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Hitting a wall at 4500rpm [SOLVED]

Posted: Sat Sep 12, 2020 10:57 am
by hobbs1412
Hello! Long time lurker, frequent searcher. Glad to be making a post. I'm in need of some help... haha

I recently got around to turboing my KA. I had to go through some standard troubleshooting issues, but I've got it running really well.... EXCEPT, I can't seem to push it past 4500rpm!

Car specs: KA24DE (S13, OBD1), Nismotronic ECU (running MAP GM3bar / IAT), LC-1 WB, OEM 550cc injectors (refurbed), ISR 255lph pump, Circuit Sports FPR, knock-off ssqv BOV, EMUSA Cast manifold, Precision WG w/ 10psi spring, NGK plug wires, NGK BRK7E plugs (.28 gap), Garrett T3 .48, running PCV to catch-can to preturbo intake, Valve cover vent just has filter, Mishimoto FMIC,

Things I've checked/additional info:
-Mapping all fuel/timing trims during a pull. Nothing I can see is trimming either one.
-Mapped knock voltage. Looks OK I think. 1.4ish under load.
-Battery voltage is consistent.
-I tried the coil hotwire mod
-AFRs are right around 12 when it starts stumbling, so it doesn't appear to be a fuel map issue.
-Put a camera on FPR gauge during a pull. Looks like its 1:1 like it should be. No loss of pressure at 4500rpm.
-Timing set to 20deg at idle. Timing matches FIGNV in Tunercode.
-Replaced fuel filter, pump sock, plug wires, plugs, cap/rotor, coil, O2 sensor (calibrated after install)
-Boost leak check looks OK. Shoots right up to 10PSI
-All injectors reading 11 to 12 ohms.
-I tried tightening the BOV all the way. I thought it might be chattering. No change.

Things I haven't done:
-I have not done a cyl leak down test. This engine has not been rebuilt. Would a bad piston ring cause this issue? Car runs great all the way up to this point.
-I've got some 370cc injectors. I thought I might try those. Maybe I've got an injector sticking at higher rpm (not even sure if that's a thing, but I'm to the point where I'm grasping).
-The only other thing I thought I might try was swapping ignition modules. The way I understand it, they either work or they don't, but again, grasping.
-I've got the timing map set up to retard about 1 deg per psi when in boost (5psi = 15deg). My set up is rather mild. I wasn't sure if that was overdoing it and maybe I need to add some timing back?

Other notes:
The turbo is only hitting about 5psi by 4500rpm. This seemed unusual to me. This is my first turbo project, but I wasn't expecting that much lag. Very minimal shaft play on the turbo (journal bearing). I was told by the seller that it's a rebuilt .48 / 50 trim. I didn't measure the wheels to confirm. I think this particular spec is pretty common for KA builds. So, I was surprised that the boost was hitting that late. Not sure if this has any bearing on my current issues, but thought it might be worth mentioning.

Apologies if the post format is hard to read.

Any help would be great.

Re: Hitting a wall at 4500rpm

Posted: Sun Sep 13, 2020 8:24 am
by OnTheChip
Your best bet is to post this in the Nismotronic FB group:

Lots of experienced Nismotronic users there and John Kerr monitors it regularly.

Re: Hitting a wall at 4500rpm

Posted: Sun Sep 13, 2020 3:41 pm
by hobbs1412
Thanks for the heads up. I'll move it over there.

Re: Hitting a wall at 4500rpm

Posted: Fri Sep 18, 2020 12:40 am
by R34SR
Is that a typo where you said you are retarding one degree per psi but yet you posted 15 degrees for 5 psi?? If that means your running 10 degrees at 10 psi.... Your ignition timing is extremely retarded. When I'm doing a ballpark tune for low boost on the street to get my fuel maps right, I pull one degree per psi starting at 28 to 30 degrees for atmospheric (0 psi of boost)

Re: Hitting a wall at 4500rpm

Posted: Fri Sep 18, 2020 12:37 pm
by hobbs1412
Haha... that was not a typo, unfortunately. I guess when I read to pull 1deg per psi, i assumed that was off of base timing of 20deg. So, yes, I’m running a final ign value of 15deg at 5psi (5deg retarded off of base idle of 20). Sounds like I may have a significant timing issue. I’ll dig into that this weekend. Thanks for pointing that out!!

Re: Hitting a wall at 4500rpm

Posted: Sat Sep 19, 2020 2:02 am
by Boosted90Hardbody
What is your coil dwell time set to? Every time I've experienced higher rpm cutout, it's been due to too high of a dwell value. Stock coil seems to like 3.0 ms.

Re: Hitting a wall at 4500rpm

Posted: Sat Sep 19, 2020 3:18 pm
by hobbs1412
I found some really good timing info in an older thread. I updated my timing map. Definite improvement in HP. Still having my stumble issue at 4500.

Looking at the dwell settings, they are set 5.5-4.7 throughout the powerband. This seems high per your 3ms recommendation. I’ll try dropping those next and see how it goes. Thanks.

Re: Hitting a wall at 4500rpm [SOLVED]

Posted: Sun Sep 20, 2020 8:35 am
by hobbs1412
It ended up being the Ign Module. Grabbed one from a Quest van in the junkyard and swapped it. Ran great after that. Super weird that it was failing right at 4500 EVERY single time, but whatev's. Just glad it runs.

Thanks again for everyone's help.

Re: Hitting a wall at 4500rpm [SOLVED]

Posted: Sun Sep 20, 2020 8:52 am
by OnTheChip

Re: Hitting a wall at 4500rpm [SOLVED]

Posted: Sun Sep 20, 2020 8:21 pm
by R34SR
Glad you got it sorted... As for your timing, .look at a full ignition timing map for stock ka24de.....IIRC it commands somewhere around 28 to 30 degrees of timing in the higher rpm/ high load section for NA setup. That's where you start to pull 1 degree for every psi of boost you make for a ball park rough tune.....excessively retarded timing can be damaging too....extremely high EGT's ( exhaust gas temperatures) can burn valves and destroy your o2 sensor in no time.

Re: Hitting a wall at 4500rpm [SOLVED]

Posted: Tue Sep 22, 2020 1:05 am
by hobbs1412
Yea... looking back that was a little boneheaded on my end. Part of what through me off was the example tune that I downloaded with the NEMU software (very similar setup to what i was running... 550s, speed density... etc) It was pretty retarded across the entire map compared to what it should be. I’m guessing this was by design so someone new to tuning (me, for example) didn’t dump the tune in the ecu and immediately damage something. I ended up using one of the maps in the thread pasted below as a guide.

This was definitely a silver lining to having a faulty ign module. I probably would have ran with the timing way off for who-knows-how-long had you not replied to my original post with your suggestion.


Re: Hitting a wall at 4500rpm [SOLVED]

Posted: Sat Sep 26, 2020 9:44 am
by R34SR
Glad I could help