1987 300E Cold Start Frustration

New to me 1987 300E. Runs beautifully when it finally gets going. Misearable to start when motor is cold.
When cold, I can eventually get it started by repeated cranking attempts
without touching the gas pedal. This morning, it took about 20 times cranking before the motor caught and continued to run. On the first crank the motor caught after about 4 seconds, sputtered and died. Over the next 18 cranks, it would catch and sputter from between not at all to 10 seconds. Finally, it caught and stumbled and shuddered itself into a sustained idle at about 500 rpms. It feels like the motor is missing after it gets going. After I get in and drive it a couple of seconds, the motor is fine and the idle is smooth.
I have tried to start it up by depressing the gas pedal to various depths but this seems to only make it worse.
On two occasions over the past couple of days, during cold start cranking attempts, the motor has caught, revved up to almost 1,000 rpms and run perfectly. This did not happen on the first cranking attempt but just happened after maybe 5 or 6 attempts. On these occasions, it feels like the cold start system has kicked in. This is making me think it could be an intermittent electrical problem rather than fuel pressure.
I have replaced the plugs with Bosch Super as specified in the owner's manual gapped to .032" I have filled the tank with premium and added Techron fuel system cleaner.
Where do I start diagnosing this problem?
Thank you,
Robert
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Did you try one kick-down on the accelerator before cranking?
DAS
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For direct contact replace nospam with schmetterling
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Any monkeying with the pedal seems to cause flooding and make it harder to start and keep running.

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In general yes. I meant only one quick kick-down on outs own, not after other "monkeying around" with the pedal. It helped me on my cars of that era.
However, from the other posts it looks like it may be something else.
DAS
--
For direct contact replace nospam with schmetterling
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9kman wrote:

I had a similar problem on my 300SL (same engine I think) and traced it to the overvoltage protection relay which controls power to both the cold start airflow valve and injector. In my case simply changing the fuse on the relay fixed it.
HTH
Ben
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Thanks for the input. I have been looking for that relay to check it out. I thought it was supposed to be behind the battery near the FI ECU. I don't see any relay with a fuse on top back there. What does it look like?
Thanks,
Robert

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On Mon, 08 Nov 2004 16:48:50 GMT, 9kman wrote:

This:
http://img.eautopartscatalog.com/live/P205618126.JPG although it may be black not red, and it may only have a single fuse on the top. This is the later, improved design (which is interchangeable). Mike W126 300SE 234,000 Miles W115 220
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Thank you, I found it. The fuse appears fine on visual inspection.
Any idea how to determine whether the relay is working correctly?
Thanks,
Robert

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9kman wrote:

Something else that might cause hard cold starts is aged sparkplug cables. Have they be changed in recent memory?
Bob
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The problem is cold start... and first thing I would check is the temperature sensor for the fuel injection system. Cold start valve is never a problem unless it leaks which causes driving problem when engine is hot.
Back to what I said... Since it is a good possibility that it never have been changed... I would do this first. The reason is the computer must know that the car is cold in order to enrichen the fuel mixture so that the engine can start and warm up.
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Further observations: This morning it was 25F outside temp. I measured resistance on the coolant temp sensor and got 3.5 ohms on both poles with the motor stone cold. For whatever reason, the motor started right up on the first crank.
Later, with the motor warm, resistance on the coolant temp sensor poles dropped to .3 ohms. Now, since cooling down again, the motor has returned to not starting when it gets cold.
One thing I noticed is that when the motor starts correctly (whether hot or cold), there is a little surge before it settles into idle. When it is not starting correctly (even when the motor is hot and it starts up quickly), there is no surge, the motor just sort of catches and hangs on at a low idle.
Thanks,
Robert

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Wierd... Clean the contacts on that sensor and the plug... make sure it is good. How old is your battery? Not long ago, Marlin had a similar problem... hard to start when cold... turned out to be the battery... one dead cell.
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Ok, I checked the sensor again by using the battery as ground and it seems within range. Most recently, I got 404 ohms at 140F. This is maybe a little off for that temperature according to the chart I was looking at but not way off.
The surging at startup made me think of the idle control valve. I am now convinced that my problem lies in the idle control circuit. To address this issue, I started another thread below titled Idle Air Control Valve not Getting Ground to Open.
It looks to me that the idle control valve on my car (1987 300E) is controlled by the fuel injection computer. I am not finding an independent idle control unit. Is that correct?
Thanks,
Robert

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There are many sensors so you can get confused on what I said. As far as I can see... the temperature sensor for the CIS (fuel injection system) is 4 pins round... located on the intake manifold or the cylinder head... this also controls the engine fan.
There is another temperature sensor at the air filter housing to measure the air temperature.
You have to understand that sometime these sensor do wear out due to age... it may be a little bit off... but means a whole lot to fuel injection system. Since you only have cold start problem... check the resistance when engine is cold.
These fuel injection system take cues from these temperature sensors to enrichen fuel mixture for cold engine or to lean it out when it get hot.
Computer is never wrong... if something is wrong with your computer, then the whole engine is affected regardless of hot or cold.
As for the battery... Marlin had trouble starting the engine when cold... you had to crank and crank and crank to get it going... it drove us nuts... in the end, he found out that one of the cell in the battery is dead... dried out... and that caused his cold start problem.
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