2,8 TD glow fu**ed up :-(

[FrodeS]

I exchanged all 6 glow plugs on my 1993 2,8 SWB yesterday. They are 3 + 3, and I put the right ones in the right place, but for some reason, the plastic spacers between the two distributors (??) (one connecting all 6 plugs, the other one connecting the rear 3) was missing, and I didn't pay attention. Probably, I had a short circuit between them, and now some thing is not right.

For those not familiar with the 2.8 glow system, it goes like this:

There are two distributors, one for all 6 plugs, one for only the rear 3 ones. The front ones are connected thru ground and the one distributor, the rear 3 ones are connected between the two distributors, NOT getting any power thru ground. Some say this has to do with after glow, and that the after glow only works on the 3 rear plugs. Sounds strange to me. Any way, this entire system seems strange.

The plugs are rated 6,5V for some reason.

Anyway, this is what happens.
When the ignition is turned on, the glow lamp is lit, and after ~3 seconds, it goes out again. For this ~3 seconds, the front three glow plugs are engaged (measuring -11,5V over them). As the light goes out, the power is removed, and the rear three plugs are engaged for ~0,5 - 1 second or so. As the light goes out, is it out for 3-4-5 seconds'ish, and start flashing. If I am lucky enough to be able to start the car, hopefully without the neighbors calling the fire dept., the light will keep flashing for ~5 minutes.


I've put all the old glow plugs back in, and made sure there is no short circuit, so it seems some thing has gone bad.

Any clues on what to do?


If I can't make this strange system work like it's supposed to, I might just pull the glow relay and harness from an older mercedes 6-syl diesel, as they are easy to work with, and some thing I am familiar with. In that case, I'd need 12V glow plugs, and I did read some were, that the TD42 plugs fit just fine. Can some one confirm that?

[Yendor]

Yes the GQ 2.8s run two different type of glow plugs, along with a 1st stage glow and an after glow.

1st stage glow you should see around 12 volts on the main busbar connecting all 6 glow plugs and zero volts on the small busbar.

After glow you should see around 12 volts on the small busbar and around 6 volts on the main busbar.

Assuming your tacho and engine temperature sensor are working correctly you more then likely have a problem with your after glow relay (relay no. 2).

Here's how you can test it.

[FrodeS]

Thanks.

Thing is, for the three front plugs to engage, they need power thru the long busbar (I learned a new word today) and ground, and for the rear ones, they need power between the 1st and 2nd bus bars. The rear ones don't have any connection to ground as I am aware of.

For the first stage I measure -11,5V (yes, minus) between ground and the long busbar, but only for 3-4 seconds. After that, the lamp goes out, there is a short period of 12V between the 2 busbars, and then it all goes out and the lamp start flashing. The car does not at all want to start.

[Yendor]

Thanks.

Thing is, for the three front plugs to engage, they need power thru the long busbar (I learned a new word today) and ground, and for the rear ones, they need power between the 1st and 2nd bus bars. The rear ones don't have any connection to ground as I am aware of.

During first stage the 3 rear glow plugs are earth via the small busbar and no. 2 relay. As per above check no. 2 relay.


For the first stage I measure -11,5V (yes, minus) between ground and the long busbar, but only for 3-4 seconds. After that, the lamp goes out, there is a short period of 12V between the 2 busbars, and then it all goes out and the lamp start flashing. The car does not at all want to start.


You can't have minus voltage on the long busbar and ground. Did you have your multimeter leads connected correctly?, battery connected correctly? Have you checked the glow plug main fusible link?

There are few things that determine how long stage one stays on for such as engine temperature, start signal...

[FrodeS]

Thanks. I appreciate all answers.

With the negative connector of the multimeter on the negative battery pole, and the positive one on the bus bar, it says -11,5V when glowing. This surprised me, as this multimeter for some reason allways shows positive numbers, even if I mess up with the leads on the multimeter. I am fairly competent of using a multimeter, but I need to look more into this system to fully understand it.

Between the long and short bars, there is only power (+11,5V) for a very short period of 0,5 second or so as the main power cuts off. I am at work now, and will do some more measuring later, when I get home. I will also look into the document you sent me, and check the two relays.

[FrodeS]

BTW. Fusible link? Is there a fuse any were? I did check all fuses in the fuse box. Nothing wrong there.

[FrodeS]

I found a fuse in the fuse box next to the battery. I wasn't aware of this fusebox. All fuses are OK, including the melt-fuse for the glow system, looking like a cable.

Both glow relays are pulled from the car, and works as supposed. I've tested them according to the document above, and they pass.


Now, with both relays pulled from the car, the glow indicator in the dashboard still behave like before. It is lit for only a short period, then goes out, and start flashing.
This makes me believe the problem is to be found in some kind of glow control unit. Were can that be found?

[FrodeS]

Arrait.
I've got a wiring diagram from a friend at Nissan. It really sums this system up.

1. The test mentioned above is not good enough. My relay nr.2 is accually toasted, but passed the test.

2. Afterglow works on ALL glow plugs, not only the rear ones.


Now..
There are 2 busbars, the long, and the short. The long one is usually positive with +12V. The front 3 glow plugs get +12V from the long bus bar, and ground from the engine. The rear 3 plugs get +12V from the long bus bar, and ground from the short bus bar, THRU relay no.2. Relay no. 2. Relay no. 2 is NC to ground, and NO to +12V.

When pre glow kicks in, relay no. 1 is shut off, and relay no.2 is activated. Relay no. 2 is now NOT any more connected to ground, but to +12V. +12V is now fed thru the short bus bar, first going thru the rear 3 glow plugs, following the long bus bar, going thru the front 3 plugs, and then hitting ground in the engine.

After glow goes thru all 6 glow plugs, but with only half the voltage, and half the current, resulting in 1/4 power.

Attaching a picture of the relay no.2. According to the test mentioned above, this one was working properly.61936

[FrodeS]

The cable in the relay didn't respond to well to soldering, so I made a new one from some speaker cable.

Appearently the relay now works, and it seems I still have a short circuit between the two busbars. Now I know how that melt-fuse looks when it is blown. Think I'll get some plastic washers to put in between the busbars, as supposed to. I think I can make this relays work, but I still think there is some thing wrong in the control unit.

Update when I've fitted a new fuse, and sorted the short circuits.

[FrodeS]

A little tired today, so any more work on the car is postponed for tomorrow. Besides, it is dark and cold outside. Better staying inside. As I blew the fuse in a quite notable way, I had to kind of un-blow it. It literally went up in smoke.

I don't know the amperage of the original one, but as I have some 150A fuses sitting around, I decided 150A is quite OK ('ish). It shuld blow if a short circuit occure.

6193761938

The wiring diagrams I got is quite interresting to read. I did think the control unit just activate the relay, and don't really have any clue on what is accually going on. From the wiring diagram, it seems there is a wire going from the far side of relay 1, back to the control unit on pin 25. (pin 5 if no EGR). This might be to inform the control unit of the glow plugs accually being engaged. I HOPE the control unit is still fine, and the reason for the lamp flashing, is because the relays have not been working properly. One can always hope.

[FrodeS]

"Whe the glow plug terminal voltage becomes extremely low or high, the glow relays automatically turn off and the glow lamp blinks for 5 minutes in order to indicate that the glow plug circuit is malfunctioning".

I'll be darned.

At start, the relay 1 and relay 2 will alternate for some time. First, relay 1 is activated, and after some seccondes, relay 2 is activated, to ensure the glow plugs are not over heating. I think it is at this change, mine stop glowing, as because of the malfunctioning relay 2. When this relay kicks in, the voltage is lost, and the above mentioned occures. It makes sence. Hope I can manufacture some spacers for the busbars tomorrow, and have another try.

[Yendor]

The wire burnt out in the relay is because the insulators are missing between the short and long busbars. I don't know how the relay passed your testing with the main lead to the contacts burnt out like that.

150 amp fuse is way to high. 100 amp is more then enough.

[FrodeS]

I did as described in the document. On relay 2, it didn't tell me to apply power, so I didn't. After looking at it, it became clear that the testing described was not enough, so I opened it and found out it was defective. The procedure also shuld have contained something about testing continuity between X and Y when relay NOT activated, and between X and Z when activated.

I am aware of the missing insulators now. I was not at the time I replaced the glow plugs, I just put it back together the way it was when I took it apart.

I am aware 150A is a little high, but in the store I found maximum 30A, and I had this 150A (and 200A) sitting around.

[Yendor]

It does say all that. Have another read. But hey what would Nissan know regarding checking their own system.

If the insulators were missing from the start the glow plugs wouldn't of worked at all. I'm guessing they fell down when you removed the old glow plugs, have a look around the manifold for them.

With a 150amp fuse you will burn the wire harness before the fuse blows. Look at fitting an aftermarket fuse holder and fuse.

[FrodeS]

You are right. I did test on relay1 only, were it did not specify relay2. I see now that I shuld have tested on both.

A short in this big cables will easily blow a 150A fuse. I tested one fuse with a 0,75mm2 cable and an 10A rated push button. Blew the fuse right up. I'll try to find a fuse of 70-100A and fit at a later time. For now, this will have to do.

It is possible to mount the two busbars without spacers, but you have to be very careful. I did wonder why the three rear nuts were very loosely tightened. I didn't know how this system worked when I changed the glow plugs, so I just put every thing in place, and tightened it thoroughly.

Hopefully, I'll be able to manufacture new spacers this evening. I didn't get around to do any work on this yesterday, except I had to hook it up, get glowing on the three front glow plugs, in order to get the car started, and put some antifreeze on it. It had only water, after I exchanged the radiator, and flushed both heaters. We had a sudden temperature drop, and 5 below freezing tonight.


Anyway, reading the documentation from Nissan is kind of interresting. This glow system looks like nothing I've touched before. I've read about it different places, and it is normally referred to as "shit", and some thing you'd want to get rid of. It isn't really that complicated, it is just different.

[Yendor]

We will have to agree to disagree regarding the 150 amp fuse.

You should be able to make up some insulators reasonably easily. If not you could try sending Nizzbits on here a PM. I don't think it would be to expensive to freight them over there.

If you still have the old plugs and the original front 3 test okay, you could put them back in the last 3 cylinders. Remove the short busbar and it's connecting wire. This would have least give you first stage glowing on all 6 cylinders until you got the insulators sorted.

Most Nissan electrical systems are very well designed and built. When people don't understand something their normal response is "it must be shit" and then proceed to remove it and normally fit an inferior aftermarket system.

[FrodeS]

I've made some insulators now, will try to fit them later today (it is noon here now).

The first stage only goes on for about 2 seconds. After that, it changes to 2nd stage, and then switches back and forth between 1st and 2nd. I suppose this is because of the glow plugs being rated 6,5V, and fed 12V. At after glow, it is alternating 50/100% below 1000 rpm, constant 50% between 1000 and 2000 rpm, and shut of if 2000 rpm is exceeded. It will also shut off if vehicle speed is exceeding 12 km/h for more than 3 minutes. It wil in any way shut off after 10 minutes, or if the water temperature reaches 60C.

[FrodeS]

Well, normal order has been restored.

Glow lamp now indicates as normal. No fuses or relays blown up. New plugs fitted, with home made spacers between the busbars.

Sadly, the car is just as grumpy to cold start as before. It starts right a way, but it does not idle very well, and it spews out lots of white smoke. It needs to idle for a couple of minutes before running smooth. It goes faster if i take it up to 1500-2000 rpm for a little while. I was hoping this was due to one or more glow plugs malfunctioning, but with all plugs replaced, and the car still acting up the same way, the reason must be elsewhere. Any thoughts?