Trying to troubleshoot a rough running 617 - PeachParts Mercedes-Benz Forum

mach4 · #1 10-12-2012, 12:29 AM

Context: '85 617.952 Cali with about 215k miles installed in a 107 chassis. EGR blocked off, ARV disabled, Trap Cat removed, motor mounts are urethane filled and engine shocks removed. Very little blow-by. Running dino diesel with 1% 2 cycle oil to add lubrication for ULSD fuel. All filters replaced in the past 7k miles. Mileage over the past 2263 miles is 29.4 mpg.

Symptoms: Rough idle at 750 rpm, smooths out by 850 rpm, smooth until 1400, rough at 1400-1900 rpm (1500 worst), smooths out at 2000 and stays smooth all the way up. These symptoms have been present since I installed the engine.

Actions: Adjusted valves. Pop tested injectors (found one marginal and replaced with a good JY injector). I bought a new set of Monark nozzles but haven't been able to get shims to reach balance, so those have not yet been installed. Found a set of great injectors at the junk yard this past weekend that popped really nice - pattern, leakdown and pressure - which I installed. No change in symptoms, except maybe a tiny bit worse. Compression checks good. Poor mans compression check was 8 sec and measured was as follows-

1- 350#
2- 360#
3- 350#
4- 310#
5- 310#

Visual on prechambers look ok.

Turbo has been inspected, spools quickly and pulls 9.5 lbs

I've done a diesel purge with relatively little discoloration in the purge during the cycle.

Today I cracked each hardline while running and got a pronounced increase in roughness which was about the same for 1-4. Number 5 was noticeably less change than the others, but there was a noticeable change and fuel came out of the hard lines.

I have not attempted to adjust nor have I replaced the rack damper (appears to be bottomed out) I have also not yet checked either chain stretch or timing.

Planned Course of Action: My next planned step is to swap injector 4 and 5 to see if the problem stays with the cylinder or follows the injector.

If the problem is the injector, I'll replace it (or swap in the Monarks when balanced) and if the problem stays with cylinder #5 it would appear that I've got an injector pump issue.

Questions:

Is there anything else that I should do in the way of diagnostics for this problem?
Am I on the right track with my next diagnostic steps?
Is this the kind of symptom that would potentially point to an injector pump problem?
Have I missed anything?

Thanks

Doktor Bert · #2 10-12-2012, 01:18 AM

Turn rack damper in 1 turn...

cho · #3 10-12-2012, 03:08 AM

Quote:

Originally Posted by mach4

2- 360#
4- 310#

50 is kind of a big difference,IIRC also could be reason for shaking

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Doktor Bert · #4 10-12-2012, 03:24 AM

Yes, but you would be amazed at what the rack damper can do....

cho · #5 10-12-2012, 05:19 AM

Quote:

Originally Posted by mach4

Questions:

Is this the kind of symptom that would potentially point to an injector pump problem?

do you have bigger shakes/roughness on idle when fully warm compared to cold idle?

mine was noticeably bigger on warm,pump has to be recalibrated
DV also adjusted....

anyways i would try Dr.B advice first....

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layback40 · #6 10-12-2012, 05:42 AM

Quote:

Originally Posted by cho

50 is kind of a big difference,IIRC also could be reason for shaking

.

X2
If those numbers are reliable, one would think you have a head gasket issue between 4 &5.
Dont get excited yet though, it maybe just that there was difficulty doing compression test on 4 &5.
I would be inclines to swap injectors from up front with the one that appears it could be bad.
Rack damper worth a try.

barry12345 · #7 10-12-2012, 08:41 AM

You could read up and try the milli volt method in the archives to find out what is going on. This is the exact kind of situation it is most usable for when the common things have been eliminated.

Or sometimes first to save time and effort. Obviously all the cylinders are not firing at the same temperature. Just take no short cuts or it can mislead. I too spoted the identical compression readings between four and five but since effects are not almost identical when disabling injectors 4 or 5 it may semi safely be put aside for now. Or at least until the milli volts suggest what is going on. Even if the milli volts determine the number five element has an issue in the injection pump you may be able to do something about it. Milli volts should enable enough proof again if done properly.

vstech · #8 10-12-2012, 08:59 AM

Quote:

Originally Posted by Doktor Bert

Turn rack damper in 1 turn...

he stated the rack damper is bottomed out...

vstech · #9 10-12-2012, 09:02 AM

Quote:

Originally Posted by mach4

Context: '85 617.952 Cali with about 215k miles installed in a 107 chassis. EGR blocked off, ARV disabled, Trap Cat removed, motor mounts are urethane filled and engine shocks removed. Very little blow-by. Running dino diesel with 1% 2 cycle oil to add lubrication for ULSD fuel. All filters replaced in the past 7k miles. Mileage over the past 2263 miles is 29.4 mpg.

the frequency of fuel filter changes is dependent on the quality of the fuel stations, and has zero to do with mileage. I would start with new filters. especially if you just did a Diesel Purge...

Zacharias · #10 10-12-2012, 11:41 AM

Two points:

1. You are supposed to replace both fuel filters after a diesel purge (in theory, anyway)

2. Not all OM617s want to idle at 750 as they get older. I had one that only liked 850-ish and one that preferred very, very slow, about 650.

You could try adjusting the idle up or down a bit, then back out the rack damper bolt and try adjusting it again.

Turning the bolt all the way in isn't always the answer to smoothing out the idle. On my SD that liked 650 rpms, I had to spend a lot of time creeping the bolt back and forth until I hit the sweet spot (which also in involved experimenting with idle speeds until I found that 650 worked best). As I recall it was about 2/3s of the way in, nowhere near tight (that was where I started).

jt20 · #11 10-12-2012, 12:32 PM

Worn injection pump.

If you can find a cheap spare from a trusted source, it may be worth the swap. Sounds like your mileage is good though. May just be easier to adjust the injectors by trial and error so they match the performance of the pump (if smoothness is your main concern).

Doktor Bert · #12 10-12-2012, 02:32 PM

Quote:

Originally Posted by vstech

he stated the rack damper is bottomed out...

That's not good. I didn't see that...

mach4 · #13 10-15-2012, 12:08 AM

I'm continuing to work on the issue, with no success so far.

I swapped injector 1 and 5, and while the initial test of cracking the hardline at idle showed 1 and 5 now about the same, the vibration is still approximately the same. Strangely the peak secondary vibration that was at 1500 has now moved up a bit to about 1700.

I did turn the rack damper in a full turn which bottomed it out. (It looked like it was bottomed out initially, but I was able to get one turn.) No noticeable difference.

I'm reading up on the milliamp method and trying to make sense of what that's all about. In the meantime, I'm thinking that the problem may be with the injector pump or possibly my urethane filled motor mounts (and lack of engine shocks) may be part of the problem as well.

I've got a couple of thoughts relative to the mounts. First to swap in a regular set of mounts just to see what the difference is with a completely stock support system, and the other possibility is to go with a softer urethane (currently using Shore 75) and possibly replace my 1/2 inch motor mount spacers with a 1/2 inch urethane to get more cushioning and vibration absorption. (I'm using filled mounts because I'm a little tight on clearance and can't tolerate a collapsed mount down the road as I'd have the oil pan hitting the subframe.

I'm at a point where it probably makes sense to go back and double check everything just to make sure - readjust valves, redo compression check, install new nozzles etc.

whunter · #14 10-15-2012, 12:35 AM

Does the power change with the high end roughness?
If not, going back to the engine mounts is a wise idea.

It sounds like you did have some injector issues, possibly resolved now.

The rack damper pin needs to be replaced, from the idle shake description.

Call me Monday to discuss other thoughts, any time after 10:00 AM eastern standard time.

I have a personal interest in the engine mounts.
http://www.peachparts.com/shopforum/general-information/324560-homemade-polyurethane-engine-mounts-bushings.html

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mach4 · #15 10-15-2012, 01:33 AM

Quote:

Originally Posted by whunter

Does the power change with the high end roughness?

No power change - just an increase in vibration moving through the range.

If I were to graph it, the perceived vibration would look something like this