GQ tough technical question!!

Submitted: Monday, May 04, 2009 at 09:31
ThreadID: 68499 Views:6536 Replies:8 FollowUps:5
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I have a 2.8 GQ diesel patrol (1996). I have intermittent problems which I need help with. Murphys law is that the few times I have taken it to the mechanic it's working so they can't fault find it :(

The glow plug light does not come on at the dash board; the glow plugs themselves are also not getting a signal as the car won't start (so it's not a simple globe fix). At the same time my rev counter on the dash board does not work.

Close reading of my Gregorys manual in the electrical section has some interesting connections but I want to see if anyone else has had this issue before I start spending money. So what I have found is this:

The glow plug control unit receives signals from two sensors. One is a water temperature sensor so the glow plugs turn off when the engine is warm. The other sensor is from a unit which screws into the transfer case and sends a signal of speed. This unit I believe must send a signal to the speedometer on the dash (I thought it was just a simple cable but maybe not).

Anyway what I am thinking is that the sensor connected to the transfer case is faulty and in some way is not completing the circuit for the glow plug control box (which sits under the fuse box inside the car) hence then not sending a signal to the glow plugs to work (??).

Has anyone experienced the same problem with their GQ and am I on the right path? My concern is that I am heading up to Innamincka in 7 weeks and if my glow plugs dont work on those cold morning up there then I'm in trouble!


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Reply By: Member - Tony & Julie (FNQ) - Monday, May 04, 2009 at 09:56

Monday, May 04, 2009 at 09:56
From things that have happened in the past I always look at the simple first now, 90% of the time it does the trick.

I have not had that model Nissan but I had an earlier model that gave me some electrical problems, after hours in the book chasing down the wiring paths my problem was the fuse box. Previous owner had been out west and it was very dusty under the dash. This had worked its way into the fuse block. Fuses were all ok but the contacts were not good. Thus sometimes a problem sometimes not. After cleaning it all up, no more problems. You never know its worth a go :-). Be interesting if the Taco is on the same circuit. Cheers Tony
AnswerID: 363108

Follow Up By: Gossy - Monday, May 04, 2009 at 10:01

Monday, May 04, 2009 at 10:01
I did find that there was a 'common' fuse (10amp) that it was all running thru. Checked that and was fine (engine management or something like that?).

I also did the old trick of turning the prongs a bit for a better contract. Problem now is that it's all working again (for now) so the fault finding is very difficult.

I was thinking of just replacing the whole glow plug control box but then I could go ahead and do this and the problem reappear again. I'll ring up Nissan today and get a quote on this box. If it doesn't cost too much I might just do this anyway.
FollowupID: 630750

Follow Up By: Member - Tony & Julie (FNQ) - Monday, May 04, 2009 at 10:12

Monday, May 04, 2009 at 10:12
OK - Just try all the simple first. Did it stop working after you did the fuse?
I have spent a lot of money buying parts that were not needed. Things like earth wires that to all appearance were in good nick, but were actually corroded inside the insulation. (At least I had spares for ron :-)). Electrical contact spray is a good thing. Best of luck Cheers Tony.
FollowupID: 630751

Follow Up By: Gossy - Monday, May 04, 2009 at 10:22

Monday, May 04, 2009 at 10:22
fuse wasn't the problem unfortunately. Just rang Nissan; 2 relays approx $100 each.

Forgot to get a quote for the speed sensor! Need to ring them back. If this is cheap then I will replace that and then sit back and see if the problem occurs again.

I remember many years ago I was in the Tanami in a landcruiser when the glow plugs died. We put the coals of the fire underneath the engine bay for 10 mins and the car started first pop every morning (freezing mornings). Worse case scenario I can do this on our trip if the problem arises.

Problem with me is that I am very anal with my car. It's a bush basher (doesn't get used much when not going away) but no excuse to not have everything running 100% so when I do find a problem like this I like to fix it ASAP.

In Nissans defence it's a credit to them that their electrical stuff has lasted this long considering the life the car has had!!
FollowupID: 630753

Reply By: DMH122 - Monday, May 04, 2009 at 14:12

Monday, May 04, 2009 at 14:12
Gday Gossy,
Try a new ECM relay it is located in the top of the cabin fuse box.
Cheers Grant.
AnswerID: 363139

Follow Up By: Gossy - Monday, May 04, 2009 at 14:36

Monday, May 04, 2009 at 14:36
Do you mean the two relays inside the glow plug control unit or the actual fuse box itself.

Sorry but on a steep learning curve with this. Never had anything go around around this part of the car before.
FollowupID: 630788

Follow Up By: DMH122 - Wednesday, May 06, 2009 at 09:48

Wednesday, May 06, 2009 at 09:48
Hi Gossy,
It is the relay in the cabin fuse box nothing to do with glow plug control unit it is only one relay, you have to remove the panel under steering colum, it is the top l/h relay from memory, a way of checking is to remove relay and check if the glow light works if doesnt then thats the one, good luck.
FollowupID: 631120

Reply By: Gossy - Monday, May 04, 2009 at 15:38

Monday, May 04, 2009 at 15:38

Crap! Over a grand :(

"Symptoms were:
1. Tacho stopped working.
2. Glow indicator on the dash no longer illumunated when ignition switched to on.
3. Couldn't hear the glow relays clicking as usual.
4. First start was a dog, heaps of black smoke and rough running till warm."
AnswerID: 363158

Reply By: Gossy - Tuesday, May 05, 2009 at 10:06

Tuesday, May 05, 2009 at 10:06
I will bore everyone and keep this forum updated. Reason is there is very little info on the net about this problem and these ExploreOZ links always come up on Google.

My glow plug light on the dash board is flashing now whilst the car is running.
I have learnt that 2 sensors feed info back into the control box to complete the whole process. The speedometer sensor which screws into the transfer case and also the water temp sensor. The purpose of this is that it sends a signal to the glow plugs when the engine is warm (usually around 30 seconds to 1 min apparantly) and then the glow plugs turn off.

Looks like my glow plug control unit is ok (located behind cover where the fuse box is next to drivers feet). checked connectivity as per Gregorys manual and looked fine.

I did find that there are two ways to test the water temperature sensor. One is via the sensor itself on the engine block which I couldn't do because I couldn't get the damn plug off (this screws into the engine block on the RHS towards the rear) and also on two terminals on the plugs for the control unit. This looked suspect using my volt meter so I will now spend extra time (during the day so I can see what I am doing) to access the two pins for the water temp sensor itself.

Also tested the two relays which sit under the metal cover next to the battery and they are fine. There are 2 because one relay turns the glow plugs on to start the car whilst the other one keeps them on until the water temp sensor tells it to turn them off (which is what I think the problem is; it's getting the wrong signal).

Prices to fix this stuff as of May 09 from Nissan:
Relay 1: $112
Relay 2: $97
Water temp sensor: $139 (screws into engine block)
Speedometer sensor: $145 (screws into transfer case)
Control unit: $1600 (so you had better hope one of the above is broken!).
AnswerID: 363302

Reply By: Gossy - Tuesday, May 05, 2009 at 10:08

Tuesday, May 05, 2009 at 10:08
forgot to mention that we crossed the Simpson desert last year where we encountered alot of rain. Though I washed the car well I have noticed mud/grime on most of my terminals inside the engine bay.

As this stuff has lots of salt in it this is not helping. though the rain was not expected it's a lesson learnt for me to spray all these before heading out on big trips 'just in case'.
AnswerID: 363303

Reply By: Gossy - Wednesday, May 06, 2009 at 10:00

Wednesday, May 06, 2009 at 10:00
More relays!!!!!! I bought this model car so there was no computer rubbish in it to go wrong! I see a rewire job coming up in years to come to eliminate all this stuff and have a manual glow plug system (redarc etc).

I think I have nailed the problem so whilst I'm here I'll also give an update incase anyone reads this with the same issue.

Murphys law is that doing things for the first time means you probably take the long way around to do it. That's the case with me. The two relays which sit under the metal cover next to the battery are a bit of a pain to access in regard to using a phillips head and getting them out (not much room to move and the screws demand your biggest phillips head in the tool bag - not very smart nissan!!). These relays passed the test in regard to connectivity etc.
the next night I got a test light from my Dad and tested that the glow plugs were doing their job (turning on AND off). This simple job took 1 minute and basically proved that the relays were doing their job anyway. Morale of the story: I didn't need to access the relays first up. Only if the glow plugs were not working correctly did I have to then go to the bother of accessing the relays.

I cannot get the electrical plug off the water temperature sensor therefore I cannot do a simple 5 second test on this. This can be tested from the glow plug control box via pins 33 and 35 (from memory). This was suspect. I believe I have now done enough testing to warrant the expenditure of $140 to replace this sensor.

keep you posted on the success or failure!
AnswerID: 363452

Reply By: Gossy - Tuesday, May 12, 2009 at 11:15

Tuesday, May 12, 2009 at 11:15
Final update:

The problem was the water temp sensor in the end which also caused another problem :(

I couldn't get the damn plug off the sensor because it has some type of clip on it. The manual was not good as it simply said "remove the cap off the plug". Took it to a mechanic and I'm glad I did now.

What he found was that the glow plugs were getting power so my basic test with a test light was correct BUT they weren't getting the amps they needed to be effective. 4 out of the 6 had basically burnt out because of the water temp sensor sending the wrong message to them all the time.

So bottom line is that I had the sensor replaced (13 yrs old so got my money's worth out of it) and all glow plugs replaced also (13 yrs old also so not too upset about that) and now as good as new. No more killing myself and the neighbours with black smoke trying to start a cold diesel.

Aftermarket glow plugs are just as good and half the price of Nissan so no need for originals.

Hope this info has helped someone in the years to come.

AnswerID: 364453

Reply By: Travelling Pixie - Tuesday, May 12, 2009 at 13:29

Tuesday, May 12, 2009 at 13:29
good onya for following this article up with an outcome!!
AnswerID: 364465

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