76 280z over fueling. Starts then dies

[tractorboy]

Hi,

 

My 76 280z has a serious over fueling problem.

 

I can only get the engine to start and idle when the Air Flow Meter is disconnected. It will run for a few seconds, however it will run very rich. The engine will then flood and stall.

 

After a bit of research its seems that there could be a few problems. One being the cold start Thermotime switch. However the problem still occurs when the cold start injector is unplugged.

 

The other possible causes could be:

 

Throttle Valve switch, (possible idle problem)

 

Air Regulator (however from research this helps with cold starts, and is not prone to being stuck open as it usually gets stuck closed)

 

Faulty Air Flow Meter (from research these do not tend to go wrong often)

 

I have the Fuel Injection manual so will being going through this over the next week. But if anyone can help with additional information, or let me know if im on the wrong/right track.

 

Thanks

[OldAndyAndTheSea]

Sounds like the air flow meter is to blame.

 

If the car will run if you pour gas in the manifold, you obviously have spark. So rule that out.

 

The AFM does a couple of different things. First, it controls fuel pump operation. Check to make sure this works. Remove the air filter boot from the AFM and physically push the flapper open with the ignition on. You should be able to hear the fuel pump running.

 

The second thing to air flow meter does, is exactly what it says: Measures the air entering the intake, this is how the ECU "knows" how long to keep the injectors open etc...

 

The internals of your AFM should look identical to the picture below. The fuel pump contact points often times get dirty, and require a little cleaning to make work again.

 

But the problems you've described indicate to me a Air Flow Meter problem. That's where I'd start.

 

Here's a picture of the internals of my 1976 AFM. The fuel pump contact switch is located on the middle left (there is an arm pointing to about the 7-8 'o clock position.) Make sure the connection between the two metals is clean and unobstructed.

Edited January 5, 2013 by OldAndyAndTheSea

[NewZed]

The 1976 FSM would be better to use than the "bible".  It's specific to your car, whereas the "bible" is general.  The Engine Fuel chapter gives a great description of how things work and how to test.

 

www.xenons30.com/reference

 

With the AFM disconnected, fuel should come from idle enrichment only.  If it's flooding, one possibility is the TPS being stuck on "full enrichment".  But OAATS makes a good point about the contact switch.  Are you sure that it's running rich or assuming based on the way it sounds and what it does?  It might just be running out of fuel pressure when the pump turns off.

[tractorboy]

Thanks for the info guys, its definitely over fueling. You should see what comes out of the exhaust! 

 

NewZed your suggestion about the TPS could be correct. I spent a little time testing some of the components with a Muti-meter and I got a fail on these:

 

Idle Throttle Switch (works at full throttle)

 

Air Flow Meter failed a continuity test (resistance test 2) Passes other tests though

 

Air Regulator and Fuel Pump Circuit failed 

 

Air Regulator Circuit test failed

 

Cold Start Circuit failed (however I may have tested it with it still unplugged   )

 

Andy thanks for the picture. I will pick up my AFM from my friends garage and inspect it tomorrow.

 

So currently im going to look down the path of getting a new Throttle Valve Switch, and to get the contacts AFM Cleaned up. Unless anyone can shed anymore light on the situation?

 

But thanks for the info guys, also now have the service manual for a 76. So will be going through this too

[wesmc]

Can you test fuel pressure?  I have read that z's will run rich if the FPR fails.

[wesmc]

OOATS- pic is great for reference.  I keep a known good one with the cover off that I can physically watch operate to help me when doing diag.