S13 Ka low throttle hesitation, bucking, flat spot.

Basic tech questions such as future setups, different turbo kits, car diagnosis, etc
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Joined: Fri Nov 23, 2018 3:22 pm

S13 Ka low throttle hesitation, bucking, flat spot.

Post by SleepyFoxxS13 » Fri Nov 23, 2018 4:42 pm

Hey everyone thanks for reading this!
I'm at my wits end with my hatch and I'm not sure what to do next or where to turn, so here I am.

So before I get into the problem ill give ya a quick rundown of my background with the car and the setup on the car.

I've owned this car for about 10 years now. I boosted it myself about 7-8 years ago with alot of information I gathered from this site and nicoclub.

The car has had no running problems prior to my current issue starting. It has been running on the same setup (turbo, ecu,etc) for almost 2 years before it started acting up.

-Its a 91 ka24de
-Running on a chipped John kerr basemap from J K tuning
-Top mount forward placement cxracing manifold (the more expensive one, not the ram horn looking one)
-T3t04e 50 trim
-38mm external wg (5psi spring)
-Godspeed fmic
-VTA bov before MAF
-Stock MAF (blow thru)
-370cc injectors
-255lph fuel pump
-ARP headstuds with felpro HG

The motor has near perfect compression and pulls good vacuum @ idle so im not suspecting anything internal.

Now, on to the crux of my issue.
My cars drivability is trash. Cruising is the worst. The main problem I have is definitely throttle % input related. The car does not like to maintain speed-cruise
Now id say that's mainly because of the fact that when cruising i am at a low throttle %. Something like 3-10% throttle about.

While in that range of percentage the car acts like it doesn't know what to do with the input it's receiving. In the past the car would start to pick up and feel lively and want to rev with even the smallest bit of throttle. Now all it does it load up the turbo and feel sluggish-late to respond. You can hear the turbo spool sound a bit even though you are low throttle low rpm, and no where near close to spooling rpm or throttle %.
While at this low rpm low throttle input state it will sometimes fall flat like its not seeing any throttle or It'll buck down the road full neckjerker style. Id also note that my mpgs are not the same and im probably running rich.

The only way to drive the car currently is to hit the throttle at least about 20% and force the turbo to spool a bit to make it "overcome" the problem area.
Now even if you do this you can still feel the car is being held back-responding sluggishly. If you hold the throttle at a position where you know boost will come on when it reaches the right range and just feel the motor climb through the rpm it feels wrong. Almost like you can feel the hang up the car is having, because sometimes it'll just click in and run and respond smoother after holding the throttle steady for awhile (only at larger throttle increments does it do this and its only really something you notice by the seat of you pants- knowing the car well) Even after it sometime clears up like that momentarily it will only be for that one pull or accel and its right back to running sluggishly and herky jerky next time.

So basically I hate driving the car currently cause my cruising ability is gone, it's harsh accel or decel, no maintaining speed for me and it's driving me nuts on practical level and a mechanical one.

What I've done so far to no avail:
-swapped maf
-rewired maf pigtail
-checked fuel rail for leaks (none)
-replaced injector o rings anyways
-checked ecu codes (all clear)

Now id also like to mention that im having a problem with my WG opening wayy early. Like it'll crack open at 2k rpms under heavy throttle wayy before boost, you can clearly hear it ( it's open dump)

The only reason I don't think it's relevant to the issue though is because that's a large throttle% problem and it stays clesed while my main problem is occuring.
I also tried disconnecting and plugging the line to my wg to see if my flat spot-hesitation-bucking at low throttle would clear up and nope, no luck.

So hey If you stuck with me through reading all that and have any kind of suggestions for me on what you think i should test please let me know!
If you have any questions or need more information ask away.

I appreciate any help you could give. Thanks

Posts: 3508
Joined: Wed May 31, 2006 6:40 am
Location: Louisville, KY

Re: S13 Ka low throttle hesitation, bucking, flat spot.

Post by adamky » Tue Nov 27, 2018 7:03 pm

I didn't see any mention of your TPS sensor. Check all of the connections and check/monitor voltage, especially when it's doing this "bucking". I bet you have a wiring short or loose connection that's causing all of this.

If it turns out that all connections are good, try resetting the TPS sensor as described here: viewtopic.php?p=485045#p485045
Wiseco/Eagle, JWT S1 cams, BC valve springs, PT5857, ID1700 injectors, SR20DET ECU w/ Nismotronic, etc, etc...
--> YouTube channel --> my build thread

Posts: 2
Joined: Fri Nov 23, 2018 3:22 pm

Re: S13 Ka low throttle hesitation, bucking, flat spot.

Post by SleepyFoxxS13 » Fri Nov 30, 2018 5:32 pm

Thanks for the suggestion.

I'll give it a go and get back and let ya know how it turns out!

Also sidenote, I just recently replaced the distributor cap in an attempt to fix the problem. My old cap was ugly so it needed replacing anyways.

Problem still exist as of now but i'll check the TPS and be back with an update asap.

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