Chasing A Buck

[Jacob1023]

Recently just traded a bike for a 97 with a s15 swap. It has been tuned with a factory s15 with 15 lbs boost. Atmosheric dump bov. z32 maf. Previous owner claimed ran great 2 months after tune and began bucking a month ago. Heres my troubleshooting story line.

Troubleshooting
Replaced fuel pump (ebay equivalent to walbro 255, they got me)

Ran like a champ for about 2 hours with 2 ignition cycles

The buck returns

Check voltage at fuel pump over 12 volts at tank cap connector

Spliced into the wires in tank reads 10.5-10 under throttle (not sure if something to do with being submerged in gas?)

Jumped relay

Changed fuel filter

Changed to another fuel pump (walbro 255)

Checked TPS (0.35-4v)

Change with unplugging MAF

No visual signs of ECU burnouts

Driving Troubleshoot

Under full throttle around 45k bucking occurs

If ease off gas the bucking lessens

Maintains boost without buck at low rpm

25-50% throttle bucking doesn't occur at all revs

Boost braking low rpm high boost no bucking


Any opinions on what to go after next?

[Prok0]

Have you checked the ECU to see if any error codes are present?

Have you boost leak tested the car to insure there are no large air leaks (torn coupler, BOV cracking open, etc.)?

What ECU tune is on the car right now? (NISTune, RS-Enthalpy, S-AFC?)

[Mikester]

Sounds like PO used octane booster. Run it as close to empty as your comfort level allows, fill it to the brim... then change the spark plugs. If he DID use octane booster, the plugs are cooked- that stuff is poison to SRs and RBs.

^^+1^^ check all of your couplings just to be sure nothing is leaking under heavy loads- small boost leak can cause similar problems.

Check the WG actuator to make sure it isn't ridiculously loose... Could be fluttering a bit under heavy throttle when everything gets hot. On that note, check all of your vacuum/boost lines- ensure they are in good condish & not cracked.

[Davidna2fi]

Check power wire at coilpack harness as you get into higher RPM, possible the voltage going to the coils is not enough since it is a high amp circuit and requires more current, so the spark would be weaker. You can't just free rev since high RPM without a load does not create the boost needed to blow out a weak spark.

[Jacob1023]

The buck finally caused me to blow the HG a few months ago.

Remove head, installed BC valve springs and retainers and used an APEXI 1.1mm HG and ARP head studs.

Got the car back running and noticed that there was a random misfire occurring with the coils. I.e. I took the missing coil off and replaced with another both were then missing swapped all around and back to running. Sometimes just moving the coil plug around would fix it and sometimes just removing it and reinstalling it would bring it back. Problem has been pointing towards an individual coil lately but rarely occurs anymore. New coil on the way to replace the coil that I actually failed resistance test then went back to okay. Still doesn't explain why random two and swapping coils wouldn't correct it.

And of course the buck is still present.

So to do some diagnostics I bought the innovative wideband and I/O box to do data logging with AFR.

Again the buck comes and goes.

Sometimes it runs strong with good AFR and then sometimes it begins to lean out until it reaches ~14 AFR and then bucks.

Heres the data log
Purple = APR
RED = %Throttle
Black = RPM

Good run on AFC settings that I bought the car with

69261

And here what the buck looks like

69262

Sometimes it trends like it running out of fuel but most of the times it quickly leans out at 3000+ RPM

Also I am getting some weird idling of it running to lean or rich at times and then out of no where fixing itself. And too get it back to 15 AFR I have to significantly change the % in the AFC

I've checked CAS, TPS, Temp, ig signal 1 and CAS are in data log, knock, changed MAF, been through wiring and moved wires around while it was missing, IAC didn't pass diagnostic manual procedure for unplugging TPS it idled higher and didn't notice a difference by unplugging it.

Tomorrow I'm going to put the MAF ECU input into the data logger to be sure my output from the AFC is okay.

Any more suggestions are greatly appreciated because I don't want to harm the engine again. Not sure what will go now that HG and bolts are upgraded.


Let me know what you all think.

[Jacob1023]

And to respond to the earlier comments

Did show a knock sensor code due to bad wire in harness and replaced.

I haven't leak tested it but as stated above I can do low throttle or RPM without signs of blow by.

There is no ECU tune that I am aware of just an APEXI neo

Have filled tank with shell supreme (92?) several times now.

WG actuator good.

All vacuum lines good. (have checked by spraying intake cleaner on all lines, plus all gaskets replaced with new after HG replacement)

I have checked voltage supply to coils but not while running while running under load (should be interesting since data logger has max of 5V have to rig up volt meter)

[fliprayzin240sx]

Ran a relay to the fuel pump...the wires might not be sending enough juice to the pump.

[Kingtal0n]

sounds like it could be the maf cut. Anyway to verify maf voltage with that ECU utility? Especially if using a SAFC it would be very easy on an OEM maf at 15psi to hit fuel cut. Are you using an SAFC? I thought it said you were. Even if you upgrade the maf it will not help.


Try lowering boost to 13~psi.

definitely sounds like a fuel issue since you popped the HG. Surprised you didnt eat up the deck too.

I've seen this on S15 swaps. The turbo just outruns the maf at that boost pressure- especially with bolt-ons.

[Jacob1023]

I did dial it down after the head rebuild, I also installed a boost controller while doing the tear down I believe its ~ 12 -13. But I do need to turn it down more because that's on zero. Manually wastegate actuator adjustment should bring it down more.

I got the MAF signal plugged into the data logger. But haven't been able to pull on it yet.

I got issues with the tune now. I noticed that the sensor type setting was no good and changed it to 2 in 6 out. Now going to need a good retune. This sound like a good path. Previous owner/tuner had it on 1 in 2 out.

From what I've read and seen from fooling with the APEXI NEO seems like it is a piece of shit. The only way I can get a stable AFR at idle is to unplug the o2 sensor. O2 compensating for the SAFC change. Not sure how that reacts at high throttle just noticed it trying to dial in the idle. This sound normal?

What's the easiest way to get this thing back to run factory setup/tune? Can I do it without removing z32 MAF.

[tom_sr20]

i have this exact same problem it comes and goes. take a look at your engine harness is it a custom engine harness made from wiring specialties or a hacked up oem harness cut up to work. i just messaged a member here that solved an issue like this, he said after all the parts he changed it came down to the engine harness and cas.

[Jacob1023]

Now that I shoot myself in the foot by messing with the safc and I have to retune. Check the maf is staying consistent. I'll try the straight power to fuel pump just because it's cheap and quick. Then move to an ecu considering multiple unusual things I've seen. I've been all through the harness but it has been hacked at quite a bit. Cas seems good from the data logger although read rate not quick enough to see individual pulses. I figure I need to just start playing swap tronics buy and selling until I find the little bastard.


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[tom_sr20]

wat do u plan on changing next. the ecu? let me know once u solve this problem. this is the exact same problem that i have.

[Jacob1023]

Began today by call apexi and asking what the in/out setting should be. They told me that z32 maf to sr20det should be 2/5. Ive read a couple places where people were claim different but Im going trust apexi.

At start up I was running an 17 afr. Check IACV by disconnecting and had major change. Disconnected o2. Both resulted in a lower afr but within about 30 sec or so it would slowly go back to 17. Disconnected fuel reg and dropped down to a steady 15. So decided to begin the tune without the vacuum connected to the reg.

Low throttle (<50%) settings are good again. Now the high throttle afr showed ok/bucking. heres the data log

purple - AFR
red - throttle %
blue - MAF ecu input

69481
+30% 3000rpm+

69482
+50% 3000rpm+

MAF signal tested good.
+ doesn't effect the fuel level at about 3500 rpm
not sure if boost should increase the pressure on the oem regulator (not connected)

its looking like a fuel supply issue. Im going to do relay with straight power to fuel pump tomorrow. And adjust the turbo actuator to reduce my boost.

Fuel regulator concerns me, but from what I've read I should have enough fuel to feed my setup.

Continue tomorrow....

[Jacob1023]

I did the straight power relay from battery. (+ only). Leaned and Bucked

Replaced suspect coil for idle miss firing. Bucked

Idle AFR still between 15-18. Rechecked for piping leaks with starter fluid with no signs of any leaking.

[Kingtal0n]

did you lower the boost to 13psi like i told you to?

also, lol @ using an SAFC with that setup. seriously get a real computer.

[Jacob1023]

My next move is to drop the boost down. I'll probably drop down to 8. I installed a boost controller and it's turned to min. I'm assuming adjustable actuator is causing it not to lower anymore.


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[kat7]

What kind of plugs are you using and what gap?

[Jacob1023]

Ngk iridiums. Somewhere around. .28-.3


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[kat7]

ngk which heat range 6,7,8.

[Kingtal0n]

its pretty obvious he is hitting boost cut and the engine is going lean. thats the main reason besides a spark blow-out that an sr20det would "buck" and its why he blew the HG previously.

get. a. real. computer.

also that Z32 maf is not helping your situation. And i do not see anywhere that it says what size injectors you are running. please do not tell me you still have 440cc injectors.

[Jacob1023]

I believe they are 7. I recall it in the part number. I'll have to check. I'm purchasing a leak down tester to check the piping. What exactly do you mean boost cut. Leak?


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[Jacob1023]

What is suggested for maf? Back to oem. And yes still factory injectors. From research I found they should supply.


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[Kingtal0n]

Use a stock maf. Stock computer. Stock injectors. Take out the SAFC (disable it with 1 wire). Turn the boost down to 13psi and drive it until you upgrade the turbo/computer/injectors/maf all at once.

[Jacob1023]

Adjusted actuator by 10 turns. Started with 8. Boost controller now allowing adjustment. Adjusted to 10. Attempted 13 and buck. But so far safe at 11.


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[Jacob1023]

Found exhaust leak on outlet of turbo flange that would explain why I'm getting lean reading from wideband at idle. Here we go again on the exhaust leaks.


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[Jacob1023]

Everything has been running great on the car @ 12 lbs. Ive got the AFR where they should be, exhaust leaks seems solved thanks to nordlock washers, brand new stage 3 clutch, replaced all worn bushings and finally coilovers.

I love the car. By far the best car I've owned.

But...

The itch to get back at the 15 lbs is killing me. Being able to break the tires loose in second without clutching was a great feeling!

I've done my research and have seen plenty of threads with people running the same set up at 15 lbs without any issues leaving me to believe there is something else going on with the car other than "boost cut." PO claimed the car ran great for months without an issue at 15lbs...

What sensor supplies the signal for when to cut the fuel from over boosting?

What are the scenarios of why the ecu would cut fuel?

[Jacob1023]

And the cold gets here... Bucking at low boost as well now. AFR have increased into the 13s and assuming leaning out causing a knock and then fuel cut. WTF? Winter tune.... I don't think so...

[Jacob1023]

I'm going to go ahead and disable the SAFC and get the stock MAF...

[Jacob1023]

Well guys.... I got everything back to stock now and running 13 lbs. it runs great! Then I had some problems with the new clutch and found PO had put the wrong sleeve in there. It's still getting lean when I'm at 0 psi when doing highway cruising. Stays steady at about 16 afr. Everything else looks great on the data logging. Any ideas?

I did a boost piping leak down test today with no concerns. And adjusted tps to 0.5 v. Stock maf and safc is set to not retard the signal.


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[Jacob1023]

Plugged the vacuum to bov today to eliminate it being a possibility. Same situation.


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