Lopey idle - pulsing oil PSI - PeachParts Mercedes-Benz Forum

oldmako · #1 06-12-2017, 07:49 PM

Took the old gal for a 500 mile trip the last two days. Now, I have a lopey (is that a word?) idle which is accompanied by a slightly flickering oil PSI needle. I can also hear a slight valve TICK. Its uneven - not crazy excessive, but its not smooth the way it used to be and I don't like it.

I adjusted the valves about 1500 - 2000 miles ago.

Is it possible that I mucked it up? The "Tick" is caused by what? The valve slapping shut on the cylinder head or the cam contacting the tip of the valve?

Readjust the valves or could this be something else?

1985 300CD

PS....how many of you guys remove the fuel lines when adjusting the valves? I recall seeing a YouTube vid in which he pulled the lines to make for easier adjustment. I just wonder if the extra work makes it worthwhile.

Diseasel300 · #2 06-12-2017, 08:30 PM

Check the valve clearance and see if you need to adjust the valves again. If you have a tight valve, it would certainly explain your rough idle.

The flickering gauge can be due to flaky sender (very common) or even due to fluctuations due to the engine loping. Remember that if the engine is loping in RPM, the oil pump is changing RPM as well.

oldmako · #3 06-12-2017, 08:36 PM

OK. Three questions,

1. Tight meaning the valve is not closing all the way correct? So, if its an exhaust valve it could be burning.

2. Think I could try and reuse the gasket? It was new when installed two months, 2000 miles ago or should I just get a new one.

3. What exactly causes the ticking?

Thanks.

Diseasel300 · #4 06-12-2017, 08:41 PM

Tight means the clearance is less than it should be. As the engine heats up, it can start to hold the valve open slightly.

Ticking is generally caused by excessive clearance. The OM617 doesn't have hydraulic lash adjusters, so a clattering valve train is due to being out of adjustment.

The valve cover gasket should be fine to reuse. You can typically reuse them several times before they get too hard and dried out to seal effectively. If it was new 2K miles ago, you should be able to use it several more times if you're gentle with it.

oldmako · #5 06-12-2017, 08:51 PM

Perfect. All as I thought.

Any opinion on the fuel lines? Even though I bought a set of hazet wrenches, I found the process a bit difficult, primarily because of them being in the way. Plus I have a bad back, so its entirely possible that operator error is to blame. I found it interesting that no valves needed to be tightened, the clearances were either OK to begin with or too tight.

NZScott · #6 06-12-2017, 10:37 PM

Lopey idle is probably rack damper bolt.

Have you got a video of this ticking? There's a good chance it's just the usual noise these clattery old engines make. Unless it's only been happening just now

Edit: woops, seems I had this page open yesterday and didn't refresh it before I replied

Maxbumpo · #7 06-13-2017, 07:36 AM

The oil gauge for a 123 is mechanical, not electrical, so I don't like the sound of that at all.

The ticking may simply be a loose valve, or something more sinister. First is double check your valve adjustment. If you still have the noise and flickering oil gauge, then I think you may have an issue with your oil pump, and a deeper diagnoses is needed.

Ceristimo · #8 06-13-2017, 12:44 PM

Does your lopey idle kind of sound like this?:
https://www.youtube.com/watch?v=3vrX2cZytBw&feature=youtu.be

That is my car, and in my case the idle gets weird whenever the engine RPM's are raised ever so slightly above idling. In the video I do it by gently pushing the go-pedal, but in real-life driving this happens every time I drive and coast to a stop. Slowing down and hitting between 15MPH and 5MPH on the way to 0 MPH and my idle is like that.

Oil pressure gauge will bounce up and down in rhythm with engine when it does that. I still haven't figured out what's causing it.

oldmako · #9 06-13-2017, 10:04 PM

I'd say that's close. I'll listen again tomorrow. When I bump up the idle (using my foot) just a tad the lopiness goes away.

I noticed recently that the first stage fuel filter is getting dirty. In my reading its been recommended several times that dirty filters can cause this, so I will change them both out - hopefully tomorrow as my first attempt to fix since its so quick and easy. The filters were last replaced in March 2016 when I bought the car. I've probably put about 5000 miles on them. I don't drive the old gal in the rain, or winter so she sat a bit.

After I change the filters I'll adjust the valves and hopefully this will take care of it.

Its a shame since the car has been rock steady till yesterday. It has always started instantly and settled down to a nice quiet (HA!) steady idle within less than a minute. It was just yesterday when I pulled off the interstate that I noticed the idle and oil PSI when I stopped at the first red light. The car also seemed a tad sluggish as well. Hopefully that is a direct result of clogging filters.

I'll try and repost if I solve this quickly for the benefit of those who follow. I am a diesel neophyte with just this car, and just 5K miles on it. So far, I have performed all the maint. Fortunately, the engine and trans have required only normal preventative care.

Thanks for the tips.

t walgamuth · #10 06-13-2017, 10:24 PM

If you have a tight valve you could drive around town a lot without permanent damage. A good long trip though might have burnt a groove in the valve and require replacement of the valve to cure.

Diseasel300 · #11 06-13-2017, 11:39 PM

Quote:

Originally Posted by Ceristimo

Does your lopey idle kind of sound like this?:
https://www.youtube.com/watch?v=3vrX2cZytBw&feature=youtu.be

That is my car, and in my case the idle gets weird whenever the engine RPM's are raised ever so slightly above idling. In the video I do it by gently pushing the go-pedal, but in real-life driving this happens every time I drive and coast to a stop. Slowing down and hitting between 15MPH and 5MPH on the way to 0 MPH and my idle is like that.

Oil pressure gauge will bounce up and down in rhythm with engine when it does that. I still haven't figured out what's causing it.

Your engine is missing/skipping. Several things could cause it, but check your valve clearances first, followed by a compression test. If you have a tight valve or low compression in one cylinder, that would cause the behavior you're showing.

You could also have issues with a delivery valve or a pumping element in your injection pump which would cause an injection misfire/skip.

Whatever the cause of the miss/skip, your oil pressure will follow the fluctuating RPM since the oil pump's pressure/volume is a direct function of its RPM. When the engine RPM is lower than normal due to a miss/skip, it is more pronounced since the oil pressure is lower than it normally would be at idle and you get surges in engine RPM as the governor tries to maintain a constant speed.

NZScott · #12 06-14-2017, 01:05 AM

Quote:

Originally Posted by Diseasel300

Your engine is missing/skipping.

Sorry, have to call bollocks on that. Rack damper bolt. Why does it run perfectly at every other RPM if it had a miss...

Rogviler · #13 06-14-2017, 01:15 AM

I have the weird lope in the video as well, but mine only occurs at idle (so it's way slower) and under specific circumstances. The weather has to be cold and I have to have driven a short distance first. Once to my destination it starts doing that only at idle until I turn the car off. Once I start it again it's gone. Also makes the oil pressure twitch, as I would expect with a slight change in RPM.

At some point I'm going to try a new rack damper bolt, but it's a very first world problem at this point so I haven't yet. Interesting thread though.

-Rog

Diseasel300 · #14 06-14-2017, 10:47 AM

Quote:

Originally Posted by NZScott

Sorry, have to call bollocks on that. Rack damper bolt. Why does it run perfectly at every other RPM if it had a miss...

Having gone through it in my SDL (different engine, same concept), I can say with 100% certainty that it is very possible to have an engine skip/miss at low RPM's and at certain operating conditions due to injection or fuel delivery problems. Was fuel supply issues in my case, namely air ingress due to worn O-ring seals in the lift pump. Mine would skip only only at idle, only at certain operating temperatures, and only after it had been returned to idle from slight RPM elevation.

For what it's worth, the OM603 has no rack damper bolt so that isn't a possibility in my example above.

Listen to the video, it is obviously not running on all 5 when it starts the shaking/loping.

For some bedtime reading, or a cure for insomnia, go check out the DV as a cause of nailing thread. When worn or failing to seal properly they can cause some strange issues at idle and low RPM.

barry12345 · #15 06-14-2017, 11:03 AM

Air getting in is potentially something to seriously check. It would enter the system at a pretty constant rate. So it would have more impact or effect at lower RPMS.

One member has pretty constantly posted over the years. That a piece of clear hose installed is a good ideal to examine for air. I have and still agree. Especially when something is not obvious.