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Discussion Starter #1 (Edited)
Newbie here, been lurking and working on my new to me 1986 300e with only 60,000 miles. I am having cold start issues. I pulled the cold start valve and it will give a little squirt when first cranking over then nothing. That would coincide with my cold start issues of when I first crank over it almost starts then I have to turn the key off and crank again and after about 6 seconds it will start. I pulled the fuel line off the valve and fuel sprays everywhere when I crank it so I think it is isolated to the valve or electrical. I do see power to the electrical fitting when cranking.

I had a shop owner tell me he has only replaced one cold start valve in 26 years and that it is usually something else. So I am looking for some advice. You guys are great, this forum is the only reason I bought an old Mercedes.

Oh, and I did do a full tune up, plugs, wires, cap, rotor, oil change, fuel filter change. And the person I bought the car from said the shop cleaned out the fuel tank and lines after it had sit for 5 years. I must say, there was some brown crap that came out of the old filter when I blew on it over the trash can. I also put in a new OVP and voltage regulator.
 

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It's important that the temp sensor that works the cold-start system is 100%. The older ones could be tested with an ohm meter, the newer ones I'm told, cannot. If it's an original sensor, it would be good form to replace it anyway. It's all the way back towards the firewall, on the top of the head. Newer ones have a four prong plug to them. After that, I would check out my fuel pump(s) pressure and replace the pump(s) check valve(s) just as a matter of course.

None of the suggestions above are just 'throwing parts' at the problem, as they should be done/checked anyway. You have to establish a baseline when you're hunting down fixes.:thumbsup:

Kevin
 

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Discussion Starter #3
I notice that there are two temp sensors. The one in back with two prongs is the one that affects the cold start? The fuel pump is 18 months old. Where are check valves on the fuel system? Also, what it the thing next to the fuel filter which is on the opposite side of the fuel pump?

I did just replace all the fuses with new ceramic copper fuses. I also pulled all the electrical plugs I could find and spray them with electronic cleaner. It seemed to help. I will get some new temp sensors. Thanks for the reply.
 

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Can I buy the sensor with more than two prongs on it and only use two that I need?
The one clear to the back is the cold -start sensor. And no, I don't think you can use a four prong sensor on a two prong plug harness. Which begs the question; 'Why would you want to?" The two prong sensors are still available.

The check valve is screwed right into the fuel pump(s). If you bought a new pump 18 months ago, it should have had a new check valve attached to it, unless the old one was transferred over (bad move).

The other part you are asking about is the pressure accumulator. Along with the check valve, it keeps pressure to the fuel distributor, so that restarts are easy. The system shouldn't lose any significant pressure over about a 30 minute interval after the engine is turned off.

Kevin
 

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do we have some pic of the cold start sensor and of the warm up regulator please
having same problems when engine cold
 

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do we have some pic of the cold start sensor and of the warm up regulator please
having same problems when engine cold
Yes, there are pics of both if you do a search in here...it's been discussed many times. Ps2cho's 124 site might have some pics as well.

Kevin
 

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Discussion Starter #8
I bought a fuel pressure tester and I have 78 and 72 lbs for upper and lower, respectively. The problem is that the pressure drops to zero within two seconds after shutting off. I don't have any visible leaksThis seems to be pointing to my starting problem. How should I proceed?
 

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I bought a fuel pressure tester and I have 78 and 72 lbs for upper and lower, respectively. The problem is that the pressure drops to zero within two seconds after shutting off. I don't have any visible leaksThis seems to be pointing to my starting problem. How should I proceed?
Fuel accumulator, fuel pump check valves for starters. Easy way to check the fuel accumulator-do a search here for the thread with pics.

Kevin
 

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1. Test fuel system pressure at fuel distributor to verify it is at 80 PSI/5.5 bar approximately key on engine running, and 40 PSI/2.75 bar key off. Residual pressure should be retained for a minimum of 30 minutes.


IT SHOULD HOLD 40 P.S.I. AFTER YOU SHUT THE KEY OFF. FOR 30 MINUTES.


2. Test lower chamber pressure at test port on side of fuel distributor, it should be approximately 5-7 PSI below measured system pressure when engine is fully warmed up.

3. Measure spark output at the spark plugs using a adjustable gap spark tester set at 20KV. Spark should consistently jump the gap key on engine running.

4. Test operation of oxygen sensor. It should have a good reaction time and operate through full voltage range from approximately 0.1v to 0.9v when the throttle is snapped.

5. Test resistance of Engine Coolant Temperature (ECT) sensor. At 68*F/20*C it should be approximately 2200-2800 ohms. At 176-194*F/80-90*C it should be 290-370 ohms. The sensor is a dual sensor and is tested from each terminal pin to engine ground.

And.


1. Disconnect the return line from the diaphragm pressure regulator and run the return into a container and see what that does to system pressure.

2. Check for blockage of the return line to the tank.

3. Check for blockage in the fuel distributor by disconnecting the line from the fuel distributor to the diaphragm pressure regulator and seeing if there is flow out of the fuel distributor with the pump running.
 

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Did a fuel accumulator test and it failed. I was passing fuel through the accumulator during Key-on and engine running.
You may have other issues as well, but I wanted you to rule out all the simple things first like fuel accumulator, fuel filter and cold start sensor etc. Your fuel pressures at the distributor are OK for a worn CIS system.

Kevin
 

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Discussion Starter #13
Ok gents,

I put a new fuel accumulator on and started it up. The pressure readings which were previously 78 and 72 psi for High and Low ports are now 70 and 72 for High and Low respectively. I lost pressure on the high side. It appears to be holding pressure though.

How do I test the return line to the tank? Is the gas line that connects by the low side test port the return line or the line coming in? How do I test the return line? Should I be able to blow back to the tank? It took the line off what looks like a diaphragm thing by the low side test port and fuel wanted to keep coming out of the hose like it was under pressure.

Thanks for your help! This sure is a slow process! Good thing I have been able to drive it. LOL
 

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Discussion Starter #14
I did unhook the line from the distributor to the diaphragm regulator and it squirted just fine. Gas everywhere in a hurry. Then I unhooked the return line from the diaphragm regulator and ran it into a bucket this time and it did not affect the high side pressure at all. Yes, I figured out which was the return line.

I then measured the pressure at the fuel line coming from the fuel pump and that pegged my guage at over 100 psi. No problem there. Please correct me if I am wrong but to me it is pointing to a bad fuel pressure relay or regulator. The pressure in the upper distributor is too low.
 

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Discussion Starter #15
I did replace the coolant temperature sensor for good measure even though the old one was within specs. Tomorrow morning will be the cold start test with the new fuel accumulator, temp sensor and a new used cold start valve that was tested to work.
 

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Discussion Starter #16
This morning was about 35 degrees F and the engine seemed to start fine, after about 2 seconds of cranking. The engine is not really running that great but it is intermittent, rough idle, low power, hesitation while accelerating hard like it just isn't getting all the fuel it wants. That sounds a little dramatic but it is intermittent and generally the car drives ok.

The one thing I haven't tested is the oxygen sensor. How do I test it?
 

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Discussion Starter #17
I might as well continue this conversation with myself...

I figured out how to test the oxygen sensor and I think I will just replace it since it is only a $62 part and some sensors are only rated to last 60,000 miles which is where my car is at.
 

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Discussion Starter #18
I tested the oxygen sensor and it showed bad so I replaced it. That was a total pain in the arse. I had to drop the exhaust and get a pipe wrench on the sensor before I could get it to turn. And then it took all I had to get it to turn. In the meantime my front muffler broke in two at the pipes so I have to replace that now.

I put back what was left of my exhaust and fired it up and tested the new exhaust sensor and it checks out! The car was running a whole lot better too! Sounded like a ricer with no mufflers on it though. I then cut the top of the tower thingy off to get access to the air/fuel ratio adjuster screw. I purchased a pocket meter at Sears for $20 that will show me the duty cycle and I adjusted the ratio so that it bounced between 48 and 50.3. It sure seemed to be running well, but I couldn't test drive it since it was up on the jack stands and I need to get a muffler on.

Thanks to you guys for pointing me in the right direction.
 

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I tested the oxygen sensor and it showed bad so I replaced it. That was a total pain in the arse. I had to drop the exhaust and get a pipe wrench on the sensor before I could get it to turn. And then it took all I had to get it to turn. In the meantime my front muffler broke in two at the pipes so I have to replace that now.

I put back what was left of my exhaust and fired it up and tested the new exhaust sensor and it checks out! The car was running a whole lot better too! Sounded like a ricer with no mufflers on it though. I then cut the top of the tower thingy off to get access to the air/fuel ratio adjuster screw. I purchased a pocket meter at Sears for $20 that will show me the duty cycle and I adjusted the ratio so that it bounced between 48 and 50.3. It sure seemed to be running well, but I couldn't test drive it since it was up on the jack stands and I need to get a muffler on.

Thanks to you guys for pointing me in the right direction.
Well, the O2 sensor is harder to get to on the 4matic, if that's any consolation to you. There are also some slick tools to remove the sensor-you should have asked. You can also test the duty cycle with a simple VOM and a calculator. Glad you did the research on how to test the O2 sensor. Some of us are pretty stretched out on a lot of threads and don't always get to walk everybody through everything, but the search feature here hits on most of this stuff from the past. And if it isn't here, it's over at peachparts.:thumbsup:

Kevin
 

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Discussion Starter #20 (Edited)
I had to crank it a couple of time to get it to start this morning and when it did it stumbled for a couple of seconds and then ran fine. This being my first Mercedes, how is it supposed to start? Just for a review here is what I have done:

Engine oil and filter
Trans oil and filter
Brake fluid
Differential oil
Power steering fluid and filter
Engine coolant flush
OVP
Voltage regulator
Plugs
Cap
Rotor
Plug wires
Fuel filter
Air filter
Fuel accumulator
Coolant sensor
Oxygen sensor
Changed cold start valve
Replaced all fuses with ceramic copper
Brake switch
Fuel fitting at distributor
Fixed odometer
Fixed ground to dash so tach would work again after odometer removal
Washer motors and grommets
Adjusted fuel/air ratio
Been running fuel treatment for a couple tanks
All the test that Mercedes Mechanic suggested

My pressure readings were weird as previously stated, they were erratic on the high end and solid at the low end.
 
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