rundwark

It's an infrared LED-based trigger module that sits inside the distributor. From what I've read so far though is that the typical failure scenario is that the LED burns out. I can't find any stories of intermittent missed sparks that actually are fixed by replacing the module.. Still, it's another piece of electronics that gets hot over time when the engine is running, so it could be the source of my problems. Makes me wish I had another distributor lying around for this car to test it with.

One crucial bit that maybe isn't clear from my earlier posts: the issue is somewhat intermittent. It's not always equally bad. Sometimes I can push the car to redline in 1st and 2nd, sometimes it'll hesitate badly around 4000rpm in 2nd. And once it gets like this, it stays like this for a while. Even if I put the car in neutral and let it idle for 10-20 seconds while coasting, it'll still run crappy once I put it back in gear and put some load on it. If I pull over, and check the fuel filter (it'll be at 50% or so), it'll still be bad right away when I start driving again. But if I let it sit for longer, say 15 minutes, the issue will get less for a bit. That makes it sound like it's heat-related to me. Maybe marginal fuel flow acts this way with engine bay heat?

Hey Chickenman, that's very helpful, thanks! Electric pump: not sure what brand or how old it is. It sits right below the fuel tank so I guess that makes it a pusher. One other thing I didn't mention in the original post: one of the POs removed the expansion tank, so the fuel tank and line setup is not stock. It ran well this way for the last 14K miles though, before these issues started. Float levels, needle/seat obstructions: I haven't checked any of these yet. Will add them to tomorrow's list. I did check the spark quality today: I took one of the plug leads off with the engine running and held it close to a strut mount bolt, spark was strong, blue, and jumped a good distance. It did seem a little uneven where not every spark seemed equally strong, but it wasn't clear enough for me to be sure it really was an issue. I'm using NGK leads and NGK BPR6ES plugs. I'll swap in a different coil HT lead tomorrow morning to see if that makes any difference. Based on what you and others wrote and the causes I eliminated today I feel pretty confident it's a fuel issue, but still not entirely sure..

Hey BJSZED, its set-on is fairly gradual, I can usually tell that power tapers off a bit at first rather than hitting an on/off switch directly but if I stay on the throttle or move past the point where power tapers off, the problem can get pretty aggressive, bucking the entire car as it rapidly goes between having and not having power.

The under-hood fuel filter is only one quarter to half full most of the time with the engine running, I can't remember if it was always that way. Is that normal?

Ran it with filler cap loose: no change. Blew out rear fuel filter: it wasn't clogged, no change. Replaced mechanical fuel pump: no change. Removed MSD ignition box: no change. Next up: either installing a wideband, which I've been putting off or checking floats on the SU's, to see if they're sticking or something like that.

Thanks David! I've been suspicious of the mech. pump. It's one of those generic aftermarket ones. I have a replacement one on the shelf, will install that tomorrow as well, after trying to drive with a loose gas filler cap.

Thanks turbogrill and jasper. I'll focus on fuel-related stuff in my troubleshooting, will try driving with the fuel cap loose tomorrow

Oh one more additional note: I'm pretty sure there's no vacuum leaks to explain the uneven idle part of the issues. Disconnected brake booster: no difference. Sprayed carb cleaner around intake manifold, around throttle shafts: didn't do anything.

Hey all, I have a real – to me – mystery on my hands. '73 240Z w/ '71 L24 with roundtops, Mallory dizzy, MSD 6A, electric pump outside fuel tank, mechanical aftermarket cam-driven pump. Started developing a hesitation under load. First only happened near redline in 1st and 2nd. Now manifests itself during highway driving. Gets worse over time during a drive. First you notice while overtaking in third, then even maintaining speed in 4th becomes a challenge. After idling for a while, it's better for a bit. Idle is also unstable in general since these issues started happening, as if it misses on one of the cylinders every now and then. Idle is especially shitty when I just come off the highway, it will fluctuate heavily around 500 rpm and almost die without gas, while before the highway drive it will have idled around 1k but still fluctuate a little. Water temp is good. Timing is the same as before the issues happened. I tried changing the timing, and changing the jet settings at each carb to richer and poorer. I disassembled, cleaned and reassembled the SU's, centered the jets, cleaned the air filter, replaced the spark plugs and ignition coil. No change with any of these. When the engine gets in this state it also sounds different at all RPMs and loads. It sounds coarse, as if it needs to clear its throat. I thought I was fouling the plugs, but immediately after changing the plugs, revving the engine in the auto parts store parking lot it still hesitated. Old plugs looked alright too. Two were a little pinkish but no black soot on any of them. My theories: 1. A clog in the fuel system. The issue first manifested itself when I ran the fuel tank lower than usual. For a while after that, it seemed like the issue was worse on a half-empty tank than on a mostly full tank. I don't really see how this theory holds up with the fact that it does get worse over time during high-load driving, but it's all I can think of. Also, I can see the fuel level in the in-bay fuel filter change when I turn the electric fuel pump on and off (it's on a switch), but see no change in how the engine runs. 2. Mechanical fuel pump marginal. It feels like I'm running out of fuel at the high end. But I'm not sure how this would get worse after driving for longer, so that doesn't compute for me either. 3. Some internal engine issue? Like a bearing that's marginal? I track the car and don't have a baffled oil pan or anything fancy like that. So oil starvation during a track session is possible. But with the problem gradually getting worse over 500 or so miles, I'm not sure that makes sense either. I would expect it to hesitate and then seize, not cool down and run decently for a while again. 4. MSD 6A box marginal. I don't see how to test this really.. I did leave my replacement spark plugs at stock plug gaps instead of the bigger gaps and saw zero improvement. So I don't think this is it. 5. Valve train issue? I don't know how this could cause these symptoms but adjusting valves on these cars is like zapping the P-RAM on an old Mac, the first thing anyone does while troubleshooting. I have a freshly built engine sitting in my workshop, waiting for me to drop it in, but really want to isolate and understand the cause of the problem before I potentially expose it to the same issue.. this can't be good for the engine. Anyone here have ideas on how to further diagnose the issue? I'm thinking I'll do an oil change tomorrow, to see if there's any shards in there..

Thanks, it felt a lot better too! It was your comment that helped me consider that I probably could go a bit lower with the stiffer springs, so I did and it definitely helped to have the CoG even lower. I didn't actually change the roll bars yet. I may do that next to further dial it in. It's definitely firmer on the road, but once I dialed in the shocks, it wasn't bad at all. At first I had the rear a little underdamped, and at a few spots on US-101 the car pretty clearly expressed its unhappiness to me by bucking pretty hard. Once I firmed them up just enough more where they actually controlled the springs, it stopped doing painful hard bounces and the ride is actually very acceptable to me. I find it just as (un)comfortable, but I'm more relaxed at high speeds since the car feels more planted and controlled. The firmness is very similar to my wife's stock 2012 Subaru BRZ, but everything is just a lot noisier (and more fun!) in my 240Z A bunch of different folks organize track days there, so there's something going on pretty much every other weekend. Personally I recommend going with Hooked on Driving. They're not the cheapest option, but their events are exceptionally well run: safe, lots of track time, and not too crowded on the track in each run group. Their next two events at Laguna Seca are March 10, and April 13-14. Do drop me a line when you plan on going so I can try to make it out there as well. It'll be fun to meet, and to be on the track with another Z-car!

Check out how much more the body is under control now compared to the previous setup: Turn 11 at Laguna Seca (driving at 1-1.2 lateral G's in this turn consistently): At the corkscrew:

http://eibach.com/sites/devperformance-suspension.eibach.com/files/catalogs/ERS_20_Catalog.pdf

Both Summit and Jegs sell them, my Eibach parts list was: - SPACER250 (seats helper/tender and main spring together) - HELPER250 (helper spring) - ISOLATOR250 (Delrin washer/spacer thing that goes between spring and top hat) All parts for 2.5" ID springs, but they also have them for other sizes – easiest way to find is Eibach's PDF catalog and then use the part numbers on Summit's site.

Here's my best lap of the day, sorry for the choppy video quality. The guy talking is the instructor who rode along with me for one session (just so y'all know I'm not paying myself compliments while driving, I do that at other times, and off-camera).

I put the 300# front, 350# rear springs in, lowered the car some more and got the alignment dialed back in after that. Had to add helper springs to keep the stiffer springs seated at full droop. Also added some Delrin isolators between the spring and top hat, which seem to help a lot with harshness when hitting expansion joints, lane markers, etc. The Koni shocks are close to their stiffest rebound setting now to control the spring motion, and the ride's definitely stiffer. But thankfully it doesn't feel too choppy on the street to me. The car also feels a lot more steady at >80 mph speeds. Took it on Laguna Seca today and it's a blast. Will share a quick 1-lap video when I succeed uploading it on hotel wifi. It's pulling 1.2G turns now without excessive body roll, so much more fun than before! Next station: more horsepower

Here's a good read on the front vs/ rear frequency: http://www.optimumg.com/docs/Springs&Dampers_Tech_Tip_1.pdf What's described there in the first two pages or so makes a lot of sense to me, and they explain it a lot better than I can. Not sure if it's the right thing to focus on though..

Yeah, my other fun car is a 510, and I have coilovers on that too. The 510 chassis is a lot stiffer in the front end. On my Z, I didn't even feel much of a difference when I went from sagging lowering springs that were on there when I bought it to the 200 lb/in springs, until I added a triangulated strut brace. The 510 feels like it can handle a lot more. @seattlejester, I think you misunderstood what I meant. The frequency of the suspension is determined by the weight, motion ratio and spring rate. The damper limits the number of oscillations, but does not affect frequency. When going over a bump, the front wheels hit it first. So, it's actually desirable to have a slightly higher frequency in the rear, so that the rear suspension "catches up" to the front by oscillating more quickly. If the damping was ineffective, this would be a terrible idea, but since each oscillation is lower and you'd get at most three or so noticeable ones with good damping, there is less pitching of the car in a setup that has a slightly higher frequency in the rear. Now, the 240Z should have almost identical motion ratios front and rear, and since mine has AC installed, it's probably fairly close to the stock 52/48 F/R split, which means that, if I ran the same rates front and rear, the rear suspension would still have a slightly higher frequency than the front. But running softer springs in the rear seems like it would be have a negative impact on the extent to which the chassis moves around over bumps.

Thanks for the great post Chickenman! Lots for me to digest and think about. Very glad you talked me out of tender springs, that doesn't sound like a good way to go at all. A little more on the car: it does sit on coilovers, but no camber plates. I have adjustable, heim-jointed, LCAs, rear CAs and TC-rods on the car, which is what lets me dial in the alignment. current wheels are 0 offset, which puts the outside sidewall of the tires very close to the (rolled) fenders, so it's sitting as low as I can get it while not rubbing on hard corners and dips. I'm hoping to drop it further once I have stiffened up the suspension a bit. The car has a 3.54 torsen LSD, and I'm using a Delrin steering coupler. I need to check the rack bushings, but overall steering is very tight. Lots of setups for S30s I read about (on HybridZ and other forums) use stiff rear springs and no rear sway bar, so that's what I've been using as a template so far. I'll measure my front bar, to make sure it's actually only 22mm. I'm thinking I may still try the 300/350 setup with no rear sway first, and if I don't like it, add a rear sway bar, and switch back to the 250 rear springs. It'll be a good learning experience for me to feel the difference between the two approaches in one car. I feel like either approach could get me to a fairly neutral handing car. It seems like the main pro for the stiff rear spring approach is that by raising the frequency of the rear suspension relative to the front, there would be less pitching over bumps, causing a flatter ride. The main con seems like the overall ride would feel a bit more jarring and choppy due to the higher rear spring rate. Does my logic make sense? I also like the additional benefit of a stiffer spring rate in the rear for lowering the car further. The sway bar would only help reduce compression in corners, not with bumps while going in a straight line. I'm into the shorter tire idea. Beyond the benefits you outlines, it would also solve my caster limitations, and let me get the car quite a bit lower without any rubbing issues. Sadly, my current tires are brand new, so I want to see what I can do in the intermediary to at least make it fun to wear them out quickly on the track

Hey all, I took my 240Z to the track last weekend, and because it was a bit wallowy at high speeds and had a lot of body roll, I'm now looking into changing up my spring rates. Current setup: 200 lb/in front springs 22mm front sway bar 250 lb/in rear springs no rear sway bar pretty thin RCAs on the front (18.5mm) lowered somewhat but not a ton 205/55R16 bridgestone RE-11s Koni yellow single-adjustable (rebound only) race shocks -2.0º camber front and rear 2.5º caster (can't run more until I modify bodywork or relocate strut mounts rearward) 0 toe front 1/16" total toe in rear Next steps I was initially thinking of: put thicker (30mm) RCAs back on increase spring rate to 300 front, 350 rear (or even 350F, 400R) add a rear strut brace (front has a triangulated strut brace already) However, I was reading about tender + main spring setups and they seem really interesting (To be clear, I'm using the same terms Eibach is here: helper springs: soft, just keep main springs seated at full droop. tender springs: have sufficient spring rate to impact driving under other conditions; I've noticed that some people use these terms the other way around). It sounds like it could provide a good compromise between a car that corners fairly flat and doesn't move around to much on load transitions, but still has higher ability to absorb bumps well. One setup I was thinking of was: 350# main springs in the front, with #300 tenders, yielding an ~160# effective rate until the tenders reach coil bind. And something similar in the back. But, I also see lots of downsides: it seems like with the simple shocks I'm using, you'll only be valved decently for either the soft or the firm part of the range. it seems like this setup would actually be worse than my current setup for high speed stability by reducing the effective rate in those conditions. the bump absorbing ability would only be improved when the suspension isn't already compressed, so it does nothing to help when cornering near the limit and hitting some uneven pavement, i.e. conditions where you actually want this. the sudden transition from 160# to 350# spring rate after an inch or so of compression sounds like a great way to unsettle the chassis. Anyone here have any experience experimenting with a setup like this? It sounded good on the face of it, but I'm not convinced it can work. But if it can't, then why does these setups exist? Is it just another compromise between comfort and handling, or are there actual rear-world handling benefits from a setup like this? My goals for the car are: 1: fun to drive on back roads, and okay to drive on regular streets and highways. and that performs well enough on the track that it's fun to push it to its traction limit (which it wasn't really with the high amount of roll and floatyness I got last weekend) doesn't have be super comfortable on our pothole ridden California highways, but I do want to be able to drive it fast-ish on less than perfect surfaces, so it should be compliant enough for tires to remain in contact with the road most of the time. Some pics to show the amount of roll:

Maxima Racing Oils makes a nice conventional oil that has higher zinc content than Valvoline VR1 and costs less. I'm running their 10W40 in my L-series: http://www.maximausa.com/product/performance/

Just read the last 55 pages, holy shit what a project. Amazing work, kudos. And congrats on getting it running so well.

Also, for rod knock, don't pull your plugs in pairs. Pull them one at a time as each piston has its own rod. So pulling one at a time changes the load on the bearings one at a time. Pulling in pairs is used to determine if you spun a main bearing.

Could still be rod knock. I had a very similar noise on a built L16 in my 510. Also didn't go away with various plugs disconnected, but on closer inspection, did change very slightly with plug #3 disconnected. It still made a bad noise without the plug because the piston was moving further up than usual (due to the pulverized rod bearing) causing it to hit the spark plug and top of the combustion chamber. It sounded like the piston was banging against the cylinder head, which it turned out it indeed was. We tore apart the engine, and #3 rod bearing was gone.

Where's the overvoltage protection in the pic? Is it the secondary white insulated wire spool that sits to the right of the one around the back of the needle? At this point I'm just curious Looking at that picture (I failed to extract my gauges this week so that's what I got) the elegant simplicity of these old-school electronics is lovely. As much as I'm tempted to rip it all out sometimes and replace it with something solid-state, modern and more precise. It's pretty impressive to see this stuff last for 40 years and somehow I don't think any of my Arduino's are gonna make it for that long…