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Old 10-13-2004, 05:56 PM
Registered User
Join Date: Oct 2004
Location: Dallas, TX
Posts: 39
91 300E - 103 warm start

First time poster, thanks for any guidance on this.

91 300E - 139K miles. On warm starts only,after sitting for 20+ minutes, any ambient temp, engine fires right up and idles like it is on 3 cylinders. Will smooth out if left alone or accelerator is pressed. Faster if accel is pressed.Classic case of fuel starvation. Fuel pumps hold pressure for 45 minutes. Check valves replaced in pumps, no change. Fuel accumulator replaced, no change. Fuel pressures holding 3bar+. Injectors cleaned and flow tested, no change. New injectors, cleaned and flow checked, no change. Fuel filter just 11K miles ago.

I'm thinking that its time to think beyond fuel and look at ignition. You need 3 things for combustion, air,fuel,spark. Ruling out fuel, look at ignition coil.?? Cap,rotor, plugs and wires were replaced in April.

Look at cap and rotor to see if they are carboned?

Cold start valve works, pressures are good and hold well.

What are some thoughts?

Plugs have about 3K miles since new and are excellent, light tan in color.

Thanks for the help
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Old 10-13-2004, 08:27 PM
Registered User
Join Date: Mar 2003
Location: Southern California
Posts: 2,097
I think it's somewhat the nature of the beast. The "cold start" emission certification starts at room temperature and it's always been my experience that cold starts at 40F are better than 70F. Since most emissions are produced during cold start and warmup, the cold start calibration at shirt sleeve temperatures is on the ragged edge of leaness.

After cooling for 20 minutes the engine temperature is in this netherworld between not hot, but not really cold.

It's my opinion that better cold start performance in mild weather can be obtained by setting the duty cycle to less than 50 percent at idle, but I would not go below 40 percent. The lower the duty cycle the richer the basic mixture, which is what is applied before the KE system goes into closed loop operation.

In case you aren't familiar with the duty cycle and its adjustment the following site has a very good writeup.

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Old 10-13-2004, 08:48 PM
Registered User
Join Date: Dec 2003
Location: Perth, Australia
Posts: 42
Warm Start

Welcome to 103 World.

Everything sounds fine and at least yours starts up on a warm start. Most start and die and then start. Much has been written and as you have demonstrated a great deal of time and money can be spent trying to solve the problem.

The stumbling seems to be part of the act until all the systems come on line.

The easy solution, as per your owners manual, give it some accelerator on a warm start to bring it into life.

It soon becomes second nature.

Do a search and check out Norm's comments regarding adjusting the EHA. I would be very interested to know if you see any improvement in adjusting this.

I have contemplated replacing injectors but was interested to note you did not see any improvement.
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Old 10-13-2004, 09:44 PM
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Join Date: Jan 2003
Location: Sydney, Australia
Posts: 627
Whilst many suffer these sorts of problems, I don't believe it is how it should be. My M103 (with 184,000km) starts perfectly cold, hot or anywhere in between (I probably should not have stated that, something is now sure to go wrong). This is despite the fact that I have not replaced any ignition components (other than spark plugs) or fuel components (other than fuel and air filters) in the more than six years I have owned it (I have no reason to believe any other ignition or fuel components have been replaced in the life of the car). I can imagine the frustration of having such issues, especially in Rick's case where he has already checked and replaced so much. I would also tend to agree with checking the base mixture setting before the O2 sensor takes over.

My 2.3 litre M102 (with 226,000km) does not start or idle as nicely as my M103, although it is not bad enough to be annoying and once running drives perfectly. Even a 1.8 litre M102 with only about 30,000km I owned several years ago was slow to fire up and rough immediately after starting. Obviously the KE systems are somewhat variable from one car to the next and it does not take much for them to be a bit cranky. A shame really because I believe the M103 to be one of their sweetest motors.
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
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Old 10-13-2004, 10:03 PM
nglitz's Avatar
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Join Date: Aug 2004
Location: Hamilton Square NJ, near Trenton
Posts: 391
Your description fits what mine used to do, '78 260E. 215,000 miles.

Check the B11/12 temp sensor. This is the two-terminal, brass bodied sensor all the way in the back of the cylinder head. Both terminals should show some resistance to ground. One senses for fuel, one for ign. They're interchangable. If one or both is open, it gives the fuel injection or the ignition the wrong temperature setting. Fuel is much more sensitive.

Another thing worth an adjustment is the EHA. See this thread. It's said to make up for old age & small vacuum leaks.

Then there's always tickling the CO idle adjustment in the fuel injection "flapper" . Sears sells a $30 DMM with "duty cycle" even though it's the opposite of MB's version of duty cycle. i.e. 30% on the meter is 70% in MB language. Kind of fun, driving around & watching the % change as you gas it & let up. Sometimes, I'm easily entertained.

Mine now starts is less than one crank revolution; hot, cold or warm. I love it.
Norm in NJ
Next oil change at 230,000miles
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Old 10-14-2004, 12:35 PM
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Join Date: Oct 2004
Location: Dallas, TX
Posts: 39
91 300E - warm start problems

Thanks to all with your replies.

Coupla points - Everything that was replaced and made no difference was not left in, so I am not throwing parts or $$$ at the problem.
My dealer mechanic and I are working through this and he has started to scratch his head regarding this and is talking with a few other "old timers" in the shop to cme up w/something.

I replaced all vacuum fittings and most vac lines awhile ago and must state that this made a HUGE difference in idle quality and increased MPG. A must for anyone that hasnt touched these things, only had about $40 and one afternoon tied up on that project.

I know the mechanic has evrything set at OEM specs, have watched him do most of the work. I feel really lucky that he has been so persistent with the problem. Methinks he is taking this as a personal challenge now!

Again thanks for the input. I'll let you all know how it comes out.
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