Distinct miss just above idle- 617 turbo - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 08-21-2013, 02:08 PM

Years ago, my bro and I put a junkyard 617 turbo from an '80 SD in his '81 300D. It had a miss in it, but found out it had a dead cylinder, so that engine was sold. I since got the car from him, and put in a good (at least I thought) 617 turbo from an'84 300D parts car. The engine has a distinct miss just above idle, but it not felt when accelerating. The car has great power (just about as quick as my former '82 300CD), and accelerates smooth and quick. However, driving down the road (35-45 MPH), it has a miss that is worst at about the RPM that is just above idle. I have checked the compression (all at 300+), replaced the injectors with rebuilt units with Monark nozzles, adjusted the valves, but it still has an annoying miss. It is almost like there is something wrong with the trans or torque converter (out of balance), as that is the only common thing to both engines. The guy I got the parts car from (bad trans), said it ran smooth when he drove it. I thought of doing a leak down test, but figured there was no need, as all 5 have 300+ compression. Any ideas?

Stretch · #2 08-21-2013, 05:16 PM

So you didn't keep the same IP / ALDA then?

ROLLGUY · #3 08-21-2013, 07:12 PM

Quote:

Originally Posted by Stretch

So you didn't keep the same IP / ALDA then?

The IP and in fact the entire engine that my bro and I got from the JY got sold. I only changed the injectors on the replacement engine, thinking I had a bad one causing the miss. No change after the rebuilt injectors. I also thought I might have had a couple tight valves (found a couple), but it still runs the same after adjusting the valves.
After getting the car warmed up today, it seemed to idle and run better. With the A/C on and idling, the miss is more pronounced when taking off from a stop. It smooths out just before shifting into second.

Stretch · #4 08-22-2013, 01:25 AM

Well the 1981 300D is the basic car then?

If so I guess this was a non turbo 300D and now you've effectively turned it into a turbo one correct?

Vacuum system - what did you do to it when you changed the engines over?

Throttle linkage - same question

ROLLGUY · #5 08-22-2013, 09:28 AM

Quote:

Originally Posted by Stretch

Well the 1981 300D is the basic car then?

If so I guess this was a non turbo 300D and now you've effectively turned it into a turbo one correct?

Vacuum system - what did you do to it when you changed the engines over?

Throttle linkage - same question

All the needed parts came from the running (before the trans went out) 1984 300D-T (throttle linkage, vac system etc). The trans is the original 1981 (722.1XX?) including the torque converter. The guy I got the donor car from does not think it ran rough at all when it was running for him.

BTW: the donor car I bought is the car that I started a thread about last year when the trans went bad. He was driving it to run some errands, and parked it. When he came out to drive it to the next place, the car would not move in any gear (forward or reverse). After being towed, we changed the fluid and filter, but still no movement. I would like to get this trans fixed eventually, but don't want to pay the big bucks to have it totally rebuilt. I am sure it is something simple.

Stretch · #6 08-22-2013, 10:21 AM

Something simple - sure - could be!

How about running the engine with the shut off vacuum line disconnected (for the sake of others who might stumble on this - not you ROLLGUY - you'll have to use the shut off lever on the IP to stop the engine)

barry12345 · #7 08-22-2013, 11:05 AM

Why not elevate the revs until what you think the miss is occurring at. Then loosen one injector nut at a time to see if you can pin it down to one cylinder?

I was sitting here and wondering if it could just be air in the fuel type of thing. If that were the case you would not be able to identify one cylinder as the culprit. Anyways fairly smooth at idle and loosing the smoothness just a little higher and then becoming normal again does not strike me as a usual type cylinder issue.

Also if it will not present the miss problem under no load critically check the transmission fluid level.

ROLLGUY · #8 08-23-2013, 10:38 AM

Quote:

Originally Posted by barry12345

Why not elevate the revs until what you think the miss is occurring at. Then loosen one injector nut at a time to see if you can pin it down to one cylinder?

I was sitting here and wondering if it could just be air in the fuel type of thing. If that were the case you would not be able to identify one cylinder as the culprit. Anyways fairly smooth at idle and loosing the smoothness just a little higher and then becoming normal again does not strike me as a usual type cylinder issue.

Also if it will not present the miss problem under no load critically check the transmission fluid level.

The first thing I tried was to loosen one injector nut at a time. All 5 make the engine stumble, which agrees with my compression numbers (all-300+). I have driven the car quite a lot since first feeling the miss, so I doubt there is still air in the fuel system. Driving the car feels exactly like the previous engine that definitely had a dead cylinder, but I am almost sure this one does not (compression numbers are consistent). I know it will be a lot of work to determine for sure, but I have this gut feeling that there is something wrong with the trans or torque converter (out of balance?). I have a rebuild-able 722.3XX trans, but I am not sure I want to go through the work and expense to change the trans, only to find out the original trans had no problem (still shifts great).
The miss is definitely there under load, at lower engine speed. once the turbo comes into play, the thing is smooth and powerful.

Stretch · #9 08-23-2013, 02:03 PM

OK - I'll go along with it - if you think the transmission is at fault, why not measure the working pressure?

You might see a change in working pressure that coincides with the stuttering.

Generally speaking if you have an out of balance rotating vibration it will get worse and worse with an increase in rotational speed. As this is between 800 rpm and 2000 rpm I wouldn't expect vibration to be the cause...

...different tack...

...have you considered fuel line and tank? {Try a different smaller fuel tank / fuel supply to see if it's that)

ROLLGUY · #10 08-23-2013, 03:59 PM

Stretch, I appreciate you hanging in with me on this, but it is definitely a weird one and I think we are both grasping at straws. The only reason I am leaning toward the trans (or something from the flywheel rearward), is the fact that the engine supposedly ran fine in the other car, and all the compression numbers are good. That being said, it still sounds and feels like a dead cylinder (my bro's 300D 2.5 has a dead #5, and my car feels exactly the same).

Stretch · #11 08-23-2013, 04:30 PM

Quote:

Originally Posted by ROLLGUY

Stretch, I appreciate you hanging in with me on this, but it is definitely a weird one and I think we are both grasping at straws. The only reason I am leaning toward the trans (or something from the flywheel rearward), is the fact that the engine supposedly ran fine in the other car, and all the compression numbers are good. That being said, it still sounds and feels like a dead cylinder (my bro's 300D 2.5 has a dead #5, and my car feels exactly the same).

Have you ever bought a second hand engine that's not "good"?

(You know what I mean)

And hang about I thought you got the same fault with two different engines - isn't that right?

And sure we're grasping at straws - but that's half of the fun.

So OK we've got injectors ticked off the list.

Do you want to try the other things?

It is a bit of fun if you have the time / energy / willingness

Put it this way it is unlikely that someone with your experience would start a thread with a weird issue and then be surprised by someone saying something like "it is a simple fix just reverse the orientation of number 2 fuse"...

Diesel911 · #12 08-23-2013, 05:34 PM

I would not rule out a possible the Air Leak issue.
You could put a longer Hose in place of the Cigar Hose and submerge the other end of the Hose in Diesel Fuel to see if Air Bubbles are coming out.

Fuel Supply issue. Like the Fuel Pressure Relief/Overflow Valve and a worn Fuel Supply/Lift Pump.
If you have a Parts Car you could swap the Over Flow Valve and eve the Fuel Supply Pump. Do one at a time so if one fixes the issue you know which one caused the problem.

If the EGR is still there an functioning is it possible the EGR is coming on when it is not supposed to?

ROLLGUY · #13 08-23-2013, 05:52 PM

Quote:

Originally Posted by Stretch

Have you ever bought a second hand engine that's not "good"?
(You know what I mean)

Well, the guy I bought the car from parked it after the trans went bad. I had just (the week before) changed the oil, changed the trans fluid and filter, and the hoses and belts. I also remember adjusting the valves sometime before that. I don't remember the engine running rough the times he stopped by, or had me work on it.

Quote:

Originally Posted by Stretch

I thought you got the same fault with two different engines - isn't that right?

The previous JY engine had a dead cylinder, so that is why I put the present engine in. However, driving the car, it feels just like it did with the old engine.

Quote:

Originally Posted by Stretch

And sure we're grasping at straws - but that's half of the fun.
So OK we've got injectors ticked off the list.
Do you want to try the other things?
It is a bit of fun if you have the time / energy / willingness

Yes it is fun. I guess that is why I browse the DD forum EVERY DAY (sometimes several times a day) to try to help out those with less experience (you do the same).

Quote:

Originally Posted by Stretch

Put it this way it is unlikely that someone with your experience would start a thread with a weird issue and then be surprised by someone saying something like "it is a simple fix just reverse the orientation of number 2 fuse"...

Why didn't I think about that! I should check the #2 fuse. You are a genius!

ROLLGUY · #14 08-23-2013, 05:56 PM

Quote:

Originally Posted by Diesel911

I would not rule out a possible the Air Leak issue.
You could put a longer Hose in place of the Cigar Hose and submerge the other end of the Hose in Diesel Fuel to see if Air Bubbles are coming out.

Fuel Supply issue. Like the Fuel Pressure Relief/Overflow Valve and a worn Fuel Supply/Lift Pump.
If you have a Parts Car you could swap the Over Flow Valve and eve the Fuel Supply Pump. Do one at a time so if one fixes the issue you know which one caused the problem.

If the EGR is still there an functioning is it possible the EGR is coming on when it is not supposed to?

I will check the Fuel Pressure Relief/Overflow Valve. I have had problems with those before. In the cars I plan to keep (or at least in the family), I always delete the EGR plumbing as much as possible, and install non-EGR manifolds from a '78 300SD whenever I can find them.

barry12345 · #15 08-24-2013, 11:57 AM

Same basic sensation with different engine kind of rules out the engine usually. I would try the fuel supply replacement first. Forgetting about the relief valve and lift pump for the time being.

I was trying to think of a transmission scenario that could cause that type of symptom but came up dry. Based on my thought abnormal loading would usually just make the engine run harder usually rather than rougher. I also think that removal of the vaccum shutoff tube might be prudent as you may have some flaky vacuum issue that was present when the old engine was in there as well.