Smokey, uneven idle - PeachParts Mercedes-Benz Forum

Doug Vazquez · #1 12-30-2001, 10:54 AM

Hello all,

I hope everybody is having a good holiday season.

When I first bought the car, it idled smoothly, although at too high of and RPM. I adjusted the idle per the shop manual CD down to as close as I could get to 750 RPM. The lowest reliable speed I could get was about 850 or 900 RPM on the dash tachometer. This idle speed was fine after initial start up, but after the engine was warm, it was slightly uneven, like one cyclinder would not fire cleanly every time. The engine has always been somewhat smokey at idle and a little trail was usually evident if one was behind the car.

I have adjusted the valves (all were tight) and ran diesel purge through the fuel system and changed the fuel filters in the last three months. This seemed to be making for easier starts and over all better running characteristics and also I thought the engine was not as smokey, at idle or driving down the road. I have also noticed that when I hit the passing kickdown switch, I do not have the James Bond smoke screen anymore.

Lately the idle seems to be getting a little lumpier, with more smoke. I thought I may try a new rack damper bolt to help out the idle lumpiness, but that would do nothing for the smokiness. I have added Power Service to the last tank full in the "clean injectors" concentration (about one ounce per gallon). Does anybody have any suggestions to offer for smoothing out the idle and alleviating more of the smoke?

Thank you,
Doug Vazquez
Stella, W116 300 SD, 200,000 miles

kweimer · #2 12-30-2001, 11:11 AM

Make sure the diaphram in your vacuum pump is not leaking---engine oil will get into the intake manifold by way of the return line to the manifold and cause rough running, smoke, and a noticable increase in foot pressure to apply brakes (because of decrease in vacuum to the brake booster). Best way to check is with vacuum guage; however, you can also remove the vacuum return line (line that goes to the intake manifold) at the vacuum pump and check for engine oil at the fitting. If you see black engine oil, you have a leaking disphram.

psfred · #3 12-31-2001, 12:25 PM

Doug:

Check your valves again. If they were tight, they probably had considerable carbon buildup on them, and when you adjusted them and the compression came up, it burned off, leaving you with tight valves again. This can happen pretty quick! It did to me -- within a few thousand miles I only had 0.005" clearance on #1 exhaust.

If that doesn't fix the smoke, it's time for a compression/leakdown test and injector check. Bad injectors will produce excessive smoke at idle, rough running, poor power, etc. So will uneven or low compression from worn cylinder walls or bad valves.

What is you oil consumption like?

At 200,000 miles a valve job may be in order, especially if you have symptoms of leaking valve guide seals.

Peter

Doug Vazquez · #4 01-01-2002, 11:24 AM

Thanks for the replies,

Kweimer,
I don't think vacuum is a problem. A P.O. had installed a vacuum gauge under the hood. I check it every once in a while and all seems to be OK. I don't experience any problems with braking, shut down, or door locks. The ACC is not quite right, and every once in a while the transmission might shift a little quircky, but generally, everything in the vacuum department seems to work properly. I will monitor vacuum a little closer to see if there may be a connection.

psfred,
I did not think of readjusting the valves. I figured since I had done the job, that I could check that off the list. Now that I think of it, it does act as it did before I adjusted the valves.

I only add one quart of oil between oil changes (every 2,000 to 3,000 miles).

If readjusting the valves does not help the condition, I would lean toward having the injectors checked. How difficult is removing the injectors? Are ther any special tools or equipment required to do the job properly?

I will have a similar job to do on the pick up (see signature), it is in need of a new injector pump and I would like to replace the injectors as well. I understand it really makes the engine run as if new.

Happy New Year and thanks for your interest,
Doug Vazquez

kweimer · #5 01-01-2002, 01:01 PM

Doug,
Removing/replacing the injectors is no problem. You will need 27mm deep socket for the injector, 17mm open wrench for the cap nuts , and 8mm box or open end to remove clamps from injector lines. You really should have a torque wrench when replacing injectors---should be 45-50 ft/lbs.
Ken

psfred · #6 01-01-2002, 01:18 PM

Doug:

Use new seals under the injectors when replacing them, too.

Bad injectors usually send out a solid stream of fuel rather than a nice atomized cone of mist, causing hard starts, rough running (the angle at which the stream exits the nozzle varies, so sometimes it ignites well, sometimes not), etc. You are probably due.

A quart in 2000 miles more or less eliminates low compression due to bad rings -- if the rings are bad enough to lower compression significantly, you generally have considerable blowby and excessive oil consumption. That leaves the valves.

For sure do another adjustment. I was stunned that the exhaust had closed up that much -- that little clearance cold means it never closed hot. I get much better performance now!

What makes you think you need a new injection pump on the Ford? I wasn't aware that the PowerStroke HAD an injection pump! I thought it had unit injectors (in the head, operated by the camshaft, electronically controlled).

Peter

Doug Vazquez · #7 01-01-2002, 02:58 PM

psfred,
I will do another valve adjust as soon as I can get my wrenches back from another MB owner. I never thought about the fact that carbon would build up on the seats. It makes good sense that another adjustment would need to be done, especially if one has no idea how long it has been since the last adjustment.

On the Ford diesel- mine is an IDI from early 1994. No computer controls and has a mechanical injector pump. The engine is the kind of engine I can work on if I want to.

kweimer,
Thanks for the injector information. Have you ever heard of the seat needing to be"reamed" before reinstalling an injector? I think I have heard of a specific tool that prepares the seat for the new injector. I may be completely wrong.

Thanks again for the posts,
Doug Vazquez

kweimer · #8 01-01-2002, 03:10 PM

Doug;
I have never heard of reaming with respect to replacing injectors and have never done that myself. The Mercedes shop manual makes no mention of reaming and does not include a reamer as one of the "special" tools needed to install an injector. Replacing seals is not a bad idea although I don't always do that myself.
Ken

Doug Vazquez · #9 01-01-2002, 03:21 PM

I knew there was something that needed to be reamed before reinstalling something. Thanks for setting that straight.

Doug

kweimer · #10 01-01-2002, 03:25 PM

Doug;
As TXBill points out there is a reamer for the glow plug holes; however, this reamer is used when you reface a cylinder head and have to use thicker sealing rings under the prechambers.
Reamer is used to insure that the glow plug hole in the prechamber lines up with the glow plug hole in the cylinder head.
Ken

Doug Vazquez · #11 01-03-2002, 08:51 PM

Thanks for the replies,

I was going to try to readjust the valves this weekend, then realized that I don't have a new valve cover gasket. Since I just replaced it in September when I initially adjusted the valves, would I have to replace the four month old gasket? It seems like a very tough gasket, like it could take being reused.

Would this be considered a wrong thing to do?

Your opinions would be appreciated,
Doug

kweimer · #12 01-03-2002, 10:17 PM

I second TXBill's response. I've reused the tough valve cover gasket many times.
Ken

Doug Vazquez · #13 01-04-2002, 08:05 PM

Thanks guys,

I guess I have a little project this weekend.

Doug

Doug Vazquez · #14 01-05-2002, 10:59 PM

I readjusted the valves this morning. Eight valves were too tight, one was too loose and one was still within spec.

Afterwards I took her for a test drive. The cold start seemed faster. After the test drive I did not notice much difference in the lumpy idle or the smokiness.

Tonight I took the kids to see The Lord of the Rings and a hamburger afterwards. When I parked the car in the garage, I let it idle for a few moments before I shut her down. The idle was rather smooth. Tomorrow I will take her for another drive and check the idle characterists again.

Any comments?
Doug

psfred · #15 01-06-2002, 04:40 PM

I think you have cured the problem. Tight valves cold usually means they stay open hot, and the resulting low compression causes all sorts of trouble.

It will take a couple hours running to get all the crud out of the cylinders from the low compression soot accumulation. Ditto for getting the valves re-seated properly.

You also have some carbon on the injectors from poor combustion -- this will clear up when you get some time on the engine with good compression.

You can speed all this up by running a full bottle of RedLine in a tank of fuel.

Peter

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