72 280SEL Cold Start Relay? - PeachParts Mercedes-Benz Forum

stackmonty · #1 09-05-2006, 09:36 AM

Hello, I'm new to the forum but have already learned lots from seaching to help get my 72 back on the road.

The problem now is the cold start injector is sticking on, so there is a short or the relay is bad. I'm asking if anyone know where the relay is so I can start checking there. I have check the TTS and it is ok, resistance is good and I repaired the faulty wires there, but the injector continues to operate once the car is running. For now I have just unplugged it so that the car will run normally.

Thanks

1972 280SEL 4.5

Nutz4Benz · #2 09-05-2006, 09:42 AM

Though the thermo-time switch checked out okay,it still may not be grounding out or the cold start injector is severely leaking.

Tomguy · #3 09-05-2006, 12:26 PM

So you unplugged the CSV and once you did so your engine noticably ran different. Therefore, 12v is obviously going to it and it's not a leaking CSV (or at least not a serious leak). You said you checked the TTS - are you 100% sure it's not reading "closed" or VERY low resistance at operating temps? If it is not reading infinite resistance (open circuit) at operating temps it may indicate a faulty CSV (I am pretty sure it's either 0 or very low resistance, and open; no status in between unlike a temp sensor). I will attatch a diagram for the CSV circuit once I get home if nobody else does (at work, don't have the images here).

stackmonty · #4 09-06-2006, 09:42 AM

The resistance is correct when the TTS is cold, but I didn't check it when hot, will do that. But I'm thinking the problem is somewhere else because the CSV was still powered up even when I had the TTS unplugged.

When the TTS grounds out at temp, does it stop power from the relay the CSV or opens the ground to the CSV?

Tomguy · #5 09-06-2006, 09:51 AM

Sorry I got sidetracked last night and didn't upload that diagram!

BUT I do see I attatched it to an older post (link: http://www.peachparts.com/shopforum/attachments/tech-help/34206d1151362624-cold-start-valve-voltage-coldstart.gif )

I don't have the actual files with me so I can't verify its operation but I believe that, at colder temps, the TTS has 0 ohms (or very low) resistance. As such, it's a closed circuit. Voltage goes to the relay, the relay triggers the CSV to open. Your relay is stuck closed or you have a short in the 2 wires for the TTS if your CSV stays open with the TTS plug off. As the voltage going through the TTS causes the windings around the bimetallic spring to heat up, it shuts off the CSV once the engine is warm enough to run without it.

Don't confuse the TTS (small sensor) with the 212°F water temp sensor (large sensor with only 1 wire) - the WTS is the one that grounds out at higher temps to turn on the aux fan and shut off the vac retard - completely different system! The TTS doesn't ground out, it's either open or closed between its two pins.

Arthur Dalton · #6 09-06-2006, 11:06 AM

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The TTS grounds the W terminal until the heater circuit [ G terminal] opens the W terminal to ground . The W ground is the CSV relays ground circuit
for the relays coil. This circuit is only energized when the Starter circuit is energized. If you have 12v at CSV with the TTS unplugged , you most likely have a stuck set of contacts in the CSV relay.. or a short to ground.
The CSV relay can not have a complete circuit until the W terminal of the TTS is complete to ground. The reason for the heater in the TTS is to regulate how long the W terminal gets grounded. As it heats up in temp, it opens the W to ground contact and that stops the CSV feed from the relay.
This feature is to prevent CSV operation at warm temps.
You can test a cold start valve circuit by simply grounding the W terminal, which will complete the relays circuit, thus energize the CSV solinoid.
As a matter of fact , many guys use the W terminal and put a cabin momentary switch between the W terminal and ground so they can energize the CSV manually from the cabin.

ftp://members.aol.com/ajdalton7/tts3.jpg

stackmonty · #7 09-06-2006, 11:24 AM

Thanks, you guys are right I just worded it wrong. I knew the TTS opens at temp. So do you know which one of the relays is the CSV relay. I think it should be one of the ones by the battery, so the short is between the relay and the TTS or the relay is stuck.

Tomguy · #8 09-06-2006, 06:49 PM

Alright, I checked my diagram (home now): The 1 pin of the CSV DOES ground out when it should be closed (colder temps). The other terminal is for the winding for the heat around the bimetallic spring to shut it off after so many seconds (hence the "Time" part).

Arthur Dalton · #9 09-06-2006, 07:12 PM

Quote:

Originally Posted by Tomguy

Alright, I checked my diagram (home now): The 1 pin of the CSV DOES ground out when it should be closed (colder temps). The other terminal is for the winding for the heat around the bimetallic spring to shut it off after so many seconds (hence the "Time" part).

Correct.
And you can actually test the time calibration of these by bringing 12 v to the heater circuit [ G ] and hooking an ohm meter to the switch circuit [ W } and time how long it takes to open the switch if you start out at 20 degrees C ..