1990 300SEL Hard to start - PeachParts Mercedes-Benz Forum

john2031 · #1 11-04-2007, 11:34 PM

I have owned this car for a year and I have been working on it when I have time. I am just now ready to put it on the road but still have several small things to repair. It was always easy to start until a few weeks ago. I am sure it is not getting enough fuel on startup. If I remove the breather cover a pour a small amount of fuel into the intake it will fire right up. I did drive it a little yesterday and it ran smooth. If it sits for a few hours it is very hard to start. It does not seem to be weather related. When I press on the flap in the intake I do have resistance but it is only pumping air no gas. Any suggestions as to the cause?

Problem #2. I was told something was killing the battery when I purchased the car. I I checked every circuit with a multitester. Circuit #2 was drawing to many amps to measure. I removed the fuse and overnight the battery was fine. Circuit 2 has the clock, radio, hazzard warning system on it.The radio is new so I don't think it is the problem. The clock does not work all the time so I think it is the problem. Can I unplug the clock without unplugging the tach? They are on the same instrument cluster.
Thanks for all the advice.

zcc · #2 11-05-2007, 04:35 AM

For problem #2, most likely it's the power antenna that keeps working.

john2031 · #3 11-05-2007, 06:56 AM

The power antenna is unplugged. The drive motor works, but will not operate with the button or with radio. I think the curcuit board is bad.

MRB · #4 11-05-2007, 08:02 PM

I have exactly the same problem with my 1984 190e. It's like the fuel drains all the way back to the tank and I drain the battery when I try to start it. (Might be related to problem #2) I have to turn it over several times before it evens wants to start. Once it starts it runs fine. Fuel filter? Pump? I don't know. I'm hoping you get an answer. I just had to replace the battery and don't want to ruin this one.

john2031 · #5 11-21-2007, 06:47 AM

I changed the fuel filter and the check valve. Car does run smoother, but was hard to start this morning. Will be looking at cold start valve soon.

MRB · #6 11-21-2007, 07:52 AM

We are just ready to replace our fuel filter and read your post. We will probably do it anyway, but are eager to find out what really causes the problem. Keep us posted and I hope the filter does it for us, but it sounds like we have the exact problem.

S-Class Guru · #7 11-21-2007, 10:50 AM

If the system loses all its pressure overnight, it could be the check valve or the accumulator. The check valve is just a little ball valve that prevents the fuel running back; the accumulator is a little air reservoir can with a diaphragm that can keep the line pressurized for extended periods, if it doesn't leak. On my car, both are located back by the pump/filter at the rear axle.
But, an easy way to check if these are the problem is to turn the key on without starting the car, wait 5 seconds, turn it on again. Each time you turn the key on, the pump will run for a few seconds, so multiple cycles will insure good pressure to the fuel distributor, If it starts better then, you may have found the problem; in the check valve, accumulator, weak pump,or maybe a badly clogged filter. My guess is, that's not it; it's probably badly carboned intake valves, vacuum leaks, bad EHA, or bad fuel distributor.

DG

david s poole · #8 11-21-2007, 11:29 AM

ditto!!!

MRB · #9 11-23-2007, 04:08 PM

This problem popped up fast. Would that suggest that it isn't the valves? Not sure how to do a good vacuum test. What is an EHA? Already bought the filter so I'll put that in soon. The outer shell of the distributer cap has a good size crack in it from our recent collision. Could that be it? Although it ran fine for a while after the crash. I also had to pull the vacuum unit away from the cap just to get the cap off and replace the broken rotor! Maybe that's where a leak is?

After the crash: New hood, fender, grille, light assem, radiator, water pump, rotor, plugs.

S-Class Guru · #10 11-27-2007, 11:33 AM

The distributor cap has a black dust cover that slips over it, to just keep major water and dust out - should not affect the working of the cap, if you're not driving in a rainstorm. But if you hit it somehow hard enough to crack it, the actual dist cap might be cracked also. This could cause havoc on a cool wet morning start.
Trace the vacuum lines to their source (the nipples in the intake manifold, and plug the nipples for vacuum testing.

The EHA is the Evil Sorcerer controlling all fuel monitoring. There is a lot of info about it here in the forum. In a nutshell, it's a little black plastic domino attached to the rear of the fuel distributor by two screws, has a 2-wire electrical connector. It is an electro-hydraulic actuator that varies the fuel pressure in the fuel chamber, based on inputs from the computer.
It can be tested by building a little wiring harness to insert a mAMP tester in-line with the wire, and measuring the current to the EHA under various conditions.

DG

john2031 · #11 12-03-2007, 06:10 PM

I adjusted the EHA 1/4 turn cw as found in other post. It will now start on first or second try but it stumbles. If it cut off it will start back on the next try. After it stumbles for 30 to 45 seconds is will smooth out and run fine. Should I adjust the screw a little more? I have to take the EHA off again to replace the o-rings.

MRB · #12 12-03-2007, 07:32 PM

I have been turning the key on to run the fuel pump before turning over the engine and it works! Starts right away every time. So...........pump? filter? check valve? We will replace the filter hopefully in a week or so, and will let you know what happens.

Pennypincher · #13 12-07-2007, 06:53 AM

Yea, I am blue. I have basically the same starting problem. Mines started maybe a couple of months ago and definetly has gotten worse with the cold weather. Just from past experiences with fuel issues I tried turning on the switch but not turning over the engine several times and no change. However what I did try that speeds the process from maybe 8 times to 5 is pressing the accelarator to the floor while cranking and then letting off as I am truning over the engine. No fore warning just one day it started this. Please tell me the 1st thing I should try down the road of ruling out things. My moto is I only buy cars I can pay for out of my front pocket! Actually this is a one owner car 213,000 miles ( I've owned it about 1 year) but with the exception of normal stuff the best used car I ever owned, the car is great. I have used the forum for about six months, just joined and I have told many people what a great catch you guys are, my girlfriend thinks it is my new best friend.

john2031 · #14 12-07-2007, 11:04 PM

I have noticed also when I press the accelarator to the floor and let of it as I crank it does start faster. I will say that I replaced the fuel filter and the check valve but it did not help my problem. I did adjust the EHA 1/4 turn cw and it helped some. I am going to adjust it another 1/4 turn cw in the morning. I have to replace the O-rings behind it. I know there is fuel at the fuel distributor. I turned the switch and let the pump run. Turned the switch off and loosened the fuel line and fuel shot out. It seems something is not regulating the fuel correctly to the intake. If I pour a small amount into the air intake the car will start on the first try. It also stumbles when started for a few minutes and will not take any fuel when I press the accelarator while it is stumbling. After it smoothes out it will take the fuel fine.

cummins · #15 01-02-2008, 10:10 PM

Has anyone checked the 10 amp fuse on th OVP relay located behind the battery? This fuse controls the cold start injector, I found a bad relay on my 86 300E.