'93 300D rough idle when cold

My 300D idles rough on cold start ups until it has been warmed some. I just checked all the glow plugs and they read .7 ohms ea. I've looked for lose fitting fuel lines, thinking it could be sucking air as it is cooling down from the night before. What else should I be looking for to solve this?

[stevebfl]

It is important to note whether the problem is a single cylinder misfiring or whether it is random misfires. Any idea of air in the pump chamber would be random.

If the misfire is a single cylinder a likely possibility is a fuel column leak down. This can happen either from the injector (into the cylinder slowly over time) or from the internal sealing of the pump element check valve (the fuel leaks back into the pump body and can't be detected except by symptom). In either leak the engine starts without fuel in one (or more) lines. It takes multiple injection pulses to refill the line, thus taking a while to run.

Our standard service for such problems is to remove injectors, bench test for leaks and spray pattern, check engine compression, verify visually the glowplugs (and carbon build-ups)through the injector hole, and reseal the pump element check valves.

We do the compression first as thats the other reason for a cylinder misfiring on start-up.

THis may be too simple of a solution

I have rough idle when i start my 84 300d for about a minute or two and it is a hot summer. I read in the forum that the relay does not shut off with the light in the car and may send voltage to the glow plugs for longer than the three seconds that the glow light is on. Now I give my car a good 10 count and she starts right up with alot less fuss.

hope this works for you too.

bob

Actually, I've realized that it isn't so much that it is rough, but it will all of a sudden cut out. I'm beginning to think that it is air bubbles in the line. It is certainly not a dead miss like low compression or a leaky injector. It will idle then jerk like a shut down then continue. It will do this several times until I rev the engine or just let it clear out. The, use to be, clear fuel lines are brown an very hard. I cannot see through them to tell if there are bubbles or not. Has anyone replaced these lines, and how much?

Thanks,

Sparky,


Did you change the fuel filters lately?
I have an 84 300d and I changed out my injectors and replaced the fuel lines from the fuel filter foward. That might be a solution for your problem. How many miles do you have on those injectors. I had 240000 on mine so I did not mind changing them out as a preventative measure. They are about 60 bucks each and about as hard to change as a spark plug, I did buy a torque wrench to get it to specs. I also replaced all 5 glow plugs. It is an easy job when you have the metal fuel lines off. consider changing that stuff out If all is still original. and try a good 10 count after the glow plugs light goes off. It makes a great difference for me.


good luck,

bob

[stevebfl]

David,

You might want to evaluate the diesel electronics for codes. The procedures are outlined in the DIY article. Your car has electronic control of idle and I have seen OVP relays cause these systems to die causing idling problems. With the system dead it still diesels but often very slowly (at idle - no effect off idle); a sudden turn of the steering wheel or A/C compressor cut-in can stop it dead.

I've replaced both filters with MB filters. The fuel lines appear to be in good condition, but a pin hole would not be visible. Because the fuel lines on the banjo fittings are so dark, I cannot see if there is any air, just the occassional hiccup at idle when first starting it. This vehicle only has 94K miles. I still want to check chain stretch and injection timing. Currently I'm working on a design for a diesel timing light. That would make the injection timing much easier. We'll see! Thanks for the info, but I think the problem might be air getting into the fuel lines when it has sat over night. What ideas might anyone have to discount this theory? All ideas are welcome.

Best regards,

[CJ]

Sparky,
I had similar problem on my 1991 300D 2.5 and I first checked the glow plugs and did not find anything wrong. The second time I checked the glow plugs, making sure that the multimeter had a good ground is when I discovered that on of the glow plugs was going bad. I would try retesting the glow plugs, your symptons are exactly what I had.
Good luck!

Thanks. The Glowplugs all checked between .71 to .75 ohms. I discovered this morning that the pressure valves 1 and 3 on the injector pump are leaking at the base. I finally got my CD for the manual and it looks as though the o'rings could be leaking. Could this bleed off enough pressure to cause a miss until the lines can break the pressure threshold of the injector? If this is the case, is it a good idea to replace all of the pressure valves or just the o'rings? Also, I pulled the valve cover to check timing chain stretch. No marks on the cam. The book just says to measure 2mm lift on the intake then guage from the crank shaft. That really creates vacuum!! Gotta get a dial indicator now! Any one have one they want to sell, cheap?

[CJ]

What state are you located within? You will need a special splined socket to remove the injector valves from the pump.