[Wyo_25]

I recently have been having a bit of startup trouble with the 300E and no good duty cycle readings. Bare with me on all the details, I don't know which may be important. Full list of all work done in 'my garage' and a short summary at the end of this post.

Prior to this weekend, the car would Never start on the first crank, but would jump to life with a second crank, NO pedal required.

The significantly hard starting occurred after this last weekend when I did a quick vacuum check and noticed a significant leak where the rubber gasket on the air flow housing attaches to the manifold near the throttle body. I ended pulling the fuel distributor off and reinstalling it with the boot down over the gasket. To accomplish this, i had to detach the air sensor plate and reach inside the airflow housing. I also replaced a few cracked electrical clips at the idle air control valve and at the EHA.

As it stands currently, the car requires a lot of cranking and lots of gas pedal to start. It will start and run with little to no noticeable problem. However, I get a 'static' lambda/duty cycle reading. I can start the car back up with minimal cranking if i try to restart it within about 1-2 minutes. After 5 minutes its back to the hard cranking and pedal.

More history, earlier this summer I had issues with the vehicle stalling out and very low RPMs when stopped (this was during the hottest part of the summer). This was a somewhat sporadic issue.
Now back to the lambda/duty cycle. I have had success getting readings not that recently.

Full duty cycle run down:
Key in ignition and turned to last position - 30.6% (based on H.D.'s sticky thread on lambda that means i probably have a meter that shows 'on'-time)
Key in ignition and air sensor plate depressed - 90% (would be 10% if i had a 'off'-time meter)
Key in ignition and throttle open - 80% (again would be 20% with an 'off'-time meter)
Engine and O2 warmed up car turned off and then restarted - initially the reading starts around 50% and slowly ticks up to 82.5% and remains static at that reading.

I'm afraid to drive it now in fear of burning up the ignition coil or doing other damage while i crank on it to get it started. What are the recommended next steps for getting this back in top shape.

Could it be fuel pump relay? OVP? The OVP appears to have been replaced with a new Kaehler OVP, but I have an extra OVP on hand.

Work Completed(based on receipts):

02 Sensor - 07/2015 (part #13953?)
Voltage Regulator - 01/2016
Fuel Pump Check Valve: - 01/2016
Fuel Accumulator - 01/2016
Fuel Filter - 01/2016 (updated)
Water Pump - 1/2016
Distributor/Rotor- ~2014
Rotor and Cap - ~2014

Work I've personally done:
Spark Plugs/Wires - 2015
Power Steering Lines - 2016
Fuel injectors, seals/insulators, o-rings, etc - Mar 2017
Air flow housing cleaned - Mar 2017
Adjusted Duty Cycle Mar 2017 - Currently Idle 43-53% (large range...)
Cleaned Idle Air Valve - Mar 2017
Idle Air Valve Hose x2 (air slide to intake & air flow meter to air slide) - Mar 2017
Crankcase breather hose (valve cover to intake manifold) - Mar 2017


Thanks in advance for any advice and help.

 

[sbaert]

That's a lot of work done already, BUT what about the simple stuff? I don't see any fuel filters, fuses, temp sender unit or fuel pump relay on this list.

And exactly what plugs and ignition components are you using? These cars are hypersensitive ignition wise.

Also, that rubber boot is known to crack. Just replace it with a new one as a old one will really test your nerves and mess with your car's behavior

 

[Wyo_25]

Sorry left those out:

Fuel filter 01/2016
Coolant Temperature Sensor 4/2017 (I'm referring to the one at the back of the block near the firewall)
Plugs are Denso 5031 T20EP-U
https://www.amazon.com/gp/product/B002FOOW12/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Fuel pump relay has not been done to my knowledge.
Which fuses are you referring to that should be replaced?

 

[Wyo_25]

Wires are these:
https://www.oreillyauto.com/detail/...re-set/9492/4586357/1991/mercedes-benz/300sel

 

[sbaert]

ALL the fuses in the fuse box. Replace them with the upgraded copper core ceramic type. These cars came with fuses that corrode and cause tons of weird issues. Cheap fix.

Also replace the OVP with a new OE MB or KAE(hler) relay if not done already. It's a wear and tear item.

Also with the car idling at full operating temp and ALL electrical consumers turned on simultaneously, measure battery voltage. You should see a value between 13.5V-14.5V. If not, you'll need to add a voltage regulator to the list.

Doing the above things will help establish a half way decent electrical baseline.

I'd stick with the proper Bosch or Beru wires if I were you. Don't know if that aftermarket set has the proper resistors built into the plug boots.

Ceramic Fuse Kit Mercedes Benz Audi BMW Porsche VW - JoeTLC

Brick and mortar stores don't really have quality parts for these cars.

 

[Wyo_25]

ALL the fuses in the fuse box. Replace them with the upgraded copper core ceramic type. These cars came with fuses that corrode and cause tons of weird issues. Cheap fix.

Also replace the OVP with a new OE MB or KAE(hler) relay if not done already. It's a wear and tear item.

Also with the car idling at full operating temp and ALL electrical consumers turned on simultaneously, measure battery voltage. You should see a value between 13.5V-14.5V. If not, you'll need to add a voltage regulator to the list.

Doing the above things will help establish a half way decent electrical baseline.

I'd stick with the proper Bosch or Beru wires if I were you. Don't know if that aftermarket set has the proper resistors built into the plug boots.

Ceramic Fuse Kit Mercedes Benz Audi BMW Porsche VW - JoeTLC

Brick and mortar stores don't really have quality parts for these cars.

Totally agree on the box store supplies. The wires were replaced by a previous owner.

As for the Fuses, I have a set of copper core ready to install from Autohaus. I'll check the voltage and install the fuses tomorrow. I also purchased a voltage regulator recently and will update tomorrow on the voltage.

Thanks for the starting point. What about the Fuel Pump Relay?

 

[sbaert]

You can test the fuel pump relay. Use the forum search tool for details

 

[Wyo_25]

ALL the fuses in the fuse box. Replace them with the upgraded copper core ceramic type. These cars came with fuses that corrode and cause tons of weird issues. Cheap fix.

Also replace the OVP with a new OE MB or KAE(hler) relay if not done already. It's a wear and tear item.

Replaced all fuses and the OVP.

Still required lots and lots of pedal to get started and still no reliable lambda/duty cycle.

Also with the car idling at full operating temp and ALL electrical consumers turned on simultaneously, measure battery voltage. You should see a value between 13.5V-14.5V. If not, you'll need to add a voltage regulator to the list.

Checked battery getting 13.7V with AC, Radio, Lights, Max fan; although I was not able to get car at full operating temperature prior to doing voltage check.


I tested the fuel pump relay by connecting pins 30 & 87. I could hear the fuel pump continuously pumping after reconnecting the battery.

Sadly I then went back and tried to start the car and it did not fix the very hard start. I assume I am correct in concluding that its not an OVP or Fuel Pump Relay.

Looking for the next diagnostic step. Check Fuel pressures? Could it be completely outside of the adjustment range?

 

[sbaert]

Next logical step is to measure fuel pump volume (output) and fuel pump pressure.

 

[Wyo_25]

Next logical step is to measure fuel pump volume (output) and fuel pump pressure.

I've got a pressure testing kit on the way and will complete that testing later this week.

I did notice, based on other people's videos, that my air flow sensor plate seems to stick and sluggishly returns to its zero position. Does that mean I have a fuel pressure issue?

Would bypassing my fuel pump relay and depressing this plate and observing its behavior give me any indication of a problem in the meantime?

 

[Wyo_25]

Clarification on the fuel pump test.

I read the sticky thread stating,

"....To test, fuel pumps jumper sockets 87 & 30. If your fuel pump turns on, you’ll have a bad relay on your hands. A good used relay is under $40 on ebay. Or you can open the relay up and check for cold solder joints. I’ve resoldered a few relays and they’re working fine to this day.

http://www.benzworld.org/forums/w124-e-ce-d-td-class/1845442-what-do-i-do-when-my.html


If I bridge the fuel pump relay at 87 and 30, reinstall it and turn the ignition on, should the pump turn on or not?

When i bridge 30 and 87 the pump turns on and stays on with my 300e.

 

[Jayare]

Bridging 30/87, should make the pumps always on just like the 300e. It's the same system.

Sent from my XT1080 using Tapatalk

 

[Wyo_25]

Test Results from fuel pressure test today:

System Pressure: 5.5 bar
Holding Pressure: 2.7-2.75 bar (held for 30 minutes twice) Slightly below 2.8 spec, but i assume this is acceptable.
Initial Lower Chamber Pressure: 4.8 bar (checked with engine at operating temp and EHA unplugged. EHA plugged back in and pressure remained the same)

Previous Owner noted to have adjusted the EHA. "adjusted the EHA clockwise to improve starting". Double checked the pressure readings and brought the pressure back into spec at ~0.4 to 0.45 bar below system pressure.

Final Lower Chamber Pressure ~5.0-5.05 Bar

Fuel pump/quantity check: Approximately 1.2-1.4 Liters in 40 seconds

Readjusted lambda; idle and startup appeared to be improved. Will see how it drives and starts over the next few days.

 

[Wyo_25]

How long should the fuel pump stay on if the keys are turned to the last position but not started?

I recently read that 8 seconds was standard and thought mine was much shorter.

Sure enough, my fuel pump literally only powers up for 1 or 1.5 seconds...

 

[Wyo_25]

How long should the fuel pump stay on if the keys are turned to the last position but not started?

I recently read that 8 seconds was standard and thought mine was much shorter.

Sure enough, my fuel pump literally only powers up for 1 or 1.5 seconds...

Anyone able to help with the aforementioned pump runtime question just before ignition?