Interesting, seemingly intermittent challenge I'm having with the Z.

I can already tell that I'm burning a bit of oil when the car is completely cold, so my natural assumption is valve seals. However, I've noticed a new quirk.

If I drive the car and get it warmed up to normal operating temp. (i.e 180/190 degrees Fahrenheit) then let it sit for a period of time (i.e. going to work, park the car for 4 hours), when I get back in and start it up I can smell the distinct aroma of gasoline. This is accompanied by what looks like gray smoke coming out the back until the car begins to reach 110/120 degrees. After this time the smell of gasoline is gone, as is the gray exhaust.

This DOES NOT happen when the car is completely cold (like say I drove home from work, and let it sit overnight). When completely cold all I notice is a bit of burning oil (blueish smoke instead of gray) and nothing more.

I know the gray indicates a "rich" condition in the fuel mixture, but this goes away after the engine is warmed up. My initial assumption is that cold-start valve thing that helps everything get going when the engine is cold has gone sorta screwy. I'd appreciate some kind of a basic overview of what the cold-start valve does, how it does what it does, and how I can go about fixing and/or replacing it. Also, anyone else who would like to diagnose my Z's condition is, as always, more than welcome to.

(Just realized this will perhaps be better placed in the Fuel Injection forum. Could a mod please move this there when you have the chance? TY)

Hello,

What it sounds like to me is possibly a bad Thermotime Switch. I've explained this before to others. It's location is in the T stat housing. When the coolant temp. increases and reaches above a certain degrees, the thermotime switch is suppose to break ground for the Cold Start Valve. When coolant temp. is below that certain degree (Can't remember exactly what the certain temperature is off the top of my head, sorry) The Thermotime switch will then provide ground again to the Cold Start Valve to inject that extra fuel needed when engine is cold. Make sence?

Sounds to me like the Thermotime Switch is not functioning properly and it's grounding the Cold Start Valve even when the coolant temperature is ABOVE the degrees shown in the FSM which is why she is running rich when you are restarting it after having it warmed up, then as you drive for while, it gets better as the extra fuel gets burned off or gets better when cold because thats the time the Cold Start Valve is suppose to operate. That would be my best guess from what your describing.

Good luck.

The thermotime switch get it's initial signal from the starter and only for 8-9 seconds and only if the engine is under certain temp. In other words, it only operates when you crank the starter.

"The thermotime switch get it's initial signal from the starter and only for 8-9 seconds and only if the engine is under certain temp."

Right, and if the Thermotime switch is faulty, the bimetal contact in the switch will remain closed (Grounding Cold Start Valve) even with warm coolant temperature correct? I'm not trying to argue but I've seen similar issues and a new Thermotime switch solved the problem. I'd for sure give the switch a test to make certain it's OK.

Here is the test procedure on the Thermotime Switch. I posted this last year for another member here.

Thermotime Switch test:

You will need a thermometer and an ohmmeter.

1) Disconnect ground cable on batt.

2) Disconnect Thermotime switch connector

3) Remove switch from T Stat housing

4) Dip the heat-sensing part of switch into cool water 50 degrees F.

5) when the Thermotime switch is about the same temp as water (50 degrees) measure the resistance between terminal numbers 45 and 46. The resistance should be about 78

6) Now increase your cool water temperature on your stove until it is more than 77 degrees then check continuity between terminal numbers 45 and 46. If your ohmmeter reading increases from about 78 to infinite, circuit is OK.

Well, I guess that could happen but in the only one I ever had go bad did the opposite. That is the contact wouldn't close therefore I'd get no signal to the cold start valve regardless of themperature.

Hrm... okeydoke. Thanks you guys!

I'll see if there's someone with a multimeter at the ZOOM show today... I don't have one yet... :sleep:

FYI, in my experince the cold start valve isnt super crucial. I took the connector off of mine when it started to leak at the connection. Ive never had a problem with it not being able to start, and I live in an area where it does get pretty cold.You could try just disconnecting the cold start and see if that solves the problem.

Good call, Deadflo, if that works the problem will be isolated to the CSV and Thermotime switch.

Okay, I'll give that a shot. I was unaware that there was simply a connector I could pull some place...

... and yeah the cold start isn't that big of a deal to me since I really only drive the Z in warm weather... the coldest it gets when I need it is like 55/60 ... you know... fall/early spring etc.

Also, at the ZOOM show today, a guy in a ZX offered the idea that perhaps one of my injectors could be leaking, so that while the car is parked a small excess of fuel is accumulating in the cylinder. Eh?

Well if you had 1 or more injectors leaking, you'd have issues with a cold engine as well so I personally doubt that but a fuel pressure test would be a good thing to do if you have the equipment to do so like I have.

That kit was about $400.00 with the discount I got from the Snap-On guy at work. If you shop around though you could probably find one that will serve your needs for less.

I still think it sounds like a Thermotime Switch issue possibly but I'm not one to play the guessing game and replace parts I don't have to so test it first with the procedure I listed above to be damn sure first.

Also you say "yeah the cold start isn't that big of a deal to me since I really only drive the Z in warm weather... the coldest it gets when I need it is like 55/60 ... you know... fall/early spring etc."

Yes it is a big deal. 55/60 degrees it should be in use. Nissan Motors designed this "set up" for a reason when the engine is cold and warming up. If found to be faulty, fix it right so the system can operate properly like it's suppose to and in return, give you the best reliability. My opinion

Best of luck to you Matt.