SD25 hard start when cold in 1984 720

Dealing with all subsystems specific to the diesel powered Datsun-Nissan 720 pickup trucks.

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CooperativeRoots
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SD25 hard start when cold in 1984 720

#1

Post by CooperativeRoots »

I have read a lot about cold starting problems on this forum, yet still am stumped about this problem.

First some background:
We have run this pickup on ASTM certified B100 for 5+ years without modifications (other than a couple filter changes and fuel line replacement with BioD compatible hoses).

A year ago I replaced the fusible link to the glow plugs at the battery terminal and replaced the glow plug timer assembly to convert the vehicle back to original starting for ease of the many people who use this rig at our cooperative houses. The truck used to have a push button glow plug control which bypassed this plug timer.

Now the problem:
If I turn the ignition to ON the glow plug indicator light on the dash lights up for a 2 or 3 seconds, and it sounds like the glow plug relay stays on for 6-8 seconds before turning off. Turning the ignition to START at this point, the engine is hard to start, smokes and stutters and stalls even if I almost floor the accelerator. It often takes 2 or 3 more attempts before it starts running. Then I have to let it warm up for about a minute with the accelerator slightly depressed or it will stall.

Any ideas? You guys seem to be the best bet for helping. The diesel mechanics around here aren't familiar with this starting system.

Some thoughts:
1) I'm thinking of trying to swap in the original Nissan glow plugs as the ones I have in there don't have very many miles on them but aren't stock. After reading the posts about quick glow systems I'm curious if that would help. Can plugs fouling over time with BioD be an issue?
2) Other than that, I can check the voltage at the glow plug bus when glowing, but what voltage should I be seeing? 12V, 10V....?

cheers, zack
1984 Nissan 720
SD25
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Re: SD25 hard start when cold in 1984 720

#2

Post by asavage »

CooperativeRoots wrote:We have run this pickup on ASTM certified B100 for 5+ years without modifications (other than a couple filter changes and fuel line replacement with BioD compatible hoses).
:)
If I turn the ignition to ON the glow plug indicator light on the dash lights up for a 2 or 3 seconds, and it sounds like the glow plug relay stays on for 6-8 seconds before turning off. Turning the ignition to START at this point, the engine is hard to start, smokes and stutters and stalls even if I almost floor the accelerator. It often takes 2 or 3 more attempts before it starts running. Then I have to let it warm up for about a minute with the accelerator slightly depressed or it will stall.
Few here have any experience with the Type II autoglow system that your rig has; too few were sold in the US. We have a couple of Canadian members with them, though.

The symptoms you describe are exactly the ones I had with one bad glow plug, and it was much worse when running B99 too.
Can plugs fouling over time with BioD be an issue?
I am very doubtful of this.
Other than that, I can check the voltage at the glow plug bus when glowing, but what voltage should I be seeing? 12V, 10V....?
You should see battery voltage minus a reasonable drop for the connections and solenoid. Glowing but not cranking, I'd like to see above 10.5V (preferably above 11V) at the GP bus while glowing, and no more than 1V drop from the battery to the GP bus. How to measure: meter positive to the center of the positive battery terminal, and meter negative to the tip of one of the GPs. You usually need a helper to run the key ;)

If the GP voltage is lower than 10.5V, you have a battery or connection resistance problem.

What you want to do (after that) is to test each GP. If you have a good, high-capacity ammeter (clamp-on or otherwise), you can figure roughly 60A steady draw after a couple of seconds. If it's less, you have one or more open GPs not drawing power. That figure is for Type I systems, which probably draws less that your faster Type II system.

The harder way to test, that doesn't require that high-capacity ammeter, is to remove the GP bus wires and use a typical 12v test lamp (or one you fabricate). Clip what is usually the ground wire on the test lamp to the positive battery terminal (does not have to be in the center of the post for this test). Touch the test lamp's probe to any ground to make sure it lights (connection OK, lamp OK). Then, with the wires OFF a GP, touch the probe to the GP terminal. It should light. If not, GP is open (bad). Repeat for all four GPs. Again, all wires have to be disconnected from the GPs for this test to work.

Also, you cannot reliably use a digital ohmmeter or continuity checker for this test. You need a real load, one that the test light's lamp provides. You will get misleading results trying this with a digital ohmmeter.

Hope this helps.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
CooperativeRoots
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Location: Berkeley, CA

#3

Post by CooperativeRoots »

Thanks for the tips on glowplug testing with multimeters. I had always thought if you measured the resistance with a digital multimeter you would get a good indicator of whether the plugs were bad. If all resistances are the same I assume it is good. Why do you say this is not reliable?

In any case, all plugs have 0.2ohm resistance, and also pass the test light procedure you describe. I will measure the bus voltage and look for no more than a 1V drop across the wiring and report back.

zack
1984 Nissan 720
SD25
Running ASTM-certified B100 for 5 years
cooperativeroots.org
plenzen
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#4

Post by plenzen »

I take it you have gone back to the "Quick Glow" system? If thats the case what glow plugs are presently in the vehicle? If it has a 12V type generic glow plug the timer for the quick glow system may not stay on long enough to get them hot enough, and, supply enough voltage to keep them warm enough in the "afer glow" cycle to smooth out the idle.

Paul
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#5

Post by CooperativeRoots »

Yeah, that was the intention, to go back to the OE glow system. It worked pretty well for the last year and only recently has had problems. The current glow plugs are SLM "with post-heating", 1106N.2 (at least that's what the box says). They are several years old but only a few thousand miles on them. I'm inclined to buy a set of the orginal Nissan plugs after eliminating the wiring as the issue. Do you think that would be wise, or are there other possibilities as to what is going on?

zack
1984 Nissan 720
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plenzen
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#6

Post by plenzen »

If everything checks out and all is working correctly I think I would try a tank of just plain old diesel in it and see if that does not aid with the cold starting. I am not certain how the cetane level(s) etc. act in cold weather with Bio, or even how cold it is where you are. Here in Canada we don't have a choice of what grade of diesel we can get. It's just "Diesel". About mid April we start to get the "summer diesel" as opposed to "winter diesel". ( less anitgel, kerosene etc.) The fuel stations here do not offer a choice between #1, #2, or Bio. My point is, try a tank of "diesel" ( #1 I think is what you want ) and see if it starts better with it. I just wonder how clean the Bio actually burns and if your engines compression is not down a bit from coke and soot etc. A tank of plain ol diesel and a good run on the highway might burn some of the soot and de-glaze the cylinders a bit and get some of your compression back.
It's just a thought and easy to try.
As for Nissan Glow Plugs I am not that certain that you will get actual Nissan ones. You may end up with ND or NGK or Champion etc.
I have Delphi GP's in mine ( HDS 283's ) and they are made for the "quick glow" system.
About -10 C is the limit to these engines starting without plugging in a block heater or activating the air heater that I made for my truck. They all HATE COLD WEATHER !

HTH

Paul
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#7

Post by CooperativeRoots »

The temperature rarely gets below 40F here in Berkeley, CA. It has trouble starting even at 55F.
The problem with running regular diesel in this engine is that California went to ultra low sulfur diesel recently and it has proven to be uber-risky to switch back and forth between BioD and diesel due to fuel pump gasket leakage that can occur from swelling and shrinking seals. With the old diesel in California you could go back and forth between BioD and regular, but unfortunately it's ill advised to do that anymore with these old vehicles.
That being said, we've been running this engine a long time on Biodiesel with no problems due to it yet, so I would be surprised if this starting issue had anything to do with that.
You mention compression though, that's interesting. I suspected it might be a compression issue if not a glow issue. I'll work on the glow system first and then move on to testing things like compression if necessary.

As for the glow plugs, what do you think of those plugs I have, are those the right ones to use in this vehicle?

thanks for the wisdom, i'm going to post the results of the wiring check shortly once I have the vehicle in my hands again.
zack
1984 Nissan 720
SD25
Running ASTM-certified B100 for 5 years
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plenzen
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#8

Post by plenzen »

We have been using ULSD here (Canada) for quite a number of years and I use an additive with every fill up. I switch between Stanadine (blue bottle) and Power Service (grey bottle summer white bottle winter) and have had no issues with seals etc. thus far. There are a number of these additives out there for the ULSD that address the very issues that you mention. There are however some "snake oils" out there but from the research that I have done the two that I mention seem to work well. (the Stanadine was reccomended by a fuel pump rebuilder) There are one or two places here in the Calgary Alberta area where you can buy Bio but it's not a big seller in the winter months with temps dipping into the -30's C on occasion. Seems the Bio does not like to flow that well at those temps and gets cloudy and waxy etc. I was just wondering if over the last months/years that you have been burning the bio your engine is not "coked up" and perhaps "glazed up" a bit to drop the compression a tad. Does not take much of a drop in compression to make a big difference in starting. (Crank over speed is another thing to look at as well). I am not that certain about the "flash point" of the bio as compared to "ULSD diesel". Mix that with the cooler temps and you may end up with an issue. That being said. If this is a "sudden onset" then I would still be looking with the glow issues. As for your question of the glow plugs that you mention, I am not familiar with those. There is however, within this forum, a topic with all that kind of information that Al or Phillip compiled and posted. I will go and look for it if you cannot find it. I do know however that the voltages for the Quick Glow and After Glow systems are a bit different. Place your meter on the glow bus and turn the key on. Watch the voltage through the entire sequence. See Here: http://nissandiesel.dyndns.org/viewtopi ... ug+voltage
I believe that the Delphi plugs that I have are rated at 9V. If the plugs you have are rated at 12V I dont think the timer will stay on long enough to get them hot enough fast enough. According to the owners manual I have with my truck, it says to start cranking when the "OE" light in the dash goes out. I have had 0 success with that starting procedure and let it cycle all the way to the after glow sequence. ( I installed a secondary light on the dash and it gets dim when the system goes to after glow). I then crank the engine and do not touch the throttle. I let it idle till the "dim light" goes out and drive then. That time will vary on ambient temp and how much heat is in the engine. There is a thermo sensor in the rear of the intake manifold.

HTH

Paul
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#9

Post by CooperativeRoots »

Ok, here are the results of my testing on the glow system:

1) The plugs are only reading about 9.5V in the quick glow portion of the cycle which lasts about 6 seconds after turning the ignition on when the truck is cold. Then in the afterglow portion, lasting another 6-10 seconds the voltage is around 5.5-6V.
2) There is indeed about a 1.8-2V drop between the connector after the battery positive terminal and the connector directly connected to the glow plug bus during the quick glow. The wire leading up to the glow plug bus connector is getting warm after repeated glowing which leads me to think that might be a problem, although there is no external indication that the wire is damaged?
3) I also tested voltage drop across all the connectors in this circuit that I could see including the one next to the fusible link near the battery positive terminal, and the one right before the glow plug bus. Neither showed an appreciable voltage drop during quick glow.

So what does this mean?
Looking at the wiring diagram it looks like the glow control unit (aka glow plug timer) just controls when the glow plug relays turn on. So in order for there to be a voltage drop in the glow plug circuit it has to be either the relay, the wiring, or the connectors that have a high resistance, right?

I don't know where to go from here, Any ideas? Should I put in some Nissan/OE glow plugs and see if that solves it, or is that foolhardy? Everything you other guys are saying seems to indicate I should have at least 11V at the glow plug bus, but plenzen's post linked in the last response says that 9.6-10V is normal for quick-glow systems. I don't understand that based on the wiring diagram however. Where is the 2V drop coming from?

thanks
zack
1984 Nissan 720
SD25
Running ASTM-certified B100 for 5 years
cooperativeroots.org
plenzen
Posts: 869
Joined: 14 years ago
Location: Cochrane Alberta Canada

#10

Post by plenzen »

The drop is done through a thermo resistor at the rear of the intake manifold. At least that is where I think it's done and the only place that I could find, I have not however put a meter there to see for sure. Perhaps a project now the weather here is a bit warmer. I did however just come in from checking a few things. I removed one of the Delphi glow plugs that I have in the vehicle (HDS283) it is rated at 11V. ( previous mention of 9 V incorrect, sorry :oops: ) It is however made for a quick glow system and I believe that Al covered the differences between these types of plugs and a standard “slow burn” type plug. ( I think LD’s use this type of system )
Just for fun I dug out my meter and did the following test.
Battery voltage was at 12.93V. The truck is warm. I hooked my meter to the negative terminal on the battery and placed the + probe on GP #4. I cycled the key and got a reading of 10.6V. I waited for the “Quick Glow” to shut off (about 3+/- seconds) and afterglow did not come on at all. (engine too warm). I then moved the “+” probe to GP P#1 and got the same reading. I started the truck and it switched to afterglow briefly (1 – 2 sec max) and I got a reading of 4.6V. This is common (for my truck at least) when there is a certain amount of heat in the engine in that the “afterglow” will only come on briefly after the engine starts. It will not come on if I just switch the key “on” and not crank.
It will, however, switch to afterglow if the engine is stone cold and, the times mentioned apply.
These voltages I just obtained are different from my previous testing and I can only assume that the thermo resistor at the back of the intake manifold has something to do with this. I know engine temp determines if the system will switch to afterglow and I can only assume that it changes the voltages at the same time. I think I might try it again in the morning as it’s supposed to get to -4C here tonight. Will post those results but am pretty sure that is how I got the original readings.
As for Glow Plugs
I dug through my collection and came up with 3 different ones that I and my dad (original owner) have collected. I have a set of “3Z” plugs. There is a Japanese symbol stamped into one of the “hexes” and 10.5V under that. (no other markings or names, just a big “3Z”)
I have NGK Y112RS1 (0373) also with 10.5 V stamped into them.
I have NGK Y705RS (8672) with 11V stamped into them.
Whether or not the above are for a “dual glow” system I do not know.
As mentioned in previous posts I chose the Delphi because of the tip design (looks like the sharpened end of a crayon), and they were listed for this engine with a dual temp glow system.

HTH and has not given you an aneurism

Paul

EDIT:
When I took the above mentioned plugs back out to the garage I tried a test on them.
Same battery and a length of 14ga. wire.
The 3Z plugs took approx 8 - 9 seconds to get hot and after 10 + seconds were glowing red. Very slow and heated from the middle to the tip
The NGK Y705RS was a bit faster but I would guess by less than 1 second
The NGK Y112RS1 was red in about 4 seconds but in the middle of the plug first and then slowly made it's way to the end
The Delphi is red in 3 - 4 seconds and only the very tip gets red.

FWIW
Paul
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#11

Post by CooperativeRoots »

No aneurysm yet, awesome science experiment plenzen!

I have the service manual in front of me and looking at page EL-41 and EL-42 for the '84 720.
There is no thermoresistor in the circuit between the glow plugs and the positive terminal of the battery. Maybe this is different with your '87. For mine there are two parallel circuits, lets call them 'glow plug 1' and 'glow plug 2'. In 'glow plug 1' there is just 'relay 1' between the + battery and the glow plugs. In 'glow plug 2' there is 'relay 2' and a dropping resistor of 0.1 ohms (Is this the thermoresistor you mention plenzen?) between the + battery and the glow plugs
I think the way this works then is that when 'relay 1' is activated the plugs should get close to 12V (quick glow), and then when 'relay 2' activates and 'relay 1' deactivates they should get (using Ohm's law V=I*R) something like 12V - 60A*.1Ohm = 6V (This assumes 60A is drawn by the four plugs in after-glow mode as per asavage's earlier message in this thread). This all agrees with what you're measuring on your rig +/- 1.5V. I think what the glow plug timer (aka glow control unit) does is just tell which relays to turn on when as per the water temperature sensor and the position of the ignition switch.
So, if all this makes sense, then it seems that I must have either:
a) a problem in my wiring or relays causing a high resistance prior to the plug
b) glow plugs that aren't rated for quick-glow
c) both a & b
d) this phantom thermoresistor or something else we don't understand


I'm taking wagers,
zack
1984 Nissan 720
SD25
Running ASTM-certified B100 for 5 years
cooperativeroots.org
plenzen
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Joined: 14 years ago
Location: Cochrane Alberta Canada

#12

Post by plenzen »

Here is what I did this AM.
Temp. -1C ambient and +2C +/- in garage. Truck has had a 15 hr + cold soak.
Battery voltage was 12.8. Initial voltage to GP #1 started at 9.8 and then climbed to 10.7 for 15 seconds. Dash light went out after 4-5 secs. After glow at 4.6-4.9V for 20+ seconds. ( I shut it off as did not want to overheat my air heater)
In regards to your question about the "Phantom Thermo Resistor."
In my manual there are 8 pages dedicated to the “Quick Glow System”. It lists times as affected by temp and there is a “dropping resistor” as well as the temp sensor located in the cooling system. The “dropping resistor" is located at the rear of the intake manifold behind where the EGR valve would go. (No EGR on the Canadian SD25). There is a two wire plug that comes from that resistor with? 14ga. wire (metric equivalent). The resistance between the two terminals at that resistor should be “approx” 0.3 ohms (can’t make that omega sign). There are also some voltage and resistance checks that can be performed on the timer unit as well as times that vary with temp etc. Voltages listed are all “Approx” with +/- 1 – 1.5 V.
All that being said
I think Al is probably right (he usually is) and you have a glow plug issue someplace.
Try this.
Take out one of the plugs (if you have the VE style pump then #2 is easiest). Get a piece of 14 ga. with a good connector on the end you can tighten with the nut. Ground the plug threads to the
– term and touch the end of the wire to the +. See how long it takes the end to glow. It should be just the tip that glows for the best starting. If it takes longer than 3 – 5 seconds to get red hot then you may want to consider a different set of plugs. DO NOT LET IT STAY RED TOO LONG AS YOU MAY BURN IT OUT. You mention that you were using a push button before and were able to keep the system on longer using that and the OE system had been bypassed. Perhaps the plugs you have in there now are of the slow burn type. What is the voltage rating stamped on the plug?

Paul
Retired Pauly
Problem with being retired is that you never get a day off.
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#13

Post by CooperativeRoots »

I'll try testing/replacing the plugs first as suggested. Are the plugs supposed to have washers on them where the glow plug wire connects? Some of mine do and others don't, not sure if they are necessary?

As for the thermoresistor... my book only has 6 pages dedicated to the glow system, so it sounds like the systems are different btw your '87 and my '84. The only components in the '84 related to the glow plug system are the 2 relays, the 4 plugs, the glow control unit (aka glow timer), the glow indicator lamp, the 0.1ohm dropping resistor, and the water temperature sensor. Interesting that they changed designed btw '84 and '87.

I still agree with asavage that there is too much voltage drop leading up to the plugs, I'll have to test the relays to see if their connectors are corroded or something.
Any advice on how to clean up these spade type connectors to get a better connection?

thanks much for all your time,

zack
1984 Nissan 720
SD25
Running ASTM-certified B100 for 5 years
cooperativeroots.org
plenzen
Posts: 869
Joined: 14 years ago
Location: Cochrane Alberta Canada

#14

Post by plenzen »

I think they are supposed to have flat washers for them to sit against and locks at the front with that large nut. Some plugs have a larger flange at the back of the terminal to allow more surface contact, those type do not need ( in my poinion) the flat washer at the back, but as much surface contact with the connector on the bus wire I think is best.
Brass brush and some baking soda and water I think. Dielectric grease afterwards to prevent further issues.

Good Luck

Paul
Retired Pauly
Problem with being retired is that you never get a day off.
1987 D21-J SD25 KC
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CooperativeRoots
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#15

Post by CooperativeRoots »

Ok, I replaced the glow plugs and you are right that the Nissan plugs were actually made by NGK. The old plugs had a bunch of what looked like carbon deposit built up on them. Not sure if this is normal. The new plugs make it start significantly easier now when cold. I also found the battery is only at 12.4V, so I'm going to try an AGM charger to see if it can be reconditioned and help with these problems (it's an Optima Redtop). I still suspect some high resistance in the wiring so will continue looking into that. In the meantime, I just wanted to post this update and thank everyone for the help.
1984 Nissan 720
SD25
Running ASTM-certified B100 for 5 years
cooperativeroots.org
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