FastWoman

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.

Ben, you need to measure the pressure with a T-fitting inserted between the fuel filter and the fuel rail. (Just add another little length of hose.) Normal pressure should be 36.3 psi with the vacuum hose removed from your fuel pressure regulator. Then with the vacuum hose reconnected, the pressure should drop about 7 psi to 29 psi (at idle). When you rev the engine hard, you should see the pressure surge to 36.3 and then drop into the low 20's as the RPM comes back down. In addition to Zed's suggestions, a stuck cold start injector can also richen your mix. BTW, I just finished installing a "permanent" gauge under my hood, fashioned from fittings from True Value hardware. I used a cheap, generic gauge and a brass T-fitting -- total cost about $12. The gauge and two 5/16" hose barbs both screwed into the T via 1/4" NPT threads. I came up from the fuel filter to the first barb at the base of the "T". Then one side of the T went to the fuel rail, and the other side went to the gauge. No brackets were necessary, as the gauge is small and is held nicely in place just by the hoses.

I go back and forth on the LEDs. This year LED Christmas lights made their big splash in my neighborhood, and the older tungsten lights had mostly died during previous years. It just wasn't the same. The LEDs were cold and unsatisfying. To me there's something magical about a hot, glowing filament that we will miss someday. However as a spotlight on our sailboat.... That's entirely a different issue!

The new kid at my local AutoZone has one of those newer-fangled turbo V6 Z cars, but he knew all about my '78 Z. After discussing common failure modes in my Saturn's O2 sensor (why I was there), we talked archaic analog L-Jetronic stuff for several minutes. I was impressed. Yes, there's hope.

Dude, check the breaker plate in your dizzy to see if it still rotates freely with vacuum applied to the vacuum advance. The vacuum advance mechanisms in Z dizzies aren't very well designed and often/frequently/usually stick. For $100 you can buy a rebuilt dizzy from your local auto parts store (e.g. AutoZone), but supposedly supplies are getting a bit scarce. Backfiring through the carbs strongly suggests a fuel/air mix that's too lean. I bet your engine vacuum is pretty low too.

I'm assuming it's important to you to stick to 100% stock. If not, you might want to install MaxiFuses to replace that fusible link mess. I did it and am still very happy I did. My saga is here: http://www.classiczcars.com/forums/showthread.php?35588-Upgrade-from-fusible-links-to-circuit-breakers&highlight= If you do stick with the stock fusible link assemblies, you need to be careful with the bases, as they can break. (Mine were both broken when I bought my car, and the fusible link blocks were hanging off the end of the wiring harness.) There are no new replacements for those, and in fact they are an integral part of the wiring harness. Your only replacement option would be salvage, and I didn't have much luck finding the things. Obviously I gave up.

Dunno... Tapping with a vice will wear most people out! :cheeky:

I'm not saying household AC is different from automotive DC. I'm only saying the standards are different. You won't find 10 ga wire anywhere on an automobile's 30A circuit, and you won't find a car anywhere that would meet US household wiring codes. .7 ohms/km?! Wow... Impressive!

Rob, I found that the main alternator-to-fusible-link wire in my '78 was pretty small -- perhaps 10ga, if I remember correctly. That's already too small to carry the sort of current that might be sent through that wire. A 10 ga wire is rated to carry 30A in household wiring, and automotive wiring seems to be twice as permissive in general. So Steve's quote of 55A for 10 ga would seem fitting. He says the rating drops a little bit in a bundle, but I think more correctly that it drops quite a lot. When you put the 10 ga wire inside an insulated wall, that's how you get a 30A rating. The alternator wire lives inside a rather large chunk of wiring harness, and it sees quite a lot of engine heat (another adverse factor). As such, I doubt it can really carry the rated 55A before melting its insulation. In my car, I upgraded my alternator wire to 8 ga, if I remember correctly, and then I fused it at 80A. However, if I still had the same 10 ga wire, I'd probably go with a 60A fuse and be rather uncomfortable that the wire might not be adequately protected. Of course I never like risking such things, which is why I upgraded the gauge of my wire. Keep in mind that if your wire gets hot enough, it will melt not only its own insulation, but also the insulation of surrounding wires. Pretty soon your wiring harness becomes toast, and you will have weird electrical problems you couldn't begin to imagine.

I believe the red/white wire is from the fusible link. This establishes that your fusible link is good and that you're getting power to the switch. Try testing for continuity between the switch terminals on the disconnected switch when you turn the key. That's the most direct approach to determining whether your switch is good. Again, red/white is the power supply to the switch, so test for continuity between that terminal and the others.

Yikes, they're now NLA? That makes me wonder how they're going to honor the lifetime warranty. I'm sure more will become available, but I suppose the supply will be trickling away. I guess I got in towards the tail end of a good thing. Anyway, glad you found your problem!

Ezzzzzzz, I don't know the specifics of the Pertronix rig, so I'm just making an educated guess: I would presume different magnetic lobes correspond to different cylinders. If there's anything marginal about the operation of the system (e.g. distance of sensor from lobes being incorrect or marginal sensitivity), and if there's any difference at all in the strength of the trigger for each cylinder (e.g. magnetic field strength generated by each magnetic lobe), then at least one cylinder will be prone to fail while the others are still (barely) operational.

FAIW, Autozone sells a remanufactured dizzy for around $100 with a lifetime warranty. These things don't actually last anywhere near 38 years, due to a bad breaker plate design. It doesn't take long before the breaker plate freezes up and the vacuum advance sticks. The reman parts often aren't very good, but I figure if the R&R is an easy one, why not do it? So far my reman AZ dizzy is doing great. My original reman AZ alternator did start putting out slightly too high a voltage at one point, and AZ was very good about replacing it.

Green tape?! Are you serious?! Hmmm.... Yeah, that's where I'd look.

D'oh! I can't read. Might still be in your distributor. You can try swapping BOTH your #5 and #6 wires AND plugs to see if the problem migrates to #5. If it doesn't, well, that's the entire ignition system after the distributor. I would think that would mean the problem is in the distributor.

In trekkie alien voice: What IS... "carbs?" But seriously... :bulb: Do you also have points? I'm just guessing here, but if the cam (correct term?) in your distributor is worn a bit more on the #6 than the other positions, OR if your distributor shaft is wobbling just right, AND if your points are adjusted so that they barely break as the distributor cam rotates, then you might be (barely) breaking on #'s 1-5 and not on #6.

This is all great news! You might need to lean your mixture out just a bit, so that the TPS can make the appropriate enrichments for idle and WOT without making the mix too rich. I suspect the adjustment would be so minor that you might be able to tighten the AFM's clock spring a bit to do it. Isn't it great to be pulling strong on all 6?! IMO, there is nothing more delightful than a properly running inline 6 motor. It's the only configuration of motor that has inherently perfect primary and secondary balance -- well, that and a V12, which is essentially two inline-6 motors stuck together.

Run your engine in the dark, and look for stray sparks. Your current might be shorting to ground prior to the plug. Check the connection to your #6 injector to make certain it's firing. Obviously check compression. Your problem is probably in there somewhere. FAIW, a weird problem one forum member had (argneist) was that the EGR port on his intake had eroded through to the manifold, bypassing the EGR valve. The leak was dumping lots of exhaust exhaust into his #4-#6 cylinders, causing them not to fire. There was possibly some blockage that prevented the exhaust gas from reaching #'s 1-3. I've not heard of this problem in any other car, but I thought I'd mention it.

I could easily be wrong, but I think having the right fuel/air mix will eventually result in the burning/eroding away of carbon deposits in your cylinders. I suspect there's no compelling reason to clean the valves or intake, beyond clearing varnish from the valve guides and injectors. Flushing the motor oil will clean up the valve guides, albeit a bit slowly, and running a bit of a strong solvent through the gas will slowly clean the injectors. I think that's about the best you can do. That said, the old-school way of cleaning carbon out of a flathead engine was to open up the head and dump rice into the intake. Apparently the rice would bounce around inside the cylinders, and the pulverized carbon would come shooting out the exhaust -- not that I'm recommending that to anyone, but I just find it fascinating!

I think your #2 is the vacuum supply from the throttle body to the thermal vacuum valve, which supplies vacuum to the EGR system. I don't know what year your car is ('78?), but there's a vacuum tubing diagram in the Emissions Control section of the factory service manual, fig. EC-14. You can download the FSM for free, or you can buy a used hardcopy off of Ebay or Amazon. I prefer having the book, myself, because you can spread it out over your work area, unlike your computer.

Oddly, that part on the throttle body (the dashpot) isn't really supposed to have a hose attached to it, appearances to the contrary. All the part does is to ease the throttle down when you come off the pedal.