Glow plugs - installing an in-cab switch

[Quack_Addict]

I did a search and didn't come up with a whole lot to help me out (most of the topics I saw were pre `84)...

I have a 1987 Suburban, originally outfit with a 6.2L that I now have a 6.5L crate engine in. The glow plugs cycle occasionally - it seems the plugs only come on when it is warm outside but don't when it's cold. As an added bonus, if I do manage to start the engine, the glow plugs will cycle... sometimes... but only if the engine is running.

The relay is on the back side of the driver side head, so I am guessing it is a newer style relay. If I understand correctly, the relay actuates from ground and not +12V. Is it as easy as figuring out which wire is the actuator and running a switched ground wire to it or do I need to install a switched, grounded relay? Please forgive me for my apparent lack of electrical knowledge; I'm a mechanical engineer ;)

If a relay is needed, I have several new hi-current relays for my Western snow plow that I think should fit the bill.

Thanks for any help.

[CleviteKid]

Hello Quack,

The first recommendation of TheDieselPage.com is to get your factory glow system running properly. If you go to the on-line troubleshooting guide, Chapter 13. 1985-93 Glow Systems (http://www.thedieselpage.com/members/guide13.htm) you will find what you need to get it working correctly.

You are correct, for you system you will need another relay in parallel with the glow controller if you want a manual override. Go to Chapter 12. 1982-84 Glow Systems (http://www.thedieselpage.com/members/guide12.htm) in the Guide to learn about the earlier system; you just need the relay part, not the glow controller.

I am a mechanical engineer too, but these days with all the electronic instrumentation and control, that is a weaker and weaker excuse for not playing with electrons.

Dr. Lee

[Quack_Addict]

About a week ago, I installed a different glow plug controler from another engine. I figured that even though they are both used; chances are one is good. Well, the other controller performs the same as the old one did - no glow plug illumination at first but if I do get the engine running, the plugs will cycle a couple times for a second or two.

Last night, I swapped the glow plug interrupters between the engines - again figuring one of the two used would be good. No difference.

As a last ditch effort to see if the interrupter is the culprit, I ran a jumper wire between the 2 pins on the interrupter plug - still no difference.

The fuses in the fuse block all show continuity.

I got some time after work today to spend troubleshooting the glow plug system in more depth. I used the article "Chapter 13" as a guide. Here's what I came up with...

I have power to the controller. Batteries have charge sufficient to spin the engine up to starting speed.

One difference I noted is that the "double heavy red wire" on my engine is actually two orange wires w/ black stripe that feed into what appear to be fusible links with smaller gauge dk gray wires going to the controller. No power here, no matter what I do.

Pin A: Not used
Pin B: Is this applicable to the problem I'm having? As I read, this is only for post-start GP illumination.
Pin C: Should have power here if the GP's illuminated, but that is the root problem.
Pin D: Good... power with key on.
Pin E: Good ground

Basically, this leads me to question the controller itself - but is it really that likely both controllers I have are bad? I have I don't want to spend $90+ on a new controller/relay if it's not the problem child; then be stuck with a part I don't need and I can't return.

Help? :confused:

[dieselbegreat]

Sounds like you only have afterglow, but no glow. I know the Haynes manual goes into great detail about this in their Glow Controller troubleshooting section. I think you may have a wiring problem, but I'm on the road right now and don't have the manual with me. Sorry. :(

[Quack_Addict]

I wired in the snowplow relay a couple days ago and it works great with a push button switch. I mounted it onto the firewall right above the GP controller, behind the air cleaner so it won't be a big deal to convert back to the stock system when it gets warmer out to mess with it.

The GP system was working perfectly until this past October when it started acting up. If there is a wiring problem I haven't been able to find it yet.

Seeing how everything is working well with the new relay I think the issue may be in the old controller - it just seems strange that both used controllers I had in there did the same exact thing. I guess I'll have to invest in a new relay/controller some time soon and go from there.

Thanks!