FastWoman

You're quite welcome, Darom! Yes, when you keep adding fuel, the engine will start choking, and both vacuum and RPM will fall. There's a sweet spot where the mix is just right and will maximize vacuum and RPM. I try to figure out the limits of adjustment where the engine starts dropping off on the lean and rich sides. Then I adjust to the middle, just a tiny bit towards the rich side -- maybe 2/3 into that adjustment range. So are you saying your engine does need additional resistance in the CTS circuit to richen it enough to reach that peak of 17 in Hg, even after replacement of the fuel pump? If you're still adding resistance, how much are you using? Just curious. I also had my fuel pump fail, but that wasn't the source of my mixture problem. I had hoped that it might be, but alas I still need about 2.6 kOhms in series with the CTS to reach my peak vacuum of 18.5 in Hg. Without the added resistance my engine runs quite poorly. Oh, and I do find my engine runs better with a bit more advance than the stock 10 deg. I'm currently running at about 13 deg BTDC. My engine will idle down as low as 450 RPM before stalling out, but it seems to "like" about 900.

Well, contrary to popular belief, all that emissions junk does really make the engine run more cleanly and efficiently if it's working correctly. However, if it's in disrepair, it will screw your performance and smog up even worse than if you removed it. It's illegal in most states to remove or modify emissions equipment, by penalty of not passing state inspection -- and possibly fines imposed in some places??? It's a pretty safe bet that the BCDD on the bottom of your throttle body doesn't work. Most people remove and plate over that. Your carbon canister is probably fine, is required by law, and does nothing to dampen performance. Just check it out to verify it works and doesn't leak. Some people remove the EGR stuff, without much ill effect. That cleans up the engine compartment a lot. Some of your spaghetti might have to do with the A/C high idle and not emissions. You can do without the A/C high idle (which is helpful), but you can't do without the vacuum supply to your air handler, which controls heater doors and such. If you have an air pump (doubt it), that probably can be removed. Non-California 280s had no catalytic converter, so if you can make the "California" go away, I suppose you could remove the cat. I have no knowledge of the altitude switch and whether you could delete that. I think the throttle let-down dashpot on top of the throttle body is helpful if it works. It should have no tubes connected to it. I think that's all your engine compartment junk, but there might be something else.

I *think* there's an intake screen in all these tanks, but there are some variations from year to year. I know my '78 tank has an intake screen. That said, if you acid-washed the inside of your tank, that could have eaten up the intake screen. Also if you coated an intact intake screen with epoxy, that could clog it up. So you could have problems either way. Some of us have inserted coarse inline filters between the tank and pump as a pre-filter. I'm running one on my system, and it seems to flow quite well. In hind-sight, I'd probably have installed one of those clear, decorative polycarbonate bodied fuel filters of a type that's popular in an American muscle car. That would give you a good view of what's in your fuel line. I think fuel flow would be adequate for EFI, so long as the filter is a coarse one and not some fan-folded paper filter. It sounds like your fuel pump MIGHT be for a carbureted system, and hence lower pressure. You can still get the OEM fuel pumps. I bought mine from a local Nissan dealer. It's an excellent pump that will be hands-down better than anything aftermarket you'll find.

The TPS is almost certainly the culprit with the rev limiting, but the problem suggests your computer is seeing the no-throttle condition, in which case there would be a slight idle enrichment. The "middle" position on the TPS, in which no contact is made, would be the leanest condition. Then at maybe 2/3 throttle you'll get a "full throttle" enrichment. So considering that you're running lean (hence the backfiring), I suspect there's other stuff going on besides the TPS. But there usually is. In my experience, the most common problem on any old car is rotted vacuum hoses. If you go all over your vacuum spaghetti, I bet you'll find a few rotted hoses. I'd replace them all, so that you know they're good. Also look for cracks between the bellow-folds in the boots between your air cleaner and air flow meter (AFM) and between the AFM and throttle body. A crack in the latter one can result in unmetered air leaning your mixture. You could also have a leaking intake manifold gasket. A quick test of the tightness of your engine intake can be done very quickly with my "yogurt cup test" ™. See here: http://www.google.com/search?q=%22yogurt+cup+test%22+site%3Aclassiczcars.com&sourceid=ie7&rls=com.microsoft:en-us:IE-SearchBox&ie=&oe= And then there are other reasons for lean running. We'll discuss those with you after you've ruled out the simple stuff.

Tomo, we didn't even think of the tool bins! There was probably no need to lap-carry any of our groceries! Grant, back in college, I'd stuff the back of my '75 Z with all sorts of camping gear for a week of camping. Who needs a truck? I'd also use it to haul around equipment. I would often carry maybe 10 rack-mount items back there. I think I once brought a dishwasher home in the hatch (open, of course). AJM, we had an elderly little dog that loved the hatch of my Z. It was like the observation car of a passenger train. He'd stand back there and enjoy a 360 deg view!

Not a myth, but a misperception: So my partner and I went to the grocery store last night, as we have company coming in -- LOTS of people. I asked, "should we take the Saturn," as I knew we needed lots of groceries. She said, "No, let's take the Z. The groceries will fit." At the store I had erred towards the light side, getting less, rather than more, of the bulky items like TP. My partner did the opposite. So when we got to the checkout, whe had a couple of well loaded carts that packed into three carts of bagged groceries. My partner said, "Well, I THINK it will fit," and I looked at her skeptically. (Note here: I have the '78 raised floor hatch area, with a big subwoofer already eating up some of the rear of the compartment.) As the bag girl was bagging all our groceries, she asked, "Is ALL of this yours?!" I nodded, and she exclaimed, "NICE!" She tagged along to roll the third cart out to the car, and when she saw what it was going into, she said, "You're going to fit all of THIS into THAT?!" I said, "Supposedly," still skeptical. So we packed the hatch up to the ceiling, nestled bottles of wine and milk in the passenger floorboard, put one bag in my partner's lap, and.... it all fit! Amazing! I said to the bag girl, "And you had your doubts!" That was 17 paper bags, each fairly well loaded, one big box of kitty litter, 2 bags of wine, 2 gallons of milk, and a large package of TP -- almost $400 worth of groceries. Oh yeah, the misperception/underestimation was on MY part!

That's very interesting that the block under the air regulator never reaches the operating temp of the EGR system. FAIW, the 1981 (?) ZX has a rubber boot around the air regulator. Perhaps that stops some of the heat loss. You might also have a kink in the rubber "L" hose connected to that block or a blockage somewhere in the tubing. Surely the system designed for the '78 must have worked at some time. I would think fixing it would be easier than modifying it. Or just stick with the '76's electric EGR. Something's wrong if power isn't interrupted to the system. Did you install the diode when you upgraded your alternator?

I wish I could tell you I was successful, but I wasn't.

With a bit more wear, you'll be able to start the car with a house key, screwdriver, or popsicle stick! A locksmith can replace the cylinder for you (keyed to match your doors), and it will work like new. It's not a very expensive job -- somewhere between $25 and $50, as I recall.

There's a diagram of the EGR's vacuum tube routing in the '78 FSM, Fig. EC-14 on p. EC-10. The Black vacuum tube runs to a vacuum port on the throttle body. The red vacuum tube runs to a vacuum delay valve (California only) and then to the BPT valve, which is the big, round doodad on the intake manifold just forward of the EGR valve.

Hmmmm.... Of course the tranny output shaft and beyond rotates with road speed, not engine speed, so the 3000 RPM mark would be irrelevant. Sounds like the issue would have to be in the tranny itself, specifically something to do with the meshing of the gears.... I guess... Hmmmm....

Honestly, if I were you, I'd just make the subharnesses myself out of different connector styles. I found a water resistant connector system out of Hong Kong that I can highly recommend. You can get them on Ebay. Here are some 3-pin connectors... http://cgi.ebay.com/3-Pins-Waterproof-Electrical-Wire-Connector-Plug-5-sets-/140543777986?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item20b90fdcc2 ...but you can buy from 1-pin to as many as 6-pin, last time I checked. The seller's name is 2allbuyer. The connectors are very sturdy, made of reinforced plastic with silicone rubber seals. They're very economical. The seller put together a package of several of each pin configuration for me. To my disappointment, the silicone rubber seals were a bit too small on the 2-pin connector, but were fine with the 3-6 pin connectors. I left the guy good feedback, but I pointed out the problem to him. I asked him to send me a set of rubber seals for the 2-pin connectors if they ever became available. Somewhat to my surprise, I got an envelope with the seals later -- even some extras. This seller has unusual integrity! I'd say the connectors are good for a few amps per contact -- probably adequate for everything I see in the subharnesses. You might use bullet connectors for the heavier current items like the starter wire and the reverse lamp.

Happened to me in a '75 280, not a 240, but it might be the same problem: My car was only 10 years old at the time. I would fill up the tank, and by the time I had used approx 1/2 of the tank, I'd be "out of gas" and stranded on the side of the road. I took the car to my mechanic (because I didn't work on cars as much back then and had a really good mechanic -- rare). He found that the siphon tube inside my fuel tank had a rust hole in it. I could draw gas as long as the fuel covered the rust hole. He fixed the problem for very little money. I guess he was able to braze the tube closed through the gas sender hole. I suspect this isn't a common problem, but it *might* be what's happening in your case.

sweaty/salty hands? If you left enough salt and moisture behind, you might have a short to ground.

Well, I recognized the '77/'78 engine from the pics on your first post. I guess I'm having trouble figuring out specifically what you're trying to find (Trans/starter/oil switch + Thermal switch / trans vac switching valve). Perhaps you're using unfamiliar terms, or perhaps I just don't understand how you're combining and separating the terms with "/" and "+". Are these the terms used in your factory service manual? (You need the FSM for the year of your engine. Find it here: http://www.xenons30.com/reference.html -- downloadable for free.) If you aren't certain of the correct terminology, perhaps you could tell us what the parts do. I believe reproduction wiring harnesses are available, but I don't know where they can be found. Perhaps Dave (ZsOndabrain) might know. He's the wiring harness guru here. You can find vintage Japanese electrical connectors here: http://www.vintageconnections.com/ Here's Banzai Motorworks: http://www.zzxdatsun.com/ There's no harm in splicing connections if you do it well. Opinions vary, but I like to twist, solder, and heat-shrink on low-amperage connections and crimp, solder-sweeten, and heatshrink on higher-amperage connections. Then I wrap up the harness with electrical tape when I'm done.

I'm guessing you have a '77 or '78 automatic? (You need to tell us.) As far as I'm aware, Z junkyards are very few and far between. I think I saw photos from one in Arizona. These cars are usually stripped and their parts stored. The best marketplace for used parts is probably Ebay. (Beware Reddat. Do a search for Reddat on this forum to find out why.) Courtesy Nissan is probably the best mail-order source for dealer parts, some of which are still available. There are several mail-order/internet businesses that you can check -- Motorsport Auto, Bonzai, Black Dragon. Also don't forget your local auto parts store (e.g. AutoZone). You'd be surprised how many Z parts you can get from them. The parts are all out there and for sale, for the most part.

If the lower half of your dash looks OK, I'd recommend a half-dash cap. The half cap looks quite good, and it will not give you quite as much grief if/when you need to R&R your speedo or tach.

Yeah, if it will burn out, burn it out. Then you'll have 8 dimples inside. Roughen up the end of the new string with very coarse sandpaper. Then put some gorilla glue in the hole, dampen the end of the string, insert, and let cure. Then trim the excess. That gorilla glue (dense polyurethane foam) is incredibly tough stuff. Another great adhesive is 5200 adhesive/caulk -- the regular stuff, not the fast cure. It's another polyrethane product. Give it about a week to cure.

Well, if you've got spark, you probably don't have fuel. Quick test: Spray some starter fluid in the intake and give it a crank. If your ignition is good and your fuel is not, the engine should fire up for a second or so and then die. To check whether your injectors have got power, go find a christmas light bulb -- one of the tiny ones maybe 3/16" in diameter. Pull one of your injector connectors, and plug the bulb into the connector. Then crank the engine. You should see the bulb flash as the engine turns. You might also check around your thermostat housing to see if all the connectors are still good. Those connectors on the front of the engine get pretty crusty.

Ztrain, I didn't say messing with the clock spring is a big deal. I've done it -- and then undone it. I also don't see much harm in it if the adjustment is only a few teeth. However, if the "correct" adjustment is around 15 teeth richer (as it was in my case), that introduces a serious issue with the overall response of the AFM. If you look at the AFM's design, the vane stays almost closed at idle, under some spring tension. It would not make sense to actuate the potentiometer farther than that. Why meter air at lower-than-idle flow rates? From there, the vane will open up fully with a certain (large) air flow rate that's well within the operating parameters of the engine, and it will continue to add fuel beyond that point based on temp readings and RPM. If the two ends of the potentiometer are to correspond correctly to idle and that larger airflow rate beyond which the AFM readings are ignored, the clock spring has to be at a certain tension. If it's adjusted 15 teeth richer, it will peg out prematurely. No correction will be applied beyond 4000 or 4500 RPM, and the engine will be running very lean in the peak of its power band at WOT. That's definitely not a good thing! :nervous: By altering the CTS resistance, a proportional correction is applied throughout the AFM's response range and (more importantly) beyond its response range, into the higher RPM ranges. It's very interesting to read BRAAP's approach in the above-linked thread: "In short, I found the AFM works as originally designed and works INCREDIBLY well, and due to the narrow range that it functions, which is only below 4500 RPM and mostly under cruise conditions, the only tuning or alterations I perform to the AFM is to adjust the spring tension, but only after the WOT tune is set by altering the water temp sensor resistance. " So he basically uses the CTS circuit to tune the mix under heavy flow and sets the clock spring to calibrate to low flow. That's a bit more sophisticated than my approach. (A dyno would help.) However, it's plain to see his primary adjustment is of the CTS circuit, because "this offers a linear AFR change across the entire RPM range under all conditions." That's basically the point I'm making. BRAAP and I reinvented the same wheel, more or less. I made educated guesses from the info in the FSM, and he did one better by actually reverse engineering the ECU. Our primary approach is essentially the same.

Hi all, I notice when I let off of the gas that the engine RPMs plummet as the throttle slams shut. It's not a serious problem, but it's still a bit inelegant and ill mannered. I realize the job of the dashpot is to ease the slamming shut and possibly prevent the momentary dip in RPM below the normal idle set point. I remember when I was much younger and owned an 8 year old '75 Z. I refurbed and adjusted the dashpot and apparently kept it. However, I can't remember whether it really did anything or whether it was somewhat of a "rhubarb" (useless part) that I never bothered to remove and toss in the trash. So... Question to all you old-timers who remember these machines when they were young... Does the dashpot really do its job and gracefully ease that last bit of falloff? Is there any benefit to keeping/restoring it? And then the corollary questions... Is there such a thing as a functional 280Z dashpot? And if not, is there a dashpot from some other vehicle that will mount up? (Mine is quite rotted and is sitting in a box of odd parts.) Thanks!

Thanks! I've saved a copy to my hard drive in my 280Z reference folder. Great stuff!

Wow, Dave, fantastic! My next stop will be HybridZ to dig up your postings! It might be nice to set up an ECU with 20-turn trim pots accessible through the case for periodic recalibration. Jeff, the "right" way is only some other person's opinion. I don't think Nissan ever meant for us to mess with the clock spring, or else it would be in the FSM. To me, messing with the CTS circuit makes much more sense. Better still, I might be able to mess with the base pulse, per the info Cygnus cites! It was a good day for my Z. This was the first evening it got out since the humbling experience of being towed back from Richmond (poor baby). We met some friends at a nearby pub. They had questions about their VW beetle, parked next to my Z. As I was chatting with them about it, some guy piped up and said, "THIS is the car you should be interested in!" I smiled and said, "Thanks! That's my car." We had a long chat, going down memory lane about his 280ZX from long ago. Then some 20-something kids walked by. One of them circled my car and said, "This car is SO SICK!" Made my day. Anyway my engine ran like a top again. No more misses.

Jeff, I'm leary of adjusting the clockspring in the AFM. That was my first approach to correcting my mix, but it rendered the vane tension too loose. Using this approach, the AFM would have swung wide open with too little air flow, leaving the mixture too lean after that. I think it's important to preserve the aerodynamic properties of the AFM and then to adjust the ECU's response to the AFM data electronically, hence the CTS mod. This mod seems to apply the same pulse width correction across all operating conditions. Horseman, OUCH! Yeah, different coolant temp sensor!

Hi all, As you may recall from my "purs like a kitten" thread, I installed a potentiometer in the coolant temp sensor circuit last fall to richen my fuel/air mixture. I did this because my ECU had apparently drifted in its calibration to a progressively leaner state (shorter injector pulses). Inserting resistance in the CTS circuit results in enrichment proportionally throughout all operating conditions -- or so it would seem. My car has been running like a top ever since, with vacuum in the 18.5 in Hg vicinity. I did have one glitch recently, in that I decided to drive my car to Richmond. My fuel pump died en route, and I had to be towed back home. I replaced the pump and noticed my engine missing a bit when it got warm. I mistakingly took this to be a sign my engine was about to die from some unknown problem, so I quickly returned home both times this happened. My car has sat until today, as I didn't have time to sift through the problem until now. The first thing I did was to read my plugs. Happily, all are a nice mocha color, so my mix has been great, more or less, since last fall. I noticed a bit more carbon on 5 and 6, while 1 looked a bit leaner than the rest. However, I think these differences were probably relatively minor. Then I installed a cheap fuel pressure gauge between the fuel filter and fuel rail, so that I could observe whatever fuel pressure irregularities might occur on the road. The gauge, T-fitting, and brass nipples were incredibly cheap from my local True Value. So I started my car, observed a peppy fuel pressure response, and let the car warm up. As it got warm, it started missing a bit, but only slightly. I noticed that my engine temperature was a bit on the warm side when this was happening. D'oh! The A/C was running, and it was somewhat hot today. After I turned off the A/C, the temp dropped a bit, and the missing improved but didn't resolve. Then I checked my engine vacuum. I was getting only about 17 in Hg. I found that I was running a bit leaner than optimal, and I richened the mixture by dialing in more resistance into the CTS circuit. That raised the vacuum to 18.5 after I dropped the idle speed to spec. Revving was good, and missing was no longer a problem. It might be too soon to tell, but there might be subtle differences between optimal wintertime and summertime adjustments when the CTS circuit is adjusted by adding resistance. It might be that my cooling system is a bit strained by the A/C and summer heat, resulting in a leaning out of my mixture. The difference both in temp and mixture is subtle. So it seems I over-reacted to a few little misses. I should never have doubted my baby. Anyway I though y'all could use the update on how my EFI modification has performed until now.