Can Glow Plugs Only Function Partially??

WolfgangVW

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Hi there. So quick question. Can glow plugs be worn or partially bad without throwing a code???

My situation is unique. Long story short is i have a bad glow plug stuck in the head, so only fire on 3 last winter and this. Now it's super cold here. I put a new oil pan heater on a month or so ago, and have a battery blanket. Anyway it seems as if with them plugged it still struggles to start. Like preheat mulitple times etc and cranks long. I scanned thinking perhaps i have two bad plugs, but still only get one fault on the plug i know is bad. Is it possible that some of the working plugs aren't heating to 100% capacity without throwing a code??

Any input is appreciated. I realize there's the potential the pan heater isn't as good as the last, tho it is the equivalent of the one i replaced. Basically how it's starting reminds me of a time last winter it was cranking on 2, i thought i had 3 but the CEL is always on because of the one bad one so i initially suspected other issues.

This all being said i know i should throw an inline coolant heater in, and i had planned to but you know how it goes lol. As well if it sits for 6 or 7 hours it's not too bad plugged in, but 12+ it's dicey. In perspective it's like -30C or so here, aiming for -33C (-43C with windchill). thanks in advance!
 

mjydrafter

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You can check the plugs with an ohm meter. That will only tell you the plug is okay. (once you know that they are okay you can move on to the wiring/relay.
 

oilhammer

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There are just too many to list....
Other things beside the glow system can cause a long crank time and hard starts. Poor starter (slower than ideal crank speed), loss of fuel prime (leaky pump), poor nozzle condition (poor fuel atomization), low compression (worn engine), bad temp sensor info (fuel, coolant) to ECU, timing incorrect (botched timing belt install), etc.

That said, with those temps, it is going to have a really hard time starting without some sort of aid anyway. The coldest I have had to start one of my ALHs at was about -20 C, and it took three long preglows and about 5 seconds of cranking, then some coughing and sputtering for a second before it finally lit off. It was not happy. But it DID start. And that is with EVERYTHING in perfect working order.
 
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Genesis

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-20F? I've had my TDI in that, along with some gas vehicles -- but I sure try to avoid it.

I had my TDI in -15F once with only ONE working glow plug (harness issues.) I gave it two "pre-glows" before attempting to start, and it lit off -- but it didn't like it, as it fired on one cylinder and blew a lot of white smoke for the first 15 or 20 seconds. Much more important in that sort of temperature is that the battery *and all wiring, plus the starter* are in excellent condition. If you can't get sufficient cranking RPMs it will not fire - that's the biggest problem when it gets REALLY cold and you get hosed all the way around as batteries lose amp capacity as temperatures go down while the viscosity of the oil goes up and thus so does resistance to rolling the engine over.

BTW wind chill is immaterial to mechanical items, other than cooling them off faster to the ambient temperature after they've been used.
 
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pdq import repair

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I have seen glow plugs fail and not code. They do not glow properly or hot enough but are still there electronically and ohm out good too.

The only reliable test i have for a glow plug is to pull it out and hook it to power and watch it glow. You get a good idea of good and bad as you observe them. I have seen them start to glow at the base and not get out to the tip but still draw the same amperage as a good one.

Don't buy ebay or walmart glow plugs if you need them, use only Bosch or Beru or a reputable factory brand.
 

wonneber

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I prefer to test the glow plugs with an amp meter.
They should all be the same amperage.
How old is the battery and is it the correct one, group 94R I think.
Does it seem to be cranking fast enough?
There's a wire on the starter going into the starter. It's been know to corrode with time reducing the power getting inside the starter causing slower cranking.
Do you see RPM when you crank the engine?
Hope you have a garage to work in. :)
 

realslimshaver

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If you do have a bad glow plug that's hard to remove consider using your torque wrench on reverse to minimize chance of brakage(forget torque off hand think other threads have mentioned it. . Warm engine up full and have hit it with -51c electronic cooler spray available at better electronic hobby and supply stores has worked for me replaced myself . Add electrical dielectric grease after cleaning up your electrical connections with Emery cloth or wire brush
 

maxmoo

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Tis the season......

A quick and simple way of checking that glow plugs are heating, on a cold snowy day is to throw a little snow on each glowplug and then glow the plugs with the ignition switch without starting the car. You will see the snow starting to melt around the base of any glowplugs that are working.
We regularily start our tdi's no problem down to about -25c without being "plugged in".
We do use oil pan heaters to assist in very cold temps, not usualy necessary but they definately help.
As Oilhammer said above...."Other things beside the glow system can cause a long crank time and hard starts. "
 

Curious Chris

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Well I had a Peugeot 505 STD and I pulled the glow plugs and checked them with a spare battery and the tip did not get red hot (oh I had new glow plugs and the tip and part way up was glowing). My theory is that internal corrosion lowers the effectiveness.

I do replace my glow plugs about every 4 years. X2 on Oilhammers quote
 

Vince Waldon

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On a -30C Alberta morning the shortcomings of an couple hundred watts glued to the outside of the oil pan vs 750-1000W directly coupled to coolant circulating thru the entire block are gonna be sadly apparent.

/thread. :) :)
 

WolfgangVW

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Other things beside the glow system can cause a long crank time and hard starts. Poor starter (slower than ideal crank speed), loss of fuel prime (leaky pump), poor nozzle condition (poor fuel atomization), low compression (worn engine), bad temp sensor info (fuel, coolant) to ECU, timing incorrect (botched timing belt install), etc.

That said, with those temps, it is going to have a really hard time starting without some sort of aid anyway. The coldest I have had to start one of my ALHs at was about -20 C, and it took three long preglows and about 5 seconds of cranking, then some coughing and sputtering for a second before it finally lit off. It was not happy. But it DID start. And that is with EVERYTHING in perfect working order.
Thanks OH. Ya i i totally get there are other factors. In perspective the car starts great all around, the cold starts seem to be directly related to the extreme cold now. The colder it gets and longer it sits the more effort it takes. And knowing i only have 3 glow plugs at best is an issue. The battery and starter seem good, really the only reason i probably get it going is the fact that i can keep pre-heating and cranking til it fires. The heated battery blanket actually works wonders for this in cold temps. Basically your description of you starting your car in -20C , is how mine starts at -30C with the BB/OPH plugged in, i just have to repeat in 3x . The GP cycle isn't crazy long, that's why maybe i think poor GP performance. I suppose CTS could do this too but it will cycle GP's super long if the OPH isnt plugged in.

But thanks for the response, realistically if i'm getting a 15 yr old diesel going in -30C or colder with 3 GP's i probably shouldn't whine too much!
 

WolfgangVW

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-20F? I've had my TDI in that, along with some gas vehicles -- but I sure try to avoid it.

I had my TDI in -15F once with only ONE working glow plug (harness issues.) I gave it two "pre-glows" before attempting to start, and it lit off -- but it didn't like it, as it fired on one cylinder and blew a lot of white smoke for the first 15 or 20 seconds. Much more important in that sort of temperature is that the battery *and all wiring, plus the starter* are in excellent condition. If you can't get sufficient cranking RPMs it will not fire - that's the biggest problem when it gets REALLY cold and you get hosed all the way around as batteries lose amp capacity as temperatures go down while the viscosity of the oil goes up and thus so does resistance to rolling the engine over.

BTW wind chill is immaterial to mechanical items, other than cooling them off faster to the ambient temperature after they've been used.
Thanks Genesis. Ya i know windchill is a "feels like" temp. But in my opinion it makes a difference as as you said the vehicle drops to the ambient temp quicker and remains there for a longer period. So when a vehicle sits at -35C for 10hr vs 6hr it makes a difference in my experience. Not to mention a howling wind in extreme cold most likely makes my oil pan heater less effective.
 

WolfgangVW

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I prefer to test the glow plugs with an amp meter.
They should all be the same amperage.
How old is the battery and is it the correct one, group 94R I think.
Does it seem to be cranking fast enough?
There's a wire on the starter going into the starter. It's been know to corrode with time reducing the power getting inside the starter causing slower cranking.
Do you see RPM when you crank the engine?
Hope you have a garage to work in. :)
What are the specs when testing amperage?? Ya seems to crank hard, battery is OEM correct one about 4yrs old, with an electric battery blanket. In a prior post i mention it cranks hard, probabaly the only reason i even get it going
 

WolfgangVW

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On a -30C Alberta morning the shortcomings of an couple hundred watts glued to the outside of the oil pan vs 750-1000W directly coupled to coolant circulating thru the entire block are gonna be sadly apparent.

/thread. :) :)
Absolutley!! I swore to myself last winter come summer i would just throw an inline coolant heater in............. but i didn't cause i'm dumb!! Soon enough.

I see your local and given the -35C tonight i might stick my halogen work lights under the engine bay for a bit to try and help tomorrow! I think it would start anyway but any help is nice!! Thx VW
 

maxmoo

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On a -30C Alberta morning the shortcomings of an couple hundred watts glued to the outside of the oil pan vs 750-1000W directly coupled to coolant circulating thru the entire block are gonna be sadly apparent.

/thread. :) :)
With all do respect...you have obviously never used a properly installed oil pan heater........I have used both. :)

The OP has other issues besides temp. A circulating coolant heater should not be used to cover up other issues.......there will come a time when the car will sit in the cold without access to being pluged in. That's when a properly tuned and maintained tdi will start anyway, and one with issues will leave you stranded.
 

Vince Waldon

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With all do respect...you have obviously never used a properly installed oil pan heater........I have used both. :)
With all due respect my current BEW came with an oil pan heater. :)

My point was that watts are watts, and oil pan heaters have significantly fewer of 'em, which can come into play during temperature extremes like the weather this past week.
 

Vince Waldon

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i might stick my halogen work lights under the engine bay for a bit
Yup, got my dad's BEW going that way one frosty Edmonton morning when he was visiting from BC. 500W of radiant heat..in my case under the engine pointing up... and two hours later she started on the first twist. :)

That said, I drop-shipped him a Frostheater soon after. :) :)
 
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Genesis

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The reason the oil pan heaters work (and work WELL; they're actually far more efficient in terms of power consumption than a coolant heater) is that the biggest impediment that you can actually CONTROL with heating the engine is the oil viscosity and what it does to cranking resistance.

The battery has materially lower cranking amperage available in cold temperatures and when you couple that with thick oil you may not make minimum cranking RPMs.

I used to own a boat with twin Detroit 6V92s in it. Many people use a heater element that goes into one of the block's coolant pipe plugs, but I put small Wolverine pad heaters on both oil pans. That was sufficient to get the oil nice and warm and with that there was never a problem with cold starts, even in below-32F outside temperatures. Now if I had that engine on a truck or something where I needed to be able to start it in negative fahrenheit temps I'd have a different strategy, but water tends to turn into ice at those temps so one is usually not (recreationally) boating :)

Note that Detroits have NO glow plugs or other start assistance -- you can either make enough compression heat for them to fire or you can't, and they're purely mechanical with no electronics of any sort. With those in cold weather it's a function of cranking RPM and the key to obtaining enough RPM for them to light is for the oil to not be something akin to maple syrup that you've left in the refrigerator overnight -- especially considering that they use straight-40wt oil!
 

WolfgangVW

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So i replaced the 3 glow plugs I could, even tho the scanner said they were fine. The car seems to start a bit better. Still not perfect but to be honest I think it's definitely partially attributed to only having 3 functioning GP's and it's been -30C. On a side note any input on the next thing to check is greatly appreciated! I may have a look as its supposed to warm up here in a few days.
 

Curious Chris

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Parked outside my car will start down to maybe -20 degrees Fahrenheit. (That is with healthy battery and glow plugs) Below that it is a lottery. I do have a Frost Heater but since I park in the garage I have not plugged it in this year even though it was -17 degrees Fahrenheit this morning.

Long ago I had a Peugeot 505 STD and at -30 Fahrenheit it would not crank. I took the battery out and brought it inside. Let it warm up inside for 24 hours, back in the car and it cranked nicely and started. Remember Arhenius: chemical reactions rate 1/2's for every reduction of 10 degrees Centigrade.
 

maxmoo

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So i replaced the 3 glow plugs I could, even tho the scanner said they were fine. The car seems to start a bit better. Still not perfect but to be honest I think it's definitely partially attributed to only having 3 functioning GP's and it's been -30C. On a side note any input on the next thing to check is greatly appreciated! I may have a look as its supposed to warm up here in a few days.
So did you even bother to try the snow trick to see if your old plugs were working?
Just because you went and replaced your glow plugs does not mean they are working.....still need to make sure you get power to them.

Have you checked the timing with vcds to see where on the graph it is.....somewhat advanced starts best.
 
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WolfgangVW

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So did you even bother to try the snow trick to see if your old plugs were working?
Just because you went and replaced your glow plugs does not mean they are working.....still need to make sure you get power to them.

Have you checked the timing with vcds to see where on the graph it is.....somewhat advanced starts best.

Thanks maxmoo I am going to try the snow trick I just haven't had the best opportunity. And had a good chance to change the plugs on a whim so I did. But I'll let you know the result! Possibly today after work will be a good time.

Don't have VCDS to check the timing. I just had the timing belt done so one would hope the timing was looked at and set correctly then. But that being said if it wasn't that could be the issue!
 

Genesis

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Remember if you're down 1 glowplug thats 25% of your preheat capacity...
But in terms of starting it doesn't work like that.

You need ONE cylinder to fire for the engine to start, not 4. Further, in very low temperatures the battery has trouble sourcing current, so you're actually impairing the battery's ability to turn the engine over (never mind that the current drawn by the starter goes WAY up due to thicker oil) at the required RPM with the glow plugs running. On the other side of the equation the heavy draw from the glow plugs actually *warms* the battery slightly, so a couple of "pre-glows" might actually ENHANCE the ability to source current by a bit.

In short the totality of it in really cold conditions is a hell of a lot more complex than it first appears. As I noted earlier I had just ONE working glow plug in my ALH (bad harness) when I wound up taking a trip into conditions that turned out to include overnight parking exposed to negative Fahrenheit temperatures. That had never been an issue in Florida or I would have fixed it long ago, of course. It started but didn't like it one bit as the car fired on one cylinder for a few seconds and blew a hell of a lot of white smoke until the other three lit off ~5-10 seconds later. Fortunately I had filled from a near-empty tank about 100 miles previously (I was coming from a warmer place) or I might have had gelled fuel. Then again I had a fresh battery and everything else was bang-spot-on (timing, etc) -- I probably wouldn't have gotten away with it otherwise.
 

curtludwig

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I get where you're coming from, its definitely not a simple equation. Assuming one working plug and that hole actually fires it has to then drag the other cylinders. I've never seen a case where a 4 cylinder will run on just one. About 15 years ago we were living in a 3rd floor walkup, I had an '83 Mercedes 240D and it got wicked cold, like -20F most mornings for a week. We'd chain the car behind my gasser pickup and drag it around until it started firing. It wouldn't stay running by itself until at least 2 cylinders were firing at the same time and even then it was iffy. I finally bought a big battery and power inverter so I could run the block heater. After starting the car I'd drag the battery back up to my apartment to charge all day so I could repeat the next day...
 

oilhammer

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There are just too many to list....
Usually an inline 4 will barely run on two cylinders, unless the dead two have no compression.
 

UhOh

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Curious... if cylinders aren't combusting (while some are) won't those cylinders tend to get more fuel because the ECU thinks they're underpowered? Seems that this could be a little problematic (including washing cylinders a bit).
 

oilhammer

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There are just too many to list....
The ECU really cannot do a good cylinder contribution monitor until the engine is actually running, so that is likely not much of an issue.
 

Genesis

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Yeah this isn't a Detroit 2-stroke that (without a turbo modulator anyway) slams the rack to full-fuel as soon as the governor starts to turn..... :)
 

UhOh

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I think that this is a bit quick to dismiss my question in which case I'll try and clarify WHY I'm asking...

Consider the statement of "it's not running on all cylinders" AND a comment made here in this thread that the engine will fire on ONE cylinder. If an engine is firing on anything less than ALL cylinders is that engine running? When does the ECU recognize that the engine is "running?"
 
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