S14a SR20DET bucking at cruisung

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Pinto
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S14a SR20DET bucking at cruisung

Post by Pinto » Tue Sep 10, 2019 6:45 pm

Hi Guys!

At first sorry for my bad english - i give my best! :shock:

I have a 200SX S14a SR20DET with Nistune mapped by a respected company here in Austria/Vienna.

There are two problems, i think with the same cause:

1. The engine jerks at constant low speed.. For example driving at 50 km/h in 3rd or 4th gear constantly the engine tends to jerk/bump.
2. 2/3/4. gear when i leave the gas pedal to slow the car down and accelerate again it doesnt matter how smooth i touch the gas pedal, the engine makes a very unpleasant kick, sometimes continuously that i have to step the clutch again.

Very importand detail is that the problems are only when the VTC is on! When i disconnect the VTC the car goes smooth/normal...

It´s very exhausting to drive in town or at low speed. Any ideas? :)

Pinto
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Re: S14a SR20DET bucking at cruisung

Post by Pinto » Tue Sep 17, 2019 12:13 am

No ideas?? :cry:

Matt
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Re: S14a SR20DET bucking at cruisung

Post by Matt » Tue Sep 17, 2019 9:47 am

At a guess the vehicle is running lean during cruise conditions, which causes the bucking. Unsure how VCT would affect this at all, unless there is another issue (electrical when it is activated, or mechanical) vehicle related

Not enough information. It would be best to take back to the tuner, or at least get a log (with AFRs) so you can see the battery voltage, MAF, load etc to see at least what the ECU is seeing/doing

Pinto
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Re: S14a SR20DET bucking at cruisung

Post by Pinto » Tue Sep 17, 2019 8:07 pm

Okay i try to get a log!

Pinto
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Re: S14a SR20DET bucking at cruisung

Post by Pinto » Tue Sep 17, 2019 10:54 pm

Another question:

The vtc is "on" while cruising at constant speed, is this correct this way?
I think when the vtc would be "off" an goes "on" only while accelerating this problem would not exist..!?

Ist there a possibility to adjust the VTC to the throttle position?

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Re: S14a SR20DET bucking at cruisung

Post by Matt » Sat Sep 21, 2019 10:46 am

No to VCT on throttle position. It is turned on when above minimum load parameter (so yes probably on during cruise) and disabled when higher RPMs

Pinto
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Re: S14a SR20DET bucking at cruisung

Post by Pinto » Mon Sep 23, 2019 7:47 pm

Okay thanks.

Can you tell me what this parameter is? Cant find it in the manuals...

Image

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Re: S14a SR20DET bucking at cruisung

Post by Matt » Mon Sep 23, 2019 9:29 pm

See the mapping guide. VCT parameters in there. Basically when VCT is enabled (load)

louiswun
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Re: S14a SR20DET bucking at cruisung

Post by louiswun » Thu Oct 03, 2019 3:36 am

Hi Pinto,

Does your SR have aftermarket cams ? (not 100% cause by the cams, but symptom exaggerated after aftermarket cams installed).
I own my SR for 2 years now, since I change to 256 cams, it start to jerk (feels like engine pushing and pulling, bouncing back and forth ) at very low rpm, it jerk at fully warm up or hot engine, (it runs smooth on cold engine) but after the rpm climb up pass 1,200, the jerk is gone.
The same symptom only appears on my own SR and one of my friend's SR , both JDM zenki S14, both jerk after cams installed, all other customer's SR (with 256 cams) does not have this problem.
No, it is not ecu related, on my own car, I have nistune with all maps untouched except throttle enrichment, my friend have Power FC.
No, sure is not ecu or tuning related, I let my friend to use my nistune ecu and I change back to a factory ecu temporary, the jerk still there.
And the strange thing is, if I change back to a factory cat for annual inspection, the jerk is gone.

I'm not 100% sure but I think this problem is cause by timing chain slack (or the timing chain tensioner worn, SR timing chain tensioner is operate by oil pressure) , at very low engine rpm, the oil pressure is low, so low that not enough pressure to press tight on the timing chain, causing the cam angle sensor NOT 100% following the crank (bouncing back and forth causing timing drift).

When parked my car overnight, when I start the engine, my timing chain is so loose that I can hear my timing chain hitting the chain guide for a second , the guide in between 2 cam's pulley, but after the oil pressure build up, the timing chain is pressed firmly by the tensioner, the noise gone, cold engine with higher oil pressure.

I'm still using the early style coarse teeth tensioner thats come with my car, the tensioner teeth is normally one way engaged, the one way lock is still there, but too coarse to allow the chain to slack. I think I should change to S15 fine teeth tensioner.

Louis

Edit:
The jerk exaggerated after cams installed.
The jerk exaggerated slightly more after LSD installed, mostly dead stop trying to start move with steering turn.
The jerk exaggerated obviously after new ORC 409D clutch installed (ie: clutch disk damper spring softer than the old aftermarket strengthen clutch)

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Re: S14a SR20DET bucking at cruisung

Post by louiswun » Fri Oct 04, 2019 9:33 pm

Today I swap out the original coarse teeth chain tensioner, replace it with a USED S15 fine teeth tensioner, it did make a different.
The chain no longer hitting the chain guide on the first start up.
The jerk only appear at 800 rpm off throttle, once the throttle crack open, between 800 rpm to 1,200 rpm, the jerk is progressively disappear.
It used to be progressively increase jerk till 1,200 rpm to 1,500 rpm, I usually need to clutch disengage and free rev to climb the rev to clutch engage again to avoid the jerk, now no need to do that , just slightly increase throttle and jerk is gone.
Only a used/old fine teeth tensioner already fix the jerk and chain guide noise. I think a new one even better.

edit: The jerk now left, is cause by the clutch disk damper spring, it only appear at off throttle, and the bounce is less brutal.
Last edited by louiswun on Fri Oct 04, 2019 9:55 pm, edited 1 time in total.

louiswun
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Re: S14a SR20DET bucking at cruisung

Post by louiswun » Fri Oct 04, 2019 9:41 pm

Coarse teeth tensioner outlooking.
Attachments
20191004_183055.jpg
The original S14 Zenki coarse teeth tensioner , the hump is round and smaller .
20191004_183055.jpg (2.39 MiB) Viewed 168 times

louiswun
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Re: S14a SR20DET bucking at cruisung

Post by louiswun » Fri Oct 04, 2019 9:43 pm

S15 fine teeth tensioner, the hump is higher and NOT round .
Attachments
20191004_183047.jpg
20191004_183047.jpg (2.71 MiB) Viewed 168 times

PL
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Re: S14a SR20DET bucking at cruisung

Post by PL » Wed Oct 09, 2019 11:18 am

Hi Pinto,

I've seen SR's do this a few times. Mostly with aftermarket cams as Louis mentioned (hi Louis!).

Things that will make it worse:

- cams with more overlap
- leaner mixtures
- advanced IGN timing

I suspect you have a combination of these. The VTC advances the cam across the midrange but will only do this once warmed up and above a certain load point. It sounds like your VTC is active at cruise, so you may be able to adjust the load point at which it activates a bit higher.

You could also check mixtures and IGN timing in the problem area. You may be able to help by adding fuel and removing timing. But once again as Louis said - the problem is usually cam timing related.

Pete L

Pinto
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Re: S14a SR20DET bucking at cruisung

Post by Pinto » Thu Oct 10, 2019 9:44 pm

Hey Guys!

Yes, you are absolutely right, i have the HKS Step 1 cams!!
And in the last days i found two other guys with the same problem at the german sx-forum.

So the problem is definitiv from the cams in combination with the oem VTC...!!!

The "VTC Load Enable" ist set at 40 (should be oem). I will try to increase this value.
What do you think would be good for a first try?

Edit: I have the a brand new chain tensioner (new model oem Nissan) so this is obiously not the problem...

Pinto
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Re: S14a SR20DET bucking at cruisung

Post by Pinto » Fri Oct 11, 2019 10:29 pm

So...

Increase the load value doesnt change anything, because the "rpm enable" overrules the "load enable"
...so this doesnt solve the problem.

Do you have other ideas? Would it help to adjust the ignition timing in this "no-load-area"?

Today is set the "rpm enable" to 2.200 rpm, so i can cruise in town relaxed.. Dont think this is an otpimal final solution, but the jerk is sooo annoying :cry:

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