Gasser to Diesel swappers

[asavage]

The GP Relay 2 and the dropping resistor run the GPs at a reduced voltage while cranking and after the engine has started. That system reduces cold diesel misfire and some attendant cold smoking, and it works. You can use "any" heavy relay for GP Relay 2, even another GP Relay 1. The dropping resistor -- damn, I almost pulled one at the JY last weekend, but figured I'd never need it. It's kind of special.

The GP Controller might be best done aftermarket, rather than OEM. Several of use Maxima diesel folks are finding problems with the OEM timing curve shifted after all these years. I've got a spare controller, and want to look into testing some of the components someday.



Other afterglow systems merely cycle the main GP relay ON and OFF to provide the same effect as Nissan's afterglow system.

You will want to look at the Addy LD28 Bus Bar retrofit upgrade too.

[DMS]

I will have to recalibrate my tach but its a $14 solution.

Thanks to Mega Squirt

[DMS]

Here comes a lack of knowllege questionaire

So the glow plugs are needed to help warm the combustion chamber while the engine is cold.

At what point do they turn off?

Are they on constantly during this time?

I keep reading about the After Glow System. Does the stock GP unit cycle the plugs on and off after the engine is at opperating temp? if so why?

I would like to try and run my engine in the car and was wondering if I could use a switch to power one relay and just turn it off after it warms up. This way I could at least run the engine until I get the other relay and GPU.

Thanks

[asavage]

There is a very good description of the GP system operation in the FSM.

So the glow plugs are needed to help warm the combustion chamber while the engine is cold.

At what point do they turn off?

The first stage (full battery voltage) times out eventually -- I do not have the chart memorized, but it's about eight seconds on my '82 at 50°F.

Are they on constantly during this time?

Yes.

I keep reading about the After Glow System. Does the stock GP unit cycle the plugs on and off after the engine is at opperating temp?

No. You are thinking of rigs like Ford and GM: they do that; the LD28 does not. Ford & GM also use 6v GPs that will fry if you cross your eyes at them, and you never want to try to manually control them. They require cycling to stay alive.

if so why?

To improve the stability of the cold idle (prevent cold misfire) and improve cold emissions (same reason) and reduce cold smoke (same reason).

I would like to try and run my engine in the car and was wondering if I could use a switch to power one relay and just turn it off after it warms up. This way I could at least run the engine until I get the other relay and GPU.

Yes.

On the LD28 Maxima (NOT for other Nissans): Key ON, the main GP relay AND the afterglow relay are ON for some period -- until the engine starts or until the timer times out. When either of those conditions occurs (engine starts or GPC times out), the main GP relay turns OFF, the afterglow relay continues ON for some longer length of time -- this one is even more variable depending upon coolant temperature.

You can power the GPs manually, but only the afterglow phase is truly "safe" to manually control, because it's at reduced voltage to the GPs via the dropping resistor. If you don't exceed maybe nine seconds on the main GP (full battery voltage to the GPs), you will probably not fry a GP. I think you could probably safely go twice that long, but I am not going to be the pioneer on this one.

The afterglow phase is safe to run nearly forever, because it runs at reduced voltage.

Get a FSM or read the wiring diagram and/or wiring schematics I posted links to above. The FSM does a good job of saying what I just typed.

[83_maxima]

I manually glow my plugs every day via a PO installed "button".

I cycle the plugs 2-3 times in the summer and maybe 4-5 or more in the winter depending on how cold it is.

I put in a NOS set of Diesel-Kiki (Zexel) GPs and tested them all before I put them in. They all take 7 seconds to glow bright red. Subsequently, I glow for 12-12-17, crank. Typically always starts. If not, I cycle them quick for 7 or 8 seconds and it will start.

The plugs I pulled out of the car were Autolite and the woman I bought the car from was sitting on the button for as long as 30 seconds she said. I was able to get them all out, none had mushroomed and all worked - glowed red in 7 secs just like the Zexel plugs.

I have a generic relay running from the battery, through the dropping resistor, then to the GP bus bar. It works, but there is still a reason why it does not fire off immediately with the factory glow system connected, like my parts car, so it is an imperfect soultion at best.

[asavage]

Ben, I just want to get this clear: is your button toggling the main GP relay or the afterglow relay?

With those cycle times, I'm thinking afterglow. I use 15 secs. of afterglow to get mine fired up after a 17 mi. drive and 35 minutes cooling, otherwise it I have to crank a long time anyway.

[DMS]

So maybe I could use a thermotime switch like the one used on the gas maxima to control the injector fan to switch a low current relay during cold and then when it gets heated I could have that relay switch to another relay that utilizes the low voltage GP relay and just have that on a switch. Im going to have to find out at what temps that thermo time switch opperates still and what the time limit is. It might not be anywhere what I need but its worth a look see.

Ray

[83_maxima]

Ben, I just want to get this clear: is your button toggling the main GP relay or the afterglow relay?

With those cycle times, I'm thinking afterglow. I use 15 secs. of afterglow to get mine fired up after a 17 mi. drive and 35 minutes cooling, otherwise it I have to crank a long time anyway.

Neither #1 or #2. Aftermarket "Ford" 4-pole relay. Takes it's juice straight off the + terminal and runs thru the dropping resistor before going to the bus bar.

Like I mentioned before, I've got a problem. Maybe w/ 1 or 2 cylinders with low compression (I need to invest in a diesel compression tester to verify). I can often hear several of the cylinders trying to fire, but it seems as if a couple are slow to come up. The additional cycles bring them up.

I'd like to test both engines side by side so I can try and determine what is going on. I thought my hard starting was typical until I bought that parts car. It sat for a week (last) and when I went to fire it up over the weekend it glowed for 5 seconds, light went out, cranked for 1 revolution and all the cylinders came up instantly. I'm halfway tempted to swap them, but I think I should spend some time troubleshooting before I invest all of that time.

[goglio704]

What you describe would be the equivalent of afterglow. If I read what you wrote correctly, the power to the plugs always goes through the dropping resistor and would be at reduced voltage, current, and heat as a result. You could install another button and drive another relay which would deliver full voltage directly to the plugs or you could keep the single button and run it through a single pole double throw switch which would serve as a selector choosing between full or reduced voltage.

Also, the term 4 pole relay refers to the number of isolated current carrying paths and corresponding contact sets. It does not refer to the number of connections on the relay. In other words, your 4 pole relay is almost certainly a single pole relay.

[83_maxima]

This is the relay I am referring to (no it in not a 4-pole)


I'd like to know more about the single pole double throw switch. I've never heard of such a thing before.

The odd thing with this car is that I restored the OE glow system to working condition. Re-connected the system. Put a tester on the bus bar to show me when the plugs are glowing and I get 13 seconds of glow time with a cold engine on an average day (maybe 70 outside). But the car still won't start. If I try to cycle the system on and off (IIRC) it will glow for a reduced time each cycle , but was locking me out in a sense when I would try to cycle, cycle, cycle.

I imagine I could probably connect the relay direct to the bus bar with minimale effort. Might try it to see what happens.
The dropping resistor also gets EXTREMELY hot with all of this cycling and that is something I am not comfortable with either.

[asavage]

A Single Pole Double Throw (SPDT) switch has three positions: center, up, down;
and three terminals: Top, Center, Bottom.

[later edit: whoops: the center-off position for a SPDT is optional, but assumed for this application. Sorry 'bout that.]

Center = all terminals open
Down = Center -Top connected
Up = Center - Bottom connected.

You can buy a SPDT with a spring-to-center toggle, which is what you want: when you let go of the toggle, it returns to center (off). They are also available without the spring-to-center, and that would be undesirable in your application, probably. Although I can't quite envision actually leaning on a switch (afterglow) after the engine is running, that's better handled by a timer.

You might connect a SPDT switch like this:

Battery -> Fuse -> SPDT switch Center terminal

SPDT switch Bottom terminal to Main GP relay
SPDT switch Top terminal to Afterglow relay

Lift switch toggle for Main glow; push toggle down for afterglow.

[goglio704]

I had a neat little schematic drawn in paint, but I can't seem to log on to Imageshack right now to host it. Oh well, Al summed it up nicely. I think a two position switch with the same contact arrangement is also a SPDT switch, but it lacks the center = off position.

[goglio704]

OK, here's my schematic...

[asavage]

Call me old-school, but I've always found that particular style of schematic representation too easily confusing. I know what that circuit is supposed to do, and I had to stare at that for about fifteen seconds to recognize that you've got the relays broken into two "functional block" representations. I much prefer the older method that uses an actual symbol for a monolithic device, then brings the wires to it, rather than putting half of a device's functions on one rung, and the other half on another.

That reminds me a lot of having to work with late-model VW's electrical diagrams (blech). That style of diagramming is convenient for the designer to draw, but a lot less useful if you don't know how a circuit works or should be wired, and have to try to figure it out from that info.

If I had an electrical symbol library loaded for ACAD, I'd draw up something, but I am just too lazy, and besides: anybody who can contemplate modifying an OEM thermotime switch for timer duty doesn't need a schematic anyway; this circuit is too simple.

[goglio704]

I guess it is all in what you get used to. To me, a short little ladder diagram like that is second nature.

I don't know the correct term for the type of drawing you prefer. My mental shorthand calls it a pictorial representation. If you are dealing with real world devices with numbered terminals or a physical arrangement that lends itself to 2 dimensional drawing, a pictorial representation is a fantastic wiring guide and troubleshooting tool. I was just trying to represent a concept, and I'm terrible with Paint. I made a mistake too in not showing the momentary pushbutton to the left of the SPDT. Oh well, you get what you pay for - it's just a hobby...