280Z Running Rich-- How to Fix?

[brandon]

Hello all.

I'm a newbie to the Z world-- just bought a very nice 76 280Z:

http://devnulled.com/gallery/280Z-calitocolorado

I've worked on / modified DSM's for around 5 years, and can do about anything on them without a problem except rebuild engines, trannies, etc by hand, but decided it was time for something new. :)

Anyhow, on the drive home, I noticed it was running very rich. I had an emissions test done today, and they also confirmed that it was rich.

Being that it's fuel injection, I'm not quite sure where to start. I would assume that perhaps the spark is not strong enough? I have some new Taylor wires and NGK plugs to throw on this weekend, so that's a start. Any other suggestions on how to get the car running at stoich?

Also-- what is the torque spec and gap for the spark plugs? I'll order the CD Manual soon so I won't have to ask dumb questions like those last two soon. ;)

Thanks,

- Brandon

[brandon]

I should mention that switching to carbs is not an option for me. ;) I love fuel injection.

Also, the fuel system in the car was totally replaced within the last couple of years.. all new injectors, hoses, etc.

[venom42]

I have a '75, and some similar questions to yours. I am thinking that the "cold start" injector may be the culprit in my case. I am not sure though. Anyone know if it will cause any problems if I disconnect the cold start injector (leave it in place, but remove its electrical connection)?

[TomoHawk]

You "should" be able to run the engine sans cold-start injector, but it should not start up and run well until it's warmed up. That's what the cold-start injector does- extra fuel to start or run when cold. It's controlled by the thermotime sensor/switch.

Maybe you could try starting the engine, then disconnect the cold-start injector? Make sure it's not stuck upen first!

[sblake01]

The cold start valve gets it's signal from the thermotime switch if the engine is cold enough when you turn the ignition to the start position. The signal only lasts for about 8 seconds then the thermotime switch opens. If you're still getting fuel from the cold start valve at that point then it's leaking. But that is rare. Usually, the culprit in that circuit is the thermotime switch. Disconnecting the cold start valve only eliminates that part of the cold start system. Check the two terminals on the thermotime switch for continuity when the car is warm. If you have continuity at that point then the switch is bad. Richness can also be caused by the AFM being out of adjustment.

[venom42]

Is the thermotime switch something that commonly fails? What temp does it stop telling the cold start injector to open at?

[TomoHawk]

It just gets worn out sometimes, or gets stuck.

[sblake01]

Originally posted by venom42
Is the thermotime switch something that commonly fails? What temp does it stop telling the cold start injector to open at?

They don't fail very often but they seem to have a tendency to be bad on cars that have sat for a long time without being started. The temperature is not as important as the signal. The one I'm looking as says 35 deg. C.-8 sec. Meaning that if the temp is below 35 the signal will be sent for 8 sec. If the temp is above 35 the signal won't be sent. When they stick they continue to send the signal and the car will run rich to the point of being undrivable because of the extra fuel.

[TomoHawk]

I tried disconnecting my thermotime switch today. It seems to be running a little leaner, with more power/acceleration, and it seemed to go easier on the freeway. Much less effort to go from 60 to 70 MPH.

I don't know what effect it has on starting as the engine was already warm when I tried the experiment. I will try starting it cold in the morning.

I also tried starting/running the engine with the cold-start injector wires disconnected, aswell as the TPS switch disconnected. Disconnecting he thermotime switch had the biggest effect.

[sblake01]

Once the engine starts or when the engine is warm, the thermotime switch and cold start valve have no affect on performance unless there is a problem with one or both.

[venom42]

I have some "tinker time" tomorrow, so checking the thermotime switch is one of the things on my list.

[TomoHawk]

I'm able to start my engine easy in the morning with the thermotime switch disconnected, but it runs really bad until it gets warm. Bogs really bad. It's OK after it gets warm.

Any ideas?

[sblake01]

Is your air regulator functioning properly? That is, when you start it cold, do you get a fast idle (1100-1200rpm) that gradually lowers to normal as the engine warms?

[TomoHawk]

I think the answer to that question is no.

Mine starts fine, but idles at the (warm idle speed).

Sounds like there might be a vacuum leak or problem.

thx

[sblake01]

The point I left out earlier in this thread is that the thermotime switch/cold start valve combination only helps start the car. It only injects the fuel from the csv when you crank the car. After it starts the thermotime/csv are through. The fast idle/warm up is controlled by the air regulator. If the air regulator is not working properly, your car will run like a cold carbureated car with no choke.

[TomoHawk]

Is there another name for "air regulator?" I In the Haynes book, I see something on page 229, but it doesn't say much else.
thx

[sblake01]

On BMW's they call it the 'auxiliary air valve' but every Datsun manual I've seen calls it the air regulator. In 'Haynes' it's shown in the fuel flow diagram on pg. 222. The FSM gives a better description.

[TomoHawk]

O I C....

Basically, just another way to let air in & lean the mix. Good tip, Steven

[1975yellowBSPZ]

I also am having my 280 run very rich.

I have checked the archives and think I have some idea but would like some direction.


It smokes slightly when the throttle is depressed and has a heavy gasoline smell to the exhaust. It also with stutter or backfire if reved hard. At highway speeds on decelleration it seems rough.

My valves have been set recently.

My timing is a 0 with no room for adjustment - Might I be a tooth or 2 off on the timing chain? Could this affect my symtoms?

Also I have an aftermarket fuel rail, and I think the configuration is not right. It has a T style fuel regualtor with a guage at the firewall and the fuel return line exits there. The far end of the fuel rail has a plug in in instead of a fuel return line. Maybe too much gas is being sent to the rail and has no place to exit except thru thr injectors? It has been in this config as long as I have owned it. I am planning to add a line from the end of the fuel rail to a T below the output of the fuel regulator to see if this helps matters.

I am planning to use the information in the forum to check/adjust the AFM but want to rule out anything else major before doing so.

Any help would be great, as my car is almost drivable and I am anxious to AutoX it.

Bw

[TomoHawk]

I just got the engine decarbonized, and it seems to have helped a whole lot. When I first started it, the idle was significantly better, but it still bogged a little when I revved it. I'm not sure if it has more power, but drives OK.

[venom42]

Originally posted by TomoHawk
I just got the engine decarbonized, and it seems to have helped a whole lot. When I first started it, the idle was significantly better, but it still bogged a little when I revved it. I'm not sure if it has more power, but drives OK.
How did you go about it? Here is a link from the DSM VFAQ site (http://www.vfaq.com/index-main.html) of one method: http://www.vfaq.com/mods/MCCC.html . Although primarily for DSM cars, there is a great deal of excellent info that is applicable to all cars at that main VFAQ site.

[TomoHawk]

I had a professional guy do it.

[venom42]

Originally posted by TomoHawk
I had a professional guy do it.
Did they use the BG intake cleaner system? I had that done professionally on my first DSM, with excellent results. I am a big believer in the BG product line. Their "44k" is the best fuel system cleaner out there in my opinion. To be honest, if I had the money right now, I would just pay someone to do alot of the work I am currently planning on both the 280 and the Talon. However, seeing as how I have been hunting for a job for the last couple months, I will be getting dirty quite a bit in the near future. :stupid: