Alright, so I just made an account for this forum because I wasn't getting the answers I wanted from the last forum I was in. I have a 1977 280z with running issues. The engine doesn't want to an engine essentially. What's wrong is that when I start the car, it cranks over fine and will start fine but after the initial start it will immediately bog down and either die or run on like 3-4 cylinders. It helps tons when I push the AFM in about 25% of the way, but If I let it go on its own the car stutters and bogs down again. Here are some of the things I've tried:
-New cap and plug wires (with relatively new plugs)
-New fuel filter
-New seals for the fuel injectors
-New fuel regulator
-New coil
Here are some things I've done:
-Cleaned the fuel lines
-Set the timing
-Tested the fuel pump (It works and puts out about 36 pounds of pressure between the new filter and the rail)
-Tried a different ECU and a different AFM (Both came with the car and both give the same results)
-I did do a compression test awhile ago and everything was fine, and I should be able to do another compression test tomorrow afternoon
-I checked to see if the injectors work by taking them fully out of the car starting it and see them all work correctly
-I did check the voltage of the clips going to each of the fuel injectors and those all work
-I checked the points in the ECU that go to both the AFM and the fuel injectors both also came out fine
If anyone has an idea of what might be going on please reply, I feel like by now everything should be working at least sort of correctly. Would replacing the whole AFM do me any good? I appreciate anyone's input!

 

OK, I'm a Z31 guy and the 280 pros here will have way better input than me. But this sounds so much like a sensor-to-ECU problem that I had to post. My sense is that a sensor is sending your ECU either bad info or nothing. So the ECU then misdirects other stuff based on that. I bet this is easier to solve than you think. Let's wait for the 280 pros here.

Great post, BTW. Gave great info. You're a pro at posting a Q.

 

Haha thanks! And it has to be something easy. I never thought about the ECU getting a bad signal from the sensors... That would make some sense! Thanks!:

 

Thanks. But don't take my answer as a solution. 280Zs are way out of my league in every way that they are different from Z31s. And they are different.

I would wait for a 280 pro here to respond to your orig post. They know your Z better than I do. Plus, it could be a unique issue that shows up on 280s from time to time and not on Z31s.

While you are waiting, go to your Factory Service Manual (FSM) (or download the freebie at http://www.xenons30.com/) and locate your sensors (cylinder head temp, O2, crank angle, throttle position, air flow, etc., etc., as they apply to your '77 - those are all sensors in Z31s and they are all a big deal, it turns out...). Your prob could be one of 'em.

 

Hmmm... I don't have the FSM (the owners before were pretty bad about keeping things like that). And it seems like I cant download it, it says the file is invalid. Not looking up for me.

 

Let's start with the fundamentals.
1. Download the FSM and fuel injection bible (XenonS30 and XenonS130 - S130 Reference respectively) There are excellent troubleshooting guides in them.
2. From the sound of it, you may have an issue with the AFM. I believe the manuals will tell you the range for good resistance measurements on the wiper in the AFM.

You may want to post your question on classicZcars. There are plenty of 280Z owners there.

 

What does it do when you hold the throttle open? Meaning, does it run good at idle with the AFM advanced, but not at high RPM's? Or does high RPM's fix the stutter in lieu of the AFM? I had a problem like this once and it turned out to be the rotor button after I had killed a bunch of brain cells on everything else. It "looked OK" and I cleaned it up, but basically it was not getting clean spark at idle.

After going for the obvious and cheap fix, I second ZXguy's thought that you should spend some time with a GOOD multimeter and the FSM.

 

Have you checked your Throttle Position Sensor, very sensitive to moisture and corrosion, and what you are describing can be caused by a malfunctioning TPS, if the computer is confused as to whether it is at idle or at full open throttle, that is all it knows. Check your fsm for testing and adjusting your tps, check the connector, clean the contacts.

 

Make sure the intake hose from the afm and throttle body doesn't have ANY holes in it. Locate your cold start valve injector on the intake maniffold and disconnect it to see if that makes a difference. The thermotime sensor (on the thermostate housing) can give the ecu bad info too. Make sure you spark plugs are actually getting spark, your girl friend can help you with this and the coil. It will also test your relationship with her. If you don't know how to use a multimeter have someone show you. It's not that hard for the tests you will be using but it and the fsm are essential.

 

I had the same issue when I bought my 77 z, replace injectors, fuel pump and lines, did the timing, plugs, wires, cap, and others. turned out the AFM's air bypass screw had been messed with in combination with a failing IAC ( idle air control ), its a screw with a spring on top of the throttle body by the TPS, might wanna just turn it a time or 2 to see if its all the way closed, or working at all, 1 full turn should affect the idle speed to a noticeable degree. If thats the problem you can tell easily just by messin with it.

How long will it run for once started ? Can you tell if its rich or lean ? any popping noises from the exaust or the intake under throttle load ?

Has the EGR ever been replaced ?