Long time miss at cold idle, injector?

Mountainman · **Posted:** Wed Apr 15, 2015 12:57 am

So, I've had a miss for months when I start my daily driver. I assume it has to be an injector as I have no CEL, but I wanted to ask you wiser folks if I'm missing something before I start swapping injectors around. It sounds and feels exactly the same each time, and since it goes away after it warms for 30 seconds or so, I haven't been in a hurry to fix it. But, with the ARPs and new rockers going in, I might as well swap an injector out with a good spare I have when I put it back together.
My only other thought would be air? I have a flow through inline pump that works like a champ, and never have any signs of air at any other time, including WOT. It pulls like a train...

thermorex · **Posted:** Wed Apr 15, 2015 8:19 am

Does it sound like an injector knock? I have a very light knocking issue that comes and goes when outside temps are cold, it starts fine, then after about 1-2 min of running it starts that light knock that makes the rpm drop by 100-ish rpm, if I put it in drive it goes away. If I leave the engine running a bit more (idle) it also goes away once it warms up a bit more. In my case I'm sure it's an injector acting up, but since it doesn't do it all the time, I decided to ignore it for now. As the weather warmed up lately, I haven't heard it doing this. I also don't have issues while driving it, so it can't be air. If you know which injector is, it may worth trying out another good one. You may be able to hear the troublesome injector with a mechanical stethoscope.

Mountainman · **Posted:** Wed Apr 15, 2015 1:42 pm

hmm, I'm so new to diesels that I don't really know what injector knock sounds like. I think I only have it at start up, and it's definitely not firing on one cylinder when it happens. Maybe the fuel pressure builds enough after a little while and overcomes a sticky injector? Or, a lesser spray finally cooks off under more heat? I'm surprised that we don't have less power all of the time. Maybe we do! Would be nice if it pulled yet a little more with this fixed, or a little better mileage.

I'll wait until mid afternoon and go fire it up, and watch exactly what happens, and report back.

Thanks man :JEEPIN:

Mountainman · **Posted:** Wed Apr 15, 2015 7:17 pm

well, it doesn't do it when it's 70 degrees out, just like yours. hmm, I hope I can find the symptoms again before next winter. I'll try to catch it on a cold morning asap

Mountainman · **Posted:** Wed Apr 29, 2015 1:49 pm

Well, it got cold enough in the mountains the other day, and here's what I got.

Started, and the engine shakes the vehicle noticeably, the idle stayed pretty solid at 750ish. It does this for 30 seconds or so, and then not again.

It sure feels like it's missing on more than one cylinder actually, I'm thinking that something contracts enough for it to suck air when it's cold enough. Would be nice if I don't have a faulty injector. I'll report back again after I delete the suspect quick connect.

You guys agree it's air?

papaindigo · **Posted:** Wed Apr 29, 2015 2:56 pm

Where is your inline pump located? If it's in tank it's not likely air. If it's outside the tank it could be air but I'm inclined to doubt it as the problem goes away when the engine warms up. Easy "test" and something prudent to do is spend $13 for this (http://smile.amazon.com/Moeller-Univers ... ine+filter) and install it on the fuel line running to the filter head. You will probably need say 12" of marine grade diesel rated fuel line and 2 worm clamps. This does 2 things: 1) let's you visually check for any air coming in from the tank (with an out of tank inline lift pump if that happens you need to replace the quick disconnects on the supply line with similar fuel line and clamps and 2) will catch big stuff if you get a bad tank of fuel.

What are the ambient temps at startup when the problem occurs. If it's coldish (say 35F or below) I'd say it's just routine diesel cold start roughness especially since you indicate that a start at 70F did not have the problem. Either way I'd run at least a couple of tanks with a heavy dose of quality diesel injector cleaner, say PowerService white bottle and see if the problem goes away before messing with injectors.

thermorex · **Posted:** Wed Apr 29, 2015 5:12 pm

Mountainman, can you snap a quick video and put it on YouTube? That's more helpful that explaining in words.
Injector knock usually sounds like you get a hammer and smack a solid thick piece of metal, it can vary in intensity and loudness depending on how bad it is. It is caused by impartial burning (you get more diesel through than you should) or an obturated nozzle(s). So instead of diesel being pulverized you get some sort of stream. If gmctd sees this post, he may be able to add more info to it as he's pretty god with this kind of explanations.

This link for the Vw alh engine has injector knocks and few "misses".

http://m.youtube.com/watch?v=2uRbaTdg8AE

Funny that engine is a bit shy of 500k...

In my case, I get a few "misses", but only at cold and very intermittent. Once the engine warms up a bit, runs perfectly fine. Stage one of an injector knock is usually at cold and at idle/light throttle. Stage 2+ is when it knocks all the time, this can cause very high Egt temps and you may put a hole in the piston, but you shouldn't worry about this yet.

Please post a video with the sound, will help in identifying the noise. As papaindigo said, some power service or an injector cleaner may help if your nozzles are dirty, otherwise I doubt it will do much.

Another way to identify the noise is a mechanical stethoscope and listen to each injector, you'll hear the one(s) knocking.

Mountainman · **Posted:** Wed Apr 29, 2015 5:13 pm

Many thanks for the advice :rockon:

My pump is outside the tank, it was there when I bought the jeep, and has been good to me.
It definitely does this in the 30's, and maybe the 40's, but when I hiked out from 5 days in the backcountry, the jeep had been sitting the whole time. It was about 30 at night, but around 70 the day I started it, and it was evening. Maybe the engine was as low as 50, since it was probably in the shade, but that was cold enough to give me the symptoms. I'll try and see if the number of days without a start matters.

I've ran power service or Shaeffer's Diesel Treat 2000 pretty religiously at roughly the recommended concentrations for about a year, and it hasn't affected it.

Oh, I got a CEL on the way in to that trip (2.5 hours of dirt road one way) and then it disapeared on the way home. I wonder if the code will still be stored still after several starts?

Mountainman · **Posted:** Wed Apr 29, 2015 5:17 pm

thermorex wrote:

Mountainman, can you snap a quick video and put it on YouTube? That's more helpful that explaining in words.
Injector knock usually sounds like you get a hammer and smack a solid thick piece of metal, it can vary in intensity and loudness depending on how bad it is. It is caused by impartial burning (you get more diesel through than you should) or an obturated nozzle(s). So instead of diesel being pulverized you get some sort of stream. If gmctd sees this post, he may be able to add more info to it as he's pretty god with this kind of explanations.

This link for the Vw alh engine has injector knocks and few misses.

http://m.youtube.com/watch?v=3nkcxJ9bheI

In my case, I get a few "misses", but only at cold and very intermittent. Once the engine warms up a bit, runs perfectly fine. Stage one of an injector knock is at cold and at idle/light throttle. Stage 2+ is when it knocks all the time, this can cause very high Egt temps and you may put a hole in the piston, but you shouldn't worry about this yet.

Please post a video with the sound, will help in identifying the noise. As papaindigo said, some power service or an injector cleaner may help if your nozzles are dirty, otherwise I doubt it will do much.

Another way to identify the noise is a mechanical stethoscope and listen to each injector, you'll hear the one(s) knocking.

Ok, thanks man. I will try to catch it on video, but I don't think there are any loud sounds, but then again, it quit before I got under the hood.

thermorex · **Posted:** Wed Apr 29, 2015 5:20 pm

Mountainman wrote:

thermorex wrote:

Mountainman, can you snap a quick video and put it on YouTube? That's more helpful that explaining in words.
Injector knock usually sounds like you get a hammer and smack a solid thick piece of metal, it can vary in intensity and loudness depending on how bad it is. It is caused by impartial burning (you get more diesel through than you should) or an obturated nozzle(s). So instead of diesel being pulverized you get some sort of stream. If gmctd sees this post, he may be able to add more info to it as he's pretty god with this kind of explanations.

This link for the Vw alh engine has injector knocks and few misses.

http://m.youtube.com/watch?v=3nkcxJ9bheI

In my case, I get a few "misses", but only at cold and very intermittent. Once the engine warms up a bit, runs perfectly fine. Stage one of an injector knock is at cold and at idle/light throttle. Stage 2+ is when it knocks all the time, this can cause very high Egt temps and you may put a hole in the piston, but you shouldn't worry about this yet.

Please post a video with the sound, will help in identifying the noise. As papaindigo said, some power service or an injector cleaner may help if your nozzles are dirty, otherwise I doubt it will do much.

Another way to identify the noise is a mechanical stethoscope and listen to each injector, you'll hear the one(s) knocking.

Ok, thanks man. I will try to catch it on video, but I don't think there are any loud sounds, but then again, it quit before I got under the hood.

Btw, I edited the post with some minor corrections and the YouTube link is different since I used a wrong one initially...

Long time miss at cold idle, injector?

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