1985 4.3 Olds Diesel - Glowplug burnout

Hello all-

I'm not new here, but its been nearly a decade since I have logged in and had to re-create my account. I realize I am posting in the 6.2 forum, but I am hoping there was somebody with a few grey hairs that has some experience with these old 4.3's. I am really struggling with a sweetheart 1985 Olds 98 with the 4.3 diesel w/ 49k miles that I recently picked up. This little gem was a 1 owner from an elderly couple and is a true beauty. I cannot brag enough how nice the car is. It is nearly what I would consider museum quality. I love the computer voice that reminds you when the "lights are on" or 'the keys are now in the ignition". Its marvelous!

So anyway, I have an issue. An issue I created and now cannot resolve. So I serviced the fuel filter and had trouble getting the air bled out and the engine started. I did get it running, but I drained the battery in the process and had my battery booster on it. I forgot on these old girls that you cannot do that, as it would somehow backfeed through the glowplug system and burnout the glowplugs. Which it did pop all 6 of them. So, I replaced all 6 (which the rear bank of these is a real bear to get to) with #12 AC-Delco glowplugs and replaced the battery with a new one, fully charged. The plugs cycled as I feel they should and started like a champ. After a short 5 mile drive, I popped the hood, removed the glowplug wires and ohm check the plugs. Somehow I now have another set of failed glowplugs. I cannot figure out what caused this again. Things to note:

* While I was driving, the "Wait to Start" light never illuminated
* These 12G Delco plugs are failing. Am I using the correct plug for a 1985 4.3?

Any idea? The 12G plugs are getting hard to find and its getting costly to replace them. The car is just too unique to let is go. I would like to resolve the issue and show it off.

Off topic...there is a sticker in the lower/left location of the windshield that says "GM Program Vehicle." Any idea what this sticker means? Just curious.

Thanks in advance fellas.

Welcome back!

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Diggin' up bones. I love it! Early GM Diesel vehicles (4.3L and 350/5.7L) are becoming more and more rare these days. I only see them (running) on a rare occasion any more. You have a very nice find, one I wouldn't pass up. It seems, if memory serves, the "GM Program Vehicle" label suggests it was originally "issued" to a GM executive at the time it was new. They were issued new vehicles for a short period for evaluation, then exchanged for another when that period expired. I don't know what they did with them after that. There may be other possibilities, but I don't recall any.

Glow plug issues. All Diesels of every era had/has issues of some sort. The 4.3L and 5.7L engines used the 12G plugs. They are essentially the same as current 60G plugs, but longer. The early heads can be modified to accept later plugs, but, unless there's a specific need (such as compatible plugs become unobtainable), it's just easier and less expensive, overall, to pay up for the 12G's. They, as well as compatible other brands, are available. Shop around and you can find them for about the same price as modern plugs. The Navistar/Ford 7.3L (and perhaps the 6.9L, I don't recall) IDI engines used similar plugs, and most are compatible, which is an option. Use ONLY "thermistor" or "self-regulating" plugs, or plug tip swelling may become an issue.

If you're regularly burning plugs, the problem is likely the control. The GM "Wait to Start" or "Glow Plugs" lamp is powered by the actual glow plug rack power, on non-computer GM Diesels. Some of them don't illuminate during the "afterglow" cycles. If the lamp is on, the plugs are getting power, or are supposed to. If you never see the lamp, but the engine starts (plugs are getting power), the instrument panel lamp is probably failed, or the PCB that holds the lamp is failed (not too uncommon, unfortunately). It is possible the back-feed power to the lamp is interrupted, somewhere, between the controller harness and the panel. Another possibility is the GP controller, itself. If it isn't already using one, you should upgrade the controller to the 1985-1993 6.2/6.5L controller. They are readily available and relatively inexpensive. Another option is a manual glow control. A simple momentary switch to a relay to power the plugs. Not very uppity for a luxury-class vehicle, but it works.