Help with Glow Plugs

[AFC1]

Hi all- I have 2 1986 M1008s and both glow plug systems have their own issues. The first M1008 I got starts fine in cold/warm weather no real complaints there, but the glow plug system doesn't seem to have any after-glow. WAIT light illuminates, goes out, truck starts and light never comes back on. Rough idle at first, but clears up fairly soon. Don't know if this is a concern??? Also, top post at GP relay reads 24v, bottom post reads 12v-how is that? I have 24v coming into the relay and 12v going out? Seems strange to me! The second M1008 has a very noisy GP relay, but the GP system seems to work okay as well and this truck has after-glow, the WAIT light cycles a couple of times after start-up. The GP relay on this particular truck has 12v at the top post and 12v at the bottom post. What is going on??? Any info/comments would be greatly appreciated....

 

[Michael]

Have you read this thread yet?
http://www.steelsoldiers.com/cucv/20600-faq-thread-cucvs.html

There is something wrong with the first truck but it isn't that big a deal not to have the plugs cycle a few times after starting. It does help with rough idling but it mostly to decrease smoking. Does the cold idle advance work on truck number one?

The relay has 4 posts and the orientation is different depending on which relay you have. The wiring diagram with the color codes is in appendix f of the -20 TM. One large post should show 24v at rest and drop to 12v under load of the glow plugs. It is common to bypass the voltage dropping resistor and hook the relay up to the 12v buss in which case it will show 12v all the time. The other large post should show no voltage until the relay is triggered and then it should show the same voltage as the other post. The relay is feed 12v all the time to one of the small posts and is triggered by completing the ground on the other post.

 

[AFC1]

Cold Idle Advance works fine on the first truck. Is the second truck working correctly, even though there is not 24v going to the relay? Thanks for your help...

 

[mangus580]

Keep in mind... the wait light will NOT normally come on during an after glow.

 

[AFC1]

Really? OKay, maybe I do not have a problem after all. I will check the glow plugs themselves to see if they are cycling. This truck's wiring appears to be in decent shape and really not tampered with. Thanks a lot for your help!

 

[softboyled]

My wait light doesn't come on during afters. You should be able to hear the relay switching and see the VM drop when they occur, though.

The wait light seems to have only a slight relationship with the actual GP cycle...

 

[dieselpony]

It does help with rough idling but it mostly to decrease smoking.

x2
Have manual glow plug operation (without after glow) for years now and all I can say is that a rough idle after start up is mostly due to fuel delivery. Temperatures get as low as - 20° Celcius here. Smoke is another issue though . . .

Walter

 

[AFC1]

It is not seriously rough idle, just lasting maybe 8-15 seconds, that's all. I will check out the fuel delivery system thoroughly- thanks for the advice...

 

[corelokt]

That rough idle sounds like the engine getting up to running temp in the cylinders. The cylinders have to be hot to ignite the diesel correctly. My tractor does the same thing, runs crappy, then suddenly smooths out when it's ready. My cucv has a bad glow plug relay right now, and is doing the same when it starts also.

 

[dieselpony]

When 2 of my glow plugs were not connected, i also did see a somewhat rough idle for about 10 seconds.

Walter

 

[AFC1]

Found a poorly repaired glow plug wire on #7 cylinder- the old 'twist the wires together with 1/2" of electrical tap trick'. Repaired it correctly and it does seem to run slightly better. Summertime will see new glow plugs, controller, relay, etc. Thanks to all for the great help! I truly appreciate it-