Tough Diesel Idle problem

[Jim Sutton]

I have a pretty unique problem with my 1984 300sd that has had me occupied for about six months now.

I have read quite a bit about this but have not found that anyone else has seen something like this. I am now at the point that I need some serious help or will need to break down and say I can’t fix it and bring it to a mechanic.

I have owned my car for three or four years now. I have worked on it continuously fixing all the little things that break on these older cars. It ran ok, but last year I acquired a motor and trans, so I decided to rebuild both of them and swap them into my car. I take quite a few long trips with this car so I hoped to improve my reliability.

Here’s my problem:
When I take the car on a extended trip (20 miles or more), it develops a problem at idle. Almost like one cylinder is not firing. The car rocks, but stays running. Give it some "gas" and all is well, although the car does not feel as peppy as before. Let the car sit overnight and start it in the morning and the engine idles smooth again. Any ideas what this could be??? If you have an opinion, no matter how wacky it may seem, I am interested.

Let me share what I can about the car.

Valves – Adjusted properly. Timed correctly.
Compression – on a cold engine, all approx 380
IP – timed to 24 BTD with drip test.
Injectors – Monarch, purchased last year. I pop tested each and balanced to between 133 and 137 bars. New heat shields.
Run WVO, two tanks heated.

Hope you guys can help with this one. Thanks so much.

Jim

[Phillytwotank]

I'm just shootin from the hip here... Does your car have aCigar hose on the return line? Lack of one could cause that.

[Jim Sutton]

Yes I do have the cigar hose. Why would not having a cigar hose cause that problem?

[SD Blue]

Sounds like a rack dampner problem. On the Injection Pump, nearest the firewall, is a"bolt" with a locknut. Basically, it is a bolt with a spring-loaded tip that dampens the fuel rack when it returns to the idle position. (If you do a search for rack dampner, you may find a photo of this.)
First, note the color as a "gold" one is the updated version of this.
Second, after verifying the new version, adjustment may be needed. After the engine is warmed up (while it is "loping/rocking" is even better), loosen the locknut, using double wrenches, and "tighten" the rack-dampner bolt. Only adjust it 1/4 turn at a time. Too tight and you will have hard starting.

[rscurtis]

I lived with that annoyance for a couple years with my '83 300D. The hotter it was, the worse the problem. I couldn't believe a simple 10 minute adjustment fixed it.

[Diesel911]

Try a Diesel Purge. It may be the WVO is causing issues with the Injectors.

How many miles ago was the Valve adjustment?

I am assuming the Motor and Transmission Mounts are OK.

[Maxbumpo]

Does it have the problem when using the fuel it was designed to use (#2 diesel)?

After rack damper bolt and diesel purge, you could try loosening injector lines one at a time to isolate the offending cylinder, then try moving the injector to see if the problem follows. If it doesn't, then focus on the delivery valves in the injection pump. After that, perhaps it is time for a compression check.

Any evidence of coolant mixing with the engine oil?

[Jim Sutton]

Damper Bolt - I did confirm that I do have the upgraded damper bolt. I have played with it in the past but still think it could be the issue.

Problem happens with either diesel or wvo.

The break the injector line open test was unsuccessful. No difference on any of the lines.

No loss of coolant.

Last valve adjustment 1000 miles ago.

Compression test last week - 380 +- 10

Mounts are good.

Another note: I do have the valve (cant remember the name) on the IP pump adjusted to give me more pep pulling off the line. Just a light amount of smoke if I step on it.

Seems to me has something to do with the engine being hotter. Is it possible for the injectors to get hot and stick?

[cho]

you might wanna look at this thread.. beagle,whunter,army and the rest of guys helped me a lot...


edit: it seems that those rebuilt engines doesn't like the old IP pumps

valve on Ip is ALDA and IIRC can not be a reason for that rock and roll we have...
..

[shadetree77]

while we're on the topic. i put new nozzles and pop tested today, much quieter and more peppiness. but i still have the hot idle shakes too. i tried adjusting the rack dampener but it made no difference at all (went real slow, tried all the way in, all the way out (like completely removed it)) it had no effect whatsoever (got an updated gold bolt) i'm outta ideas

[Diesel911]

I had an Air leak that showed up when the Engine was Hot. But, it did not shake like yours is doing.
I found that the 2 Fuel Inet Hoses were hard and inelastic and for some reason when the Engine was Hot allowed Air into the Fuel System.
A few Dollars of Hose fixed it.

There is also this long Thread.
Long Fuel Pressure Relief Valve/Overflow Valve Thread
Fuel pressure relief valve adjustment

Related to the above is Fuel Supply/Lift Pump issues. Fastlane sells a Kit that has New Valves and Springs + Copper Crush washers needed to replace the Valves.

Not supplied is the little 5x1.5mm O-ring but you could get the somewhere.

I found this in my Notes:
Idle Shake gone after Fuel Supply/Lift Pump cleaned
http://www.peachparts.com/shopforum/diesel-discussion/284608-fuel-pump-suction-delivery-valve-post2549341.html#post2549341

Fuel Supply/Lift Pump O-ring stuff- has links to 2 sets of pics of old and NEWER LIFT PUMP
http://www.peachparts.com/shopforum/diesel-discussion/285874-190dt-mechanical-lift-pump.html#post2559787

[pawoSD]

To get the rocking to go away on some engines you need to work on it for a while while idling making minute adjustments to the idle speed and rack dampener bolt until you find the best spot. Took me close to 45 mins on mine, but its been great ever since....used to rock like crazy at a warm idle.

[sassparilla_kid]

You might want to try adjusting the IP timing to 26* BTDC, it probably won't have any affect on the rocking but it is how the cars came stock from the factory. Might have some power/mileage gains which are always good

[Diesel911]

No one has mentioned the Idle Speed.
What idle speed does it run at when it is Hot?

[reinventthewheel]

I second the IP timing, it can cause shaking if the timing is too far advanced