I've got a 84 diesel pup, and I'm getting 6 volts to the glow plug bus bar, but only for about 1 second, then it shuts off, no matter whether the engine is hot or cold. I believe the problem is in the glow plug controller, and the only place I can get one of those is thru the dealer and they want $125 for it.
Is there a way to bypass the controller and run the glow plugs manually without burning them out?

any help here would be greatly appreciated

thanx

Sheepboy--

If the glow is on only briefly with a cold engine, I can think of three possibilities:

--- One or more glow plugs are burned out. The glow controller will shut down very quickly if it does not see the normal glow current, which you would not have with a plug or two burned out.

--- The wiring from the battery thru the fusible link and the relays is corroded or loose. This may limit the available current to the glow bus and then the controller would shut down prematurely as in above.

--- The engine temperature sensor for the glow system is faulty. You can test for this by disconnecting the bullet connector to this sensor near the thermostat, a yellow wire I think. This will cause the glow controller to think that the engine is cold.

But, I cannot see how you would have 6 volts on the glow bus. The voltage here should be about 10 or 11 volts.

Unless you are measuring the voltage with the key in the cranking position, in which case the 'low glow' rely would be supplying a small current to the glow bus via the dropping resistor. I have never measured this voltage but it would be much lower than the 10 to 11 volts as above.

Check this stuff out before buying a controller as I have found these QOS boxes to be pretty reliable.

Regards--

Paul

PS-- Sure, you can use a pushbutton switch to operate the 'hi glow' relay and bypass the controller yourself. Actually, I recommend this even if the controller is working because if one glow plug burns out on a cold day you will have a very hard time to start as the controller is not smart enough to glow the remaining three.

i was testing voltage w/ a multimeter & key in 'on' position, as soon as the key comes on i see 6V, then it drops off to 0

i tried running a switch straight from the battery. BAD IDEA, cooked all 4 glow plugs, i'll get 4 new ones, then try some of your ideas.
I believe, tho, that the glow plugs are not meant to handle more than 6V, thats y the switch fried them.

on the plus side, it does start just fine w/ starting fluid, as the glow plugs are currently disconnected, but its kind of a pain to have to open the hood and unscrew the air cleaner cover to spray in the fluid. veggie oil also works <img src="/forums/images/graemlins/lol.gif" alt="" />

thanx for your help

Deep, Deep gasp!
Starting fluid is not a good idea. Since you ahve no control over the a precise amount injected/ nor the timing the engine can "auto accelerate" beyond the max allowed RPM.
I would respectfully suggest you not do this.
Eric

Sheepboy--

kravdraa is right. Starting fluid is a no no with indirect injection engines as the mixture is very likely to ignite way too early in the compression stroke which can break rings and pistons. I don't know what veggie oil will do for starting.

Re the manual glowing of the plugs, I forgot to mention that one should glow them for only a few seconds. Like three, four or five, depending on the temperature and how hard the engine is to start. If the temperature is cold and the engine starts but runs very rough, you can cycle the glow plugs on and off for a few seconds until things even out.

If you used a toggle switch, chances are that you left the plugs on too long, which will burn them out. Using a push button to operate the main glow relay works OK as long as you don't glow too long.

The plugs are, in fact, marked as six volt plugs but Isuzu (and others) feed them with twelve volts to hasten their warmup time. Maybe not such a good idea but that's what they do.

I just went out and hung a voltmeter on my glow bus and did the normal glow cycle. The voltage does start at about 7 volts and then quickly ramps up to around 11 volts. This can be explained by the positive temperature coefficient of the glow plugs which causes them to draw a very large current when first connected but as they warm up the current declines, usually to about 10 amps per plug after say 5 seconds.

So, if your system is staying on only 1 second 6 volts is probably about right.

Paul

after i disconnected the temp sensor, it started at 11V, then dropped off, so i think it probably is the temp sensor

i was using a pushbutton bypassing the entire glow system to momentarily glow the plugs, but i think if I go that route, I may put in a transformer in the circuit to drop it to 6V, or use 12V plugs, so they won't burn up immediately

if i cant get the diesel to start, my only other option may be an engine swap to a gas engine for better reliability and performance, but only as a last resort, as i do like the diesel, despite all the trouble its given me

Sheepboy--

If you have disconnected the glow plugs the voltage will certainly be in the range of 11 or 12 volts as no current will be flowing to drop the voltage.

Transformers will work only in AC circuits so not good for this problem.

This engine (even with it's quirky glow system) is usually very reliable. If you can get this problem sorted out you will probably be happy with the engine.

Paul

<img src="/forums/images/graemlins/smile.gif" alt="" /> as soon as i disconnected the temp sensor, it started perfectly. <img src="/forums/images/graemlins/smile.gif" alt="" />

except for the injection pump, which failed @ 170,000 mi, and the box being ready to fall off at any moment, its been very reliable, (and chicks dig it) <img src="/forums/images/graemlins/lol.gif" alt="" />

at one time i was considering dropping in a gm 350, but then gas hit $2/gal, then that didnt seem like such a good idea

thanx guys

Sheepboy--

Glad you found the problem. But you'll want to get a good QOS sensor in there. Otherwise the plugs will glow every time you start up, cold or hot and this will shorten their life.

'at one time i was considering dropping in a gm 350, but then gas hit $2/gal, then that didnt seem like such a good idea'

I sure agree with you on keeping the diesel engine.

Paul