Turbo AFM on '75 280Z (3.1L)

[cegrover]

Hi All: I am getting close to getting my stroker project running, and am planning to use the 280ZX Turbo AFM that I got with the engine (someone else's project once upon a time). I am swapping the NA electrics into the Turbo AFM, but have noticed two problems, one of which I can solve with solder (differing wire/lead lengths).

The other problem is that the '75 has a fuel pump switch tied to the AFM. This means there is a switch on the circuit board and a piece on rotating arm that opens a circuit if the AFM 'door' is closed. The problem is that the Turbo AFM rotating arm piece has a different center diameter for the mount, so I can just swap them and make it all work. See below for photos.

I'm hoping someone else here has run into this before - please let me know if I'm missing something or if you've resolved this before. Thanks for any help!

Edited April 16, 2011 by cegrover
Better image

[FastWoman]

I don't think you can mix and match AFMs. I would think a ZX turbo AFM would have to be used with a ZX turbo ECU, injectors, fuel pump, and fuel pressure regulator (and possibly other components). A NA AFM would need to be run with NA components. I could easily be wrong, but I don't think the fact that your engine is a stroker would impact how these systems meter air and deliver fuel. If the NA system is not sufficiently large to deliver enough air to your engine, then go to the turbo setup, but use all turbo components. (Although ironically the turbocharger might not be needed.)

[conedodger]

It can be done. I suspect though that you are going to have to source another AFM without the switch. My recollection may be faulty but I thought that the fuel pump switch came on later AFM in the 280Z series. If I am right, you may not have the correct one in the first place. I had a 'how to' on doing this modification on a website I had in the 1990's called PlanetZ. You should be able to unscrew the existing circuit board and install the NA one.

Now, having said this, I just want to say that you should prepare yourself to figure some other method of operating this engine. There is not enough flexibility in the LJet system to make it run well under load in all circumstances. This is particularly important given the expense of your engine. There is someone selling a set of Extrudabody throttle bodies with manifolds and fuel rail in the classified section. Not cheap, but probably cheaper than what you might do to that engine trying to cobble together an old LJet system to run it. I would run it with SDS + closed loop O2 sensor. Good luck though! I have seen stroker motors in Z cars at the autocross events and they are amazing!

[cegrover]

I appreciate the replies! Using gratuitous forum searching (here and elsewhere) with good results and guidance, I have already swapped the board and plug from the '75 AFM into the turbo AFM (that's why photo #1 said "old board in new AFM". Despite LOTS of info on this swap, I've never seen a definitive answer to what people do about the couple of problems I found while doing this.

1) Based on what I've read, the fuel pump switch was only present on '75 to '77 models and the later Z and ZX switched to a relay based on oil pressure and voltage. So, the turbo AFM doesn't have the switch, but my '75 ECU is looking for it. If it's an open circuit all the time, I believe it will make the pump run any time the ignition is in the 'on' position, which isn't the end of the world, as long as I'm not in a bad wreck! I'll keep people here posted as to what I do with it. I suspect the reason I didn't find details here is because people just run it with the fuel pump coming on with the key.

2) The copper contacts coming out of the '75 plug aren't long enough to reach the contact points on the '75 board when installed in the turbo AFM. So...they changed the mounting points slightly somewhere along the line. This I can fix with small wires and solder, and I guess that was implied in the directions I found, or maybe later (77+??) 280Z AFMs are more directly compatible with the turbo ones (?).

On the L-Jet and stroker - I agree it's well documented as sub-otimal. Long-term, I'll likely go with SDS or MS, which means the AFM will eventually be a moot point! But, for starters, we'll see what it does with the stock EFI using turbo AFM, 240sx TB and turbo injectors. I hope to be reporting back pretty soon!

[FastWoman]

Rob, cegrover, I think the FP switch is present on '75 and '76 AFMs. I'm not sure about the '77. My '78 has a switch but doesn't connect to it. It might not be the original AFM. I also have an AFM from a N/A '81 ZX, and it doesn't have the switch at all. It is substantially similar in operation to the '78 and will work on a '78.