Well I took the car out this weekend to do some romping and come to find out it feels like it hits a wall at about 5250 rpms. It feels like there is a rev-limiter; it revs fine up until this point and then stops reving completely, it does not studder just wont rev anymore. I checked the plugs to see if they were fouled or worn but they all checked out. I also unplugged the ecm and plugged it back in with no avail. I have been meaning to check the vaccum hoses but have not gotten around to it. Could this be causing the problem? I would think that if it was the vaccum hoses it would not rev normally thoroughout the rpm band. Thanks in advance.

 

From what I've heard, the L engines do top off at around those rpm's. I think it has something to do with the valvetrain or fuel supply not being able to keep up at high rpm's.

 

I have always been able to pull it all the way to 6k rpms without a problem before this started. I have also never had valve float either if thats what your talking about. But could the valves float out of the blue like this with out it happening before?

 

Sounds like your ECU is acting up. Especially if you say it's pulling hard all the way to that point. The computer might be getting a bad signal (or just screwed up in general), and cutting off fuel or spark at that point. Check your ignition wires and make sure everything is in good order. Make sure all your grounds are good too. I'll try to think of anything else. What year and trans do you have?

 

Not likely unless you broke or damaged something. Your valvetrain should be able to handle over 6K anyways(don't recommend it) without getting valve float with a stock cam. In which case, if something did break or get damaged, you'd probably notice it, and you'd literaly have to damage all your springs for you to just all of a sudden have valve float with doing any mods to your head.

 

Thanks for the thoughts guys. I appreciate the replies. I hope I get some more so I can figure this out.

It is a stock 5spd from and 83'. Or atleast it should be.

 

Well that means it's not your torque convertor giving out at that RPM.
I would definitely investigate your ignition system and the ECU. I doubt it's the fuel pump because that would feel more like your car is running out of gas then hitting a wall.

 

(JFAIRLADYZ:Well that means it's not your torque convertor giving out at that RPM.
I would definitely investigate your ignition system and the ECU. I doubt it's the fuel pump because that would feel more like your car is running out of gas then hitting a wall.)


So its most likly the ECU keeping it frm revving past 5250rpm??? my 280 goes all the way to 7200rpm with no problems, although it does slow alil after 6000rpm but thats the cam,starts to lose torque,

 

That or something with the ignition cutting out. Somethings cutting out though. That's for sure. The question is why.
So heres what you do. Pull everything out of your engine compartment. Order a brand new rebuilt engine. Then go to Nissan and buy a wiring harness and everything you ripped out of the engine compartment brand new. That should definitely fix your problem.

Seriously though, if the ignition checks out, go to the junk yard or ask around to see if you can get an ecu for next to nothing and see if that helps. Borrow one if you can. Oh, and one more question, does the car only do that when you're driving it or does it stop reving while it's sitting there in Neutral too?

 

Yea that would help alot but also he would have to spend alot of $$ to change everythin and get an ECU... but IDK wher the actual fuel cut is at cuz I set my shift light to 7200 and the engine went up to 7200 but i dont want to risk taking any higher

 

Check your vacuum lines. If you have that crappy auto climate control like I do, check those lines that connect to the vacuum pump and stuff, one tiny leak from them and it can cause the problems you're talking about. Check the pcv valve hose too, it tends to crack since it's on the underside of the manifold near all that heat.

 

whay is all this talk about the ecu? if there was a problem with it don't you guys think the car would have a biger problem with runing then just a minor power strugle at 5000 rpm. the most logical thing that comes to mind for me is tps. you could have a flat spot, or corosion in that position. clean the tps plug conector, and the three prongs in the tps.

 

Well I believe I have found the problem. My 11 month old Crane PS-20 coil crapped out on me... Needless to say I am not buying anymore Crane ignition products.

 

I purchased a PS-40 Crane ignition coil "USED" off eBay back in 1997. I've put over 80,000 trouble free miles on it.

 

When I bought it I did so because of storys like yours. I guess I was lucky to be one of the few who was different

 

So it did end up being the ignition after all. Congratulations on fixing it! It always brings a tear to my eye when a fellow Z enthusiast gets his car back on the road and running right Well...maybe not always...Ok, it's more like never. But I am happy for you, probably not as happy as you are though.

 

are you sure it is the coil? because you know dwell is controled by your ignition module. transistor on transistor off remember that. if you are not charging the coil on the primary side the right way then what dose that do for the spark on secoundary? also have you herd of coil sateration? these are things to think about.

 

Eat my dust is right. Hi-voltage coils develop coil saturation at a slower rate than lower voltage coils. Because of this, if the IM wasn't in good shape internally to begin with (these things are old), the IM may have overworked itself into overheating trying to charge the slower coil under less dwell and damaging itself. Inhibiting it from allowing the quick dwell needed at high RPM's. So it might not be a bad coil, it could be a bad IM. Unless of course you already replaced the coil and the problem was fixed. But if the coil did damage the IM, then you should replace the coil too. Regardless of wether or not the IM was damaged by the coil or not, the IM may be stuck in a long dwell mode which won't allow the coil to charge at high RPM's thus limiting the rev range of the engine. Which makes perfect sense to your problem. But the coil could also be internally defective so as not to charge quickly enough to allow a strong enough spark above the above mentioned RPM. The secondary voltage is generated using resistance, so if the coil some how managed to short itself internally, allowing voltage a less resistant path, the output would be diminished, especially at high RPM's where it doesn't have a chance to fully charge anyways.

So I would suggest you first replace the coil, if you haven't already. Then replace the IM if needed.

 

Are you still having truoble: TOUGEZ with your engine only reaching 5250rpm or did you fix it now?just wontdering what is actually makin your car do that..

 

jfair puts it nicely. nice to know there is somone els out ther learning this electrical stuff, insted of thinking they are. its not complicated at all. the key is steping blocks. if you know what each part dose, how it dose it, and when its suposed to do it you can put the things together, and prety much diagnose anything with the right test. knowing your engine and the electronics of your car is number one if you ask me.

 

Well I have put about 150 miles on the new coil and so far so good. It pulls hard all the way to redline now. It must have been slowly going bad for awhile because it seems much more powerful (more so than when i was running straight pipe earlier this year). No problems so far; when you refer to the IM do you mean that little black box on the side of the distributer, if so I replaced that last summer.