Persistent cold start problem - now below -11 C / 12 F
 

Story ('85 300d, 105k miles, Rotella synthetic, car runs very well and started last winter without effort):

- October - replaced glowplugs with Bosch duraterms. Strictly a preventative -- old plugs of unknown age.

- Late November - intermittent 'no-glow' (no glow light illuminating, no relay engagement. Eventually found retaining nuts were loose on 3 of 5 plugs. Tightened nuts, problem seemed gone.

- January - onset of cold snap (-18 C / ~ -1 F) resulted in no start when car left for day at work, no block heater etc. No fuel getting to injectors. Ran through Diesel 911 additive to remove any moisture in fuel, replaced fuel filters after. Tightened clamps on fuel lines (found one very loose, assumed this contributed to fuel gelling). Never had time to test this out properly as extreme cold ensued (-26 C / - 15 F) so car was either left running (at work) or plugged in. Fired right up in mornings, after two glows, at home with block heater.

- Yesterday morning - only -5 C / 23 F, car not plugged in, was very surprised it would not fire after the first glow cycles. After two cycles, ran unevenly once started, like the glowplugs were tired.

- Last night - came out yesterday from work, -11 C / 12 F, was stunned when car took a lot of cranking to fire. Again typical of what I would expect from weak plugs, one or two pots fired first but had to keep starter engaged to get the rest going.

Checked when I arrived at work and I have 12v at the plugs with the relay engaged. Don't carry an OHM meter in the car.

Right now I am leaning toward replacing the glowplugs over the weekend.

What am I missing here?

Thx

Could be tight valves....valve adjustment is probably needed if it has been done recently.

Could be a single bad plug. My daughter's 84SD with a relatively new engine won't fire below about 20 degrees with one plug out. I'd also use PowerService anti-gel if temperatures were consistently that low.

Valves were adjusted in August. Usually tight valves will show up at even higher temps, in my experience.

I had not thought of the single bad plug angle, I was banging my head on how an entire set of plugs could be no good. Will check them with a meter tomorrow when cold.

The Diesel 911 I used is the PowerService product they sell here for ungelling fuel (you can get an even stronger one from heavy equipment dealers that guarantees complete degel in 20 minutes). I guess I could add more now.

I suppose I could try filling up somewhere else too, though I would wonder how the station I am using could have that much water in their diesel tank. They're relatively busy, and installed new tanks six months ago.

Do not replace the glow plugs again since they are recent. The problem is elsewhere. MY guess: air in fuel.

I would be willing to work with that, but where do I look?

I have tightened every fuel line clamp under the hood. There isn't any smell of diesel anywhere nor signs of a seep. The cigar hose is brand new. The return lines were done at the same time as the glowplugs.

The primer pump is the new style. Do they leak with age, like the old style?

Why would it start fine, with the block heater, if the issue is air in the lines? I would expect it to still need more cranking.

Do you have a clear line in line with the cigar hose? If you have solid fuel there at all times (including when the engine is off) then you have no air problems. If you see any bubbles after the engine starts you have air in fuel.

But, you do have one at home.

So, check all the plugs and see if any good info comes from the resistance check.

If not, the requirement from Roy is to pull all five and glow them in a vice to see what you have.

Last cause scenario it may be time for new injectors....perhaps one or two aren't spraying correctly.

Are your glow plugs getting power? That is an easy test even without more than test light.

OHM test
 

Checked with the OHM meter today.

Number 3 gives a different reading each time it's checked, between 4.2 and 8.6.

The other four are 1.1.

What I don't get, is how in this parallel system, one defective plug (other than #1) would effect the glow cycle like that. Can someone explain in 'for dummies' terms?

Just for insurance, I also dumped in more Diesel911 and filled up at the station I used last winter.

Thx

The 1.1 ohm reading itself indicates a questionable glow plug. As for the inconsistencies, I'd question the quality of the battery powering the meter. Particularly with DVOM's, a weak battery will cause some pretty strange readings.

Clearly, #3 is toast.

Change #3 and see if the capability to start is improved.

If not, the readings of 1.1 ohms are at the very bottom end of acceptability and it might be time to pull them all and give them a bench test.

You did not mention if you cleaned the Carbon out of the Glow Plug holes before you installed the New ones?
Some Members have said pulling the Plugs and cleaning the Carbon out made starting easier.

I had a Glow Plug that Ohmed out OK but when I tested it over the Battery Terminals it got hottest in the Middle instead of at the Tip where it is supposed to be hottest. That meant the Heat was heating up the Cylinder Head instead of the Air in the Prechamber.

Did you unplug the harness from the relay when ohm testing? If you don't you can get funky readings.
I don't know now and why a single bad plug causes a no start condition. I was surprised when I discovered it happening on my daughter's SD. It happened at least twice on that car.

D'oh
 

Ah, someone reminded me tonight that you're supposed to cross the test leads first, then subtract whatever reading comes up from the test reading? That was missing from my extensive (cough) knowledge in this area.

Mine reads .3 across the leads, so therefore the four plugs actually measured about .8 ohms.

Yes, the harness was unplugged.

Question: I understand this test is supposed to be done on 'cold' plugs. The plugs were cold, as in not having been activated that day, but the block heater was plugged in. Would the slight amount of heat reaching the GPs alter the readings?

I doubt it. I'd swap out that one plug.

Hi Z The resistance in the plugs goes up as they heat up. The difference in resistance between 30-100 deg is negligible

For sure. I asked about the heater only because as I understand it .8 is still considered high for brand new GPs (well, depending on whose thread you read, anyway).

The meter is usually adjusted to bring this reading to zero before you measure.

Of course, if you have one of those newfangled digital gizmos.............:rolleyes:

Update
 

We've been in a cold snap and I have no garage, so I have not been able to see if replacing my single bad GP will have any bearing on my problems starting at under -10 C.

The weather 'warmed' to -10 C today on the nose. I did not use the block heater last night.

Sure enough, when I cranked it this morning I was getting fuel but no evidence of any glow. (Glow light illuminates and I can hear the relay click.)

I pulled the cap off the relay and unplugged the big connector. When I turned the key to the glow position again and tested the male pins for voltage I got nothing.

Turned the key off then on again and tried for voltage at the top right receptor on the small plug (I wasn't thinking on my feet when I switched off the key). Ok. Immediately plugged both connectors back in and waited to hear the relay click off.

Turned the key and the car started.

Now I am wondering if the GP that OHM'd out way high is just a red herring and I maybe have a temp-dependent problem with either the relay or the ignition switch.

I may try again later (still pretty cold working out there, with the wind chill factor).