91 300SE Hard start/stuttering - PeachParts Mercedes-Benz Forum

Dennikro · #1 08-23-2006, 10:32 AM

1st of all, thanks for having this forum out there.

Let me add that I am a DIY person and have been working on my own cars ever since my father allowed me to crawl around under the car with him at about 2 years old. I've always felt I can do just about any job with the right tools and instruction.

Where I get into trouble or frustration, is when it comes to troubleshooting some issues as cars become more and more technically advanced. I'm more of "vintage" engine guy so to speak.

I'm currently building a new garage that will be what I think is a DIYer's dream complete with a lift and everything. As such, I won't have a space to do my own work out of the weather until about mid-October.

Here's my issue:

When I got my 300SE about a year ago, the previous owner had it inspected and had a laundry list of things the Mercedes dealer said needed to be addressed. One of these items was a set of fuel injectors.

The leaking injectors were causing a flooding problem making the car hard to start and seemingly causing a studdering/bogging issue when starting out. Luckily, I found a set of new OEM replacements on Ebay for about $25 each.

Two weeks ago, the car quit on me at speed with the cruise set. It would start right back up but intermittantly stop time after time. As I was on a trip out of town and about an hour from my house, I ended up having it flat-towed to the dealer because I didn't have the time nor patience to try and work on it on the side of the road.

The dealer replaced the fuel pump (which was the main problem) and filter and they were kind enough to replace my injectors for me with the ones I had with me in the car already. Of course as any DIY person knows, trips to the dealer are feared and seldom cheap. This one cost me $790 (not including the $120 tow).

Since having that work done, there are two issues I am still having. I made a six-hour round trip the next weekend and after getting back, the car sat for a day and then would not start. It turned over just fine but would not fire. It took several attempts without so much as a "pop" and then just started up like nothing was ever wrong. That has only happened once and seems to be starting fine for the last week.

The other issue (which I thought was related to the bad injectors) is that it stutters or bogs down when I hit the gas too fast or hard from a start. If I try to hold the gas on to "clear its throat", it will continue to spit and sputter. If I ease into the gas, it seems to take off smoothly...it's only when I hit it harder that it bogs down to a point where if I continue this, it will die altogether. It doesn't do this ALL the time, but most of the time.

It also does not seem to have any problems at speed if I need to press hard on the gas and engage the passing gear.

Details:
91 300 SE
168K miles, gasoline engine
new cap, rotor, plugs and wires (3 weeks old)
Regular oil and filter changes (Mobile synthetic) every 2000 miles
The aforementioned new Injectors, new fuel pump and filter.

Any ideas? any more information needed?

Thanks Everyone.

Ferdman · #2 08-24-2006, 05:52 AM

Check the oxygen sensor ... should be replaced every 60,000 miles.

Rob Pruijt · #3 08-24-2006, 08:41 AM

If you have replaced ignition parts a week before the problems started, I would take them out and check them. New parts sometimes fail.
For a 103 engine always use original Bosch ignition parts.

Dennikro · #4 08-24-2006, 08:47 AM

Quote:

Originally Posted by Rob Pruijt

If you have replaced ignition parts a week before the problems started, I would take them out and check them. New parts sometimes fail.
For a 103 engine always use original Bosch ignition parts.

The problem was happening before the ignition parts were replaced. I thought they may have been the problem as the cap was cracked in two. Some joker before me GLUED the cap back together! I couldn't beleive it ran as well as it did. I was sure this was the main problem but alas, it was not. All parts Bosch.

Dennikro · #5 08-24-2006, 08:48 AM

Quote:

Originally Posted by Ferdman

Check the oxygen sensor ... should be replaced every 60,000 miles.

Never a bad idea...although it would seem like an odd componant to cause the symptoms. Never hurts though, stranger things have happened.

Ferdman · #6 08-24-2006, 10:23 AM

Replacing the oxygen sensor on our 1991 300CE eliminated sluggish acceleration like you describe on your 1991 300SE. That's why I'm suggesting the oxygen sensor may be causing your problems.

Dennikro · #7 08-24-2006, 10:53 AM

Cool thanks Fred! It's worth a shot anyway and nothing ever wrong with replacing the O2 sensor

Dennikro · #8 09-15-2006, 07:59 PM

SO, I've got the O2 Sensor in hand, know where it's at in the exhaust system and see where it enters the interior from the outside. My question is: where on the INSIDE does it come through? I don't want to rip apart the entire interior to find the plugs for it. Surely they have made SOME sort of access panel for this? Surely? Anybody?

Dennikro · #9 09-15-2006, 09:22 PM

OK..never mind on the proceedure, I took a breath and out-thought the car and got it replaced. Of course with all the interior panels off, it gave me access to the stereo system someone installed so I figure I can figure out why it's not activating the antennae or picking up any radio stations...but that's for another post if necessary.

I'll report back as to wheather or not the O2 sensor did me any good by replacing it.

Mike Murrell · #10 09-16-2006, 10:26 AM

After the O2 sensor swap out, it wouldn't be a bad idea to see what's going on(current-wise) at the EHA(electro-hydraulic actuator). Lots of yack about this device at this forum.

2 "special tool" gadgets are used to perform EHA testing/adjustment.

Both are available from Baum Tools -> pointer to it a little further down.

EHA test harness - 102-0463
CO adjustment Screwdriver - ST10507

and of course the much talked about Sears multi-meter that features "duty cycle". There are other meters that have this, but most are far more expensive than the Sears model which was $29.99 the last time I looked.

http://baumtools.com/Baum_Tools_mercedes_catalog_2006.pdf

MB service manuals located at:

http://mb.braingears.com

Dennikro · #11 09-16-2006, 01:08 PM

Thanks Mike,

I'll see what I can do.

The manuals page comes up but all the links I have tried within it don't seem to work.

As far as the tools...are you suggesting both tools PLUS the sears unit?

Thanks,
Dennis

Mike Murrell · #12 09-16-2006, 02:36 PM

Both URLs work for me. If you're on dial-up, it is SLOWWWWWWW getting around in either.

All 3 gadgets if you want to set duty cycle & work on EHA setup.

psfred · #13 09-16-2006, 02:53 PM

Hard starts after sitting have several causes you really need a pressure gauge setup to test:

Leaking fuel pressure regulator, lets all the pressure out so the pump has to run a bit before you get fuel delivery (leaking injectors ditto, except it then floods)

Bad accumulator so there is no residual pressure reserve. Worst on hot starts since you can then get vapor lock in the injection lines

flaky fuel pump relay (replace if it's old -- it if gets hot during operation, definitely replace).

Flaky OVP relay if so equipped (not sure of the 91 model year). This will cause a no fuel system and/or no ignition condition from bad solder connections in the relay. It's there to prevent voltage spike toasting the electronics.

Bog on startoff can be a leak in the air part of the fuel injection system -- you need to check the boot between the fuel distributor air horn and the throttle body, the idle control valve hoses (a bad leak here will also prevent starting, by the way -- no fuel injection because the air isn't going through the metering orifice venturi). Check the injectors for leaks (a quick squirt of brake parts cleaner on each one while idling -- if the idle changes, it's leaking air). Shouldn't be a problem for you since I'm sure the injector seals were changed whent the injectors were --the old ones likely wouldn't come off the old injectors intact. However, the 0-ring that seals the plastic sleeve for the injectors can also be bad, and leak. I just replaced all this stuff, and it make a huge difference.

Also, a bad throttle position pot on the throttle body will cause trouble. The resistor trace can wear through, causing the computer to loose track of the throttle position, and you dont' get the correct momentary enrichment you need on sudden throttle opening. Usually not a problem if you floor it, but light applications can cause momentary over-lean conditions that result in throttle lag.

Peter

Dennikro · #14 09-17-2006, 10:21 AM

Quote:

Originally Posted by Mike Murrell

Both URLs work for me. If you're on dial-up, it is SLOWWWWWWW getting around in either.

All 3 gadgets if you want to set duty cycle & work on EHA setup.

Going on a hunch, I've discovered that the links didn't like to open in Firefox.

Oh, and by the way, the O2 sensor replacement did not do a thing for my performance issues...at least the ones that I notice. It will still bog down if I hit the gas hard but not if I ease into the throttle.

A lot of the suggestions above really hit the nail on the head as far as how it's reacting to different situations so I have a bit more to go on...thanks Peter!

Now if only my contractor would stop dragging his feet so I'd have a garage to work in (especially before the snow flies!)

Mike Murrell · #15 09-17-2006, 11:39 AM

Read thru the thread further down, especially from the point where Steve Brotherton joins in.

300SE W126 Will not start