Captain Obvious

Haha! Read? Who said anything about reading? I figured it would take me 1000 hrs to reverse engineer the whole thing. :pirate: So. Simply out of misplaced academic interest... If one WERE to switch over to a new technology system like this on a stock engine, what would be the expected improvements? Should there be improvements in performance, economy, drivability, emissions? All of the above?

Haha! Against my better judgment, I clicked. I knew I shouldn't have, but I clicked anyway. :stupid: You know there's absolutely no way I could buy this thing and not spend 1000 hrs figuring exactly how it works and why. And then another 1000 hrs with the custom design improvements. I need another project like I need a hole in the head!! Yeah, that would be an interesting question in PA. The car is old enough that it is completely exempt from emissions testing, but I'm not sure how PennDOT would interpret an old car with a new system. I suspect they wouldn't care. Old enough to be exempt? Then it's exempt. That would be my guess.

Thanks for the wayback. I'm not surprised at all that our old L-jet can't compete with modern systems. The advances in electronics since our system was made are simply astounding. Today, one could probably completely replace our entire ECU with a small microcontroller and a couple external components to handle the current required by the injectors. A project I would love to take on... But probably never will. :classic:

Yeah, I understand completely. I don't fault you one bit for trying the seemingly unrelated. I'd be trying anything by now as well. Something else I forgot to ask a while ago... I wanted to confirm the circumstances of the mid-RPM misfire. Does it occur only under light load (like when you are cruising along at a steady speed at 4500 RPM-ish) or does it occur under no load just sitting still with your foot a little bit on the gas pedal? (Or both?) Thanks for the needle info. I've been messing around with my flat-tops and have measured a few different needles recently including the N-27. I should probably post my findings sometime.

A quarter inch out of spec might be enough to be noticeable, but what could a low bowl level do to mid-RPM cruise that wouldn't be worse at high RPM WOT? Hey, I forgot to ask you the other day... When you bought OEM stock needles, what needle number did you buy? Do the new needles even have numbers marked on them? My round tops have N-27's but I believe they ran a couple different numbers over the first few years.

I was assuming 3 and 3, but I was just looking at the FSM and the dropping resistors (6 Ohm) are grouped into 4 and 2. Who knows why, and who knows if that situation continues into the ECU... Seems like it would have been much better from a manufacturing standpoint to use two identical 3 packs of the same resistors, but who knows? Maybe they were able to share the 4 resistor pack with some 4 cylinder engines and the 2 pack is the outlier? I guess as long as they aren't getting anywhere near what the driver transistor is rated for, it probably doesn't matter if it's 3/3 or 4/2. The whole batch fired thing kinda makes me wonder why they didn't just run one big honkin' wire from the ECU to the engine and then split it up there into smaller wires for each injector. Seems like it would be a lot less copper. Maybe they were planning to go to individual injector control at some point and wanted to be ready? Why am I stirring around in the FI pot? Because I just bought a 280 and have to restart all my learning curve over. I just got my head wrapped around the carbs, and now I have to start all over again from practically zero. This one is at the house now... Can't wait for you to see it.

cygnusx1, At the very end of that thread, you mentioned a L-Jet Lobotmy and attached a .zip. What's that all about? http://forums.hybridz.org/index.php/topic/95316-braaps-l6-efi-induction-advice-and-tips/page__st__20 I'm not a member over there... What was that .zip file?

FastWoman, Yeah, I'm very pleased with the collective's opinions of the stock system. At this point I'm planning to do what you suggested and fix what's there. I was expecting more "It's junk. Switch to SU's" kind of replies and I'm very happy that didn't happen. I've done nothing with it yet, and will probably have to wait for warmer weather. First order of business was to decide which horse I was backing. So they're IC's in those packages? Do you remember if you recognized any of the numbers? Something that you could get today in DIP form perhaps? Those flying saucer heat sinks weren't all that unusual... Back then. Heck, there might even be some germanium on that board! Hey, while you're here, what's your take on which pair of cylinders the injectors open on? Luck of the draw when you start the engine "that time" on which pair? I was originally thinking about that when I saw your post in the 280 starts then stalls thread where you were talking about the spark events: http://www.classiczcars.com/forums/showthread.php?44646-76-280z-Starts-then-stalls The question I have is WHICH 3 sparks? Yeah, I saw those too. The big TO-3 transistors using the chassis as a heat sink. If I'm seeing it correctly there are two of them running three injectors off each. I know from the FI bible that they are low side switches so they are open collector outputs dragging one side of each injector to ground to open them.

More great stuff. Thanks everyone. My 280 runs pretty well, but the idle is too high and the fumes are stinky over the entire driving range. Before I spent time trying to see what I could do with the original system, I wanted to figure out if I would be better off working on the L-Jet, or if I should cut the cord and spend that time replacing the system with something better. Not surprisingly, it seems there are some gains to be had with a newer technology replacement. What is surprising however is that the original system still has a good reputation and the gains to be had by newer technology are not that dramatic. The original analog system, if working properly and as intended, seems to have stood the test of time.

Another question... The system is batch fired and all six injectors open at the same time once per engine revolution. The timing on this is accomplished by picking off a signal from the ignition coil. The ECU pulses the injectors once for every three spark events. The question is... Which three spark events? The injectors could seemingly open on sparking 1+4, or 2+5, or 3+6 depending on how the engine ended up when it shut off last time? Luck of the draw on which pair? Probably doesn't matter, but just unusual by today's standards that the ECU wouldn't have an absolute timing mark in addition to the relative one.

Excellent! That's some great stuff! I haven't dug through all of it, but it's clear that it is in fact analog. Dig those metal can transistors with the flying saucer heat sinks. Very 70's. :laugh: I don't see any trimpots or other adjustments for calibration. They must have been pretty consistent. I would have expected some factory adjustability. The pictures of the L-jet on that geeky probing site are very different than the ones you posted. I'm guessing that there were different variations of the L-Jet over the years but the basic block diagram is probably similar for all of them.

I'm having a little trouble justifying a typical vacuum leak. You said your idle is perfect, and I would expect the impact of your typical "constant" vacuum leak to decrease as you give it pedal. That's why I was trying to think of more atypical vacuum leak sources that might get worse off idle. Well whatever you find, I'm pullin' for ya!!

Yeah, the PCV "rattle" and blow through tests only goes so far. Capping it and going for a drive would be a better test. What happens when you go more than 3 turns out on the nozzle? It goes so rich that the car won't run at all? I'm with you on the exhaust leak and fuel delivery stuff. If you are OK at full throttle, then it's not fuel delivery, and anything downstream of the exhaust valve (like a headpipe leak) isn't going to give you any significant performance impact. Popping noise maybe, but no performance changes. So. Let me jump ahead a little just for cuiosity... So you put the wideband on and it shows you are very lean at midrange. What are you going to do then? And conversely, if the wideband shows you are very rich at midrange. What then? What's "the plan" in either event? :bulb:

sblake01, I'm not sure what you meant by "nothing but circuit boards" and equating that to an analog design. Both an analog and a digital design could utilize a circuit board. "Digital" doesn't have to look like a PC. You're right about 'micro', but it's time relative, right? Haha! So, just to be sure. Another way to ask the same question... Are there any software programmable devices inside that box, or not? Z train, is this the post you were talking about? http://www.classiczcars.com/forums/showthread.php?36903-280Z-ZX-ECM-tech

Thanks all. That's exactly the kind of info I was looking for. I'm not surprised at all that newer systems from today are much better than the L-Jet using technology from the early 70's. And it also makes sense that the stock system will run out of adjustability if you make significant enough engine modifications that it's not expecting. Another question... Is the L-Jet brain analog or digital? In other words, is there a microprocessor in there, or is the whole thing done analog? I suspect it's digital, but just have to ask. I just bought a 280 and now I gotta start my whole learning curve over again.

If the 280Z fuel injection system is in good shape and is working as originally intended, do people consider it a "good" system? Another way to ask that question is... If everything is working properly, is there any reason to be wanting something different or is the original Bosch system the best choice for a stock 280Z motor? I do see people pulling the FI system off and replacing with carbs, but that seems to only be in cases where the FI isn't working properly. What about when it IS working properly? Do people feel the reason to change to something else? I assume the FI system is expected to: Provide better gas mileage vs carbs. Provide better drivability over seasonal temperature swings vs. carbs Produce lower emissions vs carbs. What about performance vs. carbs?

72 FSM (EF-26) says to use 10W-30, but not SAE 30. They must have expected that SAE 30 would be too thick when cold, but the multigrade would be suitable. As for the evap system, I just refreshed my memory on the early (flow guide style) systems and after further review, my mistake... I cannot come up with any reasonable explanations how the (early) evap system could cause any extra air around the carbs into the engine. Later carbon canister style, yes. But the flow guide style like what you have? No.

Yeah, I'm with you. I would expect that "SU oil" would be perfect for the SU's!! I haven't downloaded all the different years of FSM's. I got 72, 73, and 74, so I don't know what 71 calls for. Another straw... I just noticed in your sig that you've done some changes to your evap system? What can you tell us about that? I can imagine scenarios where the evap system could allow too much air under certain conditions but still appear to be working correctly at idle.

The bowl and lid were designed such that they cannot be assembled properly if the pin is out of place. If the pin were so badly out of place that it had slipped completely out of one hole, then the pin would hit the bowl during assembly and you wouldn't be able to get the lid on flush. As for damper oil... The 72 manual suggests 10w-30 and the 74 manual suggests 20 weight or 10W-30. No kidding! I know I'm reaching, but I wonder if there's something wrong with the PCV system somehow. The PCV is supposed to allow a pre-determined "unfueled" amount of air around the carbs, but it takes manifold vacuum in order to make that happen. Because of the way the PCV is designed, if there's not enough vacuum (like maybe when you are at part throttle), the PCV will pass too much air. Maybe you could cap of the PCV for a test run just to see what happens? Capping it will richen your idle mixture, but once you get off idle the change should be small enough that it won't matter much.

Gotcha. Check valves ok. I don't know what cleaning the damper and dome could possibly do to help your situation, but if it helps, then more power to ya! Maybe they are binding in there or something? Only binds when engine vacuum pulls the pistons toward the engine? I know... I'm reaching here, but like I said, I'm no expert! As for swapping needles, I've found from experience that a small change can make a noticeable difference. I'm running custom modified flat tops and have tried a couple different needles. You'd think that one thousandth in diameter wouldn't make that much difference, but from experience, I can tell you that it really can. You should notice a difference between stock and SM needles. The SM needles are .001 to .0015 richer than the stock (N-27) needles at mid-cruise, which is where you are probably running at steady cruise 4500 RPM. In other locations on the needle, the SM's are even richer than that when compared to stock. Short story? If you end up being lean with the SM's then I don't know what to tell you. Shouldn't happen... All will become clear once you get the wideband installed, right?

I'm no carb expert either, but when you're talking about transition/acceleration issues with the SU's the discussion traditionally turns toward the damper function. I saw above you are running standard issue SU oil from MSA. One would hope that is suitable. I assume you have verified that the damper oil level is up to the proper level. Have you verified that the dampers actually work? I've seen some that look fine, but don't actually "damp". The check valve has worn or the shaft has misaligned to the point where the check valve don't check. Stick a finger up your carb and lift each piston. They should be hard to lift. Hard enough that it leaves an impression dent in your finger. Let it down and lift again. It should fall instantly, and be hard to lift again. And both carbs should be about the same. You're running SM needles in a mostly stock 240, right? Have your standard needles arrived yet? It sounds like you're lean at midrange, but it would be hard to believe you're lean with the SM's in there. They are richer than the stock needles. Maybe a plug chop at the offending RPM? Run it at your sputtering RPM for as long as you can and then do a plug chop. I don't think it would tell you anything if you're lean, but you might see some black fluff if you are rich.

Walter, Thanks for the response, but I've got to admit that I have no idea where you're talking about... The EGR pipes comes off the exhaust manifold near the rear of the engine, not the front. I'm not aware of anything having any relation to the PCV system back that far. PCV in the front... EGR in the rear. Have you got any pics of the area you're talking about?

Hey Blue, Do you have a pic of the filter mesh? I've not seen that one yet. I currently have my valve cover off because I'm messing with my oil spray bar and I saw a little of that milky emulsion stuff on the underside of the valve cover casting. I've got no reason to believe that I've got any had gasket issues, but was wondering what was up with the water where only oil should live. HealyZ, I don't think the PCV system lends anything to engine life. From what I remember, it lends to ROAD life because cars aren't all dripping condensed oily residue onto the roads and softening the surface. And the only thing it should have to do with operation is that since the PCV passes un-fueled air "around" the carbs, you may run rich if you plug it without dialing the carb mixture back to compensate. (But, I'm no expert on the topic! )

Yeah, me too. That's what I meant about how it doesn't matter how far the holes are from the cam if the tubes fall off, right? And you're right about the holes in the billet bar... They might be drilled at an angle. I don't know either. Seemed weird to me when I was looking at my rickety stock bar, but the holes are angled downward. If anything, I would have expected them to be angled a little upward to increase their range, but I double and triple checked... They point down, not up. It's not much, maybe ten degrees below horizontal? I'm well into my spray bar redesign and reconstruction. I'll take some pics and stuff and try to post them if things turn out right.

So I'm guessing that nobody seems to think it matters at all? Does anyone care that the holes in the original spray bar do not shoot out straight horizontal, but are in fact angled down a little on purpose?