Tachometer relationship with TPS

[FastWoman]

Yeah, there are very few unmolested AFMs. Most of us have to re-molest them to get them back to normal.

As long as the plastic cover seals (with silicone caulk), it's good. It should be a fairly durable part, so if there are some chips missing, it might not mean the cover is breaking apart. Perhaps someone mucked it up by prying on it with a screwdriver. I would recommend cutting the caulk all the way around with a razor blade. Then the cover should pop off with much less effort.

I have no idea whether MSA cares about the plastic cover, which perhaps they replace anyway. That said, it shouldn't be too hard to re-molest and put right.

[johnny haywire]

The cover seems like it is sealing, though it is caulked on there pretty well, maybe too well. The edges seem to want to crack off rather than give after cutting the silicone and trying to remove it. I think the silicone was used very excessively. I'm very tempted to let MSA deal with this end of things and then I'll clean up the cam/lash pads while she is disabled during the shipping process. I need to re-mark my timing mark as well. So...I've got a few things to do while my AFM crosses the country.

I talked to MSA and sent pictures and they said that the core seems acceptable. So, it's all packed up and will go in the mail today unless you talk me out of it

I am very excited to see how the car runs with all the sensors working.

It will probably take about a week, but I'll definitely keep you posted on the progress!

[Zed Head]

Have you done the testing of the AFM described in the FSM? At least the resistance measurements? You can do those without removing the cover.

You might be about to waste a lot of money. When the AFMs fail, the signs are usually poor, "stuttery", jerky acceleration with popping back through the intake manifold. Running rich is not a typical failure mode. I looked back through your thread and it doesn't indicate AFM problems. Replacing the AFM is not a cure-all, even though it seems like a magic piece of technology.

If the cover is chipped you might as well pry it off. There really is nothing holding it on but the silicone, not even a clip or two. It would probably fall off without the adhesive.

[johnny haywire]

I did do the testing - the resistance on both sets of pins came out fine, just a little bit over 180 and 100, respectively. I also jumped 12V to it and checked the voltage as I moved the vane open. It went from 6.37 to 0 (when fully opened). Does the voltage measurement sound like it's within spec?

I guess I was just concerned about screwing up the cover even worse than it is and recalibrating it. I don't necessarily think the AFM has failed so much as it needs to be recalibrated (I'm thinking the previous butcher cheated it to run richer) and the cover may crack in getting it off, but I am really glad you guys are talking me out of sending it in!

I spent a few more minutes trimming off excess silicone, but the cover isn't budging so far. I've dug up my x-acto knife kit and will try some more trimming this evening. I'll post some pics once the cover is off before attempting recalibration. Might not be for a few days, though, as I'll be away from the car for a few days.

Thanks again!!

[johnny haywire]

Okay, well, another round of beers for you guys. And thank you for the reality check! The AFM will not be visiting MSA. Not sure why I was so apprehensive, but eventually I was able to pull the cover off after much trimming back of silicone, careful not to crack it (I used an old chisel and a pretty massive flat-blade screwdriver to get it off). It was sloppy as hell, silicone inside the chamber and everything, and the cover does have some chips (that can be refilled). The spring has definitely been messed with, but I can't really tell which way (I'm assuming toward the richer end of the spectrum). I'm going to do the Atlantic Z method of recalibrating and then take it from there, since any tell-tale glue-blob signs of original placement are long gone.

Once again, many thanks to Zed Head and Fastwoman for the help and advice! I really appreciate the time you have taken with me on this, it means a lot. I hope I can repay the favor one of these days.

Updates to come once I get back from Cleveland.

Cheers!

[FastWoman]

You're quite welcome! I'll be watching with interest as you recalibrate!

[johnny haywire]

I had a bit of time to do the Atlantic Z calibration (with the beer can and string) and, oddly enough, it indicated that my spring was too tight (indicating that less fuel is being sent). Hmm. That kind of stumps me, because the Z runs riiiiiich. At any rate, I adjusted the spring tension to 4.9 and 9.8 fl. oz of water respectively for half open and fully open. Next step is to install it and try the finger test while she's running.

I think I also need to test my altitude compensator (it's a California car). I suppose that could be stuck on?

I'll keep you guys posted!

[Wade Nelson]

There have been plenty of high idles caused by mats and parts of the accelerator pedal and linkage chafing or getting bent. Be sure and take 30 seconds to inspect all of it.

[johnny haywire]

Good point. I'll have a look at that tonight, Wade. I have inspected the engine bay linkage and throttle butterfly and all seems well in there, but I haven't really studied the pedal area.

The idle doesn't seem to be high so much as it just doesn't like to settle where it should be. It does on occasion, or if I let the clutch out a bit to put the engine under load, but at stop lights, etc., it generally tends to stay a few hundred RPMs higher than it should and then drops to normal as soon as I start letting the clutch out.

And the exhaust fumes are very rich, at idle and while cruising.

[johnny haywire]

Here is the latest update. After calibrating the AFM according to the Altantic Z tech tips (and adjusting the spring setting to be looser to achieve this), I reinstalled the AFM and fired her up. Since it was about 90 degrees in the garage, none of the high idle, it just settled quickly at around 1000 RPM. I then noticed that with the decreased spring tension on the AFM flap, the car returns to idle as it should after a rev, and didn't change much while finger-testing the AFM.

I decided to try and get the idle down to 800 (as indicated by the FSM) and had to bottom out the idle screw on the throttle body to get there. And then it died on me. So I backed it off and then turned in the idle screw on the AFM a good bit and then tried again. It seemed to get the idle down, but initial throttle response was boggy, so I set her back up as she was (with decent response) at around 1000 RPM for the idle.

I tried the finger test at 3000 RPM to see if it sounded any better (clockwise was the same, counter-clockwise lowered the engine speed), but couldn't tell. I was alone, so I didn't have anyone to sniff around near the exhaust to see if it ran leaner if I closed the flap a bit.

At any rate, it's much more "growly" now and the response is nice, and the engine settles back to idle quickly now (as a result of calibrating the AFM?), but still running very rich.

Wade - I checked near the pedal and the linkage under the dash and there is no interference, everything seems to be working fine there.

I'm not really sure where to go next. The previous owner replaced the connectors for the injectors and I believe had the injectors cleaned, but I can't really be sure of what was done there. The connections are soldered, so at least he did that.

One thing I did notice while just having a beer and looking around the engine compartment is that the head is a different color than the block, it's silver and the paint is pretty clean, whereas the block is blue and is pretty crusty-looking. So, I'm guessing that was redone at some point in the past.

Ah, well. I'm stumped for now on this rich situation. Next phase is to replace all the connectors with the new kit I got from Kurk on HybridZ. Most of mine are in pretty bad shape as it is...

[Zed Head]

What color are your injectors and what are the numbers on the side (tiny numbers on the plastic)? The assumption has been that you're working with stock parts, but since you've found that your AFM was leaned out, maybe someone has misguidedly installed turbo injectors for "turbo" performance and leaned out the AFM to try to make them work. Just a guess, but worth confirming that you have the right ones.

The stock Nisaan injectors for the 280Zs and ZXs were either tan or green. Turbo injectors are a purplish brown color. There are other injectors that have the same form also, like Bosch injectors.

[johnny haywire]

Excellent point, Zed Head. I snapped a couple shots today so I could read the numbers. Photos below.

Cylinders 1, 3, 4, 5, 6 have green injectors with: 0 280 150 116

Cylinder 2 has a tan/brownish injector with: A46-000001

I also noticed that my AFM doesn't have a counter weight on the side opposite of the wiper. Is that correct for a '78 280z w/manual?