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bad emissions + rough idle @ 750 = no suck or bad engine?

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#1 ·
This is my first post regarding problems with my 1990 560SEL, 302k miles. Just went to get my emissions tested... came out 3x over the hydrocarbons limit and 4x over the carbon monoxide limit... in addition, there's a moderate side-to-side jiggle when stopped at idle (warm and cold). Idle stays steady at 750 but the motion it creates reminds me of a car trying to stall (as if a clutch was 1/2 way out). The only other noticeable symptom is a 'sometimes' reluctance to get-up-and-go; it wants to take a big gulp before doing so. Most recent service is motor mounts and brakes. There's no burning that I can smell and it does not leave any messes on the floor (for sure, since it's missing the undercarriage rock guard). No lights blaring from the dash. Air filter recently (1k miles ago) replaced, checked the bulbs in the dash to make sure they're working and they are. Haven't played with the O2 sensors. Haven't gotten it restested. Any ideas or plans of attack?

My first guess would be a vacuum leak somewhere. Of course, any help or links regarding that system would be a big help to me since I've never worked with one. I've read some of the other posts regarding the idle control valve / relay and I haven't replaced or cleaned those, either. My idle problem doesn't seem to be the erratic idle that others are having. Of course, a vacuum leak would explain both the 'gulp' and the emissions problem... please, someone!
 
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#2 ·
As others on this board have advised me when I had an idle problem, you first need to do a complete tune-up. I would replace rotor, cap, SP wires, plugs and clean the injectors with cleaner. Then through the process of elimination you can better understand whats going on and go from there if needed. Otherwise its a wild guess... too many variables. The vacuum leak is a very good possibility as well.

I'm impressed you have over 300k on the engine! That's encouraging since I have a 90 560 sel as well. Did you rebuild the engine and if so at what point?
 
#4 ·
First engine, no rebuilds. (I fear the worst but with 300k+ I can't complain.) I've spent a small fortune keeping the A/C working, however. New tranny around 260k. You might be impressed by this: original radiator! Woot! (My secret? I'll never tell... because I don't know how that happened... something about the stars aligning just right.) Okay, I'll see if I can scare up the tune-up parts locally and do it to it tonight.
 
#6 ·
Can't find the parts locally... I'm autohausaz.com-ing it. I'll post again when I'm done. Also, one more symptom I forgot about (because it doesn't happen much). Restart when warm is difficult. Once turned off the car won't restart for a good 5-10 minutes.
 
#7 · (Edited)
Check the fuel pressure. Check the basics and look for obvious vac leaks. Replacing the basic tune-up parts is fine but won't cause the CO% to be 4X over. Did the smog place try to adjust the CO% to see if it would? Just curious.
Fuel pressure, accumulator, cold start valve are some areas that can dump too much fuel and go super rich. Vac leaks will make the HC go up. O2 sensors are a maintenance item and should have been changed a few times by now. Also the convertors do go bad over time and with it running this rich it's probably history. It might be wise to visit a reputable shop that understands these cars and CIS systems and have them check pressures and stick the emissions probe in the pipe, rather than guess. Throwing some of these parts at it can add up real fast.
 
#10 ·
veryslowbenz said:
...and to answer your question: no, the county emissions test place doesn't adjust CO%. I haven't taken it to a shop, yet. I'm a vacuum system dummy--what are the obvious vac leak areas? Can you point me to a procedure to check the fuel pressure?
First, listen for anything that hisses. Odds are, the hissing sound is a vacuum leak.

Next, hook a volt meter up to one of your O2 sensors. Check to see that the voltage is switching between two different levels (usually around 0.1 volts at the low side and 0.9 volts at the high side). It should be going back and forth. The quicker it changes, the better the O2 sensor is.

Now, with the volt meter on the O2 sensor, spray a little bit of "throttle body cleaner" down the intake at the air flap (with the air cleaner removed). Watch what happens to the voltage at the O2 sensor. It should go up and stay at 0.9 volts or so. That's an indication that it's running really rich (the extra "fuel" from the cleaner spray).

Start spraying cleaner around the vacuum hoses, and especially around the base of the fuel injectors. Watch your volt meter and listen to the idle. If the volt meter shoots up to 0.9 volts and stays there or the idle speed increases when you spray cleaner on something, there's a leak at that point.

The O-rings at the injectors are a notorious leak spot. Vacuum hoses get old and crack. The hard plastic vacuum lines (the really thin ones) get brittle and break. Intake manifold gaskets can also crack and start leaking on a car this old. You'd see that if you spray where the manifold and head meet.

Oh, and since you have a V8, you might have a left and right O2 sensor (I don't remember on these cars, and I don't have V8's in mine). If that's the case, hook the volt meter to the right bank O2 sensor when spraying the cleaner around the right side of the engine, and hook up to the left bank O2 sensor when spraying around the left side.
 
#11 ·
US V8 W126 cars have one O2 sensor. We have the dumbest exhaust system on the planet, where the driver's side exhaust routes around the back of the engine, using a flexible hose, then dumps into the passenger side exhaust just above the first cat. 18" or so below that is the sensor.
 
#12 ·
If you are at 300K w/o heads being done they are beyond toast..Ever take a compression test on that engine? I'd do that first then see about getting on a scope to see what the ignition system is doing. If the injectors haven't been replaced they are about 200K overdue..

The list of items needing replacement could be Endless!

Jonathan
 
#13 ·
I have changed all the parts mentioned here, plus a fuel distributor and the ignition control unit, and the car passed smog easy.

If you don't have one yet, Mercedes Benz at www.mbusa.com has the official 2 CD service manual for $ 20. Outside the US the thing costs up to five or six times that. The DIY thread above has the link/information how to order, and how/with which free Steve Nervig index to download to HD. You can also type your question into the 'search this forum' box on the top right. It will get you all archived post re. your problem. There used to be an online manual at mbbraingears, but it doesn't seem to work anymore. You might try the Russian MB site. Don't put in a mod. or vin, click on cars and scroll down, until you get to yours. Good luck. http://www.detali.ru/cat/oem_mb.asp Good luck
 
#16 · (Edited)
Eric@StarSuzuki said:
First, listen for anything that hisses. Odds are, the hissing sound is a vacuum leak.

Next, hook a volt meter up to one of your O2 sensors. Check to see that the voltage is switching between two different levels (usually around 0.1 volts at the low side and 0.9 volts at the high side). It should be going back and forth. The quicker it changes, the better the O2 sensor is.

Now, with the volt meter on the O2 sensor, spray a little bit of "throttle body cleaner" down the intake at the air flap (with the air cleaner removed). Watch what happens to the voltage at the O2 sensor. It should go up and stay at 0.9 volts or so. That's an indication that it's running really rich (the extra "fuel" from the cleaner spray).

Start spraying cleaner around the vacuum hoses, and especially around the base of the fuel injectors. Watch your volt meter and listen to the idle. If the volt meter shoots up to 0.9 volts and stays there or the idle speed increases when you spray cleaner on something, there's a leak at that point.

The O-rings at the injectors are a notorious leak spot. Vacuum hoses get old and crack. The hard plastic vacuum lines (the really thin ones) get brittle and break. Intake manifold gaskets can also crack and start leaking on a car this old. You'd see that if you spray where the manifold and head meet.

Oh, and since you have a V8, you might have a left and right O2 sensor (I don't remember on these cars, and I don't have V8's in mine). If that's the case, hook the volt meter to the right bank O2 sensor when spraying the cleaner around the right side of the engine, and hook up to the left bank O2 sensor when spraying around the left side.
Okay, tried this stuff... the O2 sensor appears to be good. I got good voltages at idle and as I was spraying cleaner at the vacuum points that I could find. Spraying around the injectors did cause a little bit of a voltage jump in the O2 sensors--but about the same jump occurred with each one. I checked back through my receipts and saw that the injectors were replaced at 115k and then cleaned at 210k. However, on the receipt it doesn't list how many injectors were replaced and/or cleaned. I assume the entire system was replaced/serviced since both of those bills were $500+. Also, if anyone has experience doing so, how do you "clean" injectors on this car? What kind of tools does it take and is it recommended?

That said, is it best to replace all fuel injectors at the same time? What other do you guys recommend be done simultaneously? Spark plug wires, distributor cap/rotor, spark plugs? Anything else?

I also *listened* for vacuum leaks and it hisses just very slightly--much less than my w124... probably both have vacuum leaks. I may have to get someone in the know to check for leaks.
 
#17 ·
jhodg5ck said:
If you are at 300K w/o heads being done they are beyond toast..Ever take a compression test on that engine? I'd do that first then see about getting on a scope to see what the ignition system is doing. If the injectors haven't been replaced they are about 200K overdue..

The list of items needing replacement could be Endless!
My w126's been taken care of quite well. Most stuff has been replaced over time (I've got a good $30k in receipts from the previous owner as well as my own nice stack). I'm going to go get a compression test done on it, though. That side-to-side idle has me scared. I'll post results when I get it back.
 
#18 ·
Teutone said:
I have changed all the parts mentioned here, plus a fuel distributor and the ignition control unit, and the car passed smog easy.

If you don't have one yet, Mercedes Benz at www.mbusa.com has the official 2 CD service manual for $ 20. Outside the US the thing costs up to five or six times that. The DIY thread above has the link/information how to order, and how/with which free Steve Nervig index to download to HD. You can also type your question into the 'search this forum' box on the top right. It will get you all archived post re. your problem. There used to be an online manual at mbbraingears, but it doesn't seem to work anymore. You might try the Russian MB site. Don't put in a mod. or vin, click on cars and scroll down, until you get to yours. Good luck. http://www.detali.ru/cat/oem_mb.asp Good luck
Fuel distributor replaced with the fuel pumps at 226k. How long do they last, usually?
 
#19 ·
There is no really good means of cleaning the injectors aside from the usual techron or BG 44K....Mercedes only rates these injectors to last 100K before the internals/spray pattern is no longer ideal.

FD and pumps should still be fine (although if you have a reman FD do NOT run concentrated FI cleaner through it, the new seals don't hold up like the old ones)..although the fuel filter is due every 40-50K.

I'm still leaning towards heads which are Toast. Unless the heads have been off and the guides replaced they will be shot...no amount of maintainance will change that.

Jonathan
 
#20 ·
Teutone said:
I have changed all the parts mentioned here, plus a fuel distributor and the ignition control unit, and the car passed smog easy.

If you don't have one yet, Mercedes Benz at www.mbusa.com has the official 2 CD service manual for $ 20. Outside the US the thing costs up to five or six times that. The DIY thread above has the link/information how to order, and how/with which free Steve Nervig index to download to HD. You can also type your question into the 'search this forum' box on the top right. It will get you all archived post re. your problem. There used to be an online manual at mbbraingears, but it doesn't seem to work anymore. You might try the Russian MB site. Don't put in a mod. or vin, click on cars and scroll down, until you get to yours. Good luck. http://www.detali.ru/cat/oem_mb.asp Good luck
How much did your ICU cost? I see that they're quite pricey new... any wisdom regarding eBay purchases of this item (i.e., used)?
 
#21 ·
jhodg5ck said:
I'm still leaning towards heads which are Toast. Unless the heads have been off and the guides replaced they will be shot...no amount of maintainance will change that.

Jonathan
Are the guides a normally-replaced item? I'm assuming you're referring to the chain guides? BTW, *still* haven't gotten a compression test. This is probably something I need to learn to do vs. waiting for an open spot at the dealer.
 
#22 ·
The guides Jonathan is referring to are the valve guides. They are made out of soft brass and over time the wear will cause the valves to leak. Definitely get a compression check to see if the chambers are holding any reasonable pressure.

I concur with Jonathan that the heads are shot, and a new set will be in order to rectify the poor running condition.

Keep us posted.

Regards,
 
#23 ·
Okay, had it compression tested. All cylinders except for one is 150+, with variation +-5... except for one which is firing at 110. The educated guess is that the ring is just about shot. Also, one of the plugs was a bit oily. We cleaned that up and the idle smoothed right out. So I think I'm going to continue to drive this guy with the low compression on that one cylinder. What do you guys think--any damage in driving around with one cylinder with low compression?

Haven't diagnosed the emissions issues just yet.
 
#24 ·
I had problems with an oil fouled plug in one cylinder. After having the Valve seals replaced, the problem has cleared up.
 
#25 ·
I Doubt it's a ring..I'd wager it's a valve guide. Did you record your initial #'s? Ie, on the first crank or two? How many times did you turn the engine over to finish w/ 150?

Jonathan
 
#26 · (Edited)
veryslowbenz said:
This is my first post regarding problems with my 1990 560SEL, 302k miles. Just went to get my emissions tested... came out 3x over the hydrocarbons limit and 4x over the carbon monoxide limit... in addition, there's a moderate side-to-side jiggle when stopped at idle (warm and cold). Idle stays steady at 750 but the motion it creates reminds me of a car trying to stall (as if a clutch was 1/2 way out). The only other noticeable symptom is a 'sometimes' reluctance to get-up-and-go; it wants to take a big gulp before doing so. Most recent service is motor mounts and brakes. There's no burning that I can smell and it does not leave any messes on the floor (for sure, since it's missing the undercarriage rock guard). No lights blaring from the dash. Air filter recently (1k miles ago) replaced, checked the bulbs in the dash to make sure they're working and they are. Haven't played with the O2 sensors. Haven't gotten it restested. Any ideas or plans of attack?

My first guess would be a vacuum leak somewhere. Of course, any help or links regarding that system would be a big help to me since I've never worked with one. I've read some of the other posts regarding the idle control valve / relay and I haven't replaced or cleaned those, either. My idle problem doesn't seem to be the erratic idle that others are having. Of course, a vacuum leak would explain both the 'gulp' and the emissions problem... please, someone!
With the kind of mileage that you have, I would not be surprised if it was your fuel distriburator and/or EHA.which part regulates your fuel mix. The reason i say this is that I just changed both the eha and my fuel distriburator on my 560sel and had similar symptoms,vibrating at idle,rich emissions,high fuel consumption,and surging,and at the end power loss at speed. As it turns out my old fuel distriburator was leaking fuel directly into the engine.it would run ok until you drove for a while at speed and then it would start surging and loosing power. Also first replace your fuel filter as it just might be droping your fuel pressure which on this car must be within a set range, about 90 lbs.
 
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