Mass airflow sensor quandary

[Xenn]

So I bought a 77 (made in 76) 280z that was dead and stuck the engine/transmission from a 79 280zx 2+2 into it, the thing is, its always had an issue where it would idle really low at a rest,more so when warm, around 500, when i have the idle set to around 1600 when hot just to combat this problem. Anyway i figure out it was most likely the MAF so i ripped it out, cleaned it up, put it back in, and it was working almost perfect for awhile, but now it seems to have died completely.

The point of this post is; it never did really work quite right, and my zx engine is slightly different from that of the 76 i put it in, so which MAF do i buy? Will one for a 79zx work better than one for a 76z, or will it even be compatible with the 76's computer?

[Zed Head]

The 79 ZX engine should be almost identical to the 77 Z engine except for having exhaust liners in the head. N47 head on an N42 block vs. N42 on N42. The 79 AFM might work but it's not the correct one for your ECU and might cause more problems. Your idle speed problem should not have been caused by your AFM anyway. Are you sure the AFM is bad? There is a test procedure in the FSM.

[Xenn]

I ripped my MAF out, cleaned it up, and it worked better but slowly degraded, the main problem is on the inside under the plastic cap, the black conductive area that tells the computer where the position of the flap is has been worn away by the copper contact points, so it doesn't read position at low airflow. Im starting to think the only real difference between the two are how they bolt in.

[grantf]

Take a look at: http://atlanticz.ca/zclub/techtips/afm/index.html

I have also read up on a way to move the carbon sweep so that the contact is touching new material.

P.S. on these cars it is called an Air Flow Meter not a Mass Airflow Sensor.

[Xenn]

That's what i did (adjusting the potential meter wiper) and it worked well for a bit, but its incredibly hard to get it to touch without digging in, with that little room to bend it its either all or nothing. The other problem i found was that i could only really move it further away from the ECU, which while allowing it to make contact, the current would still have to travel around the break, most likely grounding into a different pin at either side of the groove.

Also; thanks for the link, it was a good link, and told me what i wasn't able to figure out on my own.

[grantf]

Are you trying to reposition the wiper? What I read a while back involved taking apart the AFM and moving the circuit board up or down to reposition the carbon chase. I would not try to bend the wiper is very delicate.

Edit try this: http://www.kamikazeracing.org/dl/JsAFMRebuild/

Edited March 11, 2012 by grantf

[Zed Head]

The actual differences between the various AFM models has been pondered by many people. One thing that the 79 AFM is most likely missing is the fuel pump relay contact switch. If you decide to wire around that and try the 79 AFM on your 77 engine, report back with the results. I'm interested, others might too.

What probably matters more is the difference in emissions equipment and other Nissan modifications to the system, from 77 to 79. When you swapped in the 79 engine, did you bring the whole engine over with all of the various switches, distributor and EGR stuff, or did you bolt your 77 stuff on to the 79 engine? If you did the first, you have a 79 engine, if you did the second, you have a 77 engine.

[grantf]

Zed, that being said. I would like to know if he saved the old 77 efi components. That would seem to be the best route if he continues to have difficulty. The efi system is very involved but once broken down to individual components becomes managable and even simple to diagnose.

[Xenn]

I moved both the carbon chase and the wiper to try and adjust the gap as much as possible, im gonna rip it out again tomorrow and see if i can adjust it the other way, i thought about putting a drop of soder on the tip of the wiper so it could have a further out contact point but i donno how well that would work.

The 77 had all its egr ripped out, no catalytic converter, all the egr stuff in the intake manifold was disconnected and removed (as well as the ac, heater vacuum lines, the right gas tank, etc, etc, i kept the 77 distributor because one is internally regulated and one is not, i kept all the efi stuff on my 79 engine and just plugged the 77 electrical harness into it, which worked fine, pretty much all i had to do was disconnect all the electrical connections, undo the mounts, and swap both engines/transmissions across, other than the distributer it worked out great.

[grantf]

Hmm, time for a new AFM perhaps. are you in washigton state? I just pulled parts from a 77 that had an afm at the junk yard, and I am not sure if it still there but there was a 79 zx in Olympia about 4 weeks ago.

Edited March 11, 2012 by grantf

[Xenn]

I live in bellingham yes, ive been looking into it more, and there is a 4 bolt AFM and a 3 bolt, i have the 3 bolt (im assuming non turbo), and then the style changes again in 79 with the zx, i found a place online that does $200 with a $100 core charge, which is the cheapest i can find anywhere.