'86 300E rough idle when warmed up - Page 4 - PeachParts Mercedes-Benz Forum

Theurig · #46 09-14-2003, 03:25 PM

A buddy of mine told me the exact same thing about cleaning the air intake with carb cleaner. I wanted to do it this weekend, but the super weather here in Jersey this weekend won't allow me to. I'll do it and let you folks know if there is any result. I must say though I used some fuel injector cleaner in my tank this week, and it is running a whole lot better, the hesitation and shaking is less, not gone but less. (Chevron with Techron additive.)

can-do · #47 09-14-2003, 09:20 PM

Greetings All,

Wish I'd get the same response to my post as the MB reliability post has. That one is to easy to answer for all of us that I didn't even bother. We all bought the three pointed star car for one of two reasons. Either we think it reflects our stature in society compared to others, or we truly love the ride, and for some of us it's both. For me, it's both as well as many others on this list, and the problems they cause us probably aren't any worse if we reasonably look at it compared to any other vehicle. You pay the price either in the beginning or along the way, and if you're mechanically inclined it ends up being a whole lot cheaper. Love both my Benz's because of the ride and ease of maintenance to perform on them, and they are different than the normal can't fix American cars of today. Maintenance issues on the diesel is pretty much, fuel, oil, filters, and an ongoing preventative change out and everything seems fine and the car runs great. The 300E with a gas engine is a different animal in it's own rights and too many things can and will go wrong with electronics under the hood controlling the outcome. I don't personally believe that cleaning the intake plate on the air flow meter will make a difference in how it idles as I've had the entire air cleaner assembly removed from the car and the idle problem still existed. There could be a vacuum leak as well as an injector or two that has gone bad and I can see the possibility of it leaking down into the cylinder during idle. Great post on that one pmckechnie as it could possibly be just that. Of course the only way to find out for sure is to change out all the injectors and see what happens. I believe you can clean them to some extent, but as many have already mentioned, this is only a temp fix and doesn't cure the problem on a consistant basis. I think we're dealing with worn parts more so than just dirty parts. Trust me, Techron isn't the miracle drug for sick injectors unless it was actually used undiluted and directly into the injectors as a cleaning agent an not as an additive to 10 gallons of fuel. If in doubt try this experiment. Take a jar or bowl and spray carb cleaner into it so it completely covers the bottom of the bowl, and do the same with techron cleaner. Enter a dirty fuel plate or other gummed up fuel related item to the bowls. Watch what happens to the gummed up area of each. Carb cleaner did the best job, didn't it? Now dilute the same amout of cleaner into 10 parts of fuel and look at the results. Not a big change in cleaning action is there? Why, you might ask. Easy to answer, carb cleaner is a direct contact cleaner with no additional fluids to distract the cleaning action, and Techron, even as a concentrate is meant to be a routine added cleaner, not a fix to when the problem has gotten to the crud stage inside the injector.
Just my observation from past experience.

Charles

DanielW · #48 09-14-2003, 11:59 PM

What I was relaying was not that the carb cleaner was the major correction , but that the leaky rubber gasket around air cleaner bowl was allowing dust particles in and the dust particles were "mucking" up my idle control unit. 87 300E has not repeated the irregular idle speed trouble in the 2 years since I did that repair.

Something else I did could have fixed it even tho I did not realize; possible inadvertently fixing a small vac leak when I removed the idle canister's connections, or something like that.

I always look for the simplest answers first. Don't assume major expensive parts have gone bad without first taking the time to study mechanical and obvious issues.

Luck to you,
DanielW

mike690003 · #49 09-15-2003, 03:13 PM

After about 2 years of this pesky problem, I am now leaning toward a new set of injectors. After spending a lot of $$$ on this problem, injectors are all that are left to replace.

Should I have them professionally cleaned, or just buy a new set??

can-do · #50 09-15-2003, 08:12 PM

Greetings Mike,

I think someone mentioned the leaking injector idea on this post pointing out a leaking injector could cause a problem at idle as it continues to feed excessive fuel into the engine when it's not needed. I suspect that the internal part of the injector may be defective, thus cleaning really wouldn't do the trick. They also suggested if you are changing out the injectors, to also replace the seal and the holder to prevent hold ups on installations as these parts are commonly not a reuse part.
I am curious and wanna ask anyone out there if they know what the vacuum line coming off the fuel pressure regulator going to the air inlet housing actually does, and if it doesn't work, what the effect would be?

Charles

cc260E · #51 09-16-2003, 03:13 AM

[QUOTE]Originally posted by DanielW
[B]I don't really know that's what yours is doing, but the gasket I refering to is about 4" in a circle, made of black rubber like compound. It is the one which seals the air cleaner housing to the air horn of the fuel dist.

thanks DanielW,

I will try one these days and will let you know.

#52 09-16-2003, 08:16 AM

Quote:

Originally posted by pmckechnie
Inspector1

True, CIS systems are always spraying fuel when they are running, but it takes 40-50 psi of pressure to make them open and spray. It should only let fuel through if the pressure is above its opening pressure. A leaking injector will let the fuel go through intil the pressure gets to 0 psi. So yes they can leak and put too much fuel in the cylender.

If one reads this thread carefully, the problem is at idle, that is to say the enigine IS running thus the injectors are presurrized therefore cannot leak. per say, if a CIS is leaking enough at idle to have an impact, then drivability would result and a intermentant rough idle would be the least of ones worries, see this link for an understanding of the KE jetronic system www.volvoclub.org.uk/k_jectronic2.htm

dpetryk · #53 09-16-2003, 10:03 AM

Responding to Can-Do. The line you ask about is a vent line to route any gasoline from a leak in the fuel pressure regulator to the air intake so they can be safely burned.

I too have the same problem with my 300e. I am in the middle of serious diagnosis to find the problem. I have changed the fuel distributor and all the injectors with no improvement. I was convinced at one point that the FD was the problem. I loosened all the fuel line connections at the injectors and cylinder #2 would not leak any fuel. All the others did. I replaced the FD and there was no change in the leaking fuel. So I changed the injectors and that cured the leaking fuel test. However it made no change in the way the engine runs. I am wondering about the condition of the CATS.

I am doing through diagnostics around the CIS computer systems. I am convinced it must be an electrical related issue with some sensor or input to the CIS computer. I will let you all know what I find.

can-do · #54 09-16-2003, 11:03 AM

Inspector1,

I think our theory on a bad injector was that if it failed internally, assuming there is a spring that holds the injector valve needle closed until 3.3 bar is achieved, if this needle didn't close completely or remained opened partially under all pressure situations the idle would become rough at idle as the faulty injected cylinder would actually recieve more fuel than could be burned at idle speed. Running the engine at rpm's higher than let's say 1000 would absorb the additional fuel without much effect to engine performance. Although I don't understand the injection system fully, even after reading the site on it's operation, especially when it doesn't go into much info on the break down of the actual injector operation and the parts contained there in.
What other problems do you see as happening if an injector was in fact releasing fuel below the preset 3.3 bar when the engine speed didn't call for this amount of fuel? It seems that this engine has the ability to run somewhat rich with only an idle problem as a result verses trying to add air to an almost properly propotioned mixture, which basically just stops the engine in it's tracks. Any additional light you can spread on this situation would be greatly appreciated.

Charles

Phalcon51 · #55 09-16-2003, 12:20 PM

Inspector1,

You might want to edit your post and change the link to the Volvo club. The first "c" in k-jectronic" needs to be removed to make it work.

Also, I found a link to an article that gives a good overview of the entire K Jetronic system, with some attention to each subsystem as well. Here's the link:

http://www.auto-solve.com/mech_inj.htm

Hope this helps

Gary

pmckechnie · #56 09-16-2003, 07:06 PM

Inspector1,

Maybe you can help me with a problem I now have. I have a 84 500 SEL which was missing at idle but run great at anything above idle. When I checked the plugs after it had been idling for a short time, I found one plug was black and wet with gas. When I checked it with fuel pressure, it had a very slight leak below the 40 to 50 lbs pressure cut off. New injector fixed it. Now my problem. How do I convense my car that the injector couldn't cause this problem, so replacing the injector couldn't possibly fixed it. I guess the car just wanted to take something impossible and generate a make believe problem and play with my mind. Oh well.

MARIO FARIAS · #57 09-16-2003, 07:42 PM

THANKS A LOT, for this beatifull article.

MARIO FARIAS
LAPREFAR@CANTV.NET

can-do · #58 09-16-2003, 09:14 PM

Greetings All,

Thanks, for all the responses thus far. The more knowledge about particular problems and failed part replacement attempts will get this problem narrowed down to a select few items yet.
Phalcon, I appreciate your introduction of the fuel / air system, which helped me a lot understand the internal working, first of all of the injector. Now that I know for sure that it is spring loaded, it goes without saying that it can and will fail to constant use. That's a plus in our favor.
Paul, I'm not quite sure what you meant in your last post but I'm just assuming that either the injector change made a difference in your idle, or it didn't affect it at all. Can you clarify? Did you change them all or just the suspect one? I would also be one to think that if I needed to change one injector, then all of them being of the same age of 17 years old, they would all require replacement, just as a preventative measure. If the internal needle vibrates to atomize the fuel, then I'd have to imagine the wear over a period of 185,000 miles and 17 years has to have some effect on metal and rubber.

Keep the info coming, I'm taking notes.

Charles

pmckechnie · #59 09-17-2003, 07:21 AM

Can-Do

I was being a little sarcastic. Inspector1 says a leaking injector could not cause an idle problem only. He says that if a injector was leaking it would cause many other problems. On my 84 500 SEL, a leaking injector caused an idle problem with no other symptoms, and when I changed it, my idle problem went away.
At that time, I only replaced the leaking one because at that time I wasn't completely sure that that was the idle problem so I only put in one. Because it FIXED it, and the car has 250,000 miles on it and I don't know if they had ever been replaced before, I replaced all of them. Injectors need to be replaced at the first sign of a problem as maintaince. BUT I don't recommend putting in a set of injectors until the problem is fixed.
When I am working on running problems, I always fix the problem first and then determine what else needs to be replaced as maintaince. I have seen many times a "bad" new part that was put on trying to fix a problem only to find out later that the car now has two problems instead of one.
So many times I have seen where people have put on MANY parts trying to fix ONE problem. I get the car with TWO or more problems, and then they don't understand why it cost so much to fix the ONE problem when usually the ONE problem turns out to be a simple problem which was covered up by the problems put on the car by replacing parts.
Now of course, there are parts which can be installed as maintaince and if it fixes the problem then all is well. If you know your injectors have 185,000 miles on them, then it is about time for new ones and if it fixes the problem then great. If it doesn't then it needed then anyway so that is not money wasted. But keep in mind that it could inject another problem on top of the problem you already have. I think you get the point.

Sorry for confusion.

can-do · #60 09-17-2003, 10:46 AM

Paul,

Just wondering what problems your ride exhibited. Was your car hard to start initially, did the rough idle appear from a cold start or after it warmed up, and did the rough idle get worse the longer it sat in drive at idle? How'd you manage to test out the injector pressure?

Charles