84 300 CD suddenly making HORRIBLE noises and running VERY rough
 

I really need some expert help here. I'm scared to death that my engine went belly up today.

I was driving home (about 20 miles) and when I got off the highway I noticed that it was making a little bit of a valve-ticking kind of noise when running at normal RPMs and was doing the rough-running-shaking-at-idle thing (which it does every once in a while right after getting off the highway). Didn't think much of it and stopped at Harbor Freight about 5 miles from home.

After firing it back up and heading home, after a couple of miles I noticed that the "valve ticking" had worsened and become a bit of a "clatter", and it was running progressively rougher. Almost as if it were missing on one (or more) cylinders. The oil pressure seemed just a bit on the low side of normal, but I was in stop and go traffic and I'm not sure whether it was actually low or if I was just thinking so because I was starting to get worried. The engine temp seemed to be in its normal range for the conditions - right around 100* C +/- about 10*.

The last mile it started loosing power and the "clatter" got progressively worse until it turned into almost a hammering sound. As I started up the hill a quarter mile from home I pulled over and got out and lifted the hood. The sound still seemed to be coming from the top end - but it was pretty loud. I shut it off and checked the dipstick. The oil seemed a little low, but since it is due for a change, was sitting pointed uphill, and had JUST been shut off (no drain-back time) it didn't seem alarmingly low.

When I went to start it it seemed to be cranking slow and it cranked a good 30 seconds - blowing diesel smoke - before it fired up. Driving the last few blocks home it still had no power - though it wasn't blowing smoke or anything else. Though the hammering continued to get louder and now there is an underlying squeeking sound as well - though the engine is lurching around so badly I can't tell if it part of the problem, or just a result of the rocking motion of the engine. As I turned into my street and let off the throttle it died. Cranked slowly and wouldn't restart at all initially. After letting it sit for a few minutes while I poked around under the hood, it finally did start up again - after 30 seconds or so of cranking. I got it to idle sitting in the driveway and added a little over a quart of oil - which I estimated should be enough to top it up based on my previous check of the dipstick. No change at all.

So... what do "nailing" injectors sound like? Could it be bad fuel? It has been running fine up until I headed home today. It was all the way down to the R mark on the gauge, so I stopped and got 5 gallons at a Shell station. Possibly a plugged fuel filter? Maybe a valve adustment locknut loosened up and let the valve come into contact with a piston? Or did it spin a rod bearing? At this point I'm scared spitless that something major has gone awry.

ALL diagnostic help and suggestions are welcome...

Since it became progressively worse over several miles, I'm not inclined to believe it was a sudden mechanical failure. Furthermore, the lack of capability to start is also indicative of a fuel problem. A mechanical issue in one cylinder wouldn't prevent a hot start.

Contaminated fuel could absolutely cause a knocking injector sound.........and difficulty starting.........that appears to be mechanical to a person who has not heard this in a diesel.

I would drop the secondary and carefully pour it off into a clear glass jar and see what you get. If there is significant water.........you found your problem. Whether the injectors were damaged by it is another question.

Has timing chain been replaced ever?

I hate to say it, but it sounds chain, valve, bottom end related. I would stop trying to run it and at least take the valve cover off and check out what's going on in there.

I doubt what you have is a bad injector or two--they don't tend to fail all at once. Injectors also don't cause squeaking sounds. When you had the oil filler cap off, did you notice any unusual combustion gases escaping?

I would also look in the air filter and see what's going on in there. i.e. oil, clogged.

I sympathize and wish you the best of luck.

It can't be "chain, valve, or bottom end related". Those are three completely separate and distinct possibilities.

Pick one............!

So you'd suggest starting with disconnecting the small clear filter and draining it? I was thinking about draining the spin-on too...

What kind of damage would a short exposure to watery fuel do to the injectors, and what causes it to damage them?

You could........you're looking for water.

Can't honestly tell you how much water they can take........the water tends to expand when boiled off in the tip and fracture the nozzles.

You could just use rig a small tank with fuel and directly feed it into the line.

How was the blowby?

It sounds horrible, but there's a good chance its only a minor issue.

The one time the SL left me stranded, I thought the motor was gone. It was running fine until one huge backfire when I shut it off, then it would barely restart, and sounded horrible. Smoke billowing, shaking violently, wouldn't idle.

All that happened was a fluke backfire knocked a vacuum hose off. I was out of the shop in 5 minutes. I really don't know specifics because I was 17 and could barely find a dipstick at the time. :rolleyes:

What color is the smoke?

.... too-shay ;-) ...

I should have said mechanical related to be sufficiently vague ;-) ...

Buuuuuttt, if injectors are suspected and the damage is not obvious with a visual outer inspection, then I have a set of Bosch injectors I'd be willing to let you borrow.

Oh no!

Well, I DO still have a recording of your car idling right after the valve adjustment last month. It sounded right about perfect. I can't imagine something went wrong as a result of that, but maybe some jealous fan with an SLK tampered with it at the car show....

Seriously.....I guess if it was me, I'd start with what Brian said - looking at the fuel for possible contamination, change filters, and try running some fresh fuel from a portable container first (disconnect supply & return lines & put them in the can). Were you running bio? I had heard about some problems with contaminated biodiesel a few years back in this area.....also a few stations that sold bad gasoline earlier this year and ruined a bunch of cars....funny that I have heard about more bad fuel incidents since fuel costs got above $4/gallon, but maybe I'm just paying closer attention.

If fresh fuel doesn't fix it, maybe it'd be good to pull the valve cover again & take a look to make sure things are getting lubrication, chain is OK, etc...

I've never run my fuel tank down that low, so maybe it could be that some gunk loosened up in the bottom of the tank or reserve tank & plugged the strainer filter in the tank, starving the engine of fuel?

It's certainly unnerving when things don't sound right. Mine started nailing & ticking for a few weeks, not badly but noticeably...didn't drive it for a few weeks and this week, it sounds perfect. I didn't change a thing....

-Alain

Thanks for the suggestions, though as Brian implied your suggestions are a bit of a "shotgun" since they are indeed separate sub-systems in the engine. I will be removing the valve cover though - for sure. The valves were adjusted recently and the chain stretch was between 2-3 degrees and the guide looked good, so I'm thinking that isn't the most likely culprit - though I'm not ruling it out.

Bottom end is a possibility, though it seems odd that it would go from A-O-K to total crap so quick with no apparent cause (like a blown headgasket letting water get into the oil or something). Like I said it was a little low on oil, but not enough to significantly lose oil pressure or anything.

Valves seem like a possibility - only thing I can think of is if one wasn't quite tight enough after we did the valve adjustment - though that was over a month and 1000 miles ago.

Like I said, the squeeking may just be due to the rocking motion of the rough running engine - and may or may not have anything directly to do with anything internal.

What Brian said about the effects of water in the fuel sounds like injector damage can happen pretty quickly - under the right conditions. BTW, doesn't 15-20 miles sound like about the right distance to burn up all the good fuel already in the IP, filters, and lines, and start getting the bad fuel from the tank?

I was also wondering if anyone can explain to me exactly what is happening when an injector is "nailing"? All I know is what I've read around here - that when one is really nailing it can make a very BAD noise...

While anything is possible, the chances of a failed rod bearing or wrist pin are very low.........and, they wouldn't prevent the engine from restarting hot. I suppose that a ring could have fractured and one cylinder is now offline..........a compression check would find this quickly.



Unless one of the valves let go and dropped onto a piston, an improper valve adjustment..........or valves out of spec.........cannot cause the symptoms described.

Yeah, it has been running great for a month and 1000+ miles since then. Doesn't seem like it would take that long for a problem to show up if it was due to one not getting tight enough...

I've never had a chance to run anything higher than B5 in it. I've run a few tanks of SVO/RUG/D2 mix at around 40/10/50 ratios, but the last 3 tank fulls have been straight D2.

I never even considered that, since I've run it down to R - and beyond - several times with no issues. In fact I almost always run it down below where the 1/8 would be on the gauge...

Well, the more I'm thinking about it and reading others posts the more I'm starting to think I got a slug of bad fuel... but maybe that's just wishful/hopeful thinking on my part...

As someone else said, get a jar and put the fuel return line in it. Fill the jar 1/2 full or so (enough to keep the supply hose in). Run the car from the jar for a few minutes see how it runs. Or... better yet as Brian said, you may have contaminated fuel.

GET NEW FUEL for the jar and run it off of that. It the car still runs bad, make sure your fuel filters are new. I did say new... if you had contamination in the tank you may have a plugging filter. If the car runs fine on that setup, you've found the problem is fuel related. If not, don't rule it out yet... Look for leaks at hoses. Make sure the spin-on fuel filter is tight and well sealed.

But... simple as it is, the jar experiment will get you some quick informative answers.

Well, I guess I have my plan of attack then. Tomorrow I'll be draining the filters (looking for water) and trying some fresh fuel first - then progressing to removing the valve cover once I've ruled out fuel problems...