Captain Obvious

First off, let me acknowledge that I'm sure this question has been asked a hundred times, and yes, I've searched. But unless I'm missing something, the search capabilities of the forum leave a lot to be desired.** So, I want to replace the oil pump in my 77 because I've got low oil pressure. I've checked the pressure with a mechanical gauge, so I know it's a real problem and not simply a sender or gauge issue. I've truly got low oil pressure. I don't know yet if it's the sole source of my problems, but I've pulled the oil pump out and it doesn't look too healthy inside. Any recommendations as to which oil pump to use? Direct year replacement? Higher volume ZX pump? Cheap ebay no-name? Datsun genuine? Melling? NAPA? Doesn't matter, they're all the same? I understand the differences between higher volume and higher pressure, and I understand that pressure and volume will be related if you're not bouncing off the high pressure relief inside the pump itself, so what's the deal? Why would I want either of them? **[RANT]Searching for oil pump turns up every post with either the word "oil" or "pump" in it, which is just about every post this forum has, including every fuel pump post. Searching for "oil pump" (putting quotes around the two words intending to force an exact string) does nothing different than without quotes, so I can't seem to force the word "oil" to be followed by the word "pump". Negative keywords like -fuel don't seem to have any effect. And there's no hints, helps, or anything like that which I could find, even on the advanced search page. So, am I missing something? [/RANT]

My temp switch failed closed (warm), so on my 74 the EGR system is always active. But since the passageway in my balance tube under my EGR valve is caked shut with almost forty years of crud, my EGR system isn't doing anything anyway. It's on the list of things to take care of, but it's lower priority than some other items. OK, so with just one set of points, there aren't any intentional temperature related timing changes. I'd like to back up a little bit because I'm a little unclear... What problem exactly is it that you're having right now? I understand that the car was working great for the last few months and then one recent day, you left work for lunch and some problems started. The problems got worse after lunch and when you got back to work, it died and would not restart. That much, I got. So is the car still sitting in the parking lot at your work? I know you can get it started by severly advancing the timing, but does it even run well enough to drive? Or does it just sit there and idle roughly until it sputters and dies? Haha! I hear ya on those float pins. I hated that design flaw so much that I modified mine so I would never have to go through that again. That's just one of the improvements I made during my long fought battle with my flat tops.

My point about the cat is that now realizing you have one on your car, all of your dyno sniffer diagnostic results are suspect because they aren't a true representation of how the engine is running. Basically, they dyno sniffer is telling you what's coming out of the tailpipe after the cat has modified the composition of the gasses, not what's coming out of the engine. That's why Blue said if you want a true representation of what's going on, you have to sniff between the engine and the cat. I'm not up on cat theory, but I do know cats will affect HC and O2 values. Here's your dyno sniffer results. Maybe someone who knows more about emissions can wade through this with the understanding that there's a cat installed and can provide some insight accordingly? For starters, knowing full well these readings are downstream of the cat... Does this look rich, or lean? 15 mph: HC-263 (too high), CO-1.8 (max-0.5), CO2-13.0?, NO-335?, O2-1.3, MPH-15.3, LOAD-134.3? 25 mph: HC-152 (ok), CO-2.5 (max-0.5!), CO2-13.3, NO-130, O2-0.3, MPH-25.3, load-74.6.

I don't know how your temp switch pooched, but on the 240 and 260, the temp switch is supposed to be open when cold and closed once the engine is warmed up. If the temp switch failed open (cold) then your EGR will never actuate. If the temp switch failed closed (warm), then the EGR system will always be active. Important to note however, that even though the EGR system may be "active", it does not necessarily mean the EGR valve is "open". That's because the EGR uses a port vacuum source off the rear flat-top. You can reach up under the EGR valve hat and manually lift the diaphragm which should open the valve. If it's already open at idle, then you've got a problem. Conversely, if you lift it and there's no effect whatsoever, then your balance tube is plugged with crap from the EGR system (that's what I've got). You can leave it that way if instead of removing the EGR system. Looks perfectly stock, but doesn't do anything. One other thing to consider though... I've got a 74 manual trans which has the single electronic pickup in the distributor. You've got a 73 and you have points. How many sets of points do you have? One or two? I haven't refreshed my memory on the 73, but IIRC, the temp switch controls which set of points are used. Just seems to possibly correlate with the timing issues you're having. Yeah, I understand about the flat-tops. I've done extensive work to mine as well and after a long fought battle, I finally prevailed. That's why I just can't see anything that could possibly happen with the carbs (round tops OR flat tops) that could cause ON-OFF running like what you described. I mean, if you've got fuel in the bowls verified through the sight glasses, then there isn't anything that could happen inside the carbs that could cause that. People get all uppity about the flat tops, but inside, they really aren't that much different than the round tops.

Your plan of attack seems sound. Especially the step where you go crazy. I remember from earlier posts that you had swapped the distributor for another and there was no change, but I didn't realize you had swapped Pertronix for Pertronix. I suggest that you try an old school OEM non-Pertronix distributor. Whatever configuration is original for your year. I don't see how the distributor could make you run leaner at midrange... Richer maybe (if you're getting a lean-misfire), but not leaner... But changing the distributor might reduce the popping effect of running lean in the midrange. Did I say that right? Does that make sense? What I'm saying is that maybe between ZT's recommended additional turn of richness over the entire range and a different distributor, you might get better results. With the port vacuum advance source that we (normally) use, midrange light cruise is where you would have the most amount of distributor advance. Higher than at idle, and higher than WOT. Light to midrange cruise would be the most advance. I know that you're not running any vacuum advance at all, and I'm saying that maybe you should? Also, I've got a set of round top insulators and gaskets that you're welcome to borrow if you don't find a set to purchase outright. Shipping couldn't be more than a buck or two. Just LMK.

I'm not getting it either. The black smoke says rich, but those plugs look lean. Here's a question for ya... You're in CA, right? Have you got a catalytic converter on your car? If so, how does the cat come into play with your exhaust sniffer results? Is it conceivable that the sniffer results at the tailpipe exit are very different than the composition going into the cat?

Also, forgot to ask... What are you going to do when you get the carbs back from ZT and the exact same problem still exists? What's your plan of attack?

Yeah, I guess that was kind of a rhetorical question in that I already knew the answer. I have no doubt that you would have posted results if you had tried that I'm also assuming that the "shop car" at ZT was used to test the carbs under load, right? Not just 4500 sitting still, but 4500 at light cruising load... I've got a set of round tops that I'd be glad to send for a trial, but I made some customizations and they won't fit your car. They're a direct drop-in for my 260, but if you try to put them in a 240, you'll have linkage problems. (Kinda the opposite of what usually happens when you try to put round tops on a 260.) C'mon folks! Someone has to have a set of carbs they can send to Zedyone to try.

So, while you were waiting for ZT, did you try a different set of carbs on your car?

I'm going to buck the trend... I don't think you're looking for a fuel related issue here. Especially with what you described below: I agree with your initial inclination and believe that you've got an electrical issue of some kind. Intermittent something, maybe heat related? Coil? Condenser? EGR valve hanging wide open when it shouldn't? Also, are you sure about those timing numbers? If those are your "at idle" numbers, then you've got something out of whack. Haha! That's Datsun's way of punishing the non-believers.

Whew! I've got a 74 260 and I've been all over the water temp switch circuitry for that year and I thought I had it all figured out. Then you go and throw that spanner in the works. :eek: Anyway... Cool. All is right with the world. I agree with you in that for the cars without EGR, it sure is a lot of complexity just to add six degrees of advance until the water temp comes up. I guess those are the kind of hoops you have to jump through to meet ever tightening emissions standards?

Zed Head, I'm really sorry, but your post is confusing the crap out of me... You're saying that you've got a 74 260Z stock from the factory without EGR? What did they do to cap the EGR port on the balance tube? And it's a manual, but it has a dual pickup distributor? I thought only the autos got the dual pickups in 74?

It seems to depend on the year, but from what I can tell, Datsun always used the water temp switch for the same two things... Ignition timing control, and EGR control. Basically, Datsun didn't want the EGR to kick in until the engine was warm, and they also used the switch to retard the timing on certain models (like auto trans in 74 for example) once the engine was warm. If you don't have any EGR stuff, then you sure don't need it for that, and I have no idea if the ZX ignition modules even have an input for a water temp switch. Looking at the manuals, It looks like they did away with the dual pickups in 77. How many pickups in your 79ZX dizzy?

Haha! Yes, you should look for other ways to improve cold starts. I thought horns didn't do anything for you until you get up into the higher RPM's where the air velocity into the carbs is a lot higher than at idle or when cranking to start? Could there be an effect at cranking or idle air velocities?

It looks to me like the 76 CA cars only have one distributor pickup, so I don't think the water temp switch has anything to do with ignition timing like it does in the rest of the states. It still actuates the EGR though once the engine has warmed up. So, is there a possibility that a faulty water temp switch can cause the car to stall out a couple of minutes after starting? I'm not coming up with any good theories of what a non-working switch would do to stall the car, but I can see a WORKING switch causing problems when the EGR system kicks in. Do you have a copy of the FSM? Maybe you can take a look through and see what else that switch does on a 76 CA car. Like I said, I'm no expert on the 76, and even less of an authority on CA cars. Yeah, I figured. I wasn't sure either until he said it was $60 and NLA. At that point, I knew for sure.

xubuntu, Point taken on the AAR issue. I don't think anyone here knows just how much adaptability the ECU has to compensate for something that is really out of whack. Theory is that the AAR can't possibly affect mixture ratio, but it wouldn't be the first time that theory differed from real world. rcb280z, Sorry that doesn't add anything to your quest, but I wanted to get that out there.

You are talking about the water temperature switch, not the water temperature sensor. I'm no expert on the 76, but I took a quick look at the 76 FSM. The water temp switch is closed when cold and open when warm (above 135-145 degrees F). It might do more than the below, but in my quick look I turned up two things the switch does: 1) As described starting on page EC-10 - When the switch is cold, the EGR system is disabled, and once the switch warms up and opens, it will enable the EGR system. 2) As described starting on page EE-26, it controls which of the two ignition pickups are used for non-California models. Non-CA models will used the advanced pickup when cold and the switch over to the retarded pickup once the water temp switch warms up and opens. There is supposed to be a 6 degrees timing difference between the two. You didn't say exactly what went wrong with your water temp switch, but if it failed short (cold), then your EGR system will never become active and you will always run using the advanced ignition timing pickup. On the other hand, if it failed open (warm), your EGR will always be active and you will always be using the retarded ignition pickup. So, your original question... Yes, the car will work without it, but you'll have to decide if you want it to fail "cold" (closed) or "warm" (open).

Zed Head and Willoughby Z, Thanks for the reality check! I didn't even think of the possibility that a previous owner took that stuff off my 77! I already saw that someone before me pulled the EGR system off, and it now seems they pulled the TVV and that heater block off as well. I'm not a fan of the fan either. Here's my plan A... Like I said, I've not yet owned this 280 through a summer yet, so I'm going to play ostrich and hope it doesn't get me. If that doesn't work, the second thing I'm going to try your trick of fooling the ECU into a richer mixture.

xubuntu, It sounds like you (and the guy who wrote that page) are overestimating the power of the AAR. The AAR can not make you run lean. It does not affect mixture. Ever. All it does is boost the cold idle RPM's by providing a temporary air path around the throttle body butterfly plate while the engine is warming up so you don't have to sit there with your foot on the gas to keep it running. There is no difference in operation between pushing down on the gas pedal a tiny bit with your foot and having an open AAR. Unless you push your foot down far enough to open the idle switch on the TPS, then the ECU does not know the difference between your foot and the AAR. If you are running lean on cold idle, it's not the AAR's fault. It simply cannot do that to you.

Good luck with the testing!

My guess would be that the extra heat comes from a bunch of stuff: The pistons, the head, the cylinder walls, the valves, and yes... the exhaust manifold. When the engine is running, parts of those things are much hotter than the water (hence the fact that they are cooled by the water), and when you shut off the engine and stop the water flow, everything will stabilize to a higher temperature before decaying over time. But my point about conduction is that I'm skeptical that the heat being conducted from all those sources would travel any faster to the thermostat housing than it would to something located near the spark plugs. I would expect that energy would conduct at pretty much the same rate in every direction away from the heat sources. What's an AAR pad heating line? I've got a 77 and I don't have any water going to my AAR. Did they put that on in 78? Thanks to Blue, I've been messing with AAR's lately and he told me that later Nissans included the provision to heat the AAR with engine coolant, but I didn't think he was talking about Z's. I thought he was talking about newer stuff. Just remember that the AAR might mess with your idle speed, but it shouldn't do anything to change your mixture ratios. Remember, you're already downstream of the AFM. BTW - Something else I discovered recently while poking through the parts fische was that Canadian Z's included an insulating jacket on the outside of the AAR. Kind of a little "AAR cozy", eh?

Pure speculation of course, but I'm not so sure close proximity to the exhaust manifold is the problem. I would expect something sitting right on top of the manifold might get a little hotter than something screwed into the head on the plug side, but I'm skeptical as to how much difference there would be. I suspect that the efficiency of conduction will mostly overrule even close proximity convection. By that, I mean... I bet that when you shut off the engine, the heat soak will raise the temperature of everything. But that big hunk of metal and the water that's inside it are excellent heat conductors. Way better than the air between the exhaust manifold and the thermostat housing. I wouldn't expect a big difference in temperature between something screwed into the thermostat housing and something screwed into the plug side of the head. Speculation only. I'm not an ME and thermodynamics made me, well... :sick: Nice!

Why? Because I can. Seriously though... I'm not sure my OEM stuff IS working as it should. I'm running rich and for all I know it might be a leaky cold start injector. Honestly, I don't think that's the problem, but if I didn't even HAVE a cold start injector, I could cross that off my list, right? It would just be one less potential leak source, and a little less plumbing and complexity. Just a slightly simpler, cleaner system without it. Granted, not a huge difference, but every little bit helps. Thinking about it some more, the truly elegant solution to fooling the ECU into sending more fuel would be to use the thermotime switch to actuate a NC relay in series with the CTS. That way, it would energize and open the NC relay under the same conditions that it would previously have actuated the cold start injector. (Did I say that right?)

I disabled my cold start injector a little while ago by pulling off the electrical connector. Just to see how the car would perform on cold starts without it, and decide if I really needed it or if I could do without. I've not used the car much since I disabled it, but the results are not that dramatic. The cranking times when "Pennsylvania cold" are definitely longer than with it connected, but they are not "objectionable". I'm assuming that if I were in Canada or Wisconsin, I wouldn't be able to get away with this, but here in PA it seems to be OK without. This is a fair weather car for me anyway and I don't expect it will get a lot of winter usage. I'm thinking I may remove it completely and get rid of that complexity. Pull it off and cap the holes. What say you? Anyone else disabled theirs and have advice to share? I guess I could use a switch to temporarily insert a fixed resistor in series with the CTS to fool the ECU into adding extra fuel through the injectors if I find the cranking times unacceptable. This winter hasn't really been a good test of cold weather starts...

I like it. As good a theory as the others I've heard to date. I picked up a 280 recently, but since I bought it in cold weather and haven't owned it through a summer yet, I haven't had the pleasure of dealing with hot starts after that heat soak. I'm assuming that this summer I'll be in the same boat as the rest of you guys. I've been paying more attention to the "hot start" threads than I used to. You know, if the only thing you're using your pot for is the hot start, you could measure the resistance you need to fool the WTS on your hot start and then replace it with a switch an fixed resistor instead. Two positions on the switch: "Normal Start" and "Hot Start". Simply short around the resistor for "normal" and open the short for "hot". That way, you wouldn't take the chance that you are messing with your mixture at other pot positions. (Unless, of course, you want the ability to do so. )