Captain Obvious

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.

Woof. That sucks... Hope you get to the bottom of it. Hoping to help in that endeavor, I'm no hydraulics expert, but I think you can rule out filter bypass problems. The purpose of the bypass on the filter is that as the filter gets dirty, the pressure required to force oil through it goes up. If the pressure differential between inlet and outlet of the filer gets too high (like in the event of a badly clogged filter), the bypass valve will be forced open and unfiltered oil will pass around the filter instead of through it. The engine will still get oil and the theory is that even unfiltered oil is better than no oil at all. There is a filter bypass valve built into the block, and most commercial filters have one built into the filter themselves. All that said... The opening pressure differential across the filter required to open the filter bypass is only a couple psi. I didn't look it up, but probably about five psi or so. Remember that you're only concerned with the differential between inlet and outlet. The absolute pressures don't matter. The point is that a clogged filter should not result in significantly higher oil pressure. The pressure increase even from a completely blocked filter should only be the pressure required to force open the bypass. Here's a snippet from the FSM that shows the lube scheme. You can see the pressure relief valve in the pump and the bypass valve on the filter: As for the pressure relief valve getting plugged with something? I doubt it. It's built right into the pump and essentially short circuits the pump. If the pump pressure gets too high (and we're talking absolute here) it will force open a valve that connects the outlet of the pump back to the inlet. The passages are large and if you've got a goober in there big enough to clog them, then you've got other serious issues. The valve might stick shut, but I'd be surprised if it got clogged shut. My theory is that as your bearings started to weld and the clearances went away, you started bouncing off the pressure relief in the pump. Prior to that time, your pressure was limited by the bearings, but when the bearings went south, the pressure went up until the pressure relief took over. Maybe you spun a bearing or five and blocked the oil supply holes to the crank as a result? Is that even possible? My condolences...

Yeah, the ad is NOW $30K, but it was $300K. I figured it was a typo and it sounds like he fixed it. I agree... It is conceivable that it's a $30K car if it's truly "mint".

Haha! It's fresh in my mind because I too underestimated the value in clean battery terminals myself in the recent past. The tricky part for me was that the oxide that had built up on the posts and lugs was a very hard, dark grey non-conductive coating. I had "cleaned" the terminals on several occasions, but was still having issues. The corrosion was "lead colored" and very difficult to see. It wasn't the soft fluffy white stuff you usually find.

Duplicate post

Haha! Ya don't say... There's some stuff in there that really doesn't look right to me. I'll work up a pic with some numbers on it so we can refer to hoses by name or by number. In the meantime, you really need to check your float bowl setting. Use a mirror and a flashlight and see if you can get a peek. Take off the fuel supply line and large hose between the air cleaner and engine side of the carb for more room if you need it. What's the hard-line to the turbo? Is that oil?

Haha!!! Nailed it!! First reply!!

Just took a quick look back, and I believe the Amp (TE) P/N is 825213-(color). 35-Pin "Junior Timer" series with 90 degree board mount. Price wasn't as bad as I was imagining... At quick glance at a few suppliers, Digikey was the cheapest and says they have them for a little over ten bucks with a min purchase qty 0f 176.

Haha! Yeah, but after me, Len, and Fastwoman install them, what's Len going to do with the other 9997? I recently rebuilt my FI harness with new connectors and while perusing catalogs, I saw the connector that mates with the ECU. I didn't quote it since I didn't need it, but maybe I'll look into the cost just for entertainment value.

Yeesh. You got full vacuum going to the CARB system. You got ported vacuum going to the intake manifolds which makes no sense. No idea what happens when that turbo spools up and pressurizes the intake. You got PCV coming off the top of the valve cover instead of the side of the block. I can tell you that fitting you've got uncapped (and the screw adjust that goes with it) was originally used to control idle speed. No idea what they're doing with it now though. The uncapped hole (I think it's the one you're talking about) looks to be a air bleed. Don't know why you would need one since you've already got such a thing built into the carb. What's the origin of that system you have? Is that a homegrown thing, or was it available as an aftermarket kit?

Superlen, Forgot something... What about the mechanicals? What's your plan on where is that going to come from? Are you thinking you'll harvest and re-use the case and connectors from original ECU's or are you thinking that you'll buy new connectors and fabricate a new enclosure? Have you priced the mechanical stuff? You won't be happy.

Superlen, Admirable task. My advice would be to start small and just get something that will drop in and run. Add all the other stuff like the ability to tune and use MAP for later. Don't include data logging. Skip the CAN bus and don't mess with the AAR or cold start. Run open loop with no O2 feedback, and set it up for the stock throttle body. Once you get to the point where you have one that drops in and works, then start adding features. And BTW... Personally, I would completely skip the "copy/save/email tunes back and forth between users" thing. Completely unnecessary complexity. I actually started a project like this myself, and it's fate has been the same as your project to date, stalled due to life. I know the OEM fuel injection system pretty well, and my car is running pretty well accordingly. I've unfortunately got other things on the car that are crying for more attention than a FI system that's working.