Vibration / Noise at low RPM

[ajd]

So I'v been lurking on the forum since I bought my deli a year ago, and have been able to diagnose and solve many problems from all the great info here. So thanks for that! I have done a lot of searching and reading about various vibrations, rattles, knocks, and general diesel clatter, but have yet to be able to pin down the cause of my vibration. If a thread already exists please point me in the right direction. I've done some troubleshooting of my own and now I'm at a point were I really need another opinion from someone who knows their way around old diesels. I'll be getting my diesel mechanic to take a look soon but he is also new to delicas. Maybe this is totally a newb problem, Anyway here it goes:

The vibration occurs all the time at low rpm when idling or rolling slow around town and has done so since I've owned it. It gets a lot louder when on the accelerator. I mean any input at all, a slight touch and you get a grrrrr from under your butt. It all completely smooths out in the 1000-1500 range and higher. It's only maybe slightly better when she has been running for a while and is nice and warm. Specifically the sound is hard to describe, but it's enough to rattle loose change, the rear hatch, exhaust, parts of the interior, and is generally just loud inside the cabin. grrrrrrggrrggrrrr, it doesn't sound right.

I've mostly just ignored it because the van runs great otherwise. There is a decent amount of power (I can cruise at 125 on a flat with no wind) and is nice and smooth when the rpms are up. I'm starting to worry that it is the sign of some underlying problem that could bite me at the worst time. It would be nice to have the confidence from a nice sounding engine when i'm on a long trip.

Here is my troubleshooting thus far:
New air filter: got slightly more power in the high range from this, vibration persists.
New Oil filter: very noticeable increase in power, no change in vibration
engine mounts: I installed 4 new mounts, (two at the engine, and two at the back of transmission) there was no change in vibration. The mounts I pulled out were in poor shape however, so that's reassuring.
check belts: I went straight for the timing cover with the new thought that this is a combustion performance issue. Confirmed that all three(?) timing marks are lined up (they were) and reset the tension. I turned to the accessory belts, and one of the alternator belts is totally loose (this must be it!). I put two new belts on and re-tensioned the rest which looked fine. aannd.. no change in vibration and cabin noise! damn. Although an interesting note is that prior to the belt check the motor would visibly vibrate. You could grab the valve cover at idle and your whole arm would look all fuzzy. That is pretty much gone, but you can still feel it and hear it at the same level in the cabin. humm..
Installed a hydronic heater: The reason I did this was for cold starting and winter camping, but I want to note that I tee-ed into the fuel line pre-filter and the vibration possibly got worse but it's hard to tell because I am hyper focusing on this damn sound now. I can't remember what I considered normal. I wouldn't think that the tee would resist the fuel enough to make a difference (the heater isn't usually on when the engine is on so the injection pump is not competing with the heater pump. I also installed a check valve on the heater side to be sure). btw this type of heater incredibly worth the money and time to install if you live in the cold. I probably could post some pictures of my set up as it was a trick to find space for it.
fuel additives: I've tried many and even some injector cleaners. Not noticing much difference I settled for using Howes Diesel Treat or Power Service products.

I'm beginning to get into the realm of repair that I'm new to and will probably need some assistance with (diesel injection system). I don't want to go messing with the injection pump and screw things further. On the other hand, is it possible to make small injection pump adjustments without tearing things apart?

Some other possible causes I've read about :
alternator: A dying alternator can cause belt slip, which maybe explains why it will smooth out as the engine spins it up. I could likely get it rebuilt locally.
injectors: doesn't seem likely since it runs fine at higher rpm
injection pump: not providing enough pressure at low speed. or fuel delivery is off somehow
balance belt: not clear to me where/what this is
rocker arms: yikes
valve tuning: more yikes

Well thanks for getting to the end of my saga here, and I very much appreciate any tips in advance. It would be sweet if this is something I can fix myself (I'm pretty mechanical, but new to delicas and diesel in general). Trying to avoid a long trip to a delica mechanic.

1990 L300 automatic-4
4d56
209k km

Thanks

[Growlerbearnz]

The balance belt is between the timing belt and the engine, down low. If you remove the top timing belt cover you can *just* see the balance belt in there. It's the same width as the timing belt.

[ajd]

I got in there again and took a closer look deep down. There is in fact a balance belt in place. Could it need tensioning ? The bit I can see looks ok.. To get in there looks like Ill need to remove the fan, accessory belts, then lower cover?

[Growlerbearnz]

...Could it need tensioning ? The bit I can see looks ok.. To get in there looks like Ill need to remove the fan, accessory belts, then lower cover?

If it's in one piece and moves when you turn the engine by hand, it's probably ok. A lack of tension wouldn't produce the vibration you describe (but a broken or missing belt might). You can re-tension the belt without removing the lower cover (which involves removing all the things you mentioned, plus the crank pulley. ugh), but it's tricky. Pages 11B-14 and 15 in the "4D5 & 4G7 Engine Manual" here: http://www.delica.ca/forum/viewtopic.php?f=17&t=7335.

Your warm idle speed in neutral is 750rpm, right? They do vibrate a bit, but it sounds like yours is making a noise when it vibrates, which isn't right. Is something hitting the firewall or engine cover? Something else loose that's hitting it's natural frequency at 750rpm? A video would be awesome...

alternator: A dying alternator can cause belt slip, which maybe explains why it will smooth out as the engine spins it up. I could likely get it rebuilt locally.
injectors: doesn't seem likely since it runs fine at higher rpm
injection pump: not providing enough pressure at low speed. or fuel delivery is off somehow
balance belt: not clear to me where/what this is
rocker arms: yikes
valve tuning: more yikes

Alternator- wrong frequency, and there's nothing in an alternator to cause vibration anyway. A loose belt would squeak.
Injectors- a single injector failure could cause a regular misfire, but I'd expect white smoke out the exhaust and hard starting. Clearing up at higher revs isn't unheard of though. Maybe have the injectors tested and rebuilt?
Injection pump- Unlikely. Look at this as a last resort.
Balance belt- sounds like it's ok.
Rocker arms- if they were cracked they would have failed entirely by now. Still, removing the rocker cover and having a look isn't too tricky, though you might end up with a rocker cover leak.
Valve tuning- valve clearance? Check it while you're looking at the rockers. Though it shouldn't be able to cause the vibration you're describing.

[motorang]

Hi
check the exhaust, especially at the end where it lives near the rear leaf spring mounts. The rpm range and noise would be typical for the exhaust touching any chassis part.

Andy

[ChuckBlack]

Now what your glow plug system, upon starting the glow plugs see max Voltage then should still be on until the engine produced enough heat on its own. Perhaps the relay is capout! And Even if he hears a grrrrrr, all noise would be dismiss pass 700 rpm when all is in sync. Perhaps your low idle set screw needs adjustments. get a photo tachometer rpm and record you idle at idle. It maybe time for an adjustment!

At idle it should be 650+-50 Rpm!

[ajd]

Now what your glow plug system, upon starting the glow plugs see max Voltage then should still be on until the engine produced enough heat on its own. Perhaps the relay is capout! And Even if he hears a grrrrrr, all noise would be dismiss pass 700 rpm when all is in sync. Perhaps your low idle set screw needs adjustments. get a photo tachometer rpm and record you idle at idle. It maybe time for an adjustment!

Warm idle speed (according to the dash tach) is around 780. I'm not sure that this vibration would be related to the glow system. My understanding of the glow system is that it would be completely inactive once the engine is warm, and the vibration persists no matter how long the engine has been running. I recently replaced all 4 glow plugs and resistor from Right Drive for winter prep (I also have a temp sensor in the mail). I did stick a DMM on the rail during a cold start and got about 10 volts until the relay clicked off. After the engine turns over, the relay did not come back on. I haven't had too much trouble with starting, although it does sputter a bit on occasion.

check the exhaust, especially at the end where it lives near the rear leaf spring mounts. The rpm range and noise would be typical for the exhaust touching any chassis part.

The exhaust looks clear of contact on the chassis or other components.

Your warm idle speed in neutral is 750rpm, right? They do vibrate a bit, but it sounds like yours is making a noise when it vibrates, which isn't right. Is something hitting the firewall or engine cover? Something else loose that's hitting it's natural frequency at 750rpm? A video would be awesome...

Hard to tell if something would be hitting the firewall, but there aren't any major wear spots on the inside of the cover. Also, the vibe doesn't change much when running the engine with the cover open, except for the obvious increase in engine noise.

Injectors- a single injector failure could cause a regular misfire, but I'd expect white smoke out the exhaust and hard starting. Clearing up at higher revs isn't unheard of though. Maybe have the injectors tested and rebuilt?

I'm starting to think this could have something to do with it. Now that you mention it, I do get some white smoke and sputtering on cold starts, which clears up when the engine is warm or even has run some time earlier that day. I think I will get them tested next.

I might be able to take a video today.

Thanks everyone

[ChuckBlack]

Are all your fuel line connection tight and not
Leaking? Fuel filter not plugged? I was
Thinking as soon as you get your engine revving you'll not notice any vibration that's for sure!

[ajd]

I can't find any fuel leaks and I did put a new fuel filter in a few months ago. the filter connection looked clean an unblocked.

Have a listen to this video. You may need headphones to hear the low rumble when i'm in the cab and the door is closed, it's a pretty low frequency sound and laptop speakers don't quite do it justice. This is what I'm worried about and trying to fix, the low frequency sound comes with a stout vibration that is felt all around the van; in the cab, in the back, on the outside. The rest of it (sounds from the outside and engine bay) seems like usual diesel clatter to me, but tell me what you think.
https://www.youtube.com/watch?v=se2s1VEFrXQ

[Growlerbearnz]

It must be subtle, because that sounds fairly normal to me. The engine didn't appear to be moving more than I'd expect. You might need to arrange a meet-up so you can compare it to another Delica!

You've checked the front crank pulley to make sure it's not wobbling as it spins, right? The outer steel part is bonded to the inside with rubber, if the rubber shears it can let the outside part move about.

The muffler can also collapse internally, leading to a rattle, but I would think it would be fairly obvious where the noise was coming from.

[ynwa]

Like g'day eh?! I realize this was touched on earlier but I'd really take a look at the lower alternator bolt. It might seem illogical, but It fixed my 'low RPM rattle'. It's a bit of an arse to get to but make sure the tension is good and give that a good cranking.

[ChuckBlack]

did you finally checked your timing as well as you balancer shaft time? What were the outcomes of all that vibration?

[ajd]

I never really figured it out, no. I would like to try rebuilding or getting new injectors once I get the time to. It's getting pretty warm here now (about 10C) and it still takes a few glow cycles and cranking to get it to start cold, there is a fair amount of white-ish smoke as well (plugs are new last year). No starting issues if I preheat with my coolant heater, but I was hoping to not have to rely on it during the summer.

Regarding the timing belt: I have checked that all the marks line up on the upper and lower belt. Would it be possible that the belt(s) could be stretched enough to affect the timing? I have no idea how old they are, but visually look ok and are under the right tension.

[ynwa]

You've checked the front crank pulley to make sure it's not wobbling as it spins, right? The outer steel part is bonded to the inside with rubber, if the rubber shears it can let the outside part move about.

I would certainly confirm this, from experience, I lost my keyway when the crank bolt loosened and shredded everything. It was a slow descent into inoperability (is a word?). Gradually became harder to start as the sprockets moved on the crank, low power, smoke. Also watch the belts to the alt, if they 'wobble' or flutter, there's something wrong down there, and tightening the alt will just delay the inevitable. The telltale sound is a ticking or clunking on rotation when it's bad. But if your lower timing mark (on the harmonic balancer) still points to roughly 9deg, then this isn't your issue. I wouldn't wish this on anyone. :) Bottom end rebuild is in the not too distant future.

Likely not your issue but other readers might have this symptom and this is a good place to scan before things get real bad.

[ajd]

yikes. I will definitely check that out.