... 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

I've been thinking about how to tune this system. I suppose if I were racing, I'd want peak efficiency at WOT when running the engine at the peak of the power band. However, I'm not a racer. I'm just a semi-puttery, middle-aged woman who wants a cool car and doesn't want to destroy her engine by running it at the wrong mix. I'm first going to determine which series resistance gives me the fastest cruising speed at a fixed accelerator pedal depression. Then I'm going to see how that same setting translates to WOT conditions. I suspect I'll run right much richer at WOT. I might get a tiny bit more power running a tiny bit leaner, but my preference would be to optimize for cruising and to be "safe" at WOT. I suspect that's how the Nissan/Bosch folks designed the system in the first place.

Finally, I'll see how the engine idles at this setting, and I'll make any needed adjustments to the little AFM screw.

BTW, you should remove your screw and examine it. It has a rubber O-ring near its head, which I think mostly serves to keep the screw from wandering. Mine had crumbled practically to dust. (I honestly thought it was dirt.) I replaced it with a tiny sliver of silicone rubber hose that I carefully cut with a razor knife. The screw now has a bit of "hold" to it, and I'm confident it will stay in place. At this moment I have it set rather arbitrarily at 5 turns CCW from fully closed.

Edited November 14, 201014 yr by FastWoman

BTW, I've also re-thought where to situate the series potentiometer. I think I'll put a little Molex pigtail connector on the ECU harness and make a little 20-turn potentiometer/plug doodad (incased in epoxy?) to plug into it. Then I'll make an extension cord that will allow me to make adjustments from a seated position (passenger or driver) as the car is moving. Once the correct calibrations have been determined, I'll remove the extension cord, save it in my "special tools" box, and have it available for future "while-driving" tune-ups.

Sounds like a plan. Let me know how you fair with it. I do not think you will be too lean when cold though, if anything I think it will be too rich. 2k ohms is quite a bit of change on the water temp circuit, the car will think it's 68 degrees. My car seems to run pretty good when cold, and gets leaner when warmed up.

Have you given any consideration to megasquirt with a wide band o2 setup ? I'm thinking that may be a better long term solution. I may bandaid the car with the same tuning setup as you for the time being and look further into a fuel only MS setup for the future.

Like you, I have no desire to turn this into a race car, but I would prefer it to have a decent tune at all throttle conditions. Having a smooth running car is just so much more enjoyable to drive. I've got quite a bit of experience doing EFI tuning on motorcycles for performance (I have a nasty road racing habit), so I'm familiar with wideband tuning and all the variables that come into play with different speed/throttle postions/ gear selection etc..

Thanks for the tip on the idle screw. I'll pull it out and take a look. Also, FWIW I pulled my check valve for the fuel pump yesterday and inspected it, tested it with air. It holds air pressure, so I'm pretty sure it would hold fuel pressure. My fuel rail is boiling within 5 minutes of shutting down, and I now have an inline pressure gauge permanently mounted. I found out just how quick it boils by pulling the fuel rail inlet line off to put the gauge on after it had been sitting for 5 minutes only to be greeted with boiling steaming fuel shooting out. The fuel rail only holds pressure for about an hour or so, so I think my FPR might be leaking down.

OK, well, I've modded my car. Results are pretty good. Construction details will be in the next posting.

I think the enrichment isn't quite all that it should be when the engine is cold, but it's not far off the mark. Idle is a bit unstable; however, there's now something wrong with my air regulator. It seems to be stuck in the closed (warm) position, so my idle speed isn't elevated on startup. I'm sure when I get that fixed, my cold idle will be much more acceptable.

Anyway, I've had my car out on the road now. It feels about like it did when I loosened the AFM spring. The response seems pretty well balanced. I might have a bit of missing at WOT. Also after I give the engine a good WOT rev to maybe 4000 RPM, the drop in RPM pauses/bumps at about 2500 on the way down, and when I get that little bump, there's an exhaust pop. Do you (or does anyone else) know what happens at this 2500 RPM mark and what it means and/or how to get rid of it? I know the pop means I've got raw fuel in the exhaust, but beyond that obvious point, I'm not sure why it's happening there. I'm thinking that might be where the fuel cut ends on throttle-down.

Other than that, the engine seems to be running about right. The fresh plug I put in #1 reads OK -- a bit of brown, and perhaps a touch of chalky deposit on the electrode. I might be a tad lean.

Tomorrow I'm going to pull all of my plugs, most of which are quite black and sooty from prior issues. I'm thinking they might be a bit fouled and could use a good cleaning. I'll also see if I can tweak my timing a bit. (I still have to fix my timing light.)

All in all, this seems to be a pretty workable solution. I like this approach better than playing with the AFM spring.

I promised pics and details, so here they are. I apologize for the washed out photos. I didn't take them to be pretty, but rather to be clear. There's a whole lot of black in these photos!

I decided it would be better to put the inline potentiometer at the end of a pigtail, rather than inside the ECU. The first reason is that I can change out the ECU and still have the same mod. The second reason is that I don't have to go into the kick panel to change the mixture.

I tapped into the EFI harness inside the main connector shell. There's a screw on the end of it, and the shell slides apart I clipped the small black wire in the #13 position (labeled on the inside of the connector) and connected the two pigtail leads to the ends:

Here's the pigtail coming out of the EFI harness, which has been wrapped back up. The connector does not have the potentiometer attached:

Here is the potentiometer assembly plugged into the end of the pigtail. I simply heat-shrinked the 20-turn trim pot to the side of the connector:

The connector has a slot where it can be mounted on a prong. I bolted this prong underneath my dash, just above the hood release and vent control:

... and this is the connector mounted on the prong:

Not shown here are the trim panels. The panel that goes across the bottom of the dash leaves a hole where the air/fuel mix screw remains exposed.

Also not shown is the approx 5 ft extension cord I made for this connection. It allows me to make adjustments from the hood compartment area or the driver's or passenger's seat.

Edited November 15, 201014 yr by FastWoman

Nice install. Did you put your AFM back to the stock spring setting? What resistance did you end up with on the pot?

I did the same today, but more of a temporary test install. I just setup a trim pot on some barrel connectors and put it inline with the water temp sensor under the hood. I tweaked, drove, tweaked some more, looked a vac, listened to idle, drove, repeat, repeat ,tweaked afm, drove, etc..

I found that if I put the AFM back to stock settings, and dialed up about 1100-1200 ohms on the pot, it ran smooth but lacked torque and felt a bit flat. So I richened up the AFM a bit again, not as much as before and dialed the pot back. I'm at 4 teeth rich on the AFM now, and right about 800 ohms on the pot. This is pretty close for me. It's rich enough that the lean miss fire is gone, and not too rich that it feels soggy. I may tweak it a bit more but this is close enough for me to give it some drive time to get more familiar before making any more changes. I've also got to get the suspension freshened up, bushings etc,, I've got so much rattle, bounce, and shimmy going on that it makes it hard to feel the subtle stuff on the motor at speed. I've got new tires on it, and I think they might have one not perfectly balanced but I'm sure they will blame it on my lack of strut dampening and rattling ball joint so I'll fix that stuff first.

As far as popping on deceleration, do you still have your BCDD valve on the throttle body, and is it operational?

Thanks, Cozye Yes, I used the stock spring setting and ended up with a resistance of approx 2.6 k.

I think I'm about where you are on the tuning. I'm pretty close and will be just driving it a while to get a feel for it. I'll periodically do plug readings, calculate gas mileage, etc.

BCDD: Yes, I still have it. I'm pretty sure it's operational, but I suppose that needs a re-check.

G'nite!

Thanks, Cozye Yes, I used the stock spring setting and ended up with a resistance of approx 2.6 k.

I think I'm about where you are on the tuning. I'm pretty close and will be just driving it a while to get a feel for it. I'll periodically do plug readings, calculate gas mileage, etc.

BCDD: Yes, I still have it. I'm pretty sure it's operational, but I suppose that needs a re-check.

G'nite!

Check the BCDD. That exhaust pop on decel is a pretty common thing if you BCDD is not operational. You can do a "field" adjustment of the BCDD, but disconnecting the 12v wire to the solenoid to simulate going faster than 10mph, and reving the motor. Turn the screw on the bottom until it has a hard time idling down, then back it out slowly until it idles down gradually (for me this was approx 1/2 turn).

If it doesn't do this, then the BCDD is probably bad. They are NLA, and it's hard to find a working one so you might be stuck with it if it's bad. A lot of people just eliminate it and plug the hole in the TB.

Thanks yet again! I'll try that.

Oh, and you had asked me whether I had considered MegaSquirt. I did think about it, but I didn't put too much time into studying it. I was discouraged by the fact it's incompatible (I think) with vane-type, closed-loop systems. I didn't want to get into a major redesign of the system. I think more and more of these EFI systems are going to be going south, and maybe there will be enough people wanting to stick with EFI (rather than converting to carb) that there will eventually be a turn-key retrofit for our systems (whether vane-type or something more modern). When such a system surfaces, I might well make the switch.

Oh, and you had asked me whether I had considered MegaSquirt. I did think about it, but I didn't put too much time into studying it. I was discouraged by the fact it's incompatible (I think) with vane-type, closed-loop systems. I didn't want to get into a major redesign of the system. I think more and more of these EFI systems are going to be going south, and maybe there will be enough people wanting to stick with EFI (rather than converting to carb) that there will eventually be a turn-key retrofit for our systems (whether vane-type or something more modern). When such a system surfaces, I might well make the switch.

Yeah, I do not think it is that difficult though. Just get rid of the AFM all together and all you need is an IAT and MAP sensor. From my initial research it looks to be a much more modern type EFI, will reuse everything except the AFM, and can be configured for closed loop with a wide band o2. I really like the idea of a wideband. I've used them on my motorcycles for tuning on the race track and it's extremely reliable and easy to use. Personally I think I would do fuel only with it, not spark. I'm going to go this route I think, but will stick with my temporary work around for a while and work on other repairs. (suspension, paint, etc..). One of the main things I don't like about the current EFI setup, with work around is that the changes affect every rpm under every throttle setting. A system like MS you could configure for a particular air fuel ratio on a much more granular scale, and have it calculate the changes necessary to hit your target. Much more efficient.

Ah, but there's a certain magic about a Grammaphone, in comparison to an MP3 player. Same is true of the clunky vane-type L-Jetronic fuel injection. I don't know whether that magic is worth the cost of some loss in performance and added fuel costs, but there's still something rather cool about it.

I presume if you go to the MS system you'll post all about it on this list. I think I'll let you go first!

I did sort of close things up today. I did another cold start at last night's settings, and the start-up was fine. Idle was a bit low-ish (1200), but the mix was comfortably rich and stayed rich until the engine was warm. I've decided my air regulator does work. It's just that I don't get quite as much RPM boost from it now. Before, my engine was fuel-starved, so the enrichment made the RPM pick up a lot. Now the engine is no longer fuel starved, so the added fuel perhaps drops the efficiency a bit.

I set my idle to 900 RPM. It just sounded so much smoother/quieter than the 800. I advanced the timing to 14 deg BTDC. My vacuum, in the end, was about 17.5 - 18. I don't know why I couldn't get as high a vacuum as before, especially with the slight timing advance. At a faster run the idle was more like 21, whatever that means. I also found my compression gauge and checked compression. The dry/warm readings were 165, 165, 168, 173, 165, 168. Perhaps a bit of engine wear there, but at least it's pretty even.

I might still have some engine sludge issues. My engine was the sludge monster when I bought the car. I'm now starting to see about 60% clean metal. I changed the oil again today. I'm trying Chevron Delo now (for diesel engines -- very high detergent). We'll see how it goes. Anyway, with a bit of regular use and continued elimination of sludge and varnish, I might pick up a an inch or two of Hg.