the shakes - PeachParts Mercedes-Benz Forum

rg2098 · #1 04-13-2006, 07:27 PM

I've gone over everything;

fuel system sealed (no air leaks)
new motor mounts
cam timing set (valves adjusted as well)
pump timing set fairly close
new rack dampner bolt
5 new Bosio nozzles just swapped in

Any ideas why it still wants to rip itself out of the engine bay? I just installed the new nozzles which have done next to nothing. The only thing I have noticed is now it comes to a smoothish idle for a few seconds before developing the shakes. This is my show car and is embarrassing to drive with other people with it shaking so bad.

biobenz617 · #2 04-13-2006, 08:30 PM

I have the same problem with my 300D-T.

replaced:
motor & tranny mounts
motor shocks
bosio injectors (DIY balanced with spare shims)

...and still shakes. Sometimes it does, sometimes it doesn't. I thought it was my one cylinder with low compression, but it shakes intermittently. Have you checked your compression/leakdown?

Does anyone know whether the valves rotate slowly while the engine runs? One of my exhaust valves is leaking and maybe a leak is being covered/uncovered while the exhaust valve rotates in its seat. Then there would be uneven torque per cycle at idle and would shake the engine more.

rg2098 · #3 04-13-2006, 11:16 PM

Well I did notice the #1 and #4 injector seats were covered with oil while the rest were dry. I haven't run any tests regarding compression, I figured when it started at 5 degrees without a block heater last winter, the engine was fine.

biobenz617 · #4 04-14-2006, 12:44 AM

Hmmm, I seriously doubt you have compression issues then. Mine won't start under 30F without a couple hours of block heatage.

Do you think diesel spilled on your injector seats while removing them? How does the car run otherwise? Mine runs strong besides the starting issues and shaking at idle.

Brian Carlton · #5 04-14-2006, 01:47 AM

What about a bad prechamber?

If one of the balls is in bad shape and not dispersing the fuel properly, that cylinder would be way off on power as compared to the remaining cylinders.

Couple of things you can do to verify a specific cylinder:

1) You can crack the injector lines.......one at a time.......but you'll probably need a more accurate way to measure the drop in engine speed other than your ear.

2) If you can get one of those infrared temperature sensors, and check the exhaust manifold directly at the ports, you might be able to see one cylinder lower than the other four.......this would steer you in the right direction.

3) That test that measures the small voltage from the glow plugs while the engine is running might be valuable for information........as well.

Maroon 300D · #6 04-14-2006, 02:14 AM

My car also gets the shakes, but only after more than an hour of highway driving, and then only sometimes. But my car runs cool, it usually runs around 50-60 and gets up to 70 on the highway. I'm going to replace the t-state soon, hopefully it won't make it worse.

I was thinking maybe it had something to do with the fuel filters and I'm going to replace them, too, but maybe this will require a little more work on my part

.

rg2098 · #7 04-14-2006, 08:24 AM

I didn't think about the pre-chambers. The car runs extremely well at all other conditions. When it was colder out it would always "miss" on just one cylinder for about 15 seconds (5 new glowplugs, harness and all reamed out so thats ruled out). Like I said I am not worried about compression but I was alarmed that the #1 and #4 seats were covered in oil. Is that a sign of a bad pre-chamber?

pawoSD · #8 04-14-2006, 09:31 AM

My car has a slight shake when its hot out at idle....only if I have been doing some real revving and driving in the city, or a 10+ mile highway run though. I changed rack damper pins last fall, and it made about a 60% difference in the shaking. Currently since I am running on a brew of soy oil/rug/diesel though at idle I can't even hear/feel it running! No shaking even when coming off the freeway....

Our '83 we believe has worsening injection problems, it now "lops" at idle when in gear, feels like it wants to stall, but it never does and never has (yet).....but as soon as you take off its smooth and powerful, but quite a bit of smoke. It also nails heavily at idle either in drive or in park. We ordered the bosio nozzles and are going to have a shop by here put them in and balance/pop test them. Hopefully that will cure the problem....I hope that engine's pre-chambers are still ok....

barry123400 · #9 04-14-2006, 09:58 AM

At least the number one and four prechambers should be looked at. Prechambers could be gunked up if not actually defective. Yes the reading of the glow plug milli volts could confirm less heat is being generated perhaps in those two cylinders than the others. Just read it from the glow plug harness plug in. If you could post your indicated voltages it would be appreciated. Takes so little time and might give a signifigant indication. Or it might lead you to an unsuspected cylinder. Just might give you an indication of all being equal proving perhaps it is not the problem or test is not sensitive enough for this. Try it as it cost nothing to do plus may or may not indicate something usable at this stage. Or after you have repaired the real problem its signifigance will be known. Whatever you record or do not record might be of some use in determining the sensitivity of this test too. Remember your glow plugs voltage output is going to be around ten milli volts at idle. An additional help in diagnosis might be to read them a second time at say quarter throttle. Voltage will be higher and may or may not show a greater spread of voltages. Unfortunatly the thermal reading of the individual cylinder manifold temperature on this design is hard as it is one combined manifold rather than the separate manifolds on big diesels. That could work as well and would be a very good test other than the manifolds mass and connected design. You might have to have a dead cylinder before the thermal difference would be signifignt. Compounded by the lower average temperature of a diesel exhaust compared to a gas engine. If you have an unequal power balance problem I think you have a chance of picking it up by reading the plugs but maybe not. The problem is suspect and this is just a test to verify it's existance and perhaps lead you onward. Please post the results again if tried so people can have a little fun at my expense..... To get away from my interests a little. A gentleman posted a good observation recently. With the injectors removed the ports should all puff out about equal when turning over the engine to verify pre chambers are all clear of obstructions. Made a lot of sense to me.

Afterthought, does an italian tuneup perhaps burn a lot of gunk out? People have reported a lot of improvement too many times to ignore it totally. Car been driven hard in last year or so?

barry123400 · #10 04-14-2006, 10:18 AM

Pawosd, Your kind of description plus all too many others led me to examine if there was a good valid test for hobbiests like myself to determine where the problem might be. Or verify that there was really a problem there if suspected. The power drop test was not good enough for the average ear plus it had too many inherent shortcomings. When I found out that glow plugs acted like thermocouples I saw a gleam of light perhaps. The jury will be out for awhile but only hope it turns out to be totally valid as I have nothing else in sight with even the slightest possibility at this time. Call it for the common good. When you burn vegatable oil I think the flame front is longer and softer than when burning diesel. Hence will lessen the apparent effect of problems to do with injection of the fuel. That is why the engines are so much quieter in my opinion as well. Also may be why the fuel milage is substantially less with vegatable oil. Energy release has a much longer duration interval combined with not as many total btu available. Or could be long release period with even more btu availability but compounded by it occuring with a much longer peak burn. If so you should be able to advance your timing a little I would think over burning fossil diesel. You are aware it is already established that for overall timing of engine to pump using the milli volt method has longed been applied by other manufactures? Certainly that is not the case if burn once established is a constant. Only would apply if it slowly reaches a peak burn. Guess it just depends on what is transpiring in there. I have not thought about the ramifications of alternative fuels as they are just not one of my present interests.

Fuel at 6.00 per gallon might change my attitude though. It is about 4.00 per american gallon here now. Gas about 4.40 per american gallon for regular. I just know they are going to spike it up for the summer. It has started a little already I think. Perhaps my perspective is flawed. We should band together and buy an oil company. Better put my soapbox away now and take my meds.

barry123400 · #11 04-14-2006, 11:15 AM

maroon, changing the fuel filters occasionally is of course a good ideal in itself. The odds of a car being able to cruise at 70 nicely yet having a rough hot idle periodically right afterwards being fuel filter related is a bit of a long shot. I think I would want to adjust my valves. When really hot they will lengthen the stems. If you have not adjusted them in the last while or never that is perhaps what I would start with. Remember really hot valves are going to be longer and if inadaquate clearence is not in the valve train on only one valve you have a rough hot idle.

I like simple cheap repairs myself as long as they are valid.

Of course just check them for the right clearance and only adjust if indicated. Much faster and simpler.

Maroon 300D · #12 04-14-2006, 11:40 AM

Thanks for the advice, Barry. I did have the valves adjusted 2 1/2 months ago, soon after I bought the car, but it wouldn't hurt to look at them. It would be great if it were something relatively simple.

psfred · #13 04-14-2006, 11:48 AM

Sadly, once you have eliminated other causes, the IP will eventually get to the point where it will shake at idle no matter what you do with the rack dampner pin -- the spring inside that the dampner works against gets weak and allows the rack to vibrate in sympathy with the engine (only the 5 cylinder, by the way, because of the longitudinal vibration the 4s and 6s don't have). Cure is to replace the internal spring on the rack....

Very expensive, don't bother unless the pump needs other work.

Peter

barry123400 · #14 04-14-2006, 12:57 PM

With a little luck you one might locate a used pump prefferably still on a beat engine or car for very few dollars. I preffer to get a used pump still full of diesel myself. Buy it up cheap. Take it home and submerge it in a known good storage fluid. Then if a person ever has a tired pump or even a suspect one you might luck in with it. I do not believe many of our older cars are scrapped because of maginal or tired injection pumps. I probably know where I could get my hands on 30 or so quite fast in the next few days if I wanted one. Again not rocket science and think I learnt of one possible weakness of these five cylinder pumps from the last post. Or rather than a weakness perhaps one should say possible aging symptom. I think if I desired a suspect good pump today I could have a possible good replacement tomorrow for perhaps 30.00. This option will not be there much longer as these cars are going to dissapear through the car crushers in the next few years. Perhaps in certain areas they already have.

rg2098 · #15 04-14-2006, 03:48 PM

Well I turned my idle down from 800 down to 700 and it get rid of my severe shake. I have a vibration feeling but no violence. Hopefully the injectors need to be balanced with the new nozzles and I don't need a pump.