I just posted elsewhere about the D-Jet cold start system and thought I would post here since it's often misunderstood. Really it's quite simple. Unlike the other injectors, the cold start system/wiring is not part of the FI system. The cold start is separate system. It doesn't connect to the brain/ECU at all.

The cold start valve (CSV) has two wires that connect to it, power and ground. That parts obvious, but where those wires go is the real trick.

The power side of the cold start valve is tapped into the starter wire. That means the CSV only gets power with the engine is cranking. Once you let that key off and the engine is just running (or stumbling) the CSV is no longer powered and no longer able to spray.
Power only while cranking.

The ground side of the CSV runs through the 'thermostatic switch'. This is the brass guy just hanging out near the engine case. It doesn't really sense anything, but reacts to temperature. The thermostatic switch is connected /grounded below 32-degrees. Anything above that and it's disconnected.
Ground only when below 32-degrees.

I've talked to a lot of people who have mentioned a 'problem caused by the CSV' and while it's always prudent to be thorough and double check everything, the CSV is almost never an issue.

Okay, there's two caveats -
1. the CSV can leak/drip fuel but this isn't an electrical issue, just good old mechanical failure
2. the CSV can allow an air leak where it attaches to the plenum, but that doesn't really have anything to do with the CSV system.

Excellent explanation Mark. I'll add that the activation temp is determined by the thermoswitch depending on the part number of the switch. I located these values in a tech manual somewhere, above these temps the CSV system will not activate:

◦311 906 161 : -12 to -18 deg. C / 10 to 0 deg. F
◦311 906 161 A : 0 to -10 deg. C / 32 to 14 deg. F
◦311 906 161 B : -2 to -8 deg. C / 28 to 18 deg. F
◦311 906 161 C : -6 to -14 deg. C / 21 to 7 deg. F

I had a few of these and could not figure out how to test them because the temps were so low.

Has anyone ever taken apart the grounding switch? Seems like a very stout part that doesn't fail. My guess is that it is a warp switch. I think that is where the term warp speed came from.

Well now that McMark is in MI, he can test out those low temp items...

Hey, maybe we should have a thread on "how X system works"? We can debunk the whole "AAR changes the mixture" thing while we're at it.

--DD

So for us here in the warmer states our CSV's probably have never been used or needed to operate in the past 40years?
I just disconnected mine this weekend and I should not run into any issues at start-up? I just taped-off the ends and tucked them away...good or bad idea?

Yup, that'll work. Although hooked up is still technically disconnected, so you're not gaining anything and tape is ugly. I'd hook it back up, knowing it's not doing anything anyway.

Thanks for the info fellow teeners and at least answered one of my concern that I don't need to replace my CSV since I live in SoCal. I thought one of the reason my car has a hard starting (it cranks well but takes time before it will start) but if I pressed my gas pedal to the floor when starting, it start immediately or the 2nd try. Is there something I have to replace or fix? thanks!

Stupid question, but how do I verify the little bugger is working? I had the connector break off mine. I ended up soldering a little wire and spade connector on it but wasn't convinced it was working, so I bought one off ebay. Now I'm not convinced that one is working.

I basically put the switch in the freezer for 15 minutes and see if there's continuity between the connector and the body of the switch. I think I get continuity (sometimes), but then it goes away very quickly at room temperature after I remove it from sitting next to the frozen pork chops. Is that normal behavior or am I not testing it correctly?

Click to view attachment

If the sensor is above freezing, you should not get continuity between the plug and the threads of the sensor. If it is below freezing, you should.

How quickly do you think the sensor warms up when you pull it out of the freezer and start running a (small) current through it?

Maybe you should set it on an ice cube while you are checking?

--DD

This information about the CSV is very helpful and timely. My car is very hard to start and I have suspected the CSV.
I attempted to test the valve by placing it in a glass jar and cranking the engine. No spray. I was about to post something about this issue and ask you all if I was on the right track. Now I realize that I shouldn't expect any spray because the outside temp where I live never goes much below 40 degrees. In fact, I only take the car out when it's a nice sunny day in N. CA.

So the question remains unanswered as to why my car is so hard to start. I usually need to crank it over 4-5 times until it has what it needs to get going. Once going, it runs great...

DD - just tested it. From freezer to on the kitchen floor I counted 28 seconds from when I had continuity to when it suddenly went to open. Now I know.


Or I could be more civilized and drop it in my gin and tonic and see how that works.

Dave.....


I nominate your good self for the AAR thread.

I was reading Brad Anders thread on it. However in context to his website I would substitute the "Function" to "Purpose" in the header first line.



Rob

Excellent info! Extremely helpful, especially since I'm going to be re-doing all the vacuum lines on my engine over the winter.

Test if your fuel pump is losing pressure. Next time you start it, turn the key a few time to ON (not START) and let the fuel pump run until it stops each time. You may hear a faint whine from the fuel pressure regulator or you may hear bubbles in the tank. Then try starting as usual.

My 2007 VW Rabbit was wired so that when the driver's door was opened, it would run the fuel pump for a few seconds to prime the fuel system. The expectation was that if you open the drivers door, you're probably going to start the car shortly after.

Very clever idea using the door switch to prime the pump.

I should have mentioned that I actually do switch the ignition on four times prior to trying to start the car. I don't put my foot on the pedal while cranking. However after the engine starts to catch after about four-five cranks, I can keep it from dying by pumping the "air" pedal. I realize this isn't standard procedure.

I have tried opening the air needle on the TB but it didn't help the starting problem. All that did was cause a high idle.

I wrote one on "How your headlight motors work" years ago.

subscribed to some very good information, great job