ECU: testing circuits & interpreting results '76 280Z

[TomoHawk]

I have been using two kinds of DeOxit to 'repair' the connectors & connections. DeOxit D100 is more concentrated or stronger (100% formula) and it gets most of the oxidation. DeOxit D5 is less concentrated (5% formula) and is intended as a maintenence product/lubricant, and the connectors get a coating of that second.

The combination of D100 and D5 has improved every connection that was treated, starting with the connections behind the glovebox and the headlights. Whenever I uncover a connector, it gets the DeOxit D100/D5 treatment.

thxZ

[Jennys280Z]

Since it's so sensitive (and the fact that there's red goop of some kind on the cover that will be Lord-knows-how-hard to take off after all this time ) , I'll take a minimalistic approach to tampering with it.

1. First fully charge the battery as sblake suggested.

2. Retest AFM from the ECU

3. If readings the same, pull off the cover and clean the Potentiometer contacts as sblake suggested.

Update on where I am now.

1. I fully charged the battery. Well I thought I did. It measured 12.59V when I took the charger leads off. A minute later after removing the charger leads it was already 12.35V. After I ran several more circuit tests from the ECU I measured it again at 11.99V. Was that from just leaving the door open and the dome light on and running tests? It looks to me like this battery is not holding a charge (Energizer brand). And it's been somewhat abused through the first almost two years of its life (drained, charged, drained, charged, and when not charged by a charger it was likely never fully charged by the alternator).

2. I retested the AFM for absolutely no change in the readings above. 226, 200, and 125.9 Ohms respectively.

However charging the battery did possibly have an effect on the ECU-air regulator-fuel pump circuit as it lowered from 68.7 Ohms to 64.5 Ohms. Last night I inspected, removed and cleaned the electrical connector to the air regulator. There were lots of cracks in the black rubber plug (insulator) behind the plastic box of the connector, well not really cracks but holes that go all the way through it. I tried to fit/tighten it into shape by hand when I reconnected it, and wanted to use a piece of electric tape to hold it there but it was still wet from the Deoxit and the tape didn't stick so I took it off. I'll test it again tonight to see if there's even more improvement in the 64 Ohm reading. Cleaning connectors at the fuel pump might be another option to improve the continuity though I can't remember what they look like back there. My car is so low not even I can get under there to look without jacking it up...well at least not on my creeper. Maybe if I got flat on my back on the floor...ewwww

Anyhoo I spent about an hour with a tiny screwdriver scraping most of that sealer off my AFM front cover last night. I didn't expect to get it off last night but I got an idea courtesy of my engineering prowess. Looking at the shape of the AFM housing, one can use its inherent design to manipulate a lever to apply evenly distributed force across the entire top rim of the front cover. Without an intermediary surface, a large screwdriver would only contact the lip at a non-normal angle (approx. 45deg) and this is inadequate as one is applying almost as much force up as one is out (the cosine of the angle). We want to take the cover straight out as I discovered above thanks to Zed Head. Sooooo, I used my folding straightedge, three ruler widths deep across, spanning the upper surface of my AFM housing, and used the slot screwdriver to lever off the cover with force at a nearly normal angle (90deg)with one hand while pressing the rulers down flush on the AFM housing with my other. It applied even force across the entire upper surface of the front cover's rim and didn't take long to hear that satisfying unsticking sound, that the sealer had given up its fight. That was all the time I had last night. Haven't cleaned it yet. Just left the cover mostly closed around the bottom of it and put a plastic bag around it to keep it as surgery as possible. I did open the door and look inside. I almost freaked that I could NOT see the wiper inside and my first impulse was almost to start screaming that Tom took my wiper out. I think this is due to my viewing angle and the position of the wiper at the far CCW end of its arc.

I wonder if Tom adjusted the spring (a no-no, I know) which I presume would have held the valve open a pinch more than it o/w would have, at least at idling throttle. Which might reduce the lifetime of this part, which might explain why I'm having trouble today. I'm not going to touch the Potentiometer with anything but Deoxit, regardless.

So I'll be cleaning Potentiometer and retesting the AFM and Air Regulator tonight. Hope it doesn't mind if I get contact cleaner all over it (that Deoxit can sprays out hard and its hard to control its hair trigger). Yup I got Deoxit right in the face a few times so I wear goggles now when I use it:laugh:

I was also wondering regarding parts interchangeability, Does anyone know if I can use a 1975, 1977 or 1978 AFM in my 1976 car? Or do I need the exact year, or even need to know which model in 1976 to get?

Edited February 6, 2010 by Jennys280Z
clarification; correction

[Jennys280Z]

I have been using two kinds of DeOxit to 'repair' the connectors & connections. DeOxit D100 is more concentrated or stronger (100% formula) and it gets most of the oxidation. DeOxit D5 is less concentrated (5% formula) and is intended as a maintenence product/lubricant, and the connectors get a coating of that second.

The combination of D100 and D5 has improved every connection that was treated, starting with the connections behind the glovebox and the headlights. Whenever I uncover a connector, it gets the DeOxit D100/D5 treatment.

thxZ

So that's what the 5 meant. I want some 100 too grrrrr

[TomoHawk]

Get 2 of the D100, because it seems to go fast.

[Zed Head]

I did not that realize the 68.7 reading you were worried about was through the fuel pump and the air regulator. There should be resistance there, the air regulator is a heater and the fuel pump is a motor. If the air regulator was bad, it would just affect your idle, either too low when cold or too high when warm. It bypasses the throttle, designed to raise the idle at cold startup.

Your car runs so the fuel pump is probably fine.

The Deoxit cans have an adjustment on the top. Low, Medium and High. I think they are set on High as-bought.

I think that your main problem is in the AFM. As the FSM says, the values should be close to 180 and 100. 226 and 126 is quite a bit off. The ECU determines part-throttle injector open duration based on the AFM signal.

Page EF-12 has a pretty good diagram of the AFM innards. EF-51 has a picture of the bottom of the AFM, with the connection point, and more thorough testing that you can do if you remove it.

[TomoHawk]

There is an artcle on Atlantic Z tech section about checking your AFM:

URL: http://atlanticz.ca/zclub/techtips/EFI&fuel.htm

[Jennys280Z]

Update for the general board members: I cleaned the potentiometer, let the cleaner dry, fully charged the battery, and still have the exact same resistance readings (226, 199, 125 Ohms on Bible tests 1-3a to 1-3c).

Thank you for that link, TomoHawk! I surfed to that article a few weeks ago but never found it again so now I have it bookmarked!

I think it's the case that I simply can't see the wiper from the angle I'm looking at my Pot from (I didn't take the front cover all the way off, it's still "stuck" along the bottom edge). If you look at the first big photo in the "AFM adjustment" section of the atlanticz article, you can barely see the wiper and that's pretty close to the angle I'm seeing it. Actually my angle is even worse so I can see how I missed it now. So I'm going to go back and delete incorrect info. that I wrote above. :stupid: I love that smiley! That's definitely me sometimes.

The guide explains well that it's best to be certain many other EFI parts be operating and adjusted correctly before tampering at all with the AFM or then you'll be in the unenviable position of having two (or more) parts out of whack at the same time! All in a day's work of 'Making A Mess'. So I'm not going to unscrew anything or try to adjust anything on the potentiometer.

I noticed that when I tried to gently rotate the wiper counterclockwise (with my thumb on the counterweight), it seemed stuck and wouldn't move. I was gentle though. Does the car need to be running for this to move freely? It moved about 1/2cm clockwise and then stopped. (Edit: Sorry and nevermind, it moved CCW okay, I was just too gentle with it)

Interestingly, that atlanticz guide is suggesting there is resistance (of variable nature) across pins 7 and 8 depending on flap position. With the car off, and the flap closed (I presume), should that really be "continuity"? Not sure why I'm getting 199 Ohms for something that's wanting continuity. Is continuity always defined as something extremely low (0-2 Ohms for instance) or is it all relative?

Sorry not asking anyone in particular all this stuff, just putting it out there for general discussion.

Thanks all, for this wonderful resource!!! I hope everyone has a great weekend!

Edited February 6, 2010 by Jennys280Z
answered my own question

[Jennys280Z]

I did not that realize the 68.7 reading you were worried about was through the fuel pump and the air regulator. There should be resistance there, the air regulator is a heater and the fuel pump is a motor. If the air regulator was bad, it would just affect your idle, either too low when cold or too high when warm. It bypasses the throttle, designed to raise the idle at cold startup.

Your car runs so the fuel pump is probably fine.

The Deoxit cans have an adjustment on the top. Low, Medium and High. I think they are set on High as-bought.

I think that your main problem is in the AFM. As the FSM says, the values should be close to 180 and 100. 226 and 126 is quite a bit off. The ECU determines part-throttle injector open duration based on the AFM signal.

Page EF-12 has a pretty good diagram of the AFM innards. EF-51 has a picture of the bottom of the AFM, with the connection point, and more thorough testing that you can do if you remove it.

Oh I didn't see any adjustment on the top of my Deoxit can, I'll go check it out. (edit: Wow that's cool! It's on low now and 1000% better!)

The EFI Bible said I should get continuity in that ECU-AR-FP circuit. Could 64 or 68 Ohms be regarded as continuity, perhaps when compared relative to some much larger number in the thousands of Ohms or something?

I'm going to go look at my FSM again now too. Thanks Zed Head!!

PS my Z did idle too low when I ran it the last few times, and it was cold out. *shrugs*

Edited February 6, 2010 by Jennys280Z
:)

[Jennys280Z]

[Zed Head]

Shiny. Does it run right yet?

[Jennys280Z]

Shiny. Does it run right yet?

Hi Zed Head, welp I still haven't started it yet! Thus far I've cleaned the water temp connector, Thermotime, fusible links, firewall ground, EFI power connectors, oil pressure sensor, AFM potentiator contacts, EFI bullets, air regulator, cold start valve, voltage regulator, AFM ground, ECU, ballast, battery, alternator, fuse box, etc. I couldn't budge the EFI ground (near the air regulator) with wrench or screwdriver. Despite no rust it seems to be stuck like glue. Wonder if a few days of WD-40 on it made any diff.

The ECU is back in. Doing what I could with the AFM still installed didn't affect the resistance readings at all. In fact the 199 Ohm reading changed to 214 for whatever reason. I cleaned the contacts one more time including at the ECU connector, and hooked it back up. I'm charging the battery right now. It was 11.74 volts last night and 11.71 volts today. I observed some cracks in the big vacuum hose going to the rocker cover (in pics) on careful inspection I never saw before and am wondering how much these will effect how the car runs. I'm going to try to tape them with electrical tape after I start the car and see if there is any observable effect in the car's idle at all.

On a lighter note, I got the seized bolt on my alternator freed and adjusted the belt's tightness just right! Looking at my repair records this must be the original alternator and I'm real impressed at its longevity.

Last Thursday was the first decent weather we've had (low 40s, low chance of precip) and it was basically ready to start, but the overcast skies looked ominous and I don't want to get stuck in the rain for a variety of reasons. A big one is because I have the infamous leak to the floorpan on the driver's side. Another is because the car is largely rust-free but that doesn't mean I'm not at war on rust and will thusly keep the car dry at all times. :laugh:

I put the horns back on. Still only the LH horn works. The connector on the RH felt loose so hoping that a pinch with some pliers will fix it.

I included a picture of the connector on my TPS too, not because it's having trouble just because of the cracks on it. It is representative of other similar connectors under the hood all showing the same cracked wear. The conn on my air regulator was cracked all the way through.

[Jennys280Z]

My #1 Cylinder is dead!

That would explain, I am presuming, all of the symptoms I've been having lately with my car, namely:

1. Low, rough idle

2. No power; runs rough at all throttles

3. Was misfiring badly before I changed the year-old gasoline in it. As soon as I ran the fresh gas through it, the misfires stopped immediately but it still ran crappy. Well maybe the misfires are still there but are very faint and not *popping* loudly like before.

But what about

4. Car won't (seem to) heat up to normal temperatures (doesn't reach ~140deg)??? The temperature switch/sensors are right at the front of the engine, right in front of cylinder #1. If that cylinder is not firing, could this cause a too-low reading at the temp gauge (even though the gauge is reading "coolant temp"?)

I know it's not firing because I bought a timing light, hooked it up, and it gave no readings. I didn't know if I had a faulty light, hooked it up wrong, or had a dead cylinder. So I hooked it up to cylinder #2 and everything with the timing light worked as it should. But I can't check nor set timing with a dead #1 cylinder.

So what could be wrong? I checked the spark plug wire. I cleaned both ends with contact cleaner. I pulled the spark plug and inspected it. It was wet with gas (good sign! and to be expected). It was carbon fouled, so I lightly sanded it with 400 grit and cleaned some of the carbon off so it is more of a brown color now instead of black. The gap is fine and the plug otherwise looks in great shape. It is an NGK V-POWER.

I'm going to start it again and see if there's any difference but I don't suspect there will be. I made sure both ends of the wire are plugged in correctly. There are no visible cracks in the wire, and the connectors (ends) of the wire looked pristine even before I cleaned them.

I hope that there isn't something mechanically wrong with my cylinder (compression?)

Maybe some experienced folks here know what a dead #1 cylinder might usually mean? Like maybe Zs lose their #1 cylinder more often than others and it is best to check the *blank* first? It can't be the coil or the line to the distributor because the other cylinders work fine. I guess it could be the distributor...maybe something wrong with where the rotor points at #1's position?

Thanks!

Jen