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Why won't a diesel start?

While out riding my bicycle I encountered a fellow with a VW Beetle stuck in the middle of a (non-busy) intersection, trying to push it. I stopped to help him. After we got it out of the intersection and side of the road he told me he had a new battery. I found he hadn’t tightened the contacts enough. After I tightened them the starter motor engaged and sounded as though it worked well but it still wouldn’t start. The gauge indicated a full tank. I wanted to tell him he wasn’t getting spark, but I noticed he had a diesel. Does this mean he didn’t have enough glow? His idiot lights included a coil. He doesn’t have an ignition coil. Did the light indicate a heating coil? He didn’t know what it meant. He went home (nearby) for tools and I left.

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Fuel or compression. He really probably would not need the glow plugs if it had been run recently, so my guess would be a fuel problem like a plugged filter or bad injector pump. Still shouldn’t have shut him down completely.

Well my last experience with a diesel, be it a skid steer a couple of weeks ago, you had to turn the key to the left I think for 5 seconds to heat up the glow plugs, then start it.

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My first thought would be inoperative glow plugs but there are several other possibilities.
It’s unknown, but if he’s been having some fuel and/or injector problems that can ruin the glow plug tips which can then lead to hard starting or no starting at all.

A worn engine with low compression can also act like this.

Another possibility is a lack of power to the fuel shut off on the injection pump.

Glow plugs aren’t necessary for a hot start and shouldn’t be necessary for a cold start in Albuquerque during July.

There are a number of possible failures, lift pump, diesel injection pump, fuel relay, timing chain etc.

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It’s plenty hot here in OK and when I worked for VW we saw diesels every week that would not start because of failed glow plugs, bad glow plug relay, or the most common cause of all; a fractured glow plug fuse.


Glow plugs are totally an emissions device- they are there to aid in starting, so a diesel engine won’t puff out tons of smoke once it gets going. It may not start very easy (especially a v-8 diesel,) but Nevada is correct- the glow plugs are not necessary to start a diesel. In fact, I have several in my fleet that do not have glow plugs. Compression during cranking is enough to the heat necessary to ignite the fuel.
Living in the desert, I had to manually check glow plugs to find out if they were bad- if it got to the point of a hard start on one of my diesels, then I knew I was in for a bugger of a time getting the glow plugs out of the block.

Having said that, lol- I’ve never worked on a VW diesel, is the compression that intense that they have to have the assistance of glow plugs to build enough heat to fire the engine? If so, I would lean towards a pretty serious compression issue with RandomTroll’s broke down buddy- with the initial breakdown being caused by something electric losing voltage due to loose battery cables.
or something like a bad crank/cam sensor. Those are pretty common failures on my diesels.

Glow plugs are MORE then just an emission device. Many diesels need them to start in extreme cold weather (-10 to -40 or lower).

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Glow plugs aid in starting. The diesel will start in extreme cold, it will just take a WHOLE lot of effort. possibly more than is cost effective without them. And you will get a TON of smoke out of the engine.

Never heard of glow plugs being an emissions system. The glow plugs for my Olds diesel were to get the dang thing started. Nowhere in the factory service manual was there any discussion of it being an emissions device. Maybe some VW dealer came up with that to make customers feel better or something.

I have succeeded in getting a small Kubota engine with bad glow plugs started by opening up the air filter housing and directing the heat of a heat gun into the intake while cranking.
Not all diesels use glow plugs, most industrial direct injection diesels don’t need them. Most auto diesels are indirect injected, where the fuel is sprayed into a prechamber instead of straight into the cylinder, these have glow plugs in the prechamber usually.


What is a glow plug?

I dunno if the glow plugs actually helped emissions that much. Maybe it would have been worse.

I have ot respectfully disagree that glow plugs are not needed to start a diesel. As I said, when I worked for VW diesels were towed in almost weekly for a no start problem. Most often the cause was failed glow plugs or failed power source to the glow plugs.

A diesel VW with abnormally low compression may need the glow plugs to get going even when hot.
Of course, the fly in the ointment here is that none of us know anything about the car or symptoms before it was found dead in the intersection.

Usually, only one or two glow plugs will fail and the engine will start on the cylinders with good glow plugs, the bad cylinders spewing white smoke out of the exhaust until they finally warm up enough to run.
However, a lot of people just keep driving without replacing the bad plugs as long as the car still starts until that last one goes.
A clamp on DC ammeter like a Fluke 325 is a good and fast way to find the bad glow plugs. The bad ones will draw zero amps and the meter just clamps over the wires who’s amps you wish to measure, no need to disconnect anything.
It can also measure how many amps the starter draws or how many amps the alternator is putting into the battery.

There are millions of diesel trucks on the road that do not have glow plugs. The Cummins ISB engine used in Dodge trucks since 1989 don’t have glow plugs. There is a heating grid in the intake system that can operate for up to 3 minutes during cold start-up, it does not operate at temperatures above 66 F.

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Fuel pump would be my first guess. The pump itself might be ok, but the engine computer might not be turning it on b/c of an ignition key/security problem or it isn’t seeing the engine rotating (safety feature), or there’s an electrical problem affecting the fuel pump (blown fuse, faulty fuel pump relay). If the fuel pump is pumping ok, next in line of guesses is the injection pump.

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Mike, OK’s saying glow plugs are needed. That’s what you’re saying, right?

Thanks. I completely misread that. Apologies to OK4450.