Air Flow Meter

[LBO730]

I'm getting desperate fellas! I'm sure it's been covered somewhere but here's some facts. Been working on this 75 resto for 6 years. Complete disassembly and reassembly. It's done but I can't get it started. I've been thru every test in the EFI bible at least twice. Passes all the tests. I have swapped in a refurbished ECU, still no change. I have 38 lbs of consistent fuel pressure. I have good spark at the coil and all 6 plugs. New fuel injectors and connectors. The distributor is in correctly (not off 180). I've double checked every electrical connection I can come up with. The air flow meter doesn't pass some of the tests. Can a faulty air flow meter actually prevent the car from starting? I have read that it shouldn't effect starting or idle and I have read that it does. Can A faulty water temperature switch or water temperature sensor prevent the car from starting? What am I missing? What else can prevent the car from starting?

[Zed Head]

The two most basic items to check when trying to start an EFI engine are spark and injection. Spark is pretty easy using a spare spark plug, injection takes little bit more effort.

The 280Z ECU's like everything to be wired as it was from the factory, from the blue wire at the coil negative to the tachometer to the inline resistor on the tachometer wire.

Have you checked for spark and injector operation when cranking?

[LBO730]

Thanks Zed, The basics were covered long ago. Spark is good at the coil and all 6 plugs while cranking. The voltage/ pulse at the injectors is weak. I just can't figure out why. All wiring is factory. I have performed every test I can find in the factory service manual. I'm down to the AFM. Do you know if a faulty AFM, water temp sensor or water temp switch can prevent the car from starting? Believe me, I've put in the effort in trying to solve the problem. Any suggestions on what to do next would be greatly appreciated.

[rcb280z]

Ok I need some sleep. I started to ask about fuel pressure and completely overlooked 38 pounds of pressure!

Are the plugs wet when you pull them? If you are getting fuel to the cylinder and you have spark it should at least try to start. Is it at least doing this?

If not, the injectors are not firing. Just because you have fuel pressure it doesn't mean the injectors are firing.

Edited December 25, 2013 by rcb280z

[rcb280z]

Check to make sure you have 12V at the injector connectors

[Zed Head]

The voltage/ pulse at the injectors is weak. I just can't figure out why.

What do you mean by weak? There's not really a pulse at the injectors. Start with battery voltage at the connections, the ECU lets current flow, the injectors open and the 38 psi squirts gasoline out. Have you tried starting fluid to see if you have compression and proper timing, both cam and ignition? If it runs on starting fluid, then you can focus on getting the injectors to open.

Seems like I'm over-simplifying but that's all you need to get it to start. Getting it to run well can take more work. And to be clear, when you say it won't start do you mean it won't even pop a few times or it won't stay running or it won't stay running long enough to drive. The more details the better.

[LBO730]

The noid light pulses, but very dim. I'm sure theres not enough fuel going in. It has weakly sputtered a few times but that's it. If I remember correctly, the #6 injector was showing about 3 volts when it was cranking.

[Zed Head]

You should have battery voltage with the key on, and a drop during cranking due to current flow in the injector and the starter motor. Three volts seems pretty low though. But without knowing starting voltage, three doesn't mean much. The test light flashing is a good sign though, it means the circuit is being opened and closed by the ECU.

Sounds like you're close, you just need to know a few more numbers. Do the starting fluid test, it's simple and will tell you a lot. Plus it gives a little more incentive when you actually hear the engine rev.

[siteunseen]

Could the timing be off? Can you have someone cranking while you move the distributor around? Are the wires in the right order, 153624? https://www.google.com/search?q=280z+firing+order&rlz=1C1BOFA_enUS494US494&espv=210&es_sm=93&tbm=isch&tbo=u&source=univ&sa=X&ei=qb26UtqUFo6SkQeY4YHoBA&ved=0CCsQsAQ&biw=1280&bih=619#imgdii=_

[rcb280z]

Any luck yet?

[LBO730]

No luck yet. I ran out of time yesterday. I do have over 12V at the #6 injector connector with the key on but it drops to around 3 when I crank the engine. I haven't tried starting fluid yet. I'll do that tonight or tomorrow night. I verified timing and plug wire order early on. Stay tuned.

[Zed Head]

How are you measuring voltage at the connector when you crank the engine? I'm curious. If you're doing it with the connector off of the injector then you might really just be measuring the electrical system voltage drop that results from the big draw of the starter. If that's the case and it drops to three, then you might have a bad battery or a short somewhere. I think that a starter will typically draw enough current to drop battery voltage to between eleven and twelve volts. Three volts is way too low and indicates a problem somewhere.