560SEC: Rough idle, hesitation, misfiring :( - PeachParts Mercedes-Benz Forum

johnathan1 · #1 11-12-2008, 02:30 PM

The main problem with this car is that it runs like crap. It will sometimes idle ok and accelerate smoothly, but other times it will act like it's going to stall, and a couple times already I have gotten stuck in an intersection and the car wouldn't move...I put my foot all the way down, and it doesn't respond for a few seconds (engine just shakes and bogs) and then all of the sudden the tires are spinning. It's very strange. It also won't accelerate smoothly, like there is a misfire.

Also, the o2 sensor light comes on on the dash every once in a while...what does this light mean?

I remember my 300SEL did this, and I cured the problem by replacing the plugs...

johnathan1 · #2 11-12-2008, 03:04 PM

Ok, I just took off the air cleaner, and sprayed carb cleaner here, there and everywhere. It seemed like no matter where I sprayed it, the idle would jump. Especially when I sprayed the injectors themselves. It was like i blipped the throttle with my foot. So I guess I found my problem.

Dee8go · #3 11-12-2008, 04:27 PM

New fuel filter?

johnathan1 · #4 11-12-2008, 08:24 PM

Ok, I just changed out the spark plugs and wires. I also found a small vacuum leak, which I fixed. Made sure all vac connections were tight, etc, etc (my back sure hurts).

So I replaced all of this, started it, and it really seemed like nothing had changed...the idle was still lumpy/shaky and it sounded like it was misfiring or something.

So I pulled back the passenger floor carpet, and noticed a thick green wire that was disconnected...I reconnected it as the engine was idling, and OMG the idle smoothed out considerably, the shaking almost stopped, and the idle started to increase. Took it out for a drive and WOW, it smokes the tires if I even go near the throttle. No more hesitation, and it accelerates very smoothly. The only thing is the shaky idle is still there, but not nearly as bad. I also hear what sounds like a ticking from the engine, almost like an exhaust leak. I guess I'll have to take it to the exhaust shop.

I thought it was really strange that after connecting this wire, now the AC and stereo don't work! WTF??? Also, I noticed that it BANGS when you put it into reverse, I had to look behind me to see if I hit anything.

ctaylor738 · #5 11-13-2008, 06:19 PM

If you got a lift from spraying the injectors, you should plan on replacing the injector seals.

It sounds like you re-connected the oxygen sensor to the engine control unit and now the air/fuel mixture at idle is under the control of the unit. It was probably disconnected because the sensor needs to be replaced, so do that.

Then adjust the duty cycle to 50%. Lots of posts on how to do that.

.

johnathan1 · #6 11-13-2008, 09:54 PM

Ok, I was already planning on replacing them...but I'm not sure exactly how to do so.

According to ***************, there is an "injector o-ring" and "injector holder (includes o-ring)" is this the same oring that they are talking about, and do I need to replace the injector holder, or JUST the o-ring? Also, once I disconnect the fuel line, and remove the injector bracket, do I just pull straight up on the injector to remove it?

cdplayer · #7 11-13-2008, 10:40 PM

If you are going to do some of it, I recommend do it all. Injector seals,
(O rings) and seats. The old stuff in there is brittle.(seats and seals).
Replace it all. And yes, once the fuel lines are off the injectors, unlock the injectors then just lift up with a twisting motion.

I recomend blowing the area around the injectors well with an air compressor if available or get a couple of cans of compressed air(the kind used to keep your computor keyboard clean) to avoid debris from falling into the injector hole.

johnathan1 · #8 11-14-2008, 12:32 AM

Is the Oxygen sensor just a 3-wire Bosch Universal? If so, I have one from my Toyota that I can install right now...It looks just like the one *************** shows in their parts picture, except mine just doesn't have the proper connectors.

ctaylor738 · #9 11-14-2008, 09:02 AM

The injector seal, not to be confused with the o-ring, is the most important. It seals the injector to the "jacket" and the o-ring seals the jacket to the engine. I suggest that you replace the o-rings and the seals.

A set of 6" hex-bit sockets will make this job a lot easier.

Oxygen sensors are pretty much standard as long as they have the same number of wires. When you splice the wires, make sure you get the correct hookup so that the brain gets the feed from the sensor!

hey_allen · #10 11-15-2008, 03:24 AM

The O2 sensors on my 500SEC are single wire, but they may have been fitted when it was imported, when the cats were fitted.

They shouldn't be hard to fit, as said above, just splice in sensors with the same count of wires, making sure to connect the heater and sensor wires correctly. (12v constant to the 0-1v output can't do good things to a sensor!)

As far as the ticking goes, you may find that running good oil (possibly a good synthetic for a cycle?) will clean up the valve adjusters and reduce or eliminate the ticking. Mine ticks slightly, but only really audible at low rpm.

You also might consider getting a local shop to pattern check your injectors when you have them out. They're simple nozzles with a pressure 'relief' valve that holds the fuel in the line until the pump pushes it above the release pressure, but if they dribble below that point, or stream instead of misting, they cause interesting issues. The dribbling makes for long cranking to start when warm from what I've seen, whereas the streaming makes for rough running.

It's good to hear your toy is behaving better for you though!
Happy wrenching, and best of luck keeping the foot out of the fun pedal!

johnathan1 · #11 11-17-2008, 04:06 AM

Cross-posted from another thread:

I think I may have bad manifold sealing rings. When I spray brake cleaner anywhere near the engine (literally anywhere) the idle jumps up quite a bit.

When I spray the injectors, some make the idle jump more than others... but when I spray down between the air mass meter and the distributor, the idle REALLY jumps, almost like I revved the engine using the throttle! Does this point to bad manifold seal rings/donuts?

johnathan1 · #12 11-17-2008, 04:32 PM

Anyone? I would like to get this problem fixed ASAP, but I'm not exactly sure which parts I need to order to replace while I'm in there, and which gaskets I will need when removing the intake manifold...

ctaylor738 · #13 11-17-2008, 04:58 PM

Sounds like you might have a crack in the lower air guide housing. It runs underneath the mixture control unit and conducts air from the sensor plate to the throttle valve. There is a long post by Timm9 on the SL Forum describing his adventure with this.

johnathan1 · #14 11-17-2008, 11:08 PM

Could you explain this more to me? I can't find the post you are talking about.

Is this some sort of plastic tube? Do I have to remove the intake manifold to get to it?

hey_allen · #15 11-18-2008, 02:55 AM

Here is the part that it sounds like he's talking about. On my car it was cracked as well, and it seems to be a fairly common wear/aging item on the older engines with the CIS fuel injection system that our cars have.
Air Duct Housing
This part may be required if your car isn't already retrofitted for the newer housing. Air Duct Flange

I did a bit of quick searching to find the article detailing the troubleshooting to find this, but I'm having little luck.
Here is one that has some pictures of the area below, but it's not specifically talking about the part that is likely to leak. HERE

Best of luck!