400 SEL BREAKING UP AROUND 1500 RPM
 

My 93 420SEL started acting funning the other day . At first I thought it was a bad shift between the 2nd and 3Rd gear but thats just the RPM range that I first notice the problem

The engine hesitated and almost stalled around 1700 RPM under fairly aggressive acceleration ( heavy load). I sorta babied the throttle, and backed off when I first felt it , thinking it was the tranny. It happened a few more time when I test drove it around trying to figure out if it was engine or tranny .
I was able to drive back 30 miles home at highway speeds and nothing seemed out of the ordinary. It seemed to happen only when pulling away aggressively from a stop.

Engine idled smoothly but quit once after starting it up and being very cold here in NYC

I brought it to my 2 partner mechanics who worked 15 years for Benz dealership and the one mechanic reved the engine in drive (1600 RPM to load it ) and replicated the breaking up. He says it breaks up under load prolly because of the coils. His partner says to replace the rotors and caps. Two partners cant agree and want to start changing parts without even putting a diagnostic tool on the engine? I ran away !

I brought it to the Dealer and the 25+ year mechanic said it gave him no codes but he replaced 3 resisitors that go between wires and plugs and the 8 plugs, scraped the rotor caps with a wire brush and told me put a can of techron in a full tank . His suggestion was if it continues to hesitate, to change plug wires and then possiblely injectors.

Drove 350 mixed miles over last 9 days and in the last 4 days I can usually go all day with 3-4 engine turn offs and restarts and maybe one HICCUP/FLAT SPOT / hesitation per day.

Once past 3000 RPM it pulls like a beast on the highway . So I thought the trend was going in the right direction and dropped by my dealer mechanic to say so, give him a tip etc . and ask if I should try another techron in a full tank of gas and he said ok., and to not change any parts and see if it continues to get better.

No sooner did I leave the dealer and it had that same hiccup . Also after buying the techron and not having a chance to put it in, it stumbled once in 10 mins driving . Then I turned it off for 40 minutes to get something to eat and when I started it up it sorta stubled on idle, and once accelerating aggressively, and then again accelerating aggressively, but this time about about 2800 RPM.

So much for the trend. It never happens if I feather the throttle and when I back off the throttle when its doing its hiccup, it recovers and I feather thru that spot and it drives fine. I have had it running at 60-80 MPH smoothly for more than 300 miles .

He said I can put a resistor on a bench and it tests perfect then put it in a car and it does not perform correctly. What scares me is that even he was not really certain what caused it, and told me to not change anything yet, but as soon as I left his shop it got a little worse.

Sorry for my being so lengthy, any ideas ?:)

Sounds like a secondary ignition problem for sure.

Caps, rotors, & spark plug wires are the most likely issues.

Can be costly, but since the car is 17 years old..most likely the issue!

Would you start with wires since plugs have been changed , and then if that does not work do caps and rotors?

OR caps and rotors that the Benz mechanic scraped with a wire brush?

I just ordered Caps and Rotors . Will take about a week to get here. Hope that is the problem.

Will post back results, and if successful or not

you should try Ford caps and rotors.

Is that supposed to be a joke?? What number Ford caps and rotors fit a 119 MB engine?

Yes, it's kind of a joke. There's another thread about Ford caps and rotors fitting on MBs.

Ok Now any ideas as to what is going on with my car. I have heard eveything from caps/rotors, coils, MAF ,and plug wires plus suppressors, basically the entire ignition system .

Anyone want to follow the AND SEE if they can help either from similar symptoms , or from repairing a similar car can also check this thread

http://www.benzworld.org/forums/w140-s-class/1493456-s420-sel-breaking-up-under-load-5.html

All help is appreciated

Peter

Today I looked at my cap and rotor. I pulled off the coil wire from the cap and saw a bit of corrosion. You might take off each wire, check it and put it back on. Also check the coil wire at the coil.

Is your car running well ? If I find corrosion on the wire ends what do I need to do , clean them or replace them ?

I just got mine and it seems to be OK but sometimes it runs rough and sometimes when I give it full throttle it hesitates. I would clean the corrosion because I don't like spending extra money that I don't have too.

Well thats sounds a little like mine. It seldom has a rough idle, occasionally it does, but it hesitates when I give it 3/4 throttle more frequently. A small amount of rough idling is usually accompanied by at least 3-4 flat spots and then I feather the throttle till it goes away , or I get to my next destination.

I just realized that although it is infrequent the rough idle only occurs when it is hesitating . So the 2 are definitely related and part of the same problem.

But I can have the hesitation without the rough idle , but not the other way around.

An easy item you may wish to check is the breather hose that runs from the rear of the passenger side valve cover to the electronic throttle actuator. A member on benzworld had symptoms very similar to yours on his 140 and it turned out to be a large hole in the breather hose causing a vacuum leak. I replaced that hose on my S420 last year because I noticed that it was broken when I was doing a routine inspection of the belts and hoses. My S420 still ran fine even though that hose was broken, though. It was so brittle that it crumbled apart in my hands as I was taking it off. It's an easy part to visually inspect, so you might want to just rule that out as a possible cause.

Is there any way I can find exactly where it is and how it looks?

I just looked and saw a few green and red hoses in that area. Are those the ones you are referring to? They actually looked like hard plastic and almost look brand new, and I was amazed that anything 17 years old could look that good. They plugged into connectors and had 2 hoses plugging into one connector in a few spots.

Actually, the hose I as referring to is black and approximately 1" in diameter. Below is a link to a DIY article. Take a look at the sixth picture, the one with the circle around the socket. The breather hose is in the upper right hand corner of that picture. You can see where it connects to the valve cover (on the edge of the circle), runs toward the center of the engine, turns and runs along the fuel rail, and then heads down to the electronic throttle actuator just below the mass airflow sensor. It's part# 119 090 19 82. You simply have to remove the air filter components on top of the engine and it will be right there. Shouldn't take more than 10-15 minutes.

http://www.peachparts.com/Wikka/M119OilGuides

Thanks We had the air filter and valve cover off and I do not remember seeing that hose, but that does not mean it was not there. Will look at it when changing caps and rotors

Really?

I mean inside an engine compartment. LOL

still seems to be temperature sensitive
 

I just drove for 1 hour 20 minutes on a highway to go skiing. Car ran fine again. Drove back the same distance and when I got caught in traffic and after runnng for 1 hour and 15 minutes temperature got up to 92C .

Stopped for a light on a small upgrade and when I pulled away, I got that hesitation at around 1500 RPM again . This time it might have felt like an entire bank was not firing.

What is normal operating temp for my car in traffic with outside temp around 2 Celsius ?

It seems like the only thing that is fairly constant, is that the flat spot shows up around 85 C and above . Does that mean anything specific to you?

I ordered rotors and caps and am waiting to have them installed this wednesday

Ask them to save the old cap and rotor. That way you can have a good look at them and probably clean them up and keep them as backups.

Will do Take a look at this thread may apply to my problems

http://www.peachparts.com/shopforum/showthread.php?t=269100&highlight=OVP


post #9

My problems much, much, much, more likely when engine warm. As a matter of fact , I only remember having problems one time with engine cold if that.

Thx

This just screams spark plug wires to me. If you are like me, (and I think you are), you like to be sure something is bad before you replace it. The way to do that in this case is get the car to a VERY dark area at night and look under the hood with the engine running. If the plug wires are bad you will see them arcing all over the place. When they are really bad you can even hear the arcing! 32 years of screwing with cars and it's always the same. Spark plug wires are the most overlooked, neglected parts on the car. Both my M119s put on very impressive, noisy light shows when I first got them.

Don't install those caps and rotors until you know for sure you really need them. I don't think you do. Send those puppies back.

Please post your results. Good luck!
Regards, Eric

Well since I intend on keeping the car for years to come if I can solve this problem, I dont mind puttng on the caps and rotors and then changing plug wires if the caps and rotors dont fix the problem.

I dont even mind spending money on things that will make the car run better and longer as long as thats considered prudent maintenance, I just dont want to take a parts changing approach as that can cost $2500 (MAF COILS HARNESS etc ) and find out it is a simple vacuum line, or one plug suppressor that is the problem.

So I will have the new Mechanic change rotors and caps , check vacuum lines to CTS, breather hose to intake manifold,vacuum lnes to ignition module, and check any other obvious possibilities that could be causing the problem.

If that does not clear the problem I will change the plug wires next , and if that does not work , then have him clean MAf sensor. Did I miss anything ?

UPDATE
 

New strategy
My Dealer Mechanic replaced the plugs,and he gave the old ones back to me . Three looked worse than the rest , and I assume the 3 suppressors he replaced on plug wires were the ones that matched up with the bad burning plugs.

I am in the middle of the second tank of gas that I am running with techron, and aside from that, scraping rotor caps, changing plugs and 3 suppressors thats all I have had done.

Tomorrow the caps/rotors should get here and I hope the new Indy Mechanic will have time to put them in tomorrow or thurs. at the latest.

I would prefer to not do two things at a time , so I can identify what was the problem when I finally get it resolved . But I am tempted to let him use the MAf cleaner if he wants to , because he is 30 miles from me on Long Island and it would save time and trips, but not give a definite answer.

Maybe I will have him change caps /rotors and then drive around in traffic to let engine get really warm 90C or more, drive around and around and see if the hesitation is gone , and if not then go back and have him do the MAF cleaner.

What should the temp get up to in traffic considering the outside temp? Is there any harm in running the air conditioner to get the engine warmer faster ?

Another piece of information for everyone. I turned ignition to #2 position and all my lights are working. There is no check engine light on my car but ABS, ASR, OIL, ENGINE TEMP, BRAKES, LIGHTS, and any other idiot lights that should be operational on the DASH are working so I have not missed any CEL codes

I strongly recommend you do the wire arcing test yourself rather than relying on your mechanic unless your mechanic is one of the fine, competent, honest mechanics on this board. ;):D:)
Regards, Eric

In all my years of working on gas engines I have always heard and thought it was better to keep the spark-plug wires separated from each other and if they have to cross, to do it as perpendicular as possible . Looking at the engine of my MB I was quite surprised to see all the wires running close together and parallel. This seems like a recipe for crosstalk or what ever you would call it.
I agree with 400Eric that you should have a look at the wires with the engine warm and running (revving it up to the 1500 rpms) in a very dark place. I don't mean you should pull into a small one car garage with the door closed and run the engine for a half hour while you look under the hood and breath deeply (good night). Be safe about it!

Yeah, he might go night night while enjoying the pretty light show under his hood!

Wire separation. Yes, you bring up a very good point. That's why I don't ever put any of that plastic shrouding nonsense back on. When ever I have a reason to take it of, it stays off for good. That allows me to allow the wires to be as separate as possible. I didn't bring that little factoid up because most folks seem to be too concerned with how pretty things are and I'm too tired arguing with folks about it. I'll admit though that the wires hanging everywhere is not pretty.

However, if his spark plug wires are bad like I think they are, simply separating them won't help much. I would recommend separating the new set though just for good measure. I'd rather have a car that runs great than one that is pretty under the hood!
Regards, Eric

Yes, check them before you separate them. I think I'm going to take that plastic wire cover off and separate the wires. I bet I can even make it look nice.

Actually I live in Manhattan and its not going to be easy to find a dark place. I also need some one else with me to rev the engine to 1500 RPM and I have heard its not good to use the throttle linkage in engine bay, but only rev via pedal.

Well I hope the caps and rotors get here today via UPS and the mechanic has the time to install them . Then I will take a ride to my wifes cousins house a little upstate and do that arcing test. He also told me he used to see arcing on his past hot rods that he worked on.

I am very reluctant to rev engine without it being under load ( parked). Maybe I am being over protective of my cars, but what is a safe RPM to rev an engine , and not for an extended perod of time in neutral?

Red line. I know what you mean not wanting to rev it up not under load. Just do it slowly. I don't think it would be bad to rev it from the throttle body but it also wouldn't hurt to have someone help you.

Red Line? You mean to rev it to 6000 RPM without being under load is not bad for it. I never went past 2000 RPM unloaded and today I was driving around in 3rd and getting the Tach to 4400 and did not think that was healthy.

I know in manual trannyd cars you can get close to red line , but I was always afraid it would cause a lot of heat in lower gears on an auto tranny.

So you think both practices are safe, and I am just babying my cars too much ?

I drove today and after 3-4 engine turn ons/off I got the hesitation again and it nearly died on me during one of the restarts. Grrr

By the way I was in the country last night where it was dark, and wanted to check for arcing before I came home, but I got into a conversation about something and forgot GRRRR.

In any event the caps and rotors are here and the mechanic said to bring it in to replace them tomorrow/thursday . I notice that the Bosch parts I bought from the internet were made in Spain . Hope they are as good as OEM .

Will change caps/rotors and drive around for enuff time to heat engine up and see if the hesitation/dying is cured. If not MAF cleaning is next and then finally plug wires.


I will post my progress for anyone following the thread.

Thanks again for all the comments :)

Actually, you don't need to rev the engine at all. You'll be able to see and hear the arcing with the car at idle. Try it, you'll see.
Regards, Eric

He's right. Actually, at lower RPMs the spark should be stronger and show more where it's arcing.

I probably wouldn't red-line it in neutral. Something just seems dangerous about that. I don't know what the difference would be though.

Is it OK to look at it immediately after start up? Or should I wait till it starts to hesitate/bogg down that happens after its warm, and it gets worse with every additional turn off /restart. Then after 3-4 restarts even the idle breaks up and almost stalls like I said in post #32 above.

If its not doing its crazy thing , would the arcing be happening , or only when it has symptoms?

If you can replicate the symptom then that's what you should do. Maybe check it when it's cold and running fine and also later when it's warmed up and running worse. Are you getting your cap and rotor on today? Remember to save the old one.

When you say check it, do you mean look for the arcing ?

Well today I drove 25 miles on a highway ( LIE) to go change caps/rotors. Got caught in traffic for the last 10 miles so engine got to around 98 C (I Use K6JRF a/c diagnostics to display engine temp in a/c window) and it missfired pretty hard 2-3 X. Actually sounded like a backfire .

Got to the mechanic who swore without seeing car that it was caps and rotors that were the problem. He changed them and said the old ones were bad. I took them with me to look at . Dont ask me what I am looking for , but you can tell me what to look for ,and he said they were bad.

Drove the car all around long island for 30 minutes and it hesitated a few times but for a much shorter duration and less frequently than before , at least in my mind thats what I thought.

I drove back to the new Mechanic and told him it is better but still not right. He said its not the MAF, as I had that in mind to work on next . He says it prolly is the suppressors on the spark plugs. I told him I should change wires totally and he said just change suppressors. I told him his ex boss at MB dealership , who is shop foreman of mechanics, changed 3 suppressors and said if that did not solve it, plus changing all the plugs that the dealer did, I should change wires next . New mechanic said wires in my model car do not go bad. Grrr . Opinions

The new mechanic said also to change fuel filter when I change wires, to protect against bad gas . I might just change filter and give that a shot before I spend $$ money on wires. Does anyone think that could be the cause ?

I thought maybe give the sensors time to acclimate to the new rotors and it seemed better for a about and hour in stop and go, start and restart. After 45 minutes driving I accellerated quickly from a toll station and it stalled for a fraction of a second as opposed to 1-2 seconds as before.

Then I got into NYC and drove around in traffic and the hesitation although "MAYBE" not as severe is still there . Obviously the car gets warmer in NYC traffic and thats where I really have to be able to have the car run perfectly, to say it is fixed.

It looks like this is becoming a parts changing , guessing game for me .
I thought I would do the MAf cleaning but this mechanic says that stuff is garbage . So many mechanics, so much disagreement .

I am going to look tomorrow night at the wires to see if they are arcing and MAYBE disregard what he says and do a MAF cleaning . Or I could just change the fuel filter, unless I have an obvious arcing that I can see .

Again the problem happens and gets more frequent the warmer the engine is . Grr .Is there no way to diagnose this problem without just changing parts arbitrarily? He did not put a diagnostic tool on the car and I will call him tomorrow and ask him why not .

What should I look for on Caps /rotors? I am getting a daily headache from this.

The only good news is that this guy is very fair, pricewise and seems very honest .

Any other thoughts guys. I am going to take 2 tylenol .:)

Caps and rotors done today. That was not the problem. Plug wires the only other candidate in your opinion?

For an engine to run properly, it needs three things.
1. Good compressing in each cylinder.
2. A good spark at the right time in each cylinder.
3. A good air/fuel ratio and volume flowing into each cylinder.

1. Compression tests and leak down tests are easy to do and cheep. Do it with the engine warm.
2. New cap and rotor is good, wires should be tested, you're about to do that.
3. A number of things on a modern engine could throw off the air/fuel ratio.

Don't give up. It usually turns out to be something simple that makes an engine not run right.

Could you post photos of the caps and rotors? Then we can tell you what we think of them.

Plug wires that "leak" spark before it gets to the plugs could be your problem.

Yes I can take photos. How do I post them to a thread .
I never did that before.


Also frustating is that car almost always runs well when cold(er). Also that once past 1400-1800 RPM it runs well and once I am on the road and doing 60-80 MPH it feels fine.

But I guess when I am doing 60-80 the engine temp drops back to under 50C so, that sorta explains that.

What do you think about replacing fuel filter before jumping in and replacing plug wires?

I personally have not checked all the vacuum lines but 2 mercedes benz mechanics, including the first one spending 2 hours diagnosing it , I find it difficult to think that was overlooked.

Also the first mechanic who is still working for the dealer said the next thing on his list to change would be plug wires , so I guess I should bite the bullet after checking tomorrow night to see if there is any arcing

When you say check it, do you mean look for the arcing ?

Well today I drove 25 miles on a highway ( LIE) to go change caps/rotors. Got caught in traffic for the last 10 miles so engine got to around 98 C (I Use K6JRF a/c diagnostics to display engine temp in a/c window) and it missfired pretty hard 2-3 X. Actually sounded like a backfire .

Got to the mechanic who swore without seeing car that it was caps and rotors that were the problem. He changed them and said the old ones were bad. I took them with me to look at . Dont ask me what I am looking for , but you can tell me what to look for ,and he said they were bad.

Drove the car all around long island for 30 minutes and it hesitated a few times but for a much shorter duration and less frequently than before , at least in my mind thats what I thought.

I drove back to the new Mechanic and told him it is better but still not right. He said its not the MAF, as I had that in mind to work on next . He says it prolly is the suppressors on the spark plugs. I told him I should change wires totally and he said just change suppressors. I told him his ex boss at MB dealership , who is shop foreman of mechanics, changed 3 suppressors and said if that did not solve it, plus changing all the plugs that the dealer did, I should change wires next . New mechanic said wires in my model car do not go bad. Grrr . Opinions

The new mechanic said also to change fuel filter when I change wires, to protect against bad gas . I might just change filter and give that a shot before I spend $$ money on wires. Does anyone think that could be the cause ?

I thought maybe give the sensors time to acclimate to the new rotors and it seemed better for a about and hour in stop and go, start and restart. After 45 minutes driving I accellerated quickly from a toll station and it stalled for a fraction of a second as opposed to 1-2 seconds as before.

Then I got into NYC and drove around in traffic and the hesitation although "MAYBE" not as severe is still there . Obviously the car gets warmer in NYC traffic and thats where I really have to be able to have the car run perfectly, to say it is fixed.

It looks like this is becoming a parts changing , guessing game for me .
I thought I would do the MAf cleaning but this mechanic says that stuff is garbage . So many mechanics, so much disagreement .

I am going to look tomorrow night at the wires to see if they are arcing and MAYBE disregard what he says and do a MAF cleaning . Or I could just change the fuel filter, unless I have an obvious arcing that I can see .

Again the problem happens and gets more frequent the warmer the engine is . Grr .Is there no way to diagnose this problem without just changing parts arbitrarily? He did not put a diagnostic tool on the car and I will call him tomorrow and ask him why not .

What should I look for on Caps /rotors? I am getting a daily headache from this.

The only good news is that this guy is very fair, pricewise and seems very honest .

Any other thoughts guys. I am going to take 2 tylenol .:)

Test for arcing already!
You'll be able to see some arcing even during the times when you are not experiencing symptoms.
Regards, Eric

Yes, test for arcing.
To post a photo in a reply to thread, click on the little yellowish box that looks like mountains.

No, arching not arcing. I'm talking about little men under the hood with little bows shooting little arrows! Hence the term: arching.

(Just kidding. Seems I've been having a brain fart on my spelling lately.)
Regards, Eric

I will be testing for the Olympic Sport Arching or is it Archery tonight:) Then I have to dig out my camera and take the photos of caps and rotors . Thanks guys for all your patience

Little guys under the hood doing anything would be awesome. Git your camera ready!

Well waited till dark and after dinner me and my cousin opened up hood to see if there was any arcing.
We took off air filter housing and removed drivers side plug cover, no arcing. Decided to pull passengers side plug/wire cover off , absolutely no arcing.
Was sure to wait till engine temp got to over 8O Celsius no arcing . Looked at the wires when at idle, and loaded engine in gear no arcing .
I saw the 3 suppressor wires that dealer/ mechanic had said he changed, they were red colored caps so now at least I know which cylinders he thought might be suspect. Plug wires looked really good , even my cousin said he was surprised that after 17 years they were supple not dried or cracked or anything. No arcing at all
Looking around engine compartment to get an idea if anything else was obviously wrong and we found a vertical plastic hose coming out of a bundle that went in to an L shaped black rubber hose that connected to what looked to him like an EGR valve that is aprox 8-10 inches in left hand corner in front of the throttle body.

It is seen in the front left hand corner of the second photo of post #9 in

http://www.benzworld.org/forums/w140-s-class/1493456-s420-sel-breaking-up-under-load.html


In case the photo does not come thru I will describe it as best as I can.
The part that the broken hose went in to was approx 1 3/4 inches in diameter and looks like a flying saucer .

Well since the plastic hose was broken off about 1/4 inch from where it went in to the black rubber hose we pulled the broken plastic part out.

There was not much play left in rubber hose but it seemed we were able to reverse the L shaped hose, and sorta stretch it and get it back on the valve. We thought we found the problem . Drove the car and it made no difference .

My cousin was not sure that the stretched hose was making a good connection and allowing the vacuum to function, so we left the hose off the valve entirely and I drove home 25 miles. Car drove perfectly without hose attached at all, and did not exhibit any hesitation, when I got back to city upon aggressive accelleration. I did not expect it to ,as highway driving kept engine temperature around 60C and it usually only happens after 80 C is reached.
It is possible that the repair we made stretched the hose so the vaccum could not function properly , but if that in case, is not the fact, then what is this valve that made no difference being unattached ?
So no arcing, and since it is past midnight , I will buy a new L shaped hose and attach it tomorrow and hope that is the problem.

It also is possible the 2 mechanics messing around in the engine compartment changing plugs ,and then rotors broke the hose/plastic piping .

If so why put a useless vacuum line in a car ?

Still lost :)

It sounds like you are onto something.

This is the correct photo. The part is to the right of the oil filler cover, and in the front to the left of the throttle body with a black vacuum hose coming out of the top of it.

It is round like a saucer . What is it called and what does it do?

It's an Exhaust Gas Recirculation (EGR) valve. Most cars have them. They are easy to change.