Rough idle when cold 87 300D - PeachParts Mercedes-Benz Forum

engrx2 · #1 10-11-2002, 10:42 PM

Idle on my 87 300D car is rough when starting it cold. No 1 cylinder does not fire until engine gets warm. Increasing the engine rpm above 1500 make it smooth. After reading all the threads on this topic I was not able to figure out the problem.

Today I removed the intake manifold and started the car. As usual it was rough. I started to close the intake for cylinder No 1 and at on point the engine started to rum smoothly. I tried this many times and it worked every time.

Can any one figure out why reducing the air going into the cylinder makes it fire properly? I am assuming that there is not enough fuel.

#2 10-12-2002, 02:22 AM

How many miles? When it is cold out (below 40F) my car will start easily, but when I give it gas, it does not revv up, it takes a few seconds to "warm up" and be able to revv normally. My trusted mechanic told me that it is a classic symptom of a high mileage 603 engine due to a worn injection pump. I suspect you have the same problem.

engrx2 · #3 10-12-2002, 08:51 AM

I have 232K on the car, but if the injection pump is worn out then the question is why it is just the No 1 cylinder causing problem.

Somebody suggested to replace the copper seals on the injector pump. I am not sure if this can be done on 87 300D injection pump.

#4 10-12-2002, 04:10 PM

Isn't it possible that one of the lobes of the cam in the pump is worn more than the others? I don't know, just an idea. Have you thought about your injectors?

psfred · #5 10-12-2002, 06:23 PM

On a high milage engine I would suspect the injector before anything else.

You can replace the copper seals, not very difficult. Requires a special socket to unscrew the pressure valve holders. Fixed a rough idle problem for me, but that was a missing cylinder and hard injector knock at all engine temps.

Do you have excessive knock on #1 -- does it sound as if someone were tapping a large hammer on the block? Do you have excess smoke, and what color?

Does the miss go away when warm? If so, replace the glowplug -- you already have the manifold off, so it's easy at this point.

Do you have serious tappet noise?

What is the oil consumption?

Just some questions to help us pin this down. Most usual cause of rough idle cold, with white smoke, that does away as the engine warms up (only a minute or less) is a dead glowplug -- until the cylinder heats up, it won't fire. Next most likely is a worn out injector -- doesn't spray like it should, so the fuel ignites poorly.

Diesels aren't affected much by air/fuel mixture -- only run at max fuel ratio at full throttle and full boost, the rest of the time very, very lean.

Peter

#6 10-12-2002, 06:31 PM

A bit off topic, but I'll throw this out to Peter to see if he has any ideas;

Before my timing chain was changed I used ZERO oil in 4000 miles. After the chain was changed, I still used zero oil but the chain was one tooth off (driven for ~4000 miles that way). After it was corrected, the engine sounds beautifully and runs great, but is now using some oil, and this all happned after the chain was corrected, any ideas?

Billybob · #7 10-12-2002, 07:35 PM

Have you already tried the easiest stuff first, tried Lubro Moly Diesel Purge yet?

You could quickly easily and cheaply swap the glow plug from a working cylinder with the intake off, any change would indicate a GP problem. Probably could compare the voltage and amperage of working and nonworking cylinder GPs to eliminate any problems of an electrical nature while you can get to things so easy, also.

If you swapped the injector with another that you know had been working you would be able to determine if a clogged/malfunctioning injector was the actual problem if the symptom of a cylinder "not firing" moved to the swap-out cylinder. If things remain the same I would suspect the actual problem is upstream of the injector.

You could also pull two injectors, the one from the malfuncioning cylinder and a "known working cylinder" lossen and reposition the feed pipes, reattach the injectors so that you can turn the engin over without running it (hold down the shutoff/use a remote starter switch) and compare the spray patterns and outputs as the injection occurs into a clear fruitjuice or soda bottle attatched over the injector tip (not as good as using the proper injector tester but field/price expedient if the difference is enough).

It would seem if there is no difference between injectors the next step would be the delivery valve/seals on top of the pump. Replacing the seals sounds like a job that a careful competent DIY wrench could perform pretty cheaply.

If there is still no improvement removing the pump and recalibrating, rebuilding, or replacing would be the next more expensive/extensive steps. Good Luck, as a 603 owner I'll be watching!

engrx2 · #8 10-12-2002, 09:57 PM

I have already done the easy stuff. I have an injector tester so I know that all the injectors are good. I replaced the glow plugs but it did not help. I also want to mention that the compression in all the cylinders is with in +- 15psi.

Yes there is knocking sound coming from No 1 cylinder. Since I know that the injector is good it could be the incorrect timing.

Another thing I did not mention before is that I have a switch connected to the glow plug relay and I can turn on the glow plugs manually. So after I start the car in the morning I manually turn on the glow plugs for about 20 - 30 sec and this make the engine run smooth.

The copper seal in the IP makes more sense because may be initially there is not enough pressure for the injector to work properly. It might be woth trying. Where can I get the special tool for this?

engrx2 · #9 10-12-2002, 10:03 PM

More info:

When the No 1 cylinder is misfiring a lot of white/bluish smoke come out and I loose about 1 qt every 3000 miles.

Is it possible it the valve is not opening enough or opening too much when the engine is cold?

psfred · #10 10-13-2002, 11:52 AM

engrx2

White smoke is unburned fuel.

The only way timing could be off for #1 and not for the others is a bad cam in the IP -- if you can veryify this, exchange the pump, it's cheaper that a rebuild ($2500 -- and up!)

I assume you checked the opening pressure and spray pattern, too, so all I can suggest is cracking the #1 injector line, observing the fuel delivery leakage, then close up and crack #2 and see if there is a difference. That will also show the difference between a dead miss (no fuel at all) and what you are getting.

This sounds a lot like mine -- good fuel delivery, adequate compression (low on mine on the bad cylinders), no problem above 1500 rpm, no smoke at speed, good injectors, good glowplugs, etc. Change the seal on #1.

Seals are a breeze, all you need is the Torx key for the lock ring and the splined socket to pull the pressure valve holder. Seal and o-ring are about a buck together. Torque to 20 ft/lbs three times. Seal sits on top of pressure valve, easy to pick up with a bent pick, don't forget to get the pressure valve insert and spring back in properly!.

You shouldn't have any major mechanical problems with good compression (what is the pressure, by the way?) and only a quart in 3000 miles oil consumption.

Turbodiesel:

Leaking front cover or dead valve cover gasket. No way you did any damage to the valve train and still have good running. Worst would be ruined valve guide seals from overheating the valve stems, and if that were the case, I'd expect that old puff of blue smoke on startup.

Peter

engrx2 · #11 10-22-2002, 10:38 PM

Do you know what size Trox key and the splined socket I need to replace the o-ring and the washer on the IP.

Thank you

psfred · #12 10-22-2002, 11:22 PM

Now that's a good question! I borrowed the spline socket, never paid a bit of attention to the size, and simply matched up the Torx driver from the set we have.....

Sorry.

The Torx is one of the common ones -- you will need a 3/8 drive one, you can't use a screwdriver type, the bolts are stuck. Use some antiseize on them when you re-install. Someone else on the form knows what size the spline socket is. FastLane may have it, only costs $20 or so, and I know Snap-on and Mac have it, too. Sears may, also.

I hope a seal replacement fixes the trouble. Sure surprised me when it fixed mine -- I was prepared to replace the head!

Peter

the_good_fellow · #13 10-23-2002, 10:10 AM

Trox size is either T27 or T30
Spline socket is 12mm. Check this thread Spline Socket may be you can borrow one...

Wallknight · #14 10-23-2002, 12:48 PM

Peter,
I have a similar problem with the rough idle till its warm or revved. Are you saying all this takes is a new seal? If so, would you suggest resealing all 5 at once, just to be sure?
Thanks again!

P.s. What is the seal called on fastlane?

psfred · #15 10-23-2002, 06:57 PM

Paul:

Verify that you have good compression, valve clearance is OK, glow plugs are in good condition, and injectors are OK before messing about with seals in the IP.

You have a 617 engine, not noted for the IP problem on the 603. Usually, rough idle, white smoke, and lazy start on the 617, with good compression, is either bad glow plugs or worn out injector nozzles. Can also be an air leak at the priming pump or suction line from the tank, too..... Most likely glow plugs, make sure they are OK first. The leaking seal problem is usually constant, reguardless of engine temp.

Peter