mathesius

This is a long post, but I hope the extra detail might lead to better help.

I have a 1998 C230 and on my way to work the CEL came on. I didn't notice any problem at highway speed but when I came to a stoplight a rough idle was obvious. The car has 91k miles on it. I bought it 6 months ago with 79k miles.

On the trip home (41 highway miles) there was an obvious loss of power so the situation was getting worse. I stopped by Autozone and got the codes read. They said cylinders 1 & 2 were misfiring and the EGR valve was also indicated. The exact codes are P0301, P0302, P0300, P0400.

I took a look at the wires and pulled one of the plugs which are all brand new just last month. I used OEM plugs, OEM spark plug connectors, and Magnecor wires. I had a heck of a time getting the connector out on #4 and must have damaged the spark plug seal. Now there was some oil in the area by #4.

I took it in to the dealership, because I couldn't find an easy way to take off the EGR valve to check it.

It turns out my EGR code was a stored code, not an active code. Since I didn't know when the codes were cleared last, I have no idea what set that or when.

Cylinder 2 misfire was the only active code per the Zimbrick dealership.

They found the center electrode on the plug in cylinder 2 had disintegrated (a bit of it was in the top of the cylinder, which they got out somehow). They also didn't like the oil near cylinder 4 and wanted to replace that plug too and change the valve cover gasket set. They actually ended up putting new plugs in cylinders 1 & 2. Discarding my old plugs from cylinders 2 & 4, and putting my two remaining plugs in 3 & 4. If you can follow that.

Thus at the end I had two dealership installed plugs in 1 & 2; two of my plugs in 3 & 4, and a new valve cover gasket set.

Clean running... for a week. Then today I accelerated strongly to pass a car and the CEL came back on and the engine ran rough again. Same as before, it started with a rough idle but progressed to a loss of power at highway speed.

I took it back to Zimbrick rather than deal with this. Turns out cylinder 3 & 4 were misfiring, so they changed out the plugs in 3 & 4 -- so now all four of the new plugs I put in 6 weeks ago are replaced with new plugs they put in.

Drove smooth home. Until I accelerated strongly to test things out.

Bingo, the CEL came on, the engine got rough even faster than before. I made it home, cleared the codes by unplugging the battery, and started it up.

No CEL, ran smooth at idle. Ran smooth at 2000 RPMs. At 4000 RPMs it went bad again, causing misfires and rough running at any speed just as before.

Short story:

Something is triggering at higher RPMs that causes the whole engine to misbehave.

Possibly this is causing it to misbehave so badly that it's ruining plugs.

Any guesses?

I am running a K&N air filter, but the MAS hasn't yet sent a code and from what I can tell most bad Mass Air Flow Sensors throw codes. The dealership did warn me against the K&N though. I've had the K&N in for 12,000 miles.

I am going to do more research online and probably take it back to the dealership tomorrow.

Thanks for any help!

Batman

wow, sounds like almost the same problem I'm having. only on my 98 c280 with 125k miles. I even changed the o2 sensors, the plugs, and it still has no power. Plus, mine is completely stock, so no k&n to worry about. I was wondering about the maf, because I've had to change that a few times on a 97 e320 I used to have. it would be really nice to hear what the problem is from someone on here. I'll probably go to autozone today to get the codes checked/cleared to see what's going on.

040mercedes

I have a 95' C280. I have the exact problem with my car. The only difference is there is no CEL when the problem starts. Like you described, it feels like a misfire, a really rough idle and loss of power. Also, the whole thing is triggered by giving the car a good amount of gas. The car surges and instantly idles rough with no power. However, I can shut my car off at a traffic light and start it back up again and the problem is gone. I have had this problem for almost a year now, and unfortunatley, nobody in this forum knows what the problem is. It has been a mystery for me as well. I've posted topics about this problem before and nobody can give me a straight answer. I've posted a thread on Mercedesshop.com as well. Nobody would even reply to the thread. So I second the motion, WHAT THE HELL IS THE MATTER WITH OUR CARS.

davis449

Y'all check your coil packs, some of these symptoms sound like a coil pack problem. It causes misfire and really badly might I add.

Batman

It looks like there are 6 coil packs on my 98 c280. They're $127 each, retail from the dealer or $104 each for Bosch packs from the internet. $89.70 retail for the valve cover gasket from the dealer and $153 retail for the spark plug wire kit. How can I test the coil packs? Because it would be nice if I didn't have to replace all of them ($650). Also, any way to test the spark plugs wires?

I went to autozone to get my codes scanned. no codes stored, no check engine light on the way up there, AND no power when accelerating.

mathesius

As an update, my problem isn't the ignition coils. We tried two different ignition coils and factory wires, but no change.

I've been told that the next most likely culprit is either the computer that controls ignition or the crank sensor. I'll have some more time to work on it after Christmas I suppose, so my updates will probably take a break until then.

s21701

Replace your fuel pressure regulator. It's the little round can that sits on the fuel injector rail. It costs around $70 and will solve your problem. I have a 97 c-280 that showed most of these problems and attacked it logically as you all have. Trust me, before you mess with the crank position sensor, the mass air flow sensor, or anything electrical, do yourself a favor and replace this fuel pressure regulator. It's a 10 minute job.

Batman

sounds good to me. $70 beats any of the other alternatives. any pics or tips on the procedure?
edit: Hmm, called the dealer and the part is $124 retail. anyone have a link to some place online that has it cheaper? Thanks.

s21701

Try overnightautoparts.com. I think they have the part for around $68.
It is in the fuel delivery/fuel injection part of their site once you enter in your model info.

My car is a little different than yours, but this is how I did it.

With the engine cold, I removed the black plastic cover that sits on top of the fuel rail.

There is a brass cap-like thing that I next removed. I then took a rag and my finger and pressed in the pressure relief valve that this brass cap covered.

A little gas will come out at this point, but the rag will prevent it from hitting you in the face/eyes.

Slip off the little hose from the regulator.

I modified a cheap pair of needle-nosed pliers and removed the circlip from the top of the fuel pressure regulator.

Simply wiggle out the regulator once the circlip is removed.

Put in the new one, reinstall the circlip, the hose and the brass cap.

You're done and the problem's solved. I'll see if I can figure out how to post some photos.

s21701

Here are some photos

Batman

great pictures and description!! thanks. I appreciate it. although, I didn't see the part on that site for a 98 c280. but, it's ok, I'll look around and see what I can find.

s21701

I think I may have read somewhere that the fuel pressure regulator is built in to the fuel filter on the 98 c280s. It seems strange, but it does have another tube coming off of it. Strange still that the 98 c230 has the same fuel pressure regulator as my 97 c 280. These engineers aren't happy until they're done "simplifying" everything. Maybe you're due for a fuel filter replacement anyway?

Batman

Uhh, looks like the 98 c280 has not one, but 2 fuel pressure regulators. Great. And there's some electronic part in between them. My CEL came back on today, so I'll be going to autozone to get the code scanned and see what it says. The left side looked pretty oily/greasy. You can see the picture with the bolt. Maybe oil is getting on the spark plug and causing a misfire? Don't mean to hijack the thread, but I think it's the same issue, so, hopefully this might help.

s21701

Maybe they have to be linked electronically to keep the fuel pressure balanced between the two rails. It may be worth your while to hook up with alldatadiy.com and see for sure what those components are. I must admit I'm a bit baffled that the parts aren't shown in any web site I've found. I'm not sure if the oil would cause a misfire or not. Let us know what the autozone wonks come up with for the code readout. Good Luck.

Batman

codes came out to be P0170 Fuel Trim Malfunction (Bank 1) and P0173 Fuel Trim Malfunction (Bank 2). I just changed all 4 o2 sensors not long ago. I also changed the spark plugs. I also replaced my exhaust manifold and the gaskets cause my exhaust manifold had a crack in it (thanks MB quality). I wonder if that's what started all this. If the exhaust manifold was cracked, and the computer was adjusting the fuel level to compensate for the leaking air, then that could have lead to these other problems. Is that a possibility?

by the way, I have 125,000 miles

s21701

That it's the fuel pressure regulator(s). I first replaced one of the coil packs thinking it was causing the misfire. Mine had also thrown codes for fuel trim malfunction and others for the O2 sensors, so I spent about two hours dropping the exhaust from where it connects to the exhaust manifold, and changed out both of them. It was no fun hanging this heavy exhaust again. I also replaced the crankshaft position sensor - the first one I put in was ever so slightly too long and quickly ground itself up on the fly wheel. The next one I installed with a specially modified washer to increase the spacing. I then broke down and bought a new mass airflow sensor. No help. I then moved on to the coolant temperature sensor, a new thermostat, new spark plugs and plug wires. I even bought a fuel filter, but didn't have the clamps so didn't install it.

I finally stumbled across this fuel pressure regulator, changed it out and all the problems have been gone for 20,000 miles now. I know our cars are different, but I'm still betting on this fuel pressure regulator (s).

I know there are others on this forum that can attest to this. I just wish they'd speak up.

Batman

definitely seems like a possibility. I searched the forums for those codes and just about every post points to the mass air flow meter/sensor. there was one post that said if it's not the mass air meter, then check the fuel regulators. just search the forums for p0170 p0173 and look at a few of the posts that come up. (there are only 16 of them). tough call.

shorthair

There are a few MB mechanics that frequent the Mercedes Tech Talk forum. Maybe you can PM one of them to ask if they would mind reading this thread? Or post a reference of this thread in that forum asking for some advice/help?

mathesius

I'm the OP with the C230 problem.

As a conclusion, it ended up the catalytic converters were partially blocked on my car. The dealership figured it out after measuring the exhaust gas temperature before the catalytic converter and it was too hot, indicating back pressure. Tested the theory by dropping the exhaust & it ran fine.

At low RPMs the exhaust system was clear enough to run fine. At higher RPMs the extra demand put on the exhaust resulted in back pressure which caused the cylinder misfires. The computer then shut off the cylinders until I reset the codes.

I went ahead and replaced the muffler pipe too since it had a slight rattle in it. Got the parts from the Benz Bin to save some $. The catalytic converters new from Mercedes were going to be $1,500 vs $349 for the DEC brand. I haven't yet adjusted to MB parts pricing...

It was probably a combination of things that led to the catalytic converts failing. The car is 7 years old with 92k miles; it had a rough history before I purchased it (all four springs were busted when I bought it 6 months ago); recently spark plug 2 failed and while it was failing the exhaust would have been rich.

The O2 sensors aren't throwing codes, but I'm thinking about replacing them too just to be safe. If the front sensor is bad but isn't throwing a code, it could have caused the air/fuel mixture to be too rich, causing the old catalytic converters to go bad. I'd hate to have my new cats go bad in six months due to the O2 sensor. I've read O2 sensors usually should be changed around 100k miles anyway.

Good luck to the other poster.

Thanks for all the help.

Cheers, Steve

Batman

Ok, I replaced the mass air meter (flow sensor keywords in case someone is searching for this issue) due to the overwhelming opinions about the p0170 p0173 codes in some other posts and so far, it seems to have worked. I'll update if anything happens in the next week or two. Thanks for all the help everyone.

jangle

I have a C280 elegance with cosworth sport pack (175 on the clock). I recently had an issue with a a very rough misfire when accelerating and a few bangs coming from the exhaust. I had all the plugs replaced and everything was ok until 4000rpm the garage swapped Coil Packs until they concluded which one was failling this was then replaced for £50 quid and the car fires like a dream.

My only problem is now the Remote Key fails to LOCK and UNLOCK the car.

Regards
Stuart

AVO 3VOM

I have a 1997 Mercedes C230 and had two questions regarding the posts in this forum. First, what would be the major difference between purchasing the cataytic converter through the dealership for $1500 as opposed to purchasing the product currently available through Bekkers for $375? My second question involves the O2 sensors. when replacing, will I need to purchase just one sensor for the vehicle? These may be kind of boneheaded questions, but this is the first vehicle I've had where I've had the oppurtunity to fix some of these problems myself and want to make sure I do it right. Thanks.

Batman

Ok, apparently, the mass air flow meter was not my problem. Check engine light came back on and the car still doesn't have as much power as it should. That's all I have for now. I'll post any further updates. Can anyone guess how much I love this car right about now???

Gabe

Ladies and Gentlemen,

First of all, thank you all for the wonderful contributions. Same problem here, started about 2 weeks ago, 98 SLK230, get to 4000RPM and engine wants to die, CEL... but I had codes that talked about a cylinder misfire and a problem with the Seconary Air System (shoots air into the exhaust manifold to make sure gases are fully burnt when engine is still cold).

After reading the thread I got a lot of ideas of what wasn't the problem so I proceeded to look under the hood. Both the gas pressure regulator and the secondary air system rely on vaccuum. I started to disconnect and reconnect the hoses starting from the supercharger and the second tube I grabbed practically disintegraed in my fingers. The hose was so brittle it cracked right where it makes a connection. It must have had a leak in it that reduced vaccuum levels.

Four feet of vaccuum hose from Pep Boys, some connectors and half hour later my wife tested her car and the CEL light went off after a couple of minutes. She even tried her hardest to get the symptom to come back on the highway.

I had tried a Valvoline Carbon Cleaner additive but the CEL and the problem were still there after a tank of gas.... it is important to mention that the idle is a lot smoother!

After this fix, the performance and idle are back to "as-new" state... just something else to consider. Less than a $10 fix if you get lucky.

wetherall

Two weeks ago, I changed the spark plugs in my 1998 C280. A few hours later, the Check Engine Light appeared. I used a scanner and it showed the P0400 code for an EGR Flow Malfunction. I read some posts, including the quote below, and I, therefore, believe that I may have damaged a vacuum hose while replacing the spark plugs. Unfortunately, I cannot distinguish which hoses in the engine compartment are the vaccum hoses. Could someone give a vivid description of what they look like and where they are located or, better yet, post pictures of the vaccum hoses. I have tried everything to diagnose the problem without success. Any assistance will be greatly appreciated.