eec564 Posted June 5, 2009 Share Posted June 5, 2009 Megasquirt (including II) does in fact have programmable DFCO. Drivetrain slack isn't the issue when the jerking is rapid and repeating. tech9 was still using the stock EFI, so he didn't so much have a 'tune' on his car and whatever adjustability there is in the stock system. In his case, timing seemed to be the issue, specifically improperly functioning stock distributor, giving him extra timing at low rpms and screwing with his tune. Tune being all factors being inputted into the management of the engine, stock and limited, or fully programmable. Quote Link to comment Share on other sites More sharing options...
tech9 Posted August 12, 2009 Author Share Posted August 12, 2009 To bring this post back from the dead: Let me start by letting you know what I changed: Distributor (it is nothing engine related for sure, 100%, not 99% 100%) Flywheel Clutch / disc included Transmission (t5 swap) Driveshaft from t5 and rebuilt Half-shafts were rebuilt Put in new swaybar bushings / endlinks Swapped back to my original rear end (which I might swap back because this one is a little noisier) Still has this problem, and its not just a little, its bad. Its violently thrusts when slowing down, reverse, slow 1st gear, etc. You can hear movement in the rear, not really sure where its happening, but i'm tempted to hook up a camera down there while driving. No idea what could be causing it. Nothing "appears" loose or any slack. I mean the rear has some slack but same as the other diff I put in. I even took it to a shop, and they didn't even want to look at it. (we don't do those old RWD z's ) It actually seems worse now. Any ideas please?!? Quote Link to comment Share on other sites More sharing options...
tech9 Posted August 12, 2009 Author Share Posted August 12, 2009 I tried to hook up my webcam under the car so I can see what was going on, but it was just too loud and too shaky to see anything But I did get some phone videos and you can clearly hear the knocking i'm talking about, and you can also see when it happens. Only took about 5 minutes to get some good shots. pulling up to driveway slowly slowing down to turn corner in 2nd Backing out of driveway reverse These are normal driving conditions, this should not be happening. Quote Link to comment Share on other sites More sharing options...
eec564 Posted August 12, 2009 Share Posted August 12, 2009 Try completely unhooking the vacuum advance line from the distributor and going out and back in to your driveway. I'm wondering if you don't have it hooked up to ported vacuum, but constant. -Eric Edit: Wait, aren't you running the turbo ECU with CAS sensor, rather than traditional distributor? Quote Link to comment Share on other sites More sharing options...
tech9 Posted August 12, 2009 Author Share Posted August 12, 2009 No, 280zx dissy, tried 4 different ones. (including 1 new reman one) I really really do hope it is the dissy problem, since i'm going to convert to EDIS / COP soon. Quote Link to comment Share on other sites More sharing options...
eec564 Posted August 12, 2009 Share Posted August 12, 2009 This is the non-turbo car then? Unhook the vac line and drive 100 feet. Just try it. How did you time it? Quote Link to comment Share on other sites More sharing options...
tech9 Posted August 12, 2009 Author Share Posted August 12, 2009 Non turbo, stock NA motor. I have the dissy hooked up to a constant vac on the intake. I tried without vac, same issues. I timed using a timing gun, tried different timings, etc. I mean maybe i'm not real clear, it don't happen only at low speeds, it happens all the time. Crusing at 50, 30, pulling into the driveway, out of it, etc. I can just make it happen easy at low speeds. It dont happen when there is a lot of load on the drivetrain, ie accleration/deaccleration. To me it feels like slack, and the diff is making the clunking noises. Maybe I have 2 bad diffs? Should I have the other one checked out? Im running out of options here, and funds for this damn project. About ready to switch to honda. Everything seems tight on the suspension side, the diff is really the only area that could be causing the issues i'm assuming now. I really did think it was the ujoint on the half shafts and it turned out it wasn't. Maybe it wouldn't hurt to source another rear and put it in there, i'm a pro at taking the diff out now. Quote Link to comment Share on other sites More sharing options...
tech9 Posted August 12, 2009 Author Share Posted August 12, 2009 Let me put this out there: how much slack is too much slack on the rear? I noticed that on both rears there was some noticable slack. Quote Link to comment Share on other sites More sharing options...
eec564 Posted August 12, 2009 Share Posted August 12, 2009 Slack in a drivetrain normally isn't an issue. As long as there is a smooth and constant amount of power going to the wheels then there isn't trouble. Under no normal circumstances should power be given to and then taken away rapidly. Even new cars will jerk and make clunking noises if you treat their accellerator pedals like the kick button in mortal combat. Your vacuum advance should be hooked up to ported vacuum, so there is no advance at idle, and then once you crack the throttle past perhaps 10 degrees, there is vacuum present. Time the car with that line unhooked and plugged. Which 280ZX distributor do you have? Are there one or two 2-pin connectors on the black box? Verify TDC on #1 with the tool that screws in to the spark plug hole and your rotate the engine by hand, that way you know your dampener hasn't slipped. Also, try enriching your entire fuel mixture by moving the AFM gear one tooth after marking the original position. See if you're running lean. A wideband is ideal, but making small changes to mixture to see what happens works too. Quote Link to comment Share on other sites More sharing options...
turboHLS30 Posted August 12, 2009 Share Posted August 12, 2009 Maybe your diffs are broken i had the same problem with my third gen RX7 Quote Link to comment Share on other sites More sharing options...
eec564 Posted August 12, 2009 Share Posted August 12, 2009 I kinda doubt the diff is the problem. He's tried two different ones, and in my experience with messed up gears, they work better at low speeds, and catch at high speeds. My grandpa's pickup has a chipped tooth in the 4wd transfer case, so in 4wd you can't go over 30mph, but works fine below that. Quote Link to comment Share on other sites More sharing options...
tech9 Posted August 12, 2009 Author Share Posted August 12, 2009 I would have to agree with the 2x diffs bad, since highway is almost perfect at high speeds 5th gear, but you never know. I will mess with the timing/dissy stuff this weekend when I have more time. The 280zx dissy is the one with 2x connectors on the black box, I have a few of them laying around, and I hate them, I can't wait for EDIS. Thanks for the help everyone. Quote Link to comment Share on other sites More sharing options...
eec564 Posted August 13, 2009 Share Posted August 13, 2009 When you say two connectors, do you mean two pins on the top? Or two separate connectors with two pins each? The one with two separate connections of two pins each adjusts timing in a weird way. Make sure your vacuum advance is ported, not constant, and just for kicks adjust your AFM 1/2 to 1 tooth looser to ritchen the mixture. See what happens. I won't be around for the weekend, going sailing, but I'll be back sometime later. -Eric Quote Link to comment Share on other sites More sharing options...
tech9 Posted August 14, 2009 Author Share Posted August 14, 2009 Forget the last 100 things I said. Found the problem and fixed it. A local colorado Z guy msg me, and told me he had the same issue with broken studs on the rear cover. So I inspected again, finding the previous owner put 2 different washers on the diff to mush bar, causing 1 to keep loosening even when torqued. Replaced both washers with new ones, torqued, perfect now. I can't believe it. Here is the washer in question, does this look right, the new ones I got worked perfect, just wondering what happened there? Quote Link to comment Share on other sites More sharing options...
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