Help diagnosing SR20 engine failure [Tune, Log, Pics]

[MomentFD]

This happened about 10 days ago and has been tough to post as I destroyed my motor, but I’m coming to terms with this failure and want to get beyond it by understanding it. I’d appreciate any input on my incident below, particularly on if the failure event is visible in the log and where I went wrong. This has been my project car for over a decade and learning/getting more power with Nistune was a big part of that (now regretting not having a tuner do it professionally).

S14 SR20
Stock turbo
Tomei cams
Nistune, 550cc and Z32 MAF
Innovate LM-1 wideband
California 91 gas
32400 k, 950 us latency

I had the engine running well after modifying another SR 550cc/Z32 map and proceeded to tune via WOT pulls on closed roads. AFRs under load and especially the tip-in region were rich, in the 10s & low 11s. I wanted to leave k and injector latency alone so I flattened the fuel map in the power region which led to the attached tune. Timing was never touched, although I did reduce the load scales as I was mainly in the middle of the map.

General tuning steps taken

• Got k and latency dialed in for ~14.7 idle and cruising
• Reduced load scales as max TP was ~80, on my map it was ~130
• Reduced fuel map raised portion
• Timing is stock S14 SR (80F00) but I feel like changing load scales might as well be changing the map, if I'm not careful

I thought this still left the AFRs rich enough to drive around without much risk (11s, must've been too brief of a look), but after further review even my street log is dangerously lean, in the mid-high 12s. I took the car for mountain run to get a better log. The drive was basically partial throttle in 2nd & 3rd gear with varying elevation, a few WOTs as well. After a few minutes the car started lacking power during tip-in but would eventually get moving, and also idle was loppy/rough. I was hoping I popped an intercooler coupling but after limping home the following cylinder conditions were observed with a boroscope.

My initial review of the log is that the rich tip-in condition is actually somewhat lean for the partial throttle pulls. My 2 immediate questions were

• Is there a table or value that governs tip in fueling?
• Is being lean (13s, 14s) during lower loads (~40-50 TP for example, where I max at 80TP), enough to do damage like this?

Thanks for any input, help me put this demon to rest. I can provide any more data I have if it’s helpful.

BAD CYL 4 - CYLINDER DAMAGE.JPG

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BAD CYL 4 - SPARK PLUG.JPG

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GOOD CYL1.jpg

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[MomentFD]

Tune & Log Files

Tune - modified SR20 w/ 550cc/Z32, timing should be same as stock S14 SR map.
US CA 91 gas used

MAR17 FUEL MAP ADJUST 2.bin

(64 KiB) Downloaded 242 times

Log - STREET DATA - WOT pulls on the street

ENGINE FAILURE - STREET DATA_2020-03-23_1831_16.csv

(228.92 KiB) Downloaded 216 times

Log - MOUNTAINS - partial throttle mountain run, where the failure happened

ENGINE FAILURE - MOUNTAINS _2020-03-23_1843_50.csv

(444.46 KiB) Downloaded 228 times

[MomentFD]

NISTUNE MAPS.JPG

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LOG LEAN AFR.JPG

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[unex]

I did not looked at log, but:
1. it was knocking hard;
2. too much advance in mid range;
3. does your CAS was set in proper position? Checked with strobe light? Because if not, it makes things even worse;
4. never do tuning without external knock detection system, unless you are sure that ecu is pretty good at that. And these old nissan ecu's are not.
5. if only 4cyl looks like that, i would check injectors.

[louiswun]

I think throttle enrichment is the tip in fueling

[louiswun]

Are you using Nismo 550cc injectors ? if yes, it should not 950 us latency.
Something around 710 us to 740 us .

[PL]

Wow - that's harsh. It's a terrible shame to see SR's die like that. Terminal detonation. Get yourself some knock ears. Even a garden hose and some earmuffs will do.

Looking at your logs there's one thing that stands out. Your cooling system is marginal at best. It was overheating for most of that mountain run. It was over 100C most of the time. Unless you had a good strategy in your tune (adding fuel and taking timing if coolant temp above 90C) then it was always going to knock. Having an untuned IGN map wouldn't have helped. Running stock turbo I imagine it's be about 15psi boost and WOT timing looks to be in the low 20's - so it was probably knocking even before it overheated.

This is the big thing I see mainly on people's track cars. The guys with the proper rads (eg: Koyo) seem to go season after season without a problem. The same car with a lesser radiator will have problem. The good rads make a massive difference. I've had cars that will stay below 85C even after repeated WOT dyno pulls. Yet my own S15 needs a rest after each run cos it has stock rad - for now.

In your street log you can see very clearly what's happening. It's at about 83C before the run, then after only a 6 second WOT burst it goes to 98 and continues up to 113C.

Pete L

Call_Mr_Koyo.JPG

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[PL]

Just looked up a few of my S14 tunes for T28 stock turbo and most are around around 10 degrees timing in the midrange and then up to to 16 - 18 towards redline. That's on our AUS spec 98 RON juice. Which I think = the 93 octane USA juice.

PL

[MomentFD]

Thanks PL and all, definitely some blunders which are hard to look back on but at least it makes sense. Car w/ spare SR is currently on the market in California if you know anyone interested!

[unkn0wn]

(adding fuel and taking timing if coolant temp above 90C)

Hey Pete, does nissan ecu/nistune have an easy option to do the timing pull vs temp ?

[Matt]

AFAIK SR20 doesn't pull timing, but it will add a bunch more fuel
http://nistune.com/docs/Nistune_Mapping_Guide.pdf
See page 32

[PL]

I usually just add a bit of fuel in the "Enrich Throttle" tables.

SR20 enrich at high temp.JPG

(42.34 KiB) Downloaded 1067 times

You may be able to pull timing by adding a few degrees to the whole "After Start Timing Adv" table and then taking the same amount from the entire IGN map. Then remove the same amount in the 100 - 110C area. I've never tried that but it might work. I'll try it on the bench next time I've got an SR ECU on there.

SR20 retard at high temp.JPG

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As long as you've got a good cooling system you should never need this.

PL