tehweej

my 280z runs rough at idle, and up to about 2000rpm. i checked the timing, it was about at 15 degrees BTDC, so i retarded it to 10 degrees BTDC. it helped a little, but it still does the same thing. once you get up past 2000 rpm, it smooth out. any ideas?

snwbrderphat540

could be old plugs, wires, cap, roter, cold start valve, any of those simple little things. gotta give us more info though than that, such as what you have new on it, etc.

tehweej

ive put new plugs in, havent done the wires, dizzy looks fairly new, the points inside are not corroded or anything. i ran some seafoam through the intake and into the crankcase. it was running fine earlier, but then it just started to run really rough, like it was pinging really badly. but what is really confusing is that this morning it is running fine.

BoulderZ

I'd check fuel delivery, too. Put a pressure gauge in between the filter and the fuel rail, and check that you've got the correct pressure, especially when it hits the running-rough condition. Also try spraying some starter fluid into the intake when it's running rough. If it runs better with the "manual enrichment", you know you're not getting fuel. If you're not getting fuel, and the pressure gauge is still at spec, then maybe it's a clogged or failing injector.
Dave

tehweej

ok, ill try the starter fluid. what kind of pressure gauge do i need to put in between the filter and the rail? thanks!

tehweej

when i rev the engine, or in between shifts, the engine drops to about 200 rpm, then picks back up. it still is running smooth now other than that.

naviathan

Sounds like one of two things:
1 - BCDD is malfunctioning causing your idle drop
2 - You have a vacuum leak

(Note: BCDD - Boost Controlled Deceleration Device - Yes, it's in the FSM)

BoulderZ

After revving, drops to about 200 rpm, then recovers? That almost sounds more like the throttle position switch (TPS), or maybe the air flow meter (AFM). There're a couple of regulars on here with some great info on those items: NismoPick, Theramz, J, and snow (I've probably forgotten some one, my apologies in advance). Hopefully they'll have some input on that. Sometimes it's as simple as just cleaning up those connections, but those guys have some great ways to clean/refurbish/modify those pieces to work better, too.

Oh, good info from naviathan, too. I knew I'd forget somebody. Sorry.

For the fuel pressure gauge, I just bought one at Sears because I was getting some tools there anyway. But a lot of parts houses should have them, too. Should just be a fuel pressure gauge or tester, and then thread in hose barb fittings for it. Couple of clamps and an extra piece of high pressure fuel hose, and you're all set. I think the whole setup is under $20. A lot of guys leave it hooked up permanently that way as it makes diagnosis on the EFI a lot easier, and it kinda looks nice under the hood. Some aftermarket fuel rails, like Pallnet's, even have a provision for a permanent/integrated pressure gauge for the same reasons.

Dave

tehweej

sweet thanks for the info. ive got a chilton's manual, so that will be useful. and to check for a vac leak, where are the most common places that z's have leaks at? and the vac lines all come out of the intake header correct? it will be a couple of days before i can really work on it again, but it seems to be doing better.

also vac leaks can cause a high idle, right? when i got it, it idled at 1500 rpm, so i adjust the idle screw to get it down to spec. so that would make sense if it had a vac leak somewheres.

BoulderZ

All the vac lines should be coming off of the intake. But, it seems a lot of people have had vac leaks from other parts attached to it. Like a loose injector or CSV, or a cracked boot between the AFM and the throttle body. Fortunately it's all easy to get at and test.

naviathan: is there a way to rebuild the BCDD that you know of? Or is it just a "replace it when it's dead" item?

thanks,
Dave

tehweej

upon further investigation (opening the hood and actually LOOKING for vacuum leaks) i found 2 lines that were CUT, and a couple others that were disconnected. the dist. vac line was disconnected at the fume filter thingy and the diaphragm on the dist. i am going to go down to o'reilly and get 20 some feet of vacuum line. it looks like i will need lots...

naviathan

There was a write up on one model of the BCDD on hybridz a long time ago that detailed how to "refresh" the BCDD. I considered rebuilding mine and detailing it, just need to find the time now.

BoulderZ

Props to naviathan on the vac leak diagnosis!
Hey, at least it was an easy find for you. Hope that fixes it. I can say 15 feet isn't enough vac line to replace all of it. I need to go get another 15 (I'm doing all the lines in on the a/c and heat systems, too), and that's just the skinny stuff (all mine are dried out pretty badly). The funny part was that the parts guy was at first shocked I wanted even 15 feet. Then I explained what car it was for, and he said, "Oh! Yeah, that makes sense." There's a lot of vac lines in there, for sure.
good luck,
Dave

tehweej

ok, 30 feet it is. that should keep me busy for a while. hopefully the problem goes away. if not, ill try the BCDD.

*edit* oh and do you happen to have the link for the BCDD rebuild?

BoulderZ

Note: that's only if you're going to replace all of 'em. Were all of yours looking bad, or just the couple of them that were cut/missing? Mine were all a disaster due to 1) dry climate and 2) previous owner did not understand this "maintenance" thing...

tehweej

most of them were stiff, starting to crack, cracking at ends, etc. and as long as i am at it, i might as well do them all.

naviathan

It's always good to replace them all once you start. I've seen lines that felt nice and flexible, almost new looking, start to split in the ends. One of the beautiful chores of owning a 25+ year old car. Of course it's all worth it. It amazes me even now, after two years I still enjoy driving my 81ZX NA more than any other car I've ever driven. And I've had some nice rentals on business trips. I wonder what kind of devilish things my 77 will do when it's finally on the road again....

tehweej

so i didnt realize that there were about 4 different sizes of vacuum lines. i went to my local parts store and got some 3/8" fuel line, which worked for the distributor lines, but there are small ones and even smaller lines. i am also confused on exactly how the lines are run, since some of mine were disconnected/cut when i got it. the part that i am most confused on is the passenger side, there are 2 lines that come from the int mani, the run behind the engine to what look like solenoids mounted on the passenger side wheel well. there is another line over there that goes into the firewall (heater? once i hooked the lines back up it started working...). 2 of the 3 lines were cut, and im not sure how exactly they hook up. the FSM i have only shows a vac diagram for a 1980 280zx at the earliest. ill try to post some pics tonight of what i am talking about.

i also heard that when you pull the dipstick or take off the oil fill cap, the engine should stumble, if not then you have a vac leak, or something of the like. my engine doesnt do anything when i remove the cap or dipstick, so i am thinking i didnt find all the leaks.

how important is the vac advance on the distributor? the connection for the dist vac on my canister is all busted, and that line also T's to the bottom of the throttle body. any body know what that does?

naviathan

Go to http://carfiche.com and download the appropriate FSM for your car. There are vacuum diagrams in there that will help you out a lot.

tehweej

nice, thanks. i will have to do that when i am not at work

tehweej

ok now the engine is having different problems. it idles slightly rough, but when i accelerate, the engine seems to hesitate from 1k-4k rpm. when i get past 4k, it seems to run fine. im not sure what to make of this one...

tehweej

i finally got it running smooth! its amazing what can happen when you put new plugs wires that actually have the electrode contact inside the boot... anyways, i put a new ignition coil on and now it starts faster, run a lil smoother and seems to run quieter (odd to me but hey, no harm done right?). i changed the diff oil, which when it came out seemed more the consistency of motor oil, and the tranny oil, same story.

snwbrderphat540

thats like..... what i first said to do. lol.

and as for the gear lube, how did it smell is more or less how you tell the age of diff/tranny fluid.