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.

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

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Fred Hoelzle

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.

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

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.

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Fred Hoelzle

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

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?

David,

That is one item I had not considered. I will check it when I get home and see if it's original or not. Thanks also for letting me know where to look, it certainly saves me some time.

Dennis

Hey guys! If one of you put your car up for auction, I bought it. 1991 300SE. Exactly the same issues..from the stuttering right down to the antennae and radio. I thought it was the fuel pump, but now I'm thinking that's not it. I'm a chick with limited funds, so I'm not sure if I can ask my dad to try fixing it (He's a VW dude so knows a little about German cars) or taking it to a MB specialist. Don't want to pay more in repairs than I did for the car. Let me know what you think please! Thanks!

Hello again from the Seasonal Problem Presenter!

Once again as the temperature has dropped, my starting problems have risen. If there are any more ideas as to what could be causing my problem, I sure would like to hear them and solve the problem myself before I am forced to pay the minimum $150 to drive it on the lot at Mercedes!

The Crank Angle Sensor mention above was in rough shape and I replaced it with an OEM part....no change at all. This is the only repair done in addition to everything else mentioned earlier in the thread...

The car just cranks and cranks without firing. Every now and then you may get a gurgle from it like one cylinder is trying to do all the firing but then nothing again. Eventually it starts and runs fine with exception to power take-offs. Anything more than a slow, feather touch on the pedal and it bogs down and dies. It's very frustrating as you can imagine...and right now is not the financially right time for a trip to the dealer.... ugh

Hi Dennikro,

You have certainly had this problem for a while.

1) Have you changed your OVP Relay?

2) Have you looked at the OEQ Filter at the fuel in side of the Fuel Distributor?
These can become clogged up over time.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Thanks for the reply. I have not checked either of these items. What is the OVP relay and what does it do? (Sorry, I don't have my techincal disc at work with me right now)

It the OEQ a removable and cleanable item or is it replace only?

You can remove the OEQ filter and look to see if it is clogged up or dirty, if it is, I would replace it.

I would also check the vacuum hose connected to the Fuel Pressure Regulator, they become dry/brittle and crack. It's mounted on the rear like in the photo below.



The OVP relay provides voltage for components like the Idle Control Valve.
Below is an example of an OVP relay and a 190E electronic engine control schematic that you can look at to see what the OVP relay does.

One of the main problems with the OVP relay is a blown 10 amp fuse on top, or bad solder joints inside the relay.

The OVP relay is located behind the battery on my 190E, but I believe the OVP relay on a '91 380SE is located right of brake booster according to my parts book.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Thanks again for all the comments and suggestions for this ongoing issue.

It does not appear to be the fuel related components mentioned (above) as there is plenty of fuel flowing as indicated by the strong smell of gas after cranking. It really seems to be an ignition issue.

It had been suggested that the voltage protection relay could be going. This is the aluminum bodied, black-capped relay with a fuse on the top of it. It is located on the firewall, just to the driver's side of center. While the fuse is good, it's possible the temp could still be affecting the contacts inside. Sound plausible?

I was also told that if this relay is not the problem, that it should probably be replaced anyway since it would be problematic eventually.

So with all that said, what could be affected by temperature that impacts the ignition system firing or not? And no, the car wouldn't start this morning, hence the post. Funny how such events go hand in hand.

Dennis

*Edit* Reading back, is the relay I'm talking about the same as the OVP relay mentioned above possibly? It sure seems to match the loaction and description...