Isuzu Trooper Owners Club UK™

[fatso_1234]

I've read a bunch of the posts about glow plugs/QOS system, but I would appreciate some more info and specifics from anyone who can help.  This is my first diesel so I'm still learning about some of the differences.

Now that it's getting colder (about 5C) here my 2.8 Bighorn has started puking out white smoke in the morning.  If left to idle it doesn't go away to fast, but if you load the engine by driving a bit it goes away right away.  I figured it's a problem with the glow plugs so I had a quick look last night.  With a top mounted intercooler I haven't pulled any of the plugs out, but I was able to measure the voltage going to the plugs.

Here are the symptoms:  At this temperature the glow plug light on the dash turns on very briefly when you first turn it to on.  There is no voltage to the glow plugs before, during, or after starting.  When you unplug the temperature sensor, the glow plugs get power for about 15 seconds and the dash light stays on about 4 seconds.

1. Is the system supposed to "glow" even when relatively warm (say 10-20 C)?  What about when the engine is hot?
2. There are 2 relays on the right hand fender with numbers 8-94153-848-0 and 8-94153-849-0.  The first one clicks when it glows with the sensor disconnected.  Is this other relay for glow plugs?  When is it used?
3. Where is the control box located?
4. At what temperature should it preglow? (as if the sensor is disconnected)  Is this different for Japanese imports?

Thanks for your help.  -40 is on the way and I want to get this sorted.
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1991 Bighorn LWB 2.8 TD 4JB1-T

[Google]

[Hard1]

One way to test them if, like me, you're too idle to replace them (they're only 15 sovs each) is to operate the glowplugs twice by switching on until they go out and then repeat. If the motor fires straight away without smoke then you have weak glowplugs!

I've got away with it  for 2 years now using this Fat Lazeeboy method...

One day, one day....
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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

[fatso_1234]

Problem is now if I have the temperature sensor on the thermostat housing connected it doesn't glow at all.

Sweet truck though.  It was a little strange buying a vehicle from overseas without ever seeing it.  No regrets though.  We took it to the mountains this weekend on a mountain bike trip.  Perfect vehicle for that.

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1991 Bighorn LWB 2.8 TD 4JB1-T

[Hard1]

Cool truck! and even cooler aerodynamic Top Box!  8)  

Just kidding. Just be patient and someone will no doubt pipe up with more knowledge than me.

I would have thought that with temp sensor connected and item doesn't glow then either plugs are not supposed to operate in that particular temp or (probably more likely) the sensor is U/S, or of course the relay is screwed. Mine flash on briefly in temps of 15 deg C so I'm sure yours should function at 5 deg C, so you are looking at sensor or relay, and my money is on the sensor.
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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

[fatso_1234]

I guess I'm mostly wondering how it's supposed to work - then I can figure out what, if anything, is wrong.

I've sort of gathered that when the temp is low (how low?) the plugs should get 12 V for about 15 seconds when you turn the key to 'on'.  This part seems to work when I unplug the sensor.  When the temp is higher, relay 2 should function after the engine has started and send power to the plugs through a resistor that drops the voltage.  (For how many seconds?).  Is this right? This part doesn't happen at all so it could be the resistor, relay, or controller/timer.  The relay doesn't click so that's probably the first thing to check.  Where is it?
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1991 Bighorn LWB 2.8 TD 4JB1-T

[Hard1]

You are not supposed to fire the motor until the glow plug light symbol has gone out (at which point the plug has stopped heating) I am also told that by firing the motor when the heater symbol is still lit, you will dramatically shorten the life of the glow plug.

So, the heater symbol is only lit while the plug glows. When the symbol goes out, the plug stops glowing and the fuel is at temperature ready for firing. It is not like a 'choke' on a gas motor which still operates when the motor is cold and after it has fired. When a diesel has fired - that's that.

Presumably, the plug glows for a length of time pre-determined by the temperature sensor as the fuel will be then warm (thin) enough to compress and fire.

If the plug doesn't glow when the sensor is disconnected then I would suspect the sensor in the first instance. As you have already proved that the glow plugs work OK when the sensor is disconnected, then obviously the plugs are OK. You have to find a way to eliminate or confirm the vailidity of the sensor in the chain, plus I wouldn't have thought there'd be the need for a second relay, just the main glow plug relay >  temp sensor > glow plug.
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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

[markymoan]

15 seconds  
Mine only work for about 3 seconds at -5c, and not at all in warmer weather,  the trooper has fast plugs not like the slow ones fitted to old british diesels.
And they dont heat the fuel, they preheat the cylinder ready for fuel  
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[markymoan]

As for damaging the plugs if you fire it before the light goes out,
Yup, it can crack the plug.
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[Hard1]

Well, anyway....
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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

[fatso_1234]

Just as a point of interest, the Bosch and Beru websites talk about new vehicles where the plugs stay on for up to 3 minutes for smoother running after starting.

Anyways this diagram which might be what I have.



If this is right when the sensor is open, the controller trips the bottom relay when the key is turned to on.  Mine definately glows for 15 seconds even thought the indicator light only stays on for 3-4 seconds.  The other relay looks like it sends power to the plugs at a lower voltage during starting.  Last night I pulled out the 2nd relay and jumpered the wires.  I assumed the heavy gauge wire was to glow plugs.  When I did this I tripped the starter motor, so I quit playing around.  It looks like I might have jumpered the wires that normally connect to the relay coil.  I'll test this theory later tonight.
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1991 Bighorn LWB 2.8 TD 4JB1-T

[Peej]

Is the engine actually starting readily? If it starts ok and is just smoky is it necessarily a problem with glow plugs? Not an expert just a thought.

[fatso_1234]

Yah, it starts okay, but not great.  It runs poorly at first and misfires.  There is definately no power to the plugs and I really think there should be at 5 C.

By the way, the truck's name is Suzi.  Perhaps not very original, but there aren't many Isuzus over here.

Then you can say stuff like "Big horny Suzi's a dirty girl" when she's stuck in the mud.
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1991 Bighorn LWB 2.8 TD 4JB1-T

[fatso_1234]

Anyone have any idea where this dropping resistor is located?  Should look something like this:




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1991 Bighorn LWB 2.8 TD 4JB1-T

[fatso_1234]

After reading everything about this QOS system that I could find, which is admittedly not that much, I've come to a few conclusions and raised a few more questions.

First there is more than 1 QOS system.  I thought I had the first one because it has 2 relays.  If you type the part numbers (above) of the relays into http://www.isuzuparts.com/part_number.html they come back as glow plug relays.  This also seemed to fit with one tripping on "start" and one tripping on "on" with the sensor open.

The second QOS system uses 1 relay and no dropping resistor
.  
This system seems to operate as mine does and explains the 15 second glow time and either 0.3s or 3.5 second indicator time.  Therefore I'd say there's a good chance this is the system I have.  What that other 8-94153-849-0 relay is for, who knows???  This system should glow below 0 C, but I might put in a momentary switch so I can have some manual control.

Done and done.
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1991 Bighorn LWB 2.8 TD 4JB1-T

[bedford4x4]

Hi there,  I'm new to the forum.  I bought an Isuzu Mu (Vauxhall Frontera more or less) with a 4JB1-T in it and had the same trouble as others have had on the forum.  The vehicle won't start when really cold, runs rough and smokes a lot.  

For all members' general information, this motor only pre-heats the glow-plugs when the ambient temperature is about -20 degrees.  Anything above this temperature, glow-plugs aren't needed as the motor is a direct-injection diesel.  I noticed in several posts that people had got their motor going by disconnecting a wire off a temperature sensor on the thermostat housing.  They have deduced that because the glow-plugs are now working, that that is the problem, but this is an erroneous assumption.

The temperature sensor advances the injector timing so it is suitable for starting in cold conditions and activates the glow-plug relay.  So the real trouble is not that the glow-plugs aren't working in normal temperatures, but a timing issue.  The normal culprit is the crankshaft timing belt sprocket which comes loose, stuffs the woodruff key and itself in the process and the timing is gradually retarded by the worn keyway so eventually it won't start when cold and runs like a dog.  By disconnecting the temperature sensor, you will advance the timing back to something approximating normal injector timing.  The fact that the glow-plugs will now work is incidental.

This problem is very common on these motors due to people changing timing belts by undoing the centre nut holding the crankshaft pulley hub on the crankshaft and not re-torqueing it to the required amount.  I suggest putting loctite on the crankshaft, woodruff key and both timing belt sprocket and pulley hub before assembly then torqueing it to the correct amount.  To do this you may have to remove the starter motor on auto trans models and lock the ring gear so the crank doesn't move.

So if you have one of these motors and you've trouble starting when the motor is cold, don't worry if it doesn't glow - it normally doesn't.  The issue is retarded injector timing and the timing belt sprocket on the crankshaft is the culprit.  Someone said that because it is a pushrod motor, it won't hurt the motor if the timing belt breaks.  Absolute rubbish - the camshaft is still operated by the timing belt and you'll trash the motor if the timing belt breaks, or the woodruff key on the crankshaft slogs out to the extent that it lets go entirely.  Check your crankshaft sprocket next time you do a timing belt replacement and make sure it doesn't move at all.  If it does, replace it.

I hope this helps someone!