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PostPosted: Wed Apr 20, 2016 9:45 am 
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Location: Long Island, N.Y.
I'm so enjoying this clubs members and this forum. 8) So... I've got this bug up my butt about my Z not running 100% perfect. Yeah... I know... don't you feel terrible for me :lol: ? The issue wth my 1985 300ZX n/a 5 speed is that after I first start the car, put it into 1st gear and pull away, around 1,800 rpm the car starts to buck (like she's starving for gas). If I put it into 2nd it will stop bucking until I try accelerating. This will continue for only about 1/8 -1/4 mile and then clear up. Or, if I push thru the bucking and bring the rpm's up to around 3,500, in both 1st and 2nd gear, the bucking stops and all systems are a go.

The standard solution/answer would be to just let the car warm up to proper operating temperature. That is not an option for me because if my baby has a slight "cough" I want to fix it, not ignore it. If it were normal for all babies to "cough" when they're cold then maybe I can live with that. That's why I'm asking for your opinions. I would probably start looking at the PCV or EGR systems (if it has an EGR?) since they are temperature "sensitive" systems.

Howard

Your thoughts and experiences with similar issues would be greatly appreciated. I look forward to reading them. :idea: :? :thumbs_up:

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Last edited by HowardJ on Fri Apr 07, 2017 8:40 am, edited 1 time in total.

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PostPosted: Wed Apr 20, 2016 11:21 am 
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Do you have an electronic ignition or a point/condenser ignition?

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PostPosted: Wed Apr 20, 2016 11:24 am 
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Electronic and fuel injected (with only 33,000 miles).

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PostPosted: Wed Apr 20, 2016 4:20 pm 
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HowardJ, this is fairly common on early year Z31s. It happens on my 84 turbo as well, until I hit boost (usually by the end of the street). Very similar symptoms to yours...boggy/laggy and then accelerate and all systems are a go.

Source:
http://redz31.suomiz.net/pages/fuel.html

Edit: Easiest solution is to swap ECUs. (87NA for example). Or do what is mentioned in that link.


Last edited by Filipe on Thu Apr 21, 2016 8:47 am, edited 2 times in total.

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PostPosted: Wed Apr 20, 2016 5:16 pm 
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Wow. I can't believe Nissan could have sold a single car if they all did that during the test drive. There has to be something wrong with both your cars which can be corrected. No way would Datsun release a whole year of Zs which behaved like that.

What you're describing is called a 'stumble'. It happens when the engine transitions from one set of driving conditions to another and the ignition timing and fuel delivery don't match the new driving demands. Its common among Zs with Webers if the carbs aren't tuned right; when the throttle moves past the idle jet circuit and begins running on the mid range circuit, most of them have a noticeable stumble. It's also common among cars (any cars) whose ignition advance doesn't work as quickly as it should.

The fact that temperature seems to cure the problem sort of narrows it down to some circuit or system which is designed to deliver more fuel until the engine warms up; that system or circuit or switch isn't doing its job anymore. I don't have a schematic of the ZX fuel injector system, but I'd bet there was something called the "pre-heat sensor" or something, and that's where I'd start my search.

No way Datsun/Nissan let these cars hit the showroom with a stumble people just had to live with. This is something both of you can fix in your cars, probably with the replacement of a single Widget.

I'll bet Paul knows.

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PostPosted: Wed Apr 20, 2016 6:29 pm 
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Frank. Once again, I agree with you. Accepting a "stumble" is not an option and needs to be found and eradicated. :twisted:

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PostPosted: Wed Apr 20, 2016 9:11 pm 
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ERADICATED.
What an absolutely wonderful, delicious word. :twisted:
Yes! That's exactly what should be done to both of your stumble Gremlins. Locate them, fix bayonets, close with them and ERADICATE them. :thumbs_up:

I love it.

I plead ignorance about your injector system, but from what both of you are describing, I would suspect some sensor which monitors the engine temperature (or Exhaust Gas Temperature) or something, and is supposed to make some adjustment until the engine warms up (the way an automatic choke does for carbureted cars), and it just ain't doin' its job NoMo.

Filipe, you're not describing turbo lag, are you?

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PostPosted: Thu Apr 21, 2016 12:10 am 
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GuyZ...I'm saying it's normal, not that it's "right". You can fight it till you're purple in the face, or until the cows come home (preferably the shorter of the two :lol: ) but I assure you it is as normal as it gets for early year (84 and 85) Z31s. People often refer to it as the "lean surge" issue.

As to it being a turbo lag issue, trust that it is not. 8) It literally happens for the first 50 yards, but as soon as I give it it's first shot of boost (heavy acceleration) the issue is remedied.

Again, refer to the link I posted for potential solutions. "84-85 ECU’s (all) have been reported to have a small lean surge problem during the first 30 seconds or so of engine warm up. This is most likely an issue with the cold-start enrichment and can be remedied by switching from CHTS to FTS signal during startup."

Also - in regards to it being a "warmed up" issue, I don't think it is; simply because it's impossible for a car to warm up to temps in 40 degree weather within 50 yards of where I turned it on. Not to mention even on the mornings where I have warmed it up (sitting in my driveway before work), it still tends to happen until I give it that good bit of acceleration.

It feels as if the engine isn't getting enough gas (lean) and then it gets it all at once (surge). It really wakes me up in the morning. :shock:


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PostPosted: Thu Apr 21, 2016 6:44 am 
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Thnx Filipe (What're you doing up at 0100? :lol: )

So why does it limit revs and break down when Howard shifts into 2nd and tries to accelerate? And why does that go away so quickly for him if he revvs the engine above 1800? I completely accept that the car wouldn't be "warm" in 30 seconds. So what you're describing (both of you) is that a full-throttle blast cures it, regardless of temperature? Like clearing your throat before you can sing well?

Since they used the same injector system on both your cars, the difference would be...what?...a faulty ECU code? When did they change it and why wouldn't it have become a factory-wide recall program for all early Z31s? No offense ~ it still doesn't add up for me.
Yet.

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PostPosted: Thu Apr 21, 2016 8:53 am 
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Frank T wrote:
Thnx Filipe (What're you doing up at 0100? :lol: )


You must have thought I was kidding when I said I "eat, sleep and breathe Zs"...

Frank T wrote:
So why does it limit revs and break down when Howard shifts into 2nd and tries to accelerate? And why does that go away so quickly for him if he revvs the engine above 1800?


I haven't seen Howard's car yet, but this isn't the case for me. It will go beyond 1800, but it just sounds like it's not getting enough fuel. Yes, "clearing the throat" works for me.

Frank T wrote:
Since they used the same injector system on both your cars, the difference would be...what?...a faulty ECU code? When did they change it and why wouldn't it have become a factory-wide recall program for all early Z31s? No offense ~ it still doesn't add up for me.


We actually have slightly different harnesses as well, but I am not sure what the differences are. Some things never make it to recalls. Actually, a lot of things: Re: rear hatch springs on the new Zs.


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PostPosted: Thu Apr 21, 2016 6:41 pm 
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Frank. FSM (factory service manual-for those not familiar) shows a Fuel Temperature Sensor that I'll have to "Google" (or "Frank") to find out what it's supposed to do and when. Could the CHTS (cylinder head temperature sensor) maybe cause a lean mixture on a cold start.? It has an Exhaust gas sensor, so maybe? Clogged or malfunctioning evaporative emission canister or vapor vent lines? Possibilities? Questions questions questions. :shock: :?

Filipe. I know that our shared "stumble" issue isn't a major problem but... When I do find the culprit that's responsible I will definitely let you know. :thumbs_up:

Thank you both.
Howard

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PostPosted: Thu Apr 21, 2016 11:42 pm 
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A new CHTS won't fix it, as I've changed mine. ECTS (engine coolant temp sensor) won't do the trick either. You need to change the signal from CHTS to FTS, or get a newer ECU...both of these options serve as solutions to the best of my knowledge.


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PostPosted: Fri Apr 22, 2016 8:11 am 
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Location: Long Island, N.Y.
I've been told over the years (now decades) that not everything has to be complicated. "Keep it simple, Stupid" sticks in my head whenever I'm confronted with a mystery or one-of-a-kind phenomenon. I used to be a charging bull but have evolved (somewhat) into a slower, contemplative, old pitbull. The purchase of my "barn" find 1985 300ZX is new and foreign :lol: to me. I'm trying to learn as much as I can about these cars and CTZCC and ZCar have some really knowledgeable members (and some not so much). Slow and steady is another mantra I follow, so it may take awhile for me to find the cause of the "stumble". I wouldn't ever think about "Frankensteining" (not you Frank) the car with parts from other years to skirt around a problem that didn't exist when the car was new.
Thank you for all the comments. Keep them coming. 8) :thumbs_up:

HowardJ

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PostPosted: Fri Apr 22, 2016 10:38 am 
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Best of luck. Hundreds of thousands of cars come off the showroom floor every year with problems. The manufacture doesn't catch everything, especially for new generation/first year cars. I.e. the early year 370z has issues with the CSC, rear hatch springs, and the steering column lock. The 2015/16 wrx has issues with intake piping, etc. It's really not that abnormal, and usually gets fixed in the coming years (for example, the 1986 z31 doesn't have the lean surge issue) and the CSC is considerably less prone to failure in the 2011+ 370zs.

Alas, I digress. Please let us know if/when you fix it via a method not described in the link I provided.

:D

Edit:
-Try checking the codes on the ECU. That might furnish more info. I had 23, 24, 31 (none related to this issue).
-FWIW, I've changed the CHTS, ECTS, and O2 sensor, and the issue persisted.
-I am consulting with the higher Gods of the z31 world. I am being told that a bad CHTS, IACV and EGR would give temperature related drivability issues.

I personally have not done the IACV or EGR on my car, but I'll give it a go this summer.

While you're at it - maybe read into these posts a bit.
http://www.nissanforums.com/z31-300zx-t ... artup.html
http://www.zcar.com/forum/11-84-89-tech ... oblem.html
http://www.zdriver.com/forums/300zx-z31 ... cold-5465/


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PostPosted: Fri Apr 22, 2016 11:26 am 
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"I am being told that a bad CHTS, IACV and EGR would give temperature related drivability issues....."

Hmmmmmm...... 8)

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