Captain Obvious

I had the camera out so I snapped some pics of my original oil pump: Not sure what it ate, but it's obvious that something went through there that shouldn't have. :sick:

The reason I was asking about the RPM while timing is that I'm wondering if the wacky numbers you're getting are partially caused by the vacuum advance. The vacuum advance signal comes off the front carb, and it's a port driven signal which should be zero at idle, at it's highest vacuum a little above idle, and then fall off from there as the engine load increases and manifold vacuum decreases. At 1250 RPM, it's a toss-up if you're still running on the idle tubing feed to the balance tube or not. At idle, your flat tops should be dead against the factory set linkage stops on the front (radiator side) of each carb. The epoxy plugged Phillips head screws that the manual warns you not to mess with? You're still up against those stops at idle, right? I'm assuming when you said "TDC verified on the dampener" that means that your manually rotated your crankshaft until you had #1 piston at TDC and then verified that the timing mark on the dampener was in fact in lined up with the "0" mark on the timing gauge. Is that correct? So it won't even run at all unless your idle timing is set somewhere above 20 degrees BTDC. That's just not right.

Now who in their right mind would do such a thing? Don't people have better things to spend time on? OK... So I just went out to the garage and snapped a few pics from my collection: Purolator L10241: AC Delco PF1127: Note the separation at the seam where the original filter media was never glued properly at the factory: Here's a closeup of the seam separation: I used to be sold on AC Delco until I opened this one and discovered the open seam in the filter media. Then to make matters worse, they've since changed their internal construction from a metal support structure for the filter to a plastic cage. To each his own, but my current fave is Purolator. Anyway, good idea Bonzi. It would be prudent to open the one off the 280 when I get to that point.

Exactly. That's The Plan. Fingers crossed and all that. :paranoid: The only shavings I found in the pump were small slivers visible with an eye loupe (maybe 10X). There were no big chunks. What I found was small bits pressed into the gouges that were left in the rotor from whatever went through there. Think fillings in a tooth cavity. The previous owner did a rebuild of the engine, and from all I can tell, he was very good at cleaning. I'm not sure yet about other aspects of his rebuild, but I'm confident that he cleaned everything very well. In other words, I bet he cleaned out the pan and screen already. Hopefully this will be as simple as a new pump, and I think I'm going to change the oil and filter even though it's fresh. If that doesn't take care of it, I'm going to have to get into it way deeper.

Yeah, I've been all through the ins-n-outs of the power valves as well. Dug out the epoxy and played with the screws and all that. The reason I took mine off was that I was running very rich and I wanted to eliminate as many variables as possible. Then once I had them off, I realized that my car (other than foot hard on the floor) runs pretty good without them if you use the right needles. I mean, after all, without the power valve, the flat tops function exactly the same as the round tops. I tried round tops as well, and my performance was identical. YMMV. As a matter of fact, I modified a set of round tops to be a direct drop-in to my 260 so I didn't have to muck around with the round top linkages and return springs hooked to the heat shield. Granted, the extra idle tubing is a little cumbersome with the flat-tops, but there are advantages in that as well. The engineer in me sees the beauty in the functionality. But we're getting a little off course here with all the flat top talk... So, the bottom line is that unless there's some interpretation discrepancies on what your car is doing, I don't think round tops will solve your problem, but it will certainly simplify the engine compartment and hopefully make the problem easier to find. The timing issue is really perplexing... What RPM is the engine spinning while your setting the timing? Is it as a "reasonable" idle speed (like below 1000 RPM)?

Yes, the FSM has some pics, but they're lacking in detail and it's hard to figure out what's what. Here's one from the 72 manual, and another from 77. Only reason I know that the distributor shaft and drive gear are unfiltered is from looking at the pump design iteslf.

Thanks Jeff, I appreciate it! I'm hoping for the best. On that subject... Do you know off-hand what is lubed pre-filter? Just the distributor shaft and oil pump itself? Everything else is post-filter?

Well I still can't explain ON-OFF shuddering with any carb problem. Especially since you've got the correct fuel level in the bowls. I know from experience that once my bowls are up to the proper level, my car will idle for maybe 30 seconds to a minute or so with just the fuel that's in the bowls. And the when it finally reaches the point where the fuel has been sucked down to the point where the nozzle just can't pick up fuel anymore, it sputters a little bit until it just can't sustain running any longer and finally stalls. In other words, even under that situation, I get a slow painful gradual death. Not a "lights out - no wait... lights back on... lights out again" kind of thing. Once you've got fuel in the bowls, you've already made it past the smallest of the orifices. The fuel is pretty much home free by that point. I dealt with my power valves by eliminating them and I do think I'm a little lean at WOT because of it. I'm running early round top needles in my flat tops because they're a tiny bit richer, but not enough to make up for the loss of the power valve at WOT. The car starts instantly and runs great and if I put my foot to the floor, it doesn't fall on it's face, but I think it should go a little better. So again, like my plugged EGR port, it's a lower priority for me right now. What makes you say you need new floats? You mangled them a little trying to get that $*%@#@#$ float pin out?

Funny you mention that... Mine looks like shavings were forced through causing damage in the form of dents and abrasions in the rotor and body. :laugh: I didn't even bother to measure anything. I'm assuming that something grenaded inside the engine at some point in the past before I owned the car. Under magnification I was able to pick out some small chips that were still embedded in the rotor assy. I don't know what they were from, but I can tell you that they were non-magnetic. Probably aluminum, so best case is that they were material torn off from inside the pump body itself. It's pretty gruesome. So, I understand that the oil pump might not be the only problem, but after seeing inside the pump, it's clearly at least part of the problem. At this point, I'm hoping that any debris that made it through the pump got caught up in the oil filter and my "plan" is that a new pump will take car of it without having to rip the whole engine apart. I've not yet even had a season of enjoyment out of this one yet! The PO did a rebuild on the engine shortly before I bought the car, and although I'm always skeptical of anyone's work other than my own, I'm inclined to believe he knew what he was doing. Curious though with all the money he spent on the motot that he did not replace the oil pump. Anyway, used cars are always a crapshoot. I'm hoping that a pump will fix it, but I'm aware it might not. Brand independant? No-name ebay is just as good as genuine Nissan? Anything from RockAuto is good too? And SteveJ, those search results are light-years better than what I could turn up. Thanks for the tip.

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.