OM602 - 91 300D - Idle Issues

[JamesDean]

Hi Guys,

Working on my 91 300D, hoping to get your thought on my strange idle problem.


On cold start after about 1min or so of a decently normal idle it will suddenly sound worse and worse, like a cylinder is not running right. Once that happens all kinds of white smoke comes out the tail pipe.

I took a video so you could see.


https://www.youtube.com/watch?v=S9bNJaLoGx4&feature=youtu.be

I have new injector nozzles rebuilt by greazzer and have replaced the delivery valve seals already.

What do you guys think?

[Diseasel300]

Does this car have afterglow? The delay seems like it could be enough that the glow plugs drop out and start rough running.

Checked the usual suspects such as timing, chain stretch, compression, and looked in the prechambers for intact balls?

If this engine has the ELR solenoid on the back of the IP, try unplugging it and see if the hunting idle stops. I went through a shaking idle issue in my SDL recently and it was the EDS computer setting up a hunt loop due to bad capacitors. My idle is not perfect and the EDS computer would start goosing the throttle trying to catch itself. It didn't take much of an imbalance to set it off either.

[JamesDean]

Originally Posted by Diseasel300

Does this car have afterglow? The delay seems like it could be enough that the glow plugs drop out and start rough running.

Checked the usual suspects such as timing, chain stretch, compression, and looked in the prechambers for intact balls?

If this engine has the ELR solenoid on the back of the IP, try unplugging it and see if the hunting idle stops. I went through a shaking idle issue in my SDL recently and it was the EDS computer setting up a hunt loop due to bad capacitors. My idle is not perfect and the EDS computer would start goosing the throttle trying to catch itself. It didn't take much of an imbalance to set it off either.

To answer some of these questions:

The chain has 125K on it. Replaced some 12 year ago. It has not been checked for stretch. Nor has timing or compression been checked.

I must admit I have been around diesels for a long time but I've never done much with the prechambers, what do the balls look like under normal circumstances? what do bad ones look like?

I saw a thread by mach4 with some pictures that looked pretty bad but I didn't see the balls. The side of the prechambers, in his photos, looked pretty warped/damaged.

I am suspecting this is not an EDS related problem. This doesnt feel like the engine idle is uniformly off just that one or two cylinders are firing out of order.

[dieselbenz1]

yes your car has the after glow relay so incomplete combustion when the glow plugs shut off. I'd check compression.

[Diseasel300]

With only 125K, it would be doubtful that the chain is stretched far enough to cause timing issues. It wouldn't hurt to check timing just to establish a baseline.

The OM60x prechamber has a "ball" in it that the injector sprays on to help vaporization of the fuel. In the linked image, it is the part that is pointed to with the red arrow:



If you peer down the hole that the injector screws into with a strong flashlight, you should be able to see it and the tip of the glow plug.

If the prechambers check out and the timing is good, move on to checking compression. A '91 should have afterglow, if you have low compression in 1 or 2 cylinders, you can have poor running issues once the glow plugs shut off. The earlier 80s cars didn't have afterglow, so they'd be rough right from the start.

[dieselbenz1]

Have you checked for air in your fuel system? I had a tiny amount of air observed when I installed a clear fuel filter in the return line.

[JamesDean]

Thanks for the info. Hopefully I can get some time this weekend to check out the prechambers. I've got a cheap USB camera so we'll see if I can get pictures too.

A few questions

1) Is it common for the prechambers to wear out and need replacing after so many miles? Or is that more a function of injector wear? If the injector wears to a point where it is not operating well, I would imagine that could accelerate prechamber wear and cause them to need replacing prematurely?

2) I've never done a compression test before. I've just read about them casually over the years. It is performed by removing all injectors, disabling fuel supply to the IP, unplugging the glow plug relay and putting the tester into each injector hole? I believe, just need to get my hands on a tester/kit.

[JamesDean]

Originally Posted by dieselbenz1

Have you checked for air in your fuel system? I had a tiny amount of air observed when I installed a clear fuel filter in the return line.

This is a good question. I need to look more into this. I think I have some leaks on the IP too. I'm not sure where exactly.

[Diseasel300]

Originally Posted by JamesDean

Thanks for the info. Hopefully I can get some time this weekend to check out the prechambers. I've got a cheap USB camera so we'll see if I can get pictures too.

A few questions

1) Is it common for the prechambers to wear out and need replacing after so many miles? Or is that more a function of injector wear? If the injector wears to a point where it is not operating well, I would imagine that could accelerate prechamber wear and cause them to need replacing prematurely?

2) I've never done a compression test before. I've just read about them casually over the years. It is performed by removing all injectors, disabling fuel supply to the IP, unplugging the glow plug relay and putting the tester into each injector hole? I believe, just need to get my hands on a tester/kit.

The prechambers SHOULD last the life of the engine. However, there have been cases where the rod supporting the ball has come loose or been cut off by an injector squirting instead of spraying. It's a rare occurrence, but it will definitely affect the fuel vaporization and combustion in the affected cylinder. I only bring it up as a possibility since it seems to run fine with the glow plugs activated.

Compression testing is pretty easy. Pull the injectors, tie the stop lever down, disable the glow plug relay, and crank. Watch the pressure as it builds and let it compression hit 5-6 times for each cylinder then record the value for each one. The first compression hit for each cylinder should be >200PSI in a healthy engine, and you should reach peak pressure in 2-3 compression hits. If pressure builds slowly, or if you have a low first compression hit, you know you have problems that need attention. Cylinders should have no more than 10% difference between highest and lowest pressure, and within 25-30PSI for adjacent cylinders in a healthy engine.

[JamesDean]

I'll try to get my hands on a compression test kit and carry out the test.

Just to continue the conversation, let's assume that I find low compression in cylinder 1, for example.

That could be indicative of multiple things I would imagine, most common ones being?

Just trying to see where this goes down the road.

Thanks for all the info and assistance.

[dieselbenz1]

Cylinder 1 on the 602 turbo has a habit of head gasket failure around the oil hole between the head and block. My head gasket failed at number 5 water leaked into cylinder.

[JamesDean]

I suspect that MIGHT be the root cause of this issue. MIGHT.

The compression test would at least point towards a possible HG issue, correct? More so than any other test (aside from the obvious--hey look who put milkshake in my coolant!)

[Diseasel300]

Low compression can be any number of things - head gasket breach, worn engine, worn valve guides (certainly suspect!), worn valve seats (see worn valve guides <--- ), bent connecting rod, etc. The most common sources of low compression on the 60x seem to be head gasket breaches and worn valve guides on the earlier engines.

[moon161]

Your compression test kit might work for injectors or glow plugs, best to determine before you take parts out.

[Diseasel300]

Originally Posted by moon161

Your compression test kit might work for injectors or glow plugs, best to determine before you take parts out.

The OM60x engines are WAY easier to do the injectors for compression testing. The glow plugs are buried up underneath the intake manifold. Getting to them requires removal of the manifold, or some serious contortions.