dar5052

I get nothing when I suck on the hose… (that doesn’t sound right….) if the diaphragm was cracked/torn I would be able to pull air through it. I have a timing light but I let someone use it recently and haven’t gotten it back…

Thanks @Zed Head and @Yarb. If the snip below is what you were referring to with respect to the FSMs guidance on vac advance testing, there is a lot to be desired 😂… I would hate to add resistance to the cooling system until I rule the vac advance out just because then I’m masking the problem and not necessarily fixing it. But I will keep the advice in mind once I’ve exhausted all other possible scenarios. Many thanks! Out of curiosity, I went out to my spare parts bin and found a couple partially disassembled distributors. On one of them, I was able to spin the rotor clockwise about 10 degrees and counterclockwise 10 or so degrees. In both cases, the rotor returned to the neutral position when tension was removed. At this point, I’m guessing my vacuum advance breaker plate may be seized in position and thus I’m not getting vac advance when I apply throttle? Anyway, if someone can pop off their distributor cover and confirm if they can rotate the rotor clockwise slightly, that might help me narrow down if the distributor needs to be pulled off and gone through… thanks in advance! @Zed Head I was surprised at the 27% increase… although I guess I shouldn’t have been seeing as how fast my fuel level gauge was going down!

Ever since I’ve got my car on the road, about 1 year, I’ve had a slight hesitation/stumble at low rpms. I’ve tested most if not all the components according to the fsm and efi bible and everything seems to check out and is in spec with the recommended values and “all” vacuum leaks have been addressed. The car idles fine but when trying to accelerate from low rpms, there is a stumble and hesitation. If I ‘pre rev” before letting out the clutch, it’s fine. Then when shifting, as long as I’m in high rpms, it doesn’t have any hesitation, just rips. So I did some fiddling and adjustment. The real culprit is that the car is running lean as soon as I hit the throttle, at least that’s what I think. My reasoning is, I dismounted my tps, used a screw driver to turn it to wide open throttle, and it runs like a champ but granted I’m dumping extra fuel in the cylinders at all times. Given that my sensors are reading the correct resistance during cold and hot operation led me to my vacuum advance on the distributor. I popped off the cover and when I turn the rotor, I can turn it counter clockwise about 10-15 degrees and it springs back but I have no movement clockwise. Would that indicate that my vacuum advance is not functioning? I read somewhere that mechanical advance is counter clockwise but vacuum advance is clockwise movement, is that accurate given that I only found one source of that information? This would certainly explain the hesitation I’m experiencing, or at least I think…. For reference, the hesitation is there whether the engine is cold or hot…. No difference. Another point, I adjusted the track in the afm in case there was a ‘dead’ spot and it was exactly the same afterwards. Appreciate the input/help as always…

Well the replacement master vac fixed the brake and idling issues, as expected. But after driving it for 25 miles or so, the sticking idle came back. I pulled the throttle body off again and cleaned it but to no improvement. So I took a deeper dive into trying to recreate the issue… turns out, when the car is off, the throttle has no problem returning to the closed position but when the car is on, it stays open after lightly applying throttle. I’m guessing the vacuum in the motor is providing enough resistance to hold the thottle blade open slightly. The sudden blip in the throttle forces it closed just due to the momentum. I sprayed some wd40 on the throttle body shaft/springs and it seems to be working better now. Nevertheless, seems like a short term solution… has anyone replaced the return spring to something more “heavy”? I took the spring off and it seems very easy to stretch it, might help to have a heavier spring rate on it to overcome the vacuum, if that’s the issue… any ideas for a longer term solution, apart from going to a cable setup? I have a third spare throttle body that I could completely disassemble, lubricate, etc…. Anyone have a diy for this? Including replacement components?

@Patcon I agree that a 1/4” tear is sucking some air but I highly doubt all the tears happened simultaneously so it presumably was building vacuum. Not saying it’s ideal by any means and it should be replaced, but it does build some vacuum, at least enough to be functional. Most of the tears were in the crease so it’s possible they were holding pressure just due to the location of the tears but eventually one of them must have propagated and just gave out? Idk, just speculating… but the fact that everything happened simultaneously (shitty idle, non functioning brakes, rpm spikes) leads me to believe this is certainly the culprit. I’ll revert back when I install the replacement but I’m off to Oklahoma tomorrow for work so it may be a couple weeks… I appreciate everyone’s feedback and commentary. Always good to talk about these issues with members with these, or similar, cars.

Thanks for the suggestion @Yarb . I did verify that the check valve is functioning and facing the correct way (arrow towards intake manifold). I ended up pulling the master vac out and took it apart. Found 4 or so tears in the rubber diaphragm, most were between 1/4 to 1/2”. Quite frankly, I expected it to be worse but I guess even a small few tears will prevent it from building vacuum. I ordered a new one so I’ll get that installed and see if that improves the situation.

So it seems that cleaning everything up worked…. But now I have another issue. I was intermittently getting a really hard brake pedal but now it’s just constantly hard to press down and barely stops the car. I’m thinking it’s the master vac because when the issue became constant, I noticed the idle was pretty bad on the car too. When I remove the vac hose from the booster, the idle doesn’t get much worse but when I put my finger over the check valve, it improves. So it seems like a master vac issue. Any other ideas before I go buy a new one?

I finally got around to taking things apart and taking a closer look as to what might be causing the issue. The inside of the throttle body did have some gunk in there and I assume when things heated up and expanded, it was probably just enough to bind the flaps from fully closing. I had a spare throttle body laying around so I cleaned that up really well and now ready to throw it back in the car. The replacement TB is from a non-egr so one less port to plug but while comparing the two, I noticed a really small adjustment screw on my old (egr) TB kind of close to the egr port. Any idea what that’s for? While I was here, I decided to check some other things and found that my air regulator is fried. It was stuck shut so it wouldn’t explain the holding rpm’s but does explain why it would always limp along until it got up to temp. Luckily I have a few spares of those too that are hopefully functional. Lastly, where the linkage from the firewall hooks onto the linkage on the throttle body, the hold down spring was missing… I found one in my bolts bin and fit it up. Hopefully the combination of these things clears up the issue 🤞.

Thanks @Captain Obvious your symptoms sound exactly like mine. I’ll shift my focus away from the BCDD for now. I think I have a couple spare throttle bodies laying around so maybe I’ll try to clean one up and swap it in. @Zed Head yes, I have the springs there. One helical on the throttle blade shaft and the second one drops down under the throttle body and attaches to a bracket.

@siteunseen I thought the same regarding the throttle blade but it doesn’t stick, at least when it’s cold. When i manually press the throttle and let go, it goes back to the neutral position. The only slight play is in the linkage and that doesn’t actually move the blade. I will say, the holding rpms does happen more after the car warms up. Probably takes about 15-20 mins after driving that I really start to notice it. @Patcon idk where he is but i recall seeing he was in PA in one of his posts. @Captain Obvious where you at in PA?

@Patcon were you asking me where I’m at? If so, it’s PA, one hour west of Philadelphia.

@Captain Obvious wouldn't I need to pull a vacuum on the BCDD for it to function properly? At this point, I just have the vacuum line plugged off so I assumed it’s not opening/closing properly. I’m going to look in the FSM to see if there is more info on how the thing operates. I have a couple spare intake manifold laying around so I’ll take a look at those for the ports you mentioned an ensure I have the egr capped off. I do have my vacuum advance hooked up to the distributor. @Yarb I might just do a BCDD delete as you described but I’d like to keep it if I can. I don’t have an explanation as to why…. @Zed Head i did do that… I could recreate the high idle by just pushing on the throttle linkage under the hood. When I let go, it would hold a high idle. Then I would literally pull back on the linkage ever so slightly and the rpm’s would drop. One of @Captain Obvious previous posts led me down the path of cleaning/greasing all the linkages but it didn’t really do much. That’s what lead me to the BCDD… also, if I’m driving and I notice the idle holding, I pull in the clutch, blip the throttle, and the high idle goes away… until I apply throttle again… then it’s the same thing over and over. One thing I thought about was the return spring on the throttle assembly… could that have relaxed over the years and not be applying as much force as required to bring the throttle back to zero? A couple pics of the car so far… still have some work to do but I figured if I don’t start getting it out of the garage, it’ll never come out. Probably not everyone’s style, but it’s mine…

When I reassembled my 280z, the egr system fell apart so instead of replacing the broken components, I opted to just remove it. Now that I’ve been driving the car, I noticed it holds revs and I’m thinking it is because I don’t have the vacuum line to the bcdd connected. Looking back at my photos before disassembly, looks like it was connected to the egr diaphragm for vacuum. I also removed the charcoal canister so I’m wondering if I can just pull vacuum from that connection on my manifold? Anyone have any thoughts or suggestions? I’ve tried taking apart the throttle linkage, cleaning everything, and lubricating before reassembly and it still hangs so I’m leaning towards the bcdd.

@cgsheen1 I’m sure they serve a purpose. Can you elaborate as to the purpose? Thanks

@siteunseen it’s close to a liter bike… it’s an 899. Possibly one of the best bikes I have with respect to rideability and overall use (the one in the picture is my track machine but I have 2 more for the street). I have an 1198sp and that thing is a tire hog. I’m usually lucky to get 2k miles on a street tire.