SR20 lean under load

[cash$addict]

I'm having a problem where under a load, usually rpm dependant around 4-5kish, the engine goes full lean and breaks up. this used to occasionally happen after sitting or heating up and then go away but only once or twice. I hit a really hard bump on the highway and since its a lot more consistant and less temperature based. no damage to the engine or anything from this hit fyi. just a short break down of the set up

red top sr20
s15 t28 7 psi
stock 370 injectors
stock maf
stock 63 ecu
tomei fpr adjusted to 45psi at idle 55ish under load

before you flame me for pumping up the fuel pressure and running a t28 ive had this set up for at least 3 years with no problems, yes it idles rich but under wot it always remains between 12-13 to 1

my first guess was the maf or wiring to the maf, I done a voltage drop test across all 3 wires of the maf, no issues, added an extra ground to the harness just to test and no change, I replaced the maf itself, ran good for a couple pulls down the street, drove it to get coffee about 10-15 minutes, got back on it and its still leaning out.

ive checked the fuel pressure when driving and it stays strong around 50-60 psi under boost until the engine starts to break up. 60 seemed pretty high but ive been running it like this for a while so I don't think that's the issue unless that kind of pressure has worn out the injectors somehow. I know its not over boosting as it only hits 7 psi and also the issue is not directly related to boost because I can load it in 3rd or 4th gear and hit full boost and it wont break up until 4-5kish. I also determined its not directly related to rpm since I can free rev it all the way and under light load it will travel all the way to 6-7k rpm with good afrs.

it idles fine, drives under light load fine, car feels very smooth until you try to go fast basically. ive checked the plugs to be sure it wasn't just reading wrong somehow but they're dry and white so its definitely lean. before anyone suggests its an ignition problem or boost leak, either of those would cause a rich misfire as the fuel would still be there. I haven't tried a new ECU yet and that's my next guess next to possibly the fuel injectors somehow failing. any ideas for testing would be much appreciated, thanks!

[S-Nation S13]

In for info. I'm installing my wideband today


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[lok]

Check the voltage at your ecu

[da_crew10]

Check your throttle position sensor? Bet that should be it.


Also adjust your fuel pressure where it needs to be, on an SR start the engine pull the vac hose and adjust it to 43.5psi .

[cash$addict]

ill try checking the tps later today if I can, I don't have a scope so I don't know how effective ill be able to read it for a dead spot unless its really dead after a certain point but it drives good full throttle up until a certain rpm/load as in it doesn't stumble any time I floor it only when its floored around 4-5k rpm.

what pin would you recommend checking voltage at? the main power to the ecu (pin 47)?

thanks for the replys

[Blk96t]

Do you have an upgraded fuel pump hard wired? Good z32 fuel filter? Fuel pump filter good?
Chech your ignition harness really good they get corroded. Also check the ground that goes to the back of the head from the ignition harness.

You should really get a z32 mafs, 550 injectors and Enthalpy tune..
Your missing out on a lot of easy and reliable power.

[derass]

Test your wideband sensor. Might just be a faulty reading. But you say the engine's breaking up, so maybe there's something more going on. Worth a try anyways.

[Juan@Fontananissan]

check your ignition coils and igniter, could be spark arc jumping / breaking up the spark.

[bfellini]

I'd guess coil/ignitor issue, or fuel pump failing... under light load, you won't be building full boost, so you can accelerate to red line.
What's your vacuum at idle? Take that measurement at your measured fuel pressure of 45psi, add to the 45psi the difference between your vacuum at idle and atmospheric pressure, and then add your 7psi of boost... that should be your max load fuel pressure.

i.e., if you have -14.5psi of vacuum at idle (0 kpa), add 45psi idle fuel pressure + 14.5 + 7psi of boost = 66.5psi fuel pressure at full boost is what you should have.

If fuel pressure is verified, check for clogged fuel filter... you can have pressure but inadequate fuel flow.
then try testing coil resistance... then try closing spark gap

[cash$addict]

I have a z32 filter, walbro 255 I just put in about a year ago with a new sock and completely cleaned out the fuel tank.

I have 17-20 in hg of vacuum at idle, I guess I could buy another filter. I'm skeptical its ignition related at all seeing as its going lean indicating a lack of fuel where as a failed spark would create an excess of fuel from not firing off. unless theres some reason a failed ignition component would pull fueling as well.

I have a aem ems 550s and a new wiring harness I just don't wanna throw these things in not knowing what the problem is and then have more new variables in the problem if its not fixed.

[Blk96t]

Your thinking on the ignition is logical. Checking things is free.
Do a boost leak test. Also check your intake for leaks after the MAFS!
That causes symptoms your describing.

[VTEC_lol]

I have the same issue and I've already changed O2 sensor (for elbow, I need to change the wideband O2 aswell) and changed FPR, fuel filter, checked vacuum leaks, changed dump valve, cleaned MAF, checked ignition wiring, gapped plugs to .020 and checked coil packs.
One of my coils is very oxidized, and I tried cleaning it but made no difference. Still that could be the issue, I haven't bought a new coil yet, but I suggest you check yours to see if we both have the same issue

[cash$addict]

ok so I haven't really been able to work on the car but I dropped it back off at my garage, drove it up the highway about an hour at night and it was fairly cool out, the engine temp was probably around 170-180ish, it usually stays around 180 but it didn't lean out once, pulled hard all the way through the rpm band. it did sputter and back fire at random once in a while at light load but it stayed rich so id assume that's mostly related to how rich its running with the other maf I put in. but the conclusion is its definitely temperature related. doesn't help much with out more testing but just to keep the ideas rolling

[zenkicpe]

Have you checked your injector grommets and o-rings?

[cash$addict]

Hey there i know this is old af but i just wanted anyone with the same problem to know i FIXED IT. I replaced the engine wiring harness and never had the problem again. I didnt get too into it cuz the harness was pretty aged and haggard so i replaced it all but i believe the issue was a poor ground for the injectors. Im guessing that under load when hot the current to run the injectors was too much for a weak corroded ground and the resistance would get so high the injectors wouldnt fire. Hope this helps!

[TheRealSy90]

FYI 13-1 is still too lean at WOT.

[VTEC_lol]

Originally Posted by cash$addict

Hey there i know this is old af but i just wanted anyone with the same problem to know i FIXED IT. I replaced the engine wiring harness and never had the problem again. I didnt get too into it cuz the harness was pretty aged and haggard so i replaced it all but i believe the issue was a poor ground for the injectors. Im guessing that under load when hot the current to run the injectors was too much for a weak corroded ground and the resistance would get so high the injectors wouldnt fire. Hope this helps!

I might've had the same issue, never got it fixed and my engine spun a rod bearing and died long time ago. Thanks for reply though