Captain Obvious

How many drops is this for you, Lieutenant? Me too. And I don't use the clutch to take it out of gear. Once you slow down to the point where the gear train is unloaded it slips out easily.

That's neat stuff. I've wondered about that. I like your conclusions as well. Makes sense for some small amount of additional mixing and smoothing of transients by the time gasses reach the light of day, but it should still be FIFO for the most part. Cool!

I found the first generation Integra (85-89) headlight chime to be quite polite. Not the key in the lock warning, but the headlight chime. The key left in lock is your ubiquitous "beep-beep-beep-beep", but the headlights are this very polite "bing-bong" thing. Sounded like they even used mechanical bells struck by a clapper of some sort instead of it being electrically generated. Don't know if you can buy the module aftermarket, but if you're junkyard hopping, it might give you another alternative to try. Might also be on later modules as well, but I don't know for sure.

Yeah, the original ECU is a highly trimmed black box full magic and voodoo. I didn't do a lot of reverse engineering either, but I did get through the output stage and the "After Start" enrichment section. Tough part is there are three IC's in there and I have no visibility into what's inside the cans. They predate DIP packages, and there's no discernible standard like "opposite corners are power and ground". So for the sensor inputs, I've traced the circuits up to the IC's, but once they connect to one of the IC's, I hit a wall. I hooked the ECU up on the bench with a scope and a sig-gen and tried to get it to speak, but no luck. I just stuck in fixed resistors for the sensors, but I must have missed something because I couldn't get any injector pulses. Then I ran out of time on that project and moved on to something more pressing. My car runs well so it was an academic investigation only. But think about this... All analog. Instantaneous continuous response. Smooth transfer function. And has been bulletproof reliable since 1977.

All that stuff I said about big current not flowing through the fusible links? Forget all that... I bet one or more of your fusible links fried. You should double check them to be sure. (Glad you found it!!)

I don't know anything about the supply side as I'm jut datasheet shopping. Never actually tried to buy any of the injector drivers. From fuel injection to industrial chicken skinner... You'll have to walk me through that one over drinks sometime. FYI, the original ECU used a pair of NPN Darlington BJT's to drive the injectors. Three injectors per driver pulled to ground. They segregated the ground for these drivers from the rest of the circuitry so the switching currents didn't mess with the analog front end. Separate analog and digital grounds inside the ECU.

In theory, shorting the battery post right to ground through the hold-down bracket should not have put any current through any of the fuses or fusible links at all. The loop would be: positive battery post to the body through the hold down bracket body into the harnesses through all the ground wires connected to the body the ground wires back to the battery negative post through the negative batt cable and/or the FI ground connection Of the two ways to get back to the battery negative post the negative FI connection is clearly the weaker link. I'd start there and at the body to block ground tie connections. I bet you burned up a ground wire or one of your FI components that connects to ground. If stuff got hot enough that you got smoke, there should be visible damage somewhere. Look at the smaller ground wire off the battery that goes to the FI system. If it's not there, you should probably seek the assistance of someone in your area who really really knows the FI system because it's probably gonna be a tricky hunt. I didn't look hard, but quick scan shows the FI main relay, thermotime, fuel pump relay, fuel pump control relay all connect to ground. On edit... I see that lenny types faster than I do!

Haha! If you weren't so far away, I'd put em back on for ya. I bet I could convert you to the dark side...

Wow... The temp was at "E"??? You must have been really flying!! :laugh:

Fortunately??? Wuss.

Makes sense. Moore's Law historically has been as accurate as Murphy's Law, and if memory space and processor cycles are cheap enough to burn off, then why not, right? However, for this application my plan for all assy wasn't driven so much by cost or speed, but for reliability and predictability. I wanted to know exactly what was in all the registers at all times. I'm out of touch and I'm comfortable with that. I always wrote the low level interface code for the stuff I designed, but I've never been a software jockey. I've done just enough to be dangerous. You're clearly going a lot more complex than I had planned to do. I was thinking just model the transfer function of the original ECU and that's it. Let's see... Of your vars above, the only things I need to know are AFM, IAT, CLT, TPS, and Pulse_Width. Everything else was for phase II. So I don't want to hear about it when your interrupts hiccup once every few days and you can't track it down. Are you sure you main loop will be able to keep up at 100ms worst case update at redline? You got a pulse width module timer in that beast so you don't have to babysit digital output pins to drive the injectors? About the battery voltage... The original ECU tweaks the injector pulsewidth WRT battery voltage. Higher voltage opens injectors faster and all that. However, if I were doing this, I would probably switch to one of the pre-canned injector driver IC's that has the voltage correction built in. That would be one less thing to worry about and would be much more consistent than the stock system or trying to make that adjustment yourself. If you use something that has the fast opening peak/hold current control as well, then you can get rid of the injector resistors and run Vbatt right to the high side of the injectors. The PIC stuff was intriguing. I did maybe three projects with them, and it sure was a paradigm shift from the Motorola stuff. It took a little sideways thinking to figure out that branching stuff, but once I got a handle on it, I really liked it. It's like Whaaaat? Skip the next instruction? What the crap is that? You have to use goto's? I was always taught that goto's were evil. You need to embrace the goto. But guess what... The newer bigger PIC stuff has conditional branches just like Mot. Feels like home.

Haha! No kidding. Our controls were used prominently in petrochemical, waste water treatment, food processing, steel and other metals... Oh, and Jack Daniels. :laugh: And almost everything was Motorola based. So everything embedded you wrote everything yourself in C. I'm feeling better. I've got a software engineer buddy who scoffed at me the last time I mentioned assembly. He says I'm out of touch and that the compilers of today are so much better than they were even ten years ago. He says there's really no reason to write in assembly anymore. My back of napkin sketch included something from the Microchip PIC24 family. The smallest and simplest part I could get that had at least a 12 bit A/D and enough channels to digitize the analog stuff. Then I had a beer and used my napkin to catch the condensation, and I haven't seen it since...

BTW - I'm not poo-pooing what you've done. I think it's awesome. I'm just telling you what I would do.

Nice update Lenny. If I were doing something like this, I would write everything in assembly and do it without a pre-packaged operating system. For reliability (and liability) I would want to know exactly what that processor was doing at all times. No RTOS, No high level languages. No optimizing compiler. Nothing open source. Nothing fuzzy... I would want complete control over the horizontal and the vertical.

I'm no expert on the subject, but my thinking behind the concept is: The position of the AFM vain is directly proportional to the volume of air in. The volume of air in is directly proportional to the volume of air out. The volume of air out is directly proportional to the pressure in the exhaust manifold. Therefore: The position of the AFM vain is directly proportional to the pressure in the exhaust manifold. That's why I was thinking that the AFM position could be used as an indicator of engine load. Seems like it should be proportional to backpressure. I know the backpressure measurement is available and doesn't require any translation, but the thing is... What about exhaust system changes? What happens when you put on a free flowing low backpressure exhaust system? The air in doesn't change, but the pressure in the manifold does. My PO put on a huge diameter exhaust and a free flow muffler. I don't know if I even generate enough backpressure to close off the BPT.

Lenny, I think you hit the nail on the head... I got a big arse beer trailer, and apparently you do too. I don't pull light beer. :cheeky:

Wade, I might be missing something, but that doesn't sound right to me. At a fixed RPM, the air volume passing through the AFM cannot possibly be the same at easy cruise as it is at WOT. I guarantee that there is more air flowing through the AFM at WOT than there is at light cruise. That's the whole principal behind L-Jet! If it weren't for that, then the system wouldn't work at all. At a fixed RPM... More air volume through the AFM at higher throttle openings, more gas supplied by the ECU accordingly, and more power to the wheels as a result. L-Jet in a nutshell. Think about it this way... Cruising along the highway at steady speed. Come to a hill and have to press the gas pedal down farther to maintain that steady speed. What happened? The further down gas pedal allowed the engine to suck more air through the intake system (including the AFM). The increase in air through the AFM is detected by the ECU and it injects more gas accordingly. More power to the wheels as a result, and hence, steady speed even in the face of increasing load requirements. That's why I'm thinking the AFM resistance would be a good indicator of load.

Getting off a little into the theoretical... Wouldn't AFM position be a good indication if engine load? The more air in, the more air out, right? If one were to try to come up with an electrical representation of engine load, would AFM resistance be a simple option since it's already easily available? Just thinking that might be an alternative to exhaust back pressure as a means to determine and modulate EGR vacuum.

Wade, I went through all the documents you linked to and I understand the theory now. You just threw me when you said that it "disables EGR if backpressure is too high at low-to-mid throttle openings", because the BPT never disables the EGR for high backpressure, only for low backpressure. I'm sure it's just a confusing use of words. In any event, here's the concept for the rest of the readers who haven't figured it out by now... The 280Z EGR system uses vacuum to control the amount of EGR opening. The more the vacuum, the more the EGR valve is opened. The source of that vacuum comes from a small port (small pin sized hole) which is located up in the throttle body. It's location within the throttle body is in a position such that it provides little to no vacuum at idle or at WOT. That means that even without any other manipulation of the control vacuum, EGR will always be disabled at idle and at WOT. However, Datsun decided that simply being disabled at idle and WOT wasn't good enough and used the BPT to modify the vacuum signal profile between those two points to better fit the engine and/or emissions requirements. The BPT uses exhaust backpressure as an indication of engine load... More backpressure, higher engine load, more EGR is desired. Less backpressure, lower engine load, less ERG is desired. The BPT is a normally open valve that vents (bleeds off) the EGR control signal to atmosphere, thereby disabling the EGR system. The BPT valve will close as the exhaust backpressure increases and as the valve closes, the less the EGR control vacuum will be bled off, until you reach an exhaust backpressure condition such that the BPT valve is completely closed and all the available vacuum is fed to the EGR valve with none of if bleeding off to atmosphere. Thanks again Wade for points to info. Makes perfect sense to me now.

Thanks Wade, but that's not the case. I just checked the operation of the BPT and it works just like the manual says it should... At high backpressure it passes control vacuum to the EGR valve, but at low backpressure it vents that control vacuum to atmosphere thereby disabling the EGR system. Not saying it makes sense, but I just confirmed that's really, truly what it does. Thanks for the other info as well. I haven't dug into it, but I will when I get the chance.

Thanks for the thoughts Blue. The failsafe suggestion is backwards. What you suggested makes sense, but the valve works the other way. It enables the system if there is high backpressure, not disables it. If the exhaust is clogged or crushed, the higher backpressure would open the BPT and the system would be "happy". I'm thinking you're right about the waves and pulses. It's probably a second order phenomenon. The average exhaust pressure is way higher than the average intake pressure (duh), but there might be intake and/or exhaust waves that would reverse that situation for short burst transients. However... I wonder what is the speed of response of the BPT and EGR diaphragm is. I thought I read somewhere that the EGR will stay open for 30 seconds after vacuum is removed. I'll see if I can find that again.

So... About the EGR system. What's the theory behind the Backpressure Transducer (BPT) Valve? I know what it does... It disables the EGR system if the exhaust backpressure is too low. Question is "Why?" What would be wrong with having the EGR enabled even when the exhaust backpressure is low? Seems to me that it would simply recirculate less gas under low exhaust pressure conditions. Is there really a need to disable it completely under those conditions?

I had a failed oil pump, but the failure mode was low pressure due to being all chewed up inside. Wasn't "positive" displacement anymore. Was sort of "fuzzy" displacement... I can't imagine a pump failure mode that would result in pressure too high other than a stuck pressure relief valve or incorrect spring pressure. It wouldn't take a lot of movement on a main bearing to eclipse the oil feed hole and if that happens, you'll see a pressure increase. Not sure if one main would be enough to bounce off the relief or not. So I'm still asking chicken or the egg? Did the oil galley to the mains get plugged with something and starve the mains? In order to get to that galley, it would have to have been left in there upon assembly or it would have to make it through the oil filter (or be a part of the filter itself that let go). Or did the mains grab the crank and due to too tight of an initial setup and eclipse the holes causing a chain reaction? In any event, sorry it happened and awaiting the autopsy.

And for the original question... Yes, you can pull the entire distributor out by removing the two screws at the very base where it joins with the front timing cover and doing it that way should preserve the original timing because all of the timing adjustment mechanism(s) will come out with it still locked in place. There may be some tiny clearance in the screws that could account for a fraction of a degree or so, but nothing major. You're likely to introduce more change by having a new follower riding on the cam once you change the points. And as mentioned above... It's probably prudent to check timing and dwell when you're done regardless of how you do it.

You should have stopped there... It can't be inserted 180 degrees out of phase. The drive key on the shaft is not centered. It will only engage in one position.