280z, where are the Upper RPMs ?

[Davey G]

Help! Total noob here, with my first Z bought a week ago, currently doing suspension, weatherstrip, and interior redos. Engine has had a top end rebuild within the last 10,000 miles, and runs good. I know these L28s are torque monsters and this one pulls strong as well, but this thing struggles to want to climb above 4500 RPM or so, even in 2nd. This was originally a 4-speed, now with a 5 speed, so is the original rear end not a good match, and holding it back? Or could I be looking at other problems?

[leftover z]

The transmission & rear-end gearing have nothing to do with problems exceeding 4500 RPMS. I'd give your car a complete tuneup, with new NGK spark plugs, probably new wires, dizzy cap & rotor, fuel and air filters. Make sure you have it properly timed.

 

I'd start there, and see if there's any improvement.

[Davey G]

The transmission & rear-end gearing have nothing to do with problems exceeding 4500 RPMS. I'd give your car a complete tuneup, with new NGK spark plugs, probably new wires, dizzy cap & rotor, fuel and air filters. Make sure you have it properly timed.

 

I'd start there, and see if there's any improvement.

 

It got the tuneup before I bought it, at which time it got new cap and rotor, new wires, new plugs, new air flow meter, and timing. It has new tires. I've replaced the air filter since buying it.

[Scott_M67]

Does it feel like its starving for fuel, try the fuel filter and check the fuel pressure, these old cars are notorious for rusty gas tanks.

[ModernS30]

If you mean there is no power above these RPM's, you pretty much drop off at 4500 rpms. I can post the picture of my dyno chart if you would like. Also the tach's in these are crappy, sometimes mine doesn't like to climb above that much either. Remember is a 35 year old car.

[Davey G]

If you mean there is no power above these RPM's, you pretty much drop off at 4500 rpms. I can post the picture of my dyno chart if you would like. Also the tach's in these are crappy, sometimes mine doesn't like to climb above that much either. Remember is a 35 year old car.

 

Since the engine feels strong it may be that the tach is wacky. I'll check the fuel filter and pressure also.

[rdevenz]

My 1976 280Z was not reving very well when we first purchased and after new plugs and tune up, was still not reving smoothly. After driving for a couple of weeks all of a sudden the car was reving smooth with alot more power. The car had sat a lot previously.

[leftover z]

Ok, I re-read your first post. If it runs GOOD, and pulls hard up to 4500, then it might be your tach. Mine pulls hard all the way to redline. Maybe you can borrow someone's aftermarket tach, hook it up and compare it to your factory tach. Maybe you are really pulling to redline, but your factory tach just isn't reading it past 4500. I've seen other postings with tachs that do all sorts of weird ****, including going up to 3000 and sticking or bouncing around. When you hit 4500, does it FEEL normal, or does it feel like it wants to do more but can't? Until you check your tach, I probably wouldn't try to climb past your 4500 reading. Who knows what RPM you're hitting. Be happy it runs good. Or drive it "by ear"... alot of muscle cars did not have factory tachs.

[leftover z]

My 1976 280Z was not reving very well when we first purchased and after new plugs and tune up, was still not reving smoothly. After driving for a couple of weeks all of a sudden the car was reving smooth with alot more power. The car had sat a lot previously.

 

 

Probably had old gas that finally got diluted enough and burnt out. Gas doesn't last long before it goes sour. I'd change the fuel filter, as it is probably gunked up by now.

[T-Bone028]

Struggling to climb above 4500 RPM....I would guess you have an induction (air/fuel) issue. I'm assuming this is a 280Z with EFI. Like others suggested, drain the tank, change your fuel filters, put in fresh gas, and see if that helps. If it is EFI, perhaps you have an electrical issue.

[Daeron]

First off, if you weren't already familiar with it, http://forums.hybridz.org/showthread.php?t=135748&highlight=efi+bible+step

 

What do the plugs look like? Everything sounds vaguely like it isn't getting full fuel supply at the high RPM, which would lead towards fuel filter, fuel line clog, low pressure from old pump or poor contact, etc. However, you could also be having an injector problem, leaking too much fuel in and going rich.

 

A new AFM is slightly suspect to me, for some reason. If I were in your shoes I'd be tempted to test it's calibration, but that can be a wee bit involved and is probably somewhat astray. Still, you can get a ballpark on how close the wiper pattern is set just by checking it fully closed and fully open.

 

One other potential culprit is the TPS. Not sure how up to snuff you are on EFI terminology, but this is not a Throttle Position sensor; it is a 3 contact switch. At zero or light pedal, the signal voltage is fed from the center terminal to one side. Once the throttle is opened slightly, this "idle" contact is broken, and the computer interprets it as "cruise." The third contact is hit at 75% throttle (IIRC, check the book for certain) and puts the computer into "WOT" mode.

 

Calling the ECU in this machine a "computer" is almost a stretch by modern concepts.. Its closer to a super-complex switch than it is to the simplest of cell phones anymore. I say this to emphasize a point; there are not many reasons fuel could be lacking at this RPM (or if that isn't the problem, then fill in the blank.) Becoming intimately familiar with that EFI bible will benefit you greatly in the long run, if you choose to stick with the factory EFI.

[Davey G]

Well, after all that I've determined the tachometer is screwy. Today it would not register anything above 3900 RPM, though I had the car up to 100 mph (if the speedometer is correct), and it ran well, even if not perfect. I'll have to do a little electrical troubleshooting I guess.

[leftover z]

Well, after all that I've determined the tachometer is screwy. Today it would not register anything above 3900 RPM, though I had the car up to 100 mph (if the speedometer is correct), and it ran well, even if not perfect. I'll have to do a little electrical troubleshooting I guess.

 

 

Better to have a screwy tach then a screwy motor, so glad to hear that. If you can't fix your tach, you can get a used one for around $30. Cheaper than having to work on your engine. Does your tach rev past 3900 when you hit the throttle while sitting still? If you have a tall rearend gearing, 3900 might be close to 100mph.

[PanzerAce]

Davey, don't trust the tach untill you've confirmed it against someone else's or a GPS. They tend to be pretty optimistic

[leftover z]

Davey, don't trust the tach untill you've confirmed it against someone else's or a GPS. They tend to be pretty optimistic

 

 

Kind of like having a "rust-free Z"

[angel]

Kind of like having a "rust-free Z"

hi guys

question has anyone taken the L28 motor to high revs?i mean past limit?

I ask cause I love high revs and I have built high revs in higher stock engines like the RB30 etc.

Now I look att my s30z and wonder how hi could that L28 go in N/A form????

[leftover z]

I've run mine up to about 6200. I could probably go higher, but don't feel the need to as the power bank is well below that. Besides, I don't feel like blowing her up just to see how high I can go. Not until I feel the need for a V-8

[Two80z4me]

hi guys

question has anyone taken the L28 motor to high revs?i mean past limit?

I ask cause I love high revs and I have built high revs in higher stock engines like the RB30 etc.

Now I look att my s30z and wonder how hi could that L28 go in N/A form????

 

ive heard of people building carbed 240z's to be a comfortable 3k-9k race motor, but nothing street friendly

 

 

anyway, on the upper RPM's topic, whenever my fan clutch is engaged when the car is hot, it seems to take away alot, alot of my upper RPM's I.E. above 3,000rpm. If I need the power for auto-x I usually just pop the hood and tap the clutch loose and it'll stay off and then Ill have torque for days.