plugs are on.

[Shaunous]

Yep, 6x 12v plugs installed every time, first time it happened there were 5 shot, last time 4 shot, I havn't had a chance to remove and test these ones yet, hopefully this arvo, but sounds like 5-6 are shot by the way its starting.

They dont pysically look burnt or damaged in anyway to much, but something is causing them the burn internally as they are completely open circuiting, checking resistance through the plug I get a big fat 0-ohms, the couple that work I got the normal 2-ohms (I think thats the normal reading).

As I said i've used 3 different types of plugs, the newest set I have are an Italian brand, but when I put these on, hopefully this arvo, I will be testing more thoroughly. I am definately getting a constant 12v to the busbar when starting.

As soon as i've thrown 6 working plugs in the last couple of times its happened, BAM, starting straight up soon as the glow light is gone.

This last set was only installed in early November.

Its a costly pain in the arse.


The gauge runs of a different temperature sender unit to the ECU.

To be honest, I don't think this will be your problem anyway but it's still worth doing a visual inspection of the connector at the coolant temperature sender.

If the glow plugs were staying on for excessive periods of time you should be able to see physical signs of damage on the glow plugs, such as distortion in the end or the tips missing or badly burnt.

You are fitting the correct 12 volt plugs?

Double check there is no voltage drop to the glow plugs, it should be roughly the same reading as across the battery when the glow plugs are on.

[Dales300exc]

Sure you aren't getting confused? 0 ohms would indicate perfect continuity (normally have a little bit of resistance in the leads though).

An OL on the meter would indicate open in the glow plug.

[Shaunous]

Im no electrical guru, but testing a wiring in a harness from end to end, yes you are probably right, (kind of). But testing something like a glow plug, no it should have resistance, being the resistance through the heating coil.
Leads??? Im talking glow plug on a diesel here, not spark plugs with leads.

Again im no auto electrician, i just own a multi meter and have a go.

Shaun.

Sure you aren't getting confused? 0 ohms would indicate perfect continuity (normally have a little bit of resistance in the leads though).

An OL on the meter would indicate open in the glow plug.

[Shaunous]

OK, so I've thrown in the new plugs this arvo, tested the system, and it seems to be functioning all ok, had an infrared heat gun on the cooling system and soon as the radiator hoses and radiator got around 52degree's they turned off. I'm going to install a light so I can see whats going on. Other then a short in the harness, or a weak glow relay and them vibrating on and off while driving, im near on outa idea's.

Again, if anyone has any idea's or experienced this, please let me know.

Cheers,
Shaun.

[boots]

Seems odd to me that they stay on while engine is running and it reaches 52 degrees . Surely once it is running from initial start the glow plugs job is done .

[Yendor]

Seems odd to me that they stay on while engine is running and it reaches 52 degrees . Surely once it is running from initial start the glow plugs job is done .

The after glow helps cold engines idle better and I believe it helps reduce emissions.

[Dales300exc]

Sorry. Ill keep quiet in future.

For the record i did not mean spark plugs.

[Dales300exc]

Double post. Sorry.

[happygu]

I would be checking to make sure that you don't have a poor / corroded joint on the Supply Line for the Glow Plugs....

Could be at the Power Source, Relay, Rail Connection or Earth.

As mentioned check the voltage at the Glow Plugs, to make sure that it is the same as the battery, and make sure that youy check it with the earth ( negative lead ) on the motor, as you may have a poor connection from the motor back to the chassis / battery,

[the ferret]

Sorry. Ill keep quiet in future.

For the record i did not mean spark plugs.

Why Mate, I can't see anything wrong with your posts, you were only joining in and trying to help the OP with his problem, as anyone would do.
Cheers, the ferret.

[Shaunous]

Sorry Dales300exc, I didnt mean to sound harsh if I did, also both of us were right, I just explained myself wrong. I tested them yesterday and they are reading varying amounts of resistance, all alot higher then they are meant to, all 6. Started it this morning to go to work after a cold night of rain, and BAM she's away, soon as the glow plug light went off.
Shaun.

Sorry. Ill keep quiet in future.

For the record i did not mean spark plugs.

[Shaunous]

Well in saying that, Im only getting just over 11v at the glow plug busbar, while the battery is at charging rate (over 13v), could this be a problem maybe???

The earths have all been cleaned and checked when I rebuilt the motor last year, I may have to go through all the supply side.

Cheers.


I would be checking to make sure that you don't have a poor / corroded joint on the Supply Line for the Glow Plugs....

Could be at the Power Source, Relay, Rail Connection or Earth.

As mentioned check the voltage at the Glow Plugs, to make sure that it is the same as the battery, and make sure that youy check it with the earth ( negative lead ) on the motor, as you may have a poor connection from the motor back to the chassis / battery,

[Shaunous]

BUMP!

Havnt had a chance to check the supply system properly due to flooding down here, but anyone else had the problem??

[Forsan]

If you're getting 11V between glow rail and engine I would assume a bad earth or power connection.
The relay is sufficiently robust to provide 12V minimum to the glow rail.

I'd be checking earth connections and replacing the relay if you find no issues with the earth leads.

[happygu]

Check your power feed for the glow rail, as you must have a problem there. Voltage should be the same as the battery.

Mic

[Shaunous]

Thanx lads,
Were still isolated in at the farm down here at Grafton, so will check when I get the chance to get outa here and get my tools. Will probably still throw some kind of LED light in the cab just to monitor when they are actually turning on and off.

Shaun


If you're getting 11V between glow rail and engine I would assume a bad earth or power connection.
The relay is sufficiently robust to provide 12V minimum to the glow rail.

I'd be checking earth connections and replacing the relay if you find no issues with the earth leads.

happygtu
Check your power feed for the glow rail, as you must have a problem there. Voltage should be the same as the battery.

Mic

[First Nissan]

I would be having a good look at that relay. It may have burnt or pitted contacts. If it is not a sealed relay you should be able clean the contacts with a bit of wet and dry. It is really common in aircraft relays that cycle on and off a bit.