Loud Tapping, Rough Idle, Had to Tow - Page 7 - PeachParts Mercedes-Benz Forum

kalikar85 · #91 06-10-2015, 01:28 AM

Quote:

Originally Posted by Left Coast

Fuel knock, nailing, and piston slap are not all the same thing. The info you got from the shop is essentially, "it could be any of a whole bunch of things, and we aren't going to waste our time diagnosing it for free." You have nothing new to work with.

Back in your post #66 you put up a snapshot showing what is labeled as the #2 pre-chamber. It looks fine. The ball is intact, and a clog at the bottom is a real long shot. If you got 290 lbs. coming out of it, then it isn't clogged! That's not your problem.

What you've shared already tells us that you have either a fuel delivery problem or a compression issue. You've eliminated the possibility of a bad injector, and it sounds like you've probably eliminated the possibility of a bad delivery valve. I don't think base fuel pressure is the issue. That leaves valves, rings, a broken piston (remember those chunks of iron in the oil pan?) or a faulty head or head gasket.

You didn't get a very good set of numbers on your first compression test. It is not unreasonable for your engine to run poorly if those were accurate readings. I suspect that they weren't. You should try it again. If you still see the same numbers on a second test, then the next step is going to be a leak-down test to see where the compression is going. Getting a diagnosis is a process. Unless you have much experience (which you obviously don't), or great luck, you can't skip steps. You just end up back at square one with no better idea of what the problem is than when you started.

I didnt think that picture was enough to determine any breakage that occurs in the bottom of the pre chamber as I've seen online or that a clogged or broken pre chamber does not retain compression.

Im pretty sure it isnt and they do, right? Is the pre chamber thing a stretch?

I agree there is a chance this all may be skirting around an engine rebuild, but as you say its a process; so far a 3-400$ and many a full day process with nary a smoking gun.

Im going to have this dude double check the pre chamber, compression, and do a leak down...

I spent a lot of time and $ restoring this car last summer. Before that, my experience stopped at pumping fuel. Thanks to this forum I put 20k great miles on this thing. Will follow up...

Left Coast · #92 06-10-2015, 03:12 AM

Quote:

Originally Posted by kalikar85

I didnt think that picture was enough to determine any breakage that occurs in the bottom of the pre chamber as I've seen online or that a clogged or broken pre chamber does not retain compression.

Im pretty sure it isnt and they do, right? Is the pre chamber thing a stretch?

I agree there is a chance this all may be skirting around an engine rebuild, but as you say its a process; so far a 3-400$ and many a full day process with nary a smoking gun.

Im going to have this dude double check the pre chamber, compression, and do a leak down...

I spent a lot of time and $ restoring this car last summer. Before that, my experience stopped at pumping fuel. Thanks to this forum I put 20k great miles on this thing. Will follow up...

Yes, the pre-chamber thing is a stretch. It would be a very unusual situation to burn the pre-chamber end off with the ball still intact. They do crack, but rarely. Does the glow plug look OK? A damaged tip or heavy carbon might give you a better reason to believe that something is going on in there. Not a huge job to pull it if you have the necessary tools. I wouldn't do it before I had some compression numbers that I could have confidence in. A damaged pre-chamber will not affect the compression, though heavy carbon could possibly skew the test readings a bit.

If you start throwing money at repair shop diagnostics, you might end up spending what you could have replaced the engine with. Sometimes that's just the better course. I hope it doesn't turn out that way.

Maxbumpo · #93 06-10-2015, 08:10 AM

Paying a shop $220 to diagnose a serious engine problem is reasonable. They are probably especially leery if they know that you have been attempting to diagnose / repair the problem yourself (in their minds, you are incapable and they likely think that you have made things worse). If they were the only shop that worked on the car, (and you didn't do any repairs yourself) and they were very familiar with it, then they might diagnose the problem for free because you're a good customer and they have a good idea of the baseline condition of the engine.

A compression test and a leak-down test take time, and time is money.

funola · #94 06-10-2015, 08:12 AM

"Yes, the pre-chamber thing is a stretch."

Maybe, maybe not. It is getting fuel with good spray, it has 290 psi compression, it is getting air, it should fire if all that is getting into the cylinder. I did think about the compression reading which would indicate #2 pre chamber is not blocked before posting about looking at the pre chamber. Is it possible that #2 pre chamber holes are mostly blocked with carbon and hindering combustion but still allowing a compression reading? All it needs it a small opening for a compression reading which may not be enough for combustion.

Looking at your pics, #2 ball is intact but the other one looks like it's missing? The pics are not good enough to see if it is packed with carbon or not. To see well into it, the retainer ring may have to come off. mach4 has a recent post on pre chambers with lot's of exc. pics.

Verify #2 compression is indeed 290 psi, also do a wet test by adding a teaspoon of oil, if psi goes up, the rings are leaking. Compression test readings can be misleading per a well respected machinist who do a lot of VW TDI heads. He has seen engines with stuck/ carboned up rings or broken rings produce perfectly good compression readings.
A leak down test will give you more data as to where it is leaking. Agree that it is better to diy rather than pay a shop to do the diagnosis.

mach4 · #95 06-10-2015, 10:50 AM

Quote:

Originally Posted by funola

To see well into it, the retainer ring may have to come off. mach4 has a recent post on pre chambers with lot's of exc. pics.

Prechamber Ball

kalikar85 · #96 06-20-2015, 12:36 AM

Compression: 1) 360 2) 260 3) 340 4) 340 5) 360
Leak-down: 1) 52% 2) 44% 3) 28% 4) 44% 5) 52%

This is not telling me anything, really. Pretty frustrated but trying to methodically solve still. I think Im going to have the timing checked. The shop didnt check the pre-chamber. Thoughts, comments? Any ideas on the nss repeatedly failing?

barry12345 · #97 06-20-2015, 11:03 AM

Quote:

Originally Posted by kalikar85

Compression: 1) 360 2) 260 3) 340 4) 340 5) 360
Leak-down: 1) 52% 2) 44% 3) 28% 4) 44% 5) 52%

This is not telling me anything, really. Pretty frustrated but trying to methodically solve still. I think Im going to have the timing checked. The shop didnt check the pre-chamber. Thoughts, comments? Any ideas on the nss repeatedly failing?

Number two cylinder with 260 compression and the injector spraying into it would normally run in at least some reasonable fashion. At this point I still have a suspicion that once the problem is found and fixed the compression may be higher.

Basically we go back to my amateur status here with this. Less leak down in my mind than other cylinders showing more compression plus higher leak down rates on the same engine. Really gets me thinking right or wrong.

Someone has to check the valve items for that cylinder. It requires a fresh air working intake source through the intake valve to get oxygen every other stroke. Plus the abiity to get rid of the cylinders contents through an opening exhaust valve. If the valves prove to be opening on manual rotation of the engine. . I would next pull the number two injector. Have a good visual inspection of the pre chamber.

If it looks decent run the engine for a shot period with the injector connected outside the engine. Just to make sure the injection pump is still providing the ability to spray at idle speeds. For example a element in an injection pump might deliver fuel at cranking speed and not at idle speed. Highly unlikely but something is wrong. The valve check is first though.

This is a long shot but still the cylinder is not operating for some reason. I also would do a volume collected spray test of two of the injectors simultainiously at cranking speed. This to make sure the injection pump element is producing enough fuel. Too little fuel and the cylinder will not run. I would not waste my time effort or money at this time doing the injection pump to engine timing.

Professional mechanics skills vary so much it is hard to tell on a keyboard what skill level the guys you are using have. If this has not been done yet by you or them it raises questions.

Actually your compression numbers and the results of the leak down are at least to me indicative of a valve for that cylinder may not be opening as a possibility. Or there is not enough fuel reaching that cylinder to run. But if that was really the case the cylinder would in all likelihood show a more typical compression number. Unless the raw fuel broke down the carbon.

Remember though I am not a working mechanic. Yet over the years seemingly have always still been able to deal with mechanical issues. Usually I substitute common tests and on occasion develop my own tests possibly even original tests sometimes to establish what is going on.

This at least partially compensates for the kind of intuitive thing real working mechanics develop. The problem today though we seem to have developed a lot of mechanics that do not seem to have the intuitive abilities of the older mechanics. .. Real pre chamber issue checks other than basically a visual one with an injector removed are beyond my knowledge level.

Maybe it is just me but my slight intuitive abilities about the number two cylinder. It may have a lot less carbon in it compared to the other cylinders. Something just does not seem right to me. Less or similar leak down should have produced more equal compression results. I know the leak down test indication to me is far from conclusive as there are a few other senarios I though of. Still It also makes me doubt that there is an injection pump issue or injector issue with that cylinder.

Almost everything you have posted made me me think that checking the valve mechanism for that cylinder earlier and now to me there is even more reasons in my mind to do it. Or inoperative intake valve restricting the amount of air input available to compress. Sorry about the length of this post. I can also be wrong. Keep at it as well. I do not visualse a really expensive issue yet.

kalikar85 · #98 06-20-2015, 11:35 PM

Yeah, do you know any good ones in SF bay area? This guy was recommended for mercedes diesels.

If you read back I already checked the injector.

Heres a list of what I have left to check. Maybe someone can chime in with likelyhood, and add others to the list that Im not aware of.
Fuel pressure
Timing chain tensioner
Timing
Pre chamber

What internal engine/mechanical parts are able to fail without affecting compression?

Left Coast · #99 06-21-2015, 12:19 AM

Worth noting that FSM states that allowable total pressure loss is 25%, 10% on the valves or head gasket, and 20% on the rings. Sounds like a pretty tired engine.

Seems odd to me that your mechanic would just give you the data without offering an interpretation, or at least an opinion on what might be causing the uneven compression/ leak down. Did he really have nothing to say? Is this mechanic not interested in fixing this car?

Ordinarily, the diagnosis develops from carefully listening to where the air is going. That's sort of the whole point of the exercise. So was that leakage going out the exhaust, the intake, the crankcase, or through another cylinder? If the indications are worn rings, then it's probably not worth doing anything more. But, if all of your valves are leaking, it might be possible to bring it back to good health.

kalikar85 · #**100** 06-22-2015, 04:57 PM

Right, so the mechanic said that it was not escaping from the valves or the head gasket from which one can deduce it is leaking out the cylinder as a result of a cracked piston or piston ring. He suggested that the next step would be to pull the head off and inspect the cylinder for scoring.

Left Coast · #**101** 06-22-2015, 08:11 PM

Quote:

Originally Posted by kalikar85

Right, so the mechanic said that it was not escaping from the valves or the head gasket from which one can deduce it is leaking out the cylinder as a result of a cracked piston or piston ring. He suggested that the next step would be to pull the head off and inspect the cylinder for scoring.

It's all five cylinders that are out of spec. Seems odd that compression is pretty good on four cylinders that show so much leakage. I suppose that it's possible. You won't know for sure what needs fixing until the head comes off, but it sure sounds like the rings are shot. I'd be looking for another engine if this were my problem, assuming that the rest of the car is worth it.

stukreit · #**102** 11-02-2015, 08:18 PM

kalicar85:

fyi I am in palo alto and have a dissassembled 617.952 all cleaned up
and machined, so if you're curious to see what the internals look like in
hand, you're welcome to drop by. There are other projects ahead of it,
so I won't be assembling it for a while. When it gets started, I'll be
posting a lot of newby questions to this forum.

Stuart