after the 30 or so seconds the voltage at the glow plug relay pins drops from battery voltage to roughly 2.5 V (same V at all 5 pins). Should the voltage drop to zero? I checked after it had been running 15+ minutes. Does this mean the glow plug relay is beginning to fail. Should I give it a tap on the side?

thanks

p/s

i also discovered that you can, in fact, suck on the vacuum line to the ignition and shut off the engine. I'll be making a quick fix with a 50 ml syringe or vacuum bulb. (separate issue).

Insufficient data.

What year?
What model?

If this is an unmolested W123, W126 or earlier chassis model = you have an issue.

If this is an unmolested W201 or later chassis model = this sounds like odd (voltage) behavior of the relay extended glow circuit.

.

__________________
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sorry. it's an '83 300D. I have only owned it for a few months. After starting when cold I've been unplugging the connector to the glow plugs until I have it resolved. Either find a relay box or wire a substitute sytem.

If the Battery is good and was fully charged the Voltage should not drop below about 11.5 Volts during the time the Glow Plug Relay is on.

Recharge your Battery and have a free load test done at an Auto Parts Store.

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84 300D, 82 Volvo 244Gl Diesel

If the Glow Plug Relay is on all of the time it will kill a fully charged excellent used Battery in 30 minutes to an hour but that is an estimate

__________________
84 300D, 82 Volvo 244Gl Diesel

thanks. i know. I've had a problem with a previous relay which was intermittently not turning off the voltage to the glow plugs.

My question was if anyone has checked the pins on the relay box a few minutes after starting the car. To confirm if the pins register 0 volts after the cycle finishes; which is what i would assume it would do. For the time being I am treating mine as faulty and unplugging it after starting.

so... if anyone has a multimeter handy... and a diesel; I would be curious to know what voltage is measured at the pins of the relay box (to which the connector to the glow plugs attaches), after the cycle finishes.

On my box the voltage drops from 12.45 (battery voltage) to 2.75 V. Even after several minutes of the engine running, the relay still shows 2.75 V at the 5 pins. n.b., With engine running the battery is still receiving 14.5 V at idle. Don't fret the electrical system. I am solely curious to what voltage the 5 pins in the relay box drop to.

tanks

I'll take a wild stab. Perhaps you are placing the blk lead of your DMM on the BATT- post and you have a 2.75 V drop from the engine block to BATT-, when the alternator is putting out (like right after starting). Test that. If so, remove the ground strap from the tranny bolt to frame, sand, and coat w/ silicone grease. A common problem w/ aluminum. I found that issue when I cranked the engine once with the cluster pulled out and saw smoke coming from the speedo cable (was using that path to BATT-). Another test, stop the engine w/ the "emergency stop lever" and see if the 2.75 V goes away. If so, it isn't from the GP relay. I think it very unlikely that the glow plug relay could be partially closed. It is mechanical contacts that open and shut fairly definitely.

Re the vacuum "IP shut-off valve", it sounds like the valve works since you can "suck it to stop". First, check that you have proper vacuum supply (15"Hg or more). If not, your door locks also might not work, and your tranny shift points. If a good supply, the vacuum switch that scews onto the side of the key switch could be bad. That is uncommon, but they are cheap. More likely is that someone (me once) swapped the 2 nylon vacuum tubes to that switch. It is a SPDT switch, so getting the tubes correct does matter. The "pole" should go to the shut-off valve. The switch applies either full vacuum (other tube) or vent (open to cabin) to that tube. BTW, that shut-off valve cost >$120 from most sources. I bought a lot of no-name ones from a distributor and sold on ebay ~$70 ea a year ago, but they went real slow so either not many people need them or they prefer paying big bucks for the brand names (which could be from same factory). If no buyers make a warranty claim (none yet), I might pursue that again. One buyer did say it leaked vacuum slowly when he tested w/ a hand pump. I told him to replace the stop valve w/ a plug and see if that "leaks". Didn't hear back, so probably his pump or tubes were leaking (many people lack common sense). You can also just push in the stem, block the vac port w/ your finger and see if the stem holds in (if you remove valve from IP).

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thanks. For now the syringe is doing the job. The line is a straight shot to the shut off valve so it is working (I have another spare shutoff valve from the scrapyard as well). It seems to be the vacuum "switch" that attaches to the igition. Or else maybe I will get lucky and find the vacuum supply line to that switch just needs to be replaced (haven't had a minute to contort myself under there yet).

No drop in voltage from the block. For whatever reasons my glow plug relay pins drop from battery voltage to 2.75 V after the cycle. I'm still curious if any one has waited a few minutes and put a voltmeter to the pins (on the relay).

I have another relay box from the scrapyard that I will be checking it against but if someone wants to double check and report, it is much appreciated. I'd like to confirm that other people are getting zero (0) volts after cycle finishes.