... with a bad attitude!

I just wanted to let y'all know I got my engine back together. It's all cleaned up, checked part by part, refurbished, refreshed, painted pretty, reassembled, double checked, triple checked, etc.

It started on the first try, but it ran much like it did before -- exhaust blowing hard and puffing with frequent misses. Engine vacuum a bit lower than before I started -- about 11 in Hg. I had occasional hesitation upon revving, with occasional light backfiring. I had resolved at that point, having gone through the whole system, to make my final adjustments at the AFM... which is what I did.

I first gave the vane a gentle push towards the open/enrichen direction. Engine speed and vacuum picked up A LOT. I dropped spring tension by two teeth and repeated. Higher vacuum this time, but the engine still picked up when I pushed the vane open. I adjusted by another two teeth and repeated... and repeated... and repeated...

TWELVE teeth from where I began, I had a normal engine vacuum (19 in Hg), the engine was running very smoothly, and the exhaust was no longer blowing hard and missing. It sounded like a very content kitten with an attitude.

The weird thing is that the AFM appeared to have had the factory caulk blobs on the set screws. I had assumed it had been unmolested. On the other hand, I knew it had been opened, most likely by the PO. He used clear silicone caulk everywhere on the car and had the same caulk sealing the cover. The silicone caulk on the set screws appeared to be a whitish caulk, so I'm guessing it wasn't his. Did the factory use silicone caulk/sealant/adhesive to blob against the set screws, or was that the handy work of a mechanic along the way?

Anyway, the spring was wound up pretty tight. It definitely felt a lot lighter when I was finished. A gentle push is all that is needed to open the vane now.

The test drive is tomorrow. (Caulk is curing tonight.) I'll take pictures for y'all to show off the engine. It came out quite well, I think. Only the top is painted. Cylinder head and block are as they were. I painted the intake manifold to resemble a '75 intake -- by blacking out the webbing. I think it's much more attractive that way. I have a bit of touch-up painting to do, as engine assembly is frought with nick, scratch, and bump hazards.

Anyway, knocking on wood, I think I'm in the clear now. Thanks for helping me along on this project! I don't think I could have gotten to this point without the moral support and technical advice of my fellow Z enthusiasts.

Peace,

Sarah

Hmmmmm.... Are you SURE about that, Steve? I ask because mine does. Furthermore the connector to the AFM (which is almost certainly original) is wide enough for those extra pins, although nothing connects). I'm wondering whether I have the original and correct AFM. So again, are you SURE?

There are fuel pump contacts in the 78 AFM. I've got two of them. There are not however any wires from those contacts to pins in the connector or the harness. So effectively, it has no contacts.

The AFM should be A31 604 000, at least both of mine are

There are fuel pump contacts in the 78 AFM. I've got two of them. There are not however any wires from those contacts to pins in the connector or the harness. So effectively, it has no contacts.

The AFM should be A31 604 000, at least both of mine are

This picture tells the story. From the 1978 wiring diagram.

Phew!

I was briefly seeing dollar signs.

Phew!

I was briefly seeing dollar signs.

Yeah, but if you are like me on this problem you'd be willing to spend $250 to solve it 100%

No pins on the connector for them in either the harness or on the side of the AFM itself. Same as my 79 810. If the AFM in your 78 has them (the pins), it's from a 77 or earlier.

Edited November 13, 201014 yr by sblake01

Now that I look back at post #48, I see that Sarah actually said pretty much the same thing I'm saying. So allow me to apologize since all I've really done is muddy things up.:stupid: Carry on!

Edited November 13, 201014 yr by sblake01

No problem, Steve! Hey, if we don't bring up these things (even if we're mistaken), we can miss possible problems/solutions.

While I was sick, I hit the computer a bit and satisfied myself that I indeed have the correct injectors for the '78 Z. I decided not to flow test the injectors after all. Good grief, there'd be so much stuff to take apart and put back together, and I need my life back.

I'm now feeling 95%. No more virus, anyway. I thought I was courting a secondary bacterial infection, but that seems to have cleared. Just lots of gunk, but that, too, shall pass.

... so I got back to work on the Z.

I was first curious as to how much "boost" I would need in fuel pressure to achieve the proper mix at idle. (I was still playing with the idea of an adjustable fuel pressure regulator.) It turns out that with the AFM recalibrated per Atlantic Z's specified spring tension, I'd probably need about 60 psi. I was getting pretty close to the right range at 50 psi relative to manifold vacuum, where I topped the system out. My pump will only put out 42, and with the vacuum added, that would put me around 50. Of course there's no way I'd be able to put out even 50 at zero manifold vacuum. Anyway, this solution is out of the question, without going to a new fuel pump and pressure regulator combo. I'm not going there.

Then I said, "OK, let's figure this thing out." I cracked open the kick panel and tested out my spare ECU. Same lean idle. I then did the quick FSM check of the ECU with a miniature Xmas light bulb in the #1 and #4 injector connectors. They flashed once per rotation, as they were supposed to, and they did flash brighter when I unplugged the temp sensor. I also re-checked all of the connectivity at the main ECU connector, and everything was happy and as it should be.

I also opened up one of the ECUs for a look. It honestly didn't look bad. I was rather put off by the old can-type transistors. Anything oil-filled can possibly leak its oil over time, so I was leary. More surprisingly, even the early ICs were canned in oil! I've never seen that. Anyway, I suspect there are common failure modes in these ECUs. I do know enough to know that transistors rarely fail catastrophically. They usually fade away over time, and two ECUs of the same design would be likely to fade away in the same manner. I did an exhaustive/ing search on the internet for any info about MTBF in these sorts of transistors, common failure modes, etc. I really couldn't find much at all. I take back any previous assertions that one can find ANYTHING on the internet. Apparently those can-type transistors are too prehistoric (like me).

Anyway, from what I can gather, these ECUs don't really have many failure issues at this point in their lives. I'm still somewhat leary of all that oil-filled can stuff, but I'll just hang with what I've got, with the expectation that it might work, but still develop inaccuracies over the years. In other words, my current operating theory is that the ECU will be responsive to changes in sensor readings, but otherwise a bit out of whack in its overall response to those readings. That is, some adjustments may be necessary.

I'll mention here that I'm rejecting the Atlantic Z approach to solving this problem at the AFM. That's because I would have to alter the spring tension so much that the vane would too easily peg out at wide-open, leaving the mix too lean at peak intake. That of course would not be good. I wouldn't mind tweaking by a tooth or two, but certainly not by 15 or so.

As I see it, the most obvious place to richen the mixture is with the coolant temp circuit. I was curious to see just how much an open sensor would richen the mix and was delighted to find that my poor engine was choking and gagging on fuel, barely able to run. Plenty of adjustment room there! I'll note here that the PO or his mechanic had inserted a resistor in series with the sensor, I presume to richen the mix. I suppose this is a time-honored bandaid approach. I had removed the resistor when I rewired, refreshed, replaced, etc.

Anyway, I ran upstairs and grabbed a 5k variable resistor and plugged it into the temp sensor connector. That let me tweak the mix manually. I found that the best mix was achieved in a warm engine with a resistance of 2,550 ohms, while the temp sensor's resistance had dropped to 240 ohms. Thus the mix could be richened about right by adding 2,310 ohms in series with the sensor. Interestingly, I think I remember the value of the previously added resistor being 2.2k, so apparently someone else had been down this road before me. I'm sure at one time it made the engine run very well, and then it got wonky again with age and deterioration.

Anyway, that's the solution I propose: I'm going to put a resistor in series with the temp sensor to richen the mixture. I'm going to try a more refined approach than simply splicing a fixed resistor into the wiring harness. Instead I'm going to install a mixture tuning potentiometer directly inside the ECU housing, provided there's some good place to mount it. Before finalizing the mount, though, I think I'll run a couple of loose wires into the cabin of the car, so that I can play with mixture with the car in motion. I'll have my lovely assistant drive my car down the freeway, with her foot blocked against the transmission tunnel to keep a constant throttle opening, and then I'll tweak the mix to achieve the maxiumum speed. I'll note the resistance, and then set that value when I mount the pot back inside the ECU. Further tuning will be done on the basis of plug readings and mileage calculations.

Oh, and when I'm done, I think I do probably need a couple more deg of advance in my timing (which is currently set to 10 deg BTDC, per factory specs. I'll probably do that too, and I expect that will tweak me to a perfectly healthy engine vacuum. I just have to fix my timing light first.

So there... That's my plan! Any thoughts or comments?

BTW, I'm very bad about taking all the pics I should (ironic for a photographer, eh?), but I'll make sure to document my ECU mod.

Edited November 14, 201014 yr by FastWoman

If you haven't read these "tips" from Paul Rusch of Rusch Motorsports, they are worth a look. He goes in to detail on how the sensors work and has some good examples of experiments he ran in the past.

http://forums.hybridz.org/index.php/topic/95316-braaps-l6-efi-induction-advice-and-tips/

Hey Zed, thanks for the link! Very useful info. He has basically the same approach to what I'll be taking, except that I've now learned the AFM pegs at 4500 RPM, and fuel delivery after that is based on RPM and other factors. Per his advice, I'll be adjusting the mix for WOT first and then tweaking the AFM for smooth running at cruising. Finally I'll tweak the almost useless little bypass screw on the AFM to get the idle right. Good to have these refinements in mind. Thanks!

Interesting that you are arriving at the same conclusions I have. I re flowed all the solder joints on the entire ECU last night and it didn't help. I too was wondering if degradation of the analog ecu components were to blame. I had thought of wiring a potentiometer in line with the water temp circuit, but worried that it was too broad of a fix and might make the WOT too rich.

I can tell you that I've continued to drive, and tweak on mine. I recently adjusted the idle air mixture, I put it three turns in (mine was 6.5 turns out from full rich stock). This with the 6 teeth advance and the timing at 13 is working pretty good for me. It's not 100% and I'd like to find a better work around, but it's close.

Cozye, I've also had my reservations about the potentiometer "fix," which was why I was unwilling to consider it until now. However, after studying all the EFI info I can find, after seeing empirically just how much adjustment latitude there is, and especially after reading the short description of the temp enrichment in the link that Zed posted, I'm a lot more comfortable with the solution.

I think even with roughly 2k in series with a thermistor that should level out at 240 ohms in a warm engine, I'll still have cold/warm responsiveness in the system. That's because when the resistance is infinite, gas practically pours from the tail pipe. The roughly 2-3k (??? -- from memory) from a cold engine will now become 4-5k, which will still result in enrichment. I don't know if the enrichment will be too little when the engine is cold, but I'd rather have lean running when cold (with inadequate temp compensation) than lean running when hot (from compromises to the AFM adjustment). If this becomes a problem, there is still another solution. I can insert still another thermistor in the thermostat housing (in a plugged hole), and wire it in series with the existing thermistor. That will raise the resistance right much more in a cold engine. I would still have the potentiometer in series (with roughly 240 ohms lesser resistance) to balance out the mixture when the engine warms up.

What I like about this solution is that the correction to the mix is executed the same way at all RPMs and under all conditions. It seems to be an overall gain control, so to speak.

I'll continue in next post, but I'll get this up on the board, since I see you're online, looking at this thread right this very moment! ;-)