Pagoda SL Group
W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: ctaylor738 on October 17, 2012, 12:40:02
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Over the past couple of months, I have been working to improve the hot start of a 250SL. After sitting between 15 minutes and two hours, it took a 10+ second crank to get it to fire followed by several seconds of stumbling until finally all cylinders were firing.
The first step was a rebuilt starter, which easily doubled the cranking speed and improved the delivery of the injection pump. This helped a lot, cutting the average crank time down to 3-5 seconds.
Before going further, I investigated whether the cold start valve was actually firing, and found that it was not. It was only receiving 9 volts while cranking. To get some more power to it, and the solenoid on the pump, I wired terminal 15 of the two relays directly to the battery through a fuse box. That resulted in the CSV firing and improved cold start.
Next step was a magic button to ground the thermo time switch manually as a test. We found that depressing the button for a second while cranking resulted in an instant start with no stumbling.
The final step was to make this automatic using a time interval relay from Allied Electronics (TDRSOXP-12V). As I wired it, when the starter is engaged, it supplies ground to the TTS for one second. It is adjustable with a range of .1 second to ten hours. I ran the wires through the firewall and stuck it up under the dash with some Velcro, which allows it to be detached if adjustment is needed. Cost was about $85 for the relay and the wiring base.
So far so good with the hot starts.
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I'm surprised your car starts at all with the coil wire mising. ;D
Just teasing, of course! Appreciate your description of how you approached this. I'm going to experiment with my 250, since it does not start as good as I would like it to after sitting awhile.
Thanks again....
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Chuck,
Nice work! I understand an old starter motor getting sluggish and how a new one (particularly the latest versions which apparently have a bit more RPM and HP behind them) would speed things up.
The demon at the CSV puzzles me. Before implementing your TD relay solution, did you try and investigate why there is this low voltage condition? Or, is 9V normal, and your relay acting as a "B12" shot of vitamins to a sluggish CSV?
(I guess I'm looking forward to the future!)
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Well, if you follow the current path of the CSV, it goes:
Battery +
Big lug on starter
Alternator
Fuse 2
Light switch
Terminal 30 on ignition switch
Terminal 30 on CSV relay
Terminal 87 on CSV relay
CSV
So basically the CSV gets what's left over after the starter draw and shares it with the fuel pump and anything else that's powered on with the ignition. More current can be lost through the wiring and connections. What I did was to move the power source for the CSV directly to the battery. I forget what the measurement was, but I believe it improved to almost 11 volts.
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I'll have to measure mine. I don't have any hot start issues, and wondering if I have the same voltage issues but no symptoms.
You probably have less of a voltage drop (less of a current draw) with that new starter...
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Hmmm...i like to work the CSV a bit longer at cold starts. This delay might be a good idea as well.
Thanks.
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I have an unrelated (sort of) question after seeing your photographs showing some of the engine compartment. My 230SL is black under the hood, as it appears yours is. This is an aftermarket change, right? I expect that all of these cars came with the engine compartment the same color as the body.
Thanks,
Harry
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Yes, engine bay should be body color.
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My engine hood is also black on the inside, it looks original?
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Yep, if your car is orginally black then it's 100% original. ;)