Jump to content

76Datsun280z

76 Datsun 280z throttle sticking

Recommended Posts

Hello, first off I'd like to introduce myself to you all, I'm Austen Wilcox and I'm 17 years old. Three years ago for my 14th birthday, my parents bought me a 1976 Datsun 280z fixer upper you could definitely call it off of Ebay that was about 5 hours away. Ever since, we've been fixing the car up. I couldn't possibly describe everything that we have done to it because it's been pretty extensive and we finally finished it a couple months ago to the point where it's driveable and is all fixed up you could say. There's lots of things that we have encountered along the way with it. For example, the beginning of last summer the engine blew the head gasket, so my dad just decided we pull the entire engine and tranny and have them both rebuilt (the tranny popped out of reverse at the time) because they were in need of it. After taking the engine to a machine shop, we found out that the engine was a l24 engine with the l28 fuel injection system on it!! As I'm sure you guys are aware, the l24 heads weren't designed this way at all. We could never really figure out why it ran so rough, so that day we figured it out. That's just one of the stupid things that the previous owners have done to the car. I can't even begin to describe some of stupid things that they did, my gosh it's unbelieveable. After a few phone calls, we tracked down a l28 engine with nothing on it, we would just swap the fuel injection system and exhaust maniflold on it that we already had. After two weekends, we got the engine in the car. It started up without any adjusments which was kind of surprising to us but ran very rough. After playing with the timming, it runs a whole lot better. Except when it's cold, it runs very very rich and very rough, and that's something that I'm going to ask later on but one thing at a time I guess. Well anyway I won't ramble on and on about as I could write a whole lot more, so I get to the question. A couple weeks ago of driving it, the throttle started getting stuck at around 1800-2000rpm. I'm always noticing this when I come up to a stop light or basically when ever I stop. I just kick it down and I'm on my way, but I'd like to get this taken care of. For some reason when I'm playing with the throttle in the driveway, it won't get stuck! I'ts only when I'm driving it that it gets stuck, I don't know why. I was wondering if you could give me some tips on what to look for and what might need to be replaced. Anyway, sorry for all the rambling, but I'm sure you guys would like some pictures of it, so here she is without paint.

2lx1.png

Here it is in the driveway, you can't tell in the picture but it has an air dam on it.

3rm3.png

e1es9.png

Another thing that is new is the polished/crome valve cover that my dad bought for me off ebay that really spruces up the engine, again my camera on my phone doesn't do it justice.

4rw2.png

Share this post


Link to post
Share on other sites

My Z is my first car too. I still have it after purchasing it in '77 and it has slowly transformed into what I like. I bought my daughter her own 240Z which we fixed up and she still owns it too. Good luck with your Z and hope you keep it forever too!

Share this post


Link to post
Share on other sites
A couple weeks ago of driving it, the throttle started getting stuck at around 1800-2000rpm. I'm always noticing this when I come up to a stop light or basically when ever I stop. I just kick it down and I'm on my way, but I'd like to get this taken care of. For some reason when I'm playing with the throttle in the driveway, it won't get stuck! I'ts only when I'm driving it that it gets stuck, I don't know why. I was wondering if you could give me some tips on what to look for and what might need to be replaced.

I would start at the peddle and work my way towards the engine compartment. Checking lubrication of the linkage, cable, etc. That's going to lead you to the throttle body/air meter which other members can give you more help with.

I love my '75 280Z. Take care of that car and you'll get a lot of enjoyment for many years. Keep it as stock as possible. The value of stock 280's is going up quickly.

Share this post


Link to post
Share on other sites

Thanks, guys, I will look today and throttle lingage and see what I come up with. Also, what is that yellowish "bottle" used for? You can see it in the picture that I have of the engine. Mine isn't hooked up to anything and would like to know what it's used for. I can post a better picture of it if you'd like in case you don't know what I'm talking about.

Share this post


Link to post
Share on other sites

Gorgeous looking '76.

Man I wish my dad had priorities like yours! If it'd been up to my father I'd be rollin' a beater Honda like every other college student, haha!

Anyway, the funny thing about the FI-Z's is that there are a lot of big things that can go wrong based on a bunch of tiny little sensors. The first thing I would do, if you haven't done so already, is replace every sensor you can find. Trust me on this one. The electrical on this car is what's probably going to give you the biggest headaches.

Oh, not to mention vacuum leak issues... The fuel-injection is weird about vacuum.

Anyway, there is a 'fast idle' thingamabob on the FI-Z's as far as I know. I wish I could tell you exactly where it is, but a quick look through a Factory Service Manual will find exactly what you need.

If you don't have one, you can download a FSM in .pdf format from http://www.carfiche.com/ ... I also have a copy of this, as well as the Electronic Fuel Injection handbook for the '76.

Welcome to the community, I'm glad to see another youngster like me with a '76... silver nonetheless! :)

EDIT:

Also, the yellow-bottle (which used to be clear...ish) is a vacuum container as far as I know, and is hooked up to the inside of your car. I think this is what allows you to switch from the vents on your dash to your defrost vents... if this isn't hooked up it could spell fog trouble the next time it rains, ;).

Share this post


Link to post
Share on other sites

Thanks, yeah were going to have it painted silver which was it's original color which my dad thinks will be next summer, maybe sooner, hopefully. When we got it, half the car was primer gray, and the other was the original silver so apparently the owners before us never finished the job. We had a lot of body work done to it too. We had all the rust taken care of which it had a lot of at the time. It still does in one area which the guy missed, so we'll have to get the fixed too.

Also, the yellow-bottle (which used to be clear...ish) is a vacuum container as far as I know, and is hooked up to the inside of your car. I think this is what allows you to switch from the vents on your dash to your defrost vents... if this isn't hooked up it could spell fog trouble the next time it rains, ;).

Thanks for the help on that one. I've noticed that it gets very foggy in it real quick on those rainy days! The defroster works ok on keeping the windshield defogged but other than that, it all the other windows are all fogged up. Do any of you have any pictures that you could post of these hoses hooked up by chance? Thanks.

Share this post


Link to post
Share on other sites

I know when I replaced my stock throttle body on my fuel injected Z, the linkage that connects to the body kept getting "hung up" on the intake manifold. Kind of difficult to describe, but I had to file some of the plastic off one of the ends of the linkage to get it to get past the manifold without sticking. Again I would check the throttle and linkage where it connects to the throttle all the way back to gas pedal. Even check that the pedal isnt getting hung up on the carpet.

Share this post


Link to post
Share on other sites

Sorry guys for the long awaited reply/update on this, but I seemed to have fixed the problem by lubricating the throttle lingage every couple of days spraying it with WD40. A couple weeks ago I stopped spraying it and hasn't gottan stuck once so it seemed to fixed the problem.

Share this post


Link to post
Share on other sites

If it does it again look at the BCDD on the top of the throttle body this keeps the throttle from droping off when you let off the gas so it doesn't stall and if there is a vaccum problem it will keep it at a high rmp and come down very slowly like it is sticking. Good luck.

Share this post


Link to post
Share on other sites

Sounds like you have a great dad. Wish mine had bought me a Z car to fix up. I got an old pick-up instead.

Now on to your issues with your 76. Sensors, Vacuum, corrosion in the wires :devious: , the AFM, your dash pot, BCCD valve, not to keep going but all of these can and will cause problems on your Z someday.

To fix the sticking throttle I would trace it from the pedal to the throttle body cleaning and relubricating every moving part. like stated above. Also check the spring located on the throttle body. If this does not have enough tension to return your throttle valve back to the closed position then you would also get the same problem.

As for your car running rich and rough when cold. I would say it’s a reading problem. What I mean buy that is, the computer is getting an incorrect reading of the temperature so it is feeding to much fuel for the air mixture. This could be caused buy a couple of things. A bad air temp sensor in the AFM, A bad thermo time switch, a bad water temp sensor, your cold start valve could be sticking open, which I doubt; it would run rich all the time then. Or you could be getting a bad connection to one of these items. If your Z is like mine then wires are so old they are corroded all the way back to the computer which gives the wrong resistance/readings to the brain and it causes crazy problems here and there.

Good luck with the Z and keep us posted on your progress.

Share this post


Link to post
Share on other sites
On 10/14/2006 at 2:32 PM, KDMatt said:

the yellow-bottle (which used to be clear...ish) is a vacuum container as far as I know, and is hooked up to the inside of your car. I think this is what allows you to switch from the vents on your dash to your defrost vents... if this isn't hooked up it could spell fog trouble the next time it rains,

That bottle is just a vacum reservoir, which stores some vacuum so you can change the vent function while you are at low revs or low vacuum.

Share this post


Link to post
Share on other sites

In my case, the sticking is in the large torsion bar bearing on the firewall.  I  don't think it can be disassembled, polished,  or repaired.

Share this post


Link to post
Share on other sites

Necro posto...  He hasn't been on the site since 2008.

image.png

I found that what felt like sticking was actually the bell crank being adjusted, or out of adjustment, so that the starting point was "over center".  You had to apply extra force to the pedal to get it over the top then it would gain leverage and get easier, making it feel like it had been stuck.  You can lengthen or shorten most of the little arms of the linkage to fix that problem.

 

 

Share this post


Link to post
Share on other sites

I don't feel any resistance when pressing on the throttle pedal.  In stead, when you press a bit on the throttle, like if you were just trying to get the car to roll forward slowly,  the throttle would stay where you had it, like a sort of high-idle.  Giving it a little blip will allow it to settle down  to the 800 RPM.

I looked into the bearing, and it gets cocked in the seat, so I think that's what is happening- you press on the throttle, the looseness on the bearing allows it to get cocked, and it stays where it is. 

I don't think you can disassemble that part.  It should have been designed better, with a sealed bearing instead of a ball-and-socket arrangement.

 

bearing.jpg

Edited by TomoHawk

Share this post


Link to post
Share on other sites

Could be a gummed up throttle body blade.  Nissan rerouted the PCV hoses to combat that.

Share this post


Link to post
Share on other sites

I had to move that part above when putting SU's on my 280z.  Only the two outside 3 holes are used on the 280z.  The unused middle hole aligns perfectly with the left most captive nut  the when moving the part to align with the SU intake.

 

relocate.jpg

Share this post


Link to post
Share on other sites

I fought a sticky throttle body causing a handing idle for quite some time. Here's some of my (mis)adventures:
https://www.classiczcars.com/forums/topic/45152-sticky-throttle-body-hanging-idle/

I even modified my throttle body to include delrin bushings instead of the original worn steel bushings"
https://www.classiczcars.com/forums/topic/57126-sticky-throttle-body-fix-delrin-bushings/

None of that worked. In fact, my Delrin bushings were even grabbier than the stock steel and made matters worse. Worked fine when cold, but caused significant troubles once everything got hot and expanded. That project was a complete failure.

I finally gave up and switched over to a completely different throttle body from another car, and it's awesome. I've been meaning to post up details. but haven't had the chance. I will do that soon.

Share this post


Link to post
Share on other sites
On 8/10/2018 at 6:04 PM, Zed Head said:

Could be a gummed up throttle body blade.  Nissan rerouted the PCV hoses to combat that.

That's what caused my hanging high RPM.  Cleaned the throat with lacquer thinner and an old toothbrush then rerouted the PCV hoses like the '78s.  Works good now.

 

 

Share this post


Link to post
Share on other sites
On 10/13/2006 at 7:15 PM, 76Datsun280z said:

. After taking the engine to a machine shop, we found out that the engine was a l24 engine with the l28 fuel injection system on it!! As I'm sure you guys are aware, the l24 heads weren't designed this way at all.

After a few phone calls, we tracked down a l28 engine with nothing on it, we would just swap the fuel injection system and exhaust maniflold on it that we already had.

Except when it's cold, it runs very very rich and very rough, and that's something that I'm going to ask later on but one thing at a time I guess.

the throttle started getting stuck at around 1800-2000rpm. I'm always noticing this when I come up to a stop light or basically when ever I stop. I just kick it down and I'm on my way, but I'd like to get this taken care of. For some reason when I'm playing with the throttle in the driveway, it won't get stuck! I'ts only when I'm driving it that it gets stuck, I don't know why.

On the sticking throttle, one thing about the gummed up throttle blade is that it only happened when the engine got warm.  Which might fit your symptoms.  If by "kick it down" you mean pull it up with your toe, then that's a sign.

Nissan did make a fuel injected L24 engine.  The L24E, used in the Maximas.  Could be what you had.  Might also be that you had an L24 with an L28E head.  Check the head markings for that.  N42, N47, P79, P90.  The Maxima L24E had an N47 head but it had a CHTS, which the 280Z N47 head did not have.  That's how you tell them apart.

Running rich cold but not hot is kind of odd.  Usually they just run rich all the time.  Good luck.

Share this post


Link to post
Share on other sites

It was the carpet, bunching up in the corner next to the throttle pedal.  I took off the little connection rods to find where it was sticking.  The plastic bushings were 'gunked up' a little, but didn't 'stick.'  I can smooth the carpet out, but it bunches up again after a while from your foot making the carpet move around while you drive.  The plastic protector bit  next to the throttle pedal just won't lay flat-  can you smooth it out with some heat maybe?  Maybe I can get some Velcro on the transmission tunnel to keep the carpet in place, or maybe the padding underneath  needs some work.

Bruce-  Can you just tell us the source of your awesome throttle body?

Edited by TomoHawk

Share this post


Link to post
Share on other sites

The throttle body I've been working with is (basically) from a 96-98 Sentra. There are some differences between the beginning and end of that range. Most noticeably the inclusion or lack of a vacuum port for the distributor advance. The earlier ones (96) have the port, but they stopped using the port in 97. Presumably digitally controlled instead of vacuum starting in 97.

It's not a direct drop-in swap, but it's manageable. I had to make some customizations, but here's a teaser:
P1100831.JPG

One thing to note on the above pic is the green spring in the lower left of the Sentra throttle body. That spring is part of a system that boosts the idle when cold by acting on the throttle linkage. It's essentially the same function performed by the AAR system on the 280Z. Using the throttle body above allowed me to completely remove the AAR system and all it's associated plumbing while still having a boosted idle when the engine was cold. The tradeoff is that you have to plumb the new throttle body with coolant to heat up the built-in thermostat.

If you don't mind keeping the original AAR idle boosting system, then here's another option... I didn't buy one and dissect it in my shop, but just from analyzing at the yard, I believe the throttle body from an earlier Sentra would be a pretty easy adaption as well. This is from 94, but I don't know the year range. It's simpler than the 96-98 version as it does not have the temperature controlled idle boost incorporated into the linkage. I chose the 96-98 version because the temperature controlled idle boost allowed me to get rid of the whole AAR system and still have a boosted cold idle. Note that this one has the vacuum port connection for the distributor:

P1120317.JPG

Share this post


Link to post
Share on other sites

Thanks.

Unfortunately, the cylinder head on something like the L28 is more-or-less perfectly-designed for street use.  To make use of a large-bore throttle, you'd need a cylinder head with larger combustion chambers and valves, larger ports, larger intake runners, ad a larger plenum.  There is someone on CZCC that has constructed a successful twin-cam cylinder head, but that's all I've heard of it.

It's too bad the cylinder head is about the only part that doesn't have a modern substitute, like the 4LN71 or 300ZX  transmissions and the Hellfire EFI.

Share this post


Link to post
Share on other sites

BTW-   Somene mentioned elsewhere that you could also use a Cressida or Ford Aspire throttle/AFM as well, if you need something to ponder  after 17 beers..

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×

Important Information

By using this site, you agree to our Terms of Use.