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  #1  
Old 07-02-2013, 06:24 PM
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1990 300E 2.6 Hard to Start after sitting.

Have a 2.6 gas 1990 300E that if I use everyday it starts up just fine and runs well. If I let it sit for more than three (3) days It is almost impossible to start and when it finally does after cranking and cranking it runs ruff for a mile then everything is fine and if I start it everyday I'm okay again and it runs perfect. What should I check, bad fuel pump pressure, cold start valve, how do I check these and any other ideas. Thank You for taking the time to read and respond. Roger

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Old 07-03-2013, 11:57 AM
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Check the fuel pressure - internal leak test.

I don't know about your specific car, but cars have a check valve or two in the fuel system to keep fuel from flowing back into the gas tank when the car is shut off.

Also many Mercedes have a fuel "accumulator" or "damper" which is a mini "pressurized fuel storage tank". Those hold a bit of pressurized fuel after the car is shut off (like a water well water storage tank).

Also those vent into the fuel return line and have a diaphragm inside them. If that diaphragm is leaking (internal leak), fuel will circulate right back into the gas tank and have trouble building up pressure.

And with the above problems, the fuel pressure will not be maintained after the car is shut off.
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Old 07-05-2013, 05:16 PM
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What about the cold start valve. How does that affect cold starting and how do you check it. Thank You Roger
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Old 07-06-2013, 12:41 AM
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Quote:
Originally Posted by Rogerbrener View Post
What about the cold start valve. How does that affect cold starting and how do you check it. Thank You Roger
Cold start valve only works for a few seconds when the ambient temps are below 40ish degrees.

Do you get a lot of white smoke when it starts?
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Old 07-06-2013, 02:02 PM
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No White smoke. The other person said it might be the fuel accumulator but I thought that was for hot starting. If it's for cold starting also after sitting is there a way to check ie: with a vacuum pump, should it hold pressure. Also I had a VW rabbit that was hard to start all the time and it turned out to be low pressure from a bad fuel pump. Could this be the problem or not since mine only happens after sitting for a few days and not all the time. Does anyone know what the line pressure should be when running. Thank You again for Responding Roger
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Old 07-07-2013, 03:38 PM
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Might want to check your OVP, my car had the same prob, one of the fuses was blown and it would not activate cold start. Also check voltage regulator, mine was very worn, $30 and 5 mins to replace. Possible accumulator.
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  #7  
Old 07-08-2013, 03:47 PM
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Optimum approach would be to check fuel pressures, both residual after sitting, and when running, and to monitor EHA current during start-up.
These tests of course require some amount of special equipment.
Some quick checks would be:
- Try pouring an ounce or so of fuel into the air valve and then starting - if it kicks right off, then it's definitely fuel delivery issues.
- Another test, before trying to start a cold engine, turn the key on and listen for the fuel pump hiss for about 2-3 seconds; then turn the key back off and back on, to make the pump run for 2-3 more seconds. repeat this for 3-4 times, then try to start the engine. If it helps, then you are losing pressure thru the accumulator, check valve, injectors, or fuel distributor.
- After running the car, let it sit overnight, and loosen the fuel line going to the fuel distributor - it should still have some pressure. If not, see above & do a search on testing accumulator, check valve, injector leaking, etc.
- Get a Sears multimeter #82139 with a Freq/duty cycle setting ($32). Read the meter instructions for setting up duty cycle test, and hook it up to the round diag connector on the left fender well - red to pin 2 (gnd), black to pin 3 (DC signal). Read the duty cycle when first started, should be 50%, then when it warms up, should vary up/down abound 45-55%. If it's off, need to try adjusting the air valve screw - do a search here.

Lots of other things, but these are a good easy place to start a meaningful diagnosis. And, yes, the cold start injector doesn't fire above 60 degrees, but the EHA valve does draw significant current (12ma or so) to enrich the mix during cool (>60) start.
If the above does not indicate a fuel leakdown problem, then a good next step woud be to build a little wire harness with male and female bullet plugs to tap into the EHA valve wires with the sears meter above, and measure the current during cool start (12MA) and warm running (1-2 mA). These results will open he way to the next can of worm in the search.

DG

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