crisskro

Ok, so it seems that the O2 problem and the RPM fluctuation are not related, as the fluctuation exists when starting the engine - ie cold engine. Weird that last winter I couldn't detect it.
The vacuum hoses were switched and I had no idea, I just bought a oem airbox and something seemed out of place.
The thermostat is now oem.

The more I think about it, it could be the IACV or a clogged fuel filter maybe. Weird part is that it idles ok (sometimes when I take it out of gear, the rpm drops to 800 then spikes to 1100 rpm then stabilizes at 8-900 rpm).
I'll try to get a hold of someone with an s2k to test with his IACV.

Billman250

wow its 9 months later and no fix

crisskro

Yep. It doesn't bother me too much, basically city driving and maintaining a constant speed is kind of rare.
And honda says they need it for a week to find out what's wrong with it - basically they charged me to tell me they don't know what the hell is wrong with it. Let's say I am not pleased. I swear, if it wasn't for s2ki (and you billman) I don't know what I would have done, so many cool diy-s.

Other then this, the car's been great, pulls strong, looks awesome, corners like nothing I've driven before, and no issues except this one. Kind of a bummer.

Anyway, I'll post once I find out what's wrong with it, maybe it will help someone that may have this rare problem as well.

crisskro

over 1 year later, still no fix...
Just found the one mechanic who worked on all the S2000s in our city, ex honda employee. Hopefully we will get to the bottom of this.

The local dealership where I refused to take it has closed last month. But not before screwing up another friend's s2000 by breaking 3 knock sensors, botching up a clutch job and many many others. Animals.

BlackFox

Your drop in rpm is more significant then mine. Mine only drops 200-300rpm or so.

Maybe I should fill it up with 95 octane to see if it improves or worsens.

crisskro

Tomorrow it will get another valve adjustment. Maybe a compression test.
I am trying to get a hold of another throttle body with TPS, as I have a big bore throttle body. Also the fuel pressure, maybe something wrong my walbro fuel pump.
Easter is coming so we'll see time-wise.

Car Analogy

Get the OEM fuel pump back in place. I bet there is something wrong with the install of the pump (or filter). Like sometimes its sucking air, sometimes sucking fuel, etc.

NOS killed the old motor, and lack of fuel delivery with NOS would kill a motor quickly. I am betting fuel delivery killed the old motor, and is now causing your drivability issues with new motor.

I also think you might have a vacuum leak. Who knows how they hacked things up installing the NOS. I would carefully go through routing of all vacuum connections. Also check condition of hoses, cracks, burns, etc.

When you said dealer 'wrote' the ECU (rewrote, etc), that just sounds like they reflashed the ECU with latest Honda software, as reflash is really writing data to EEPROMs in ECU. Probably just a terminology thing that is lost in translation to whatever language they speak in whatever country you are in.

crisskro

Yes, back then I wasn't as "smart" about this car.
Basically they rewrote the keys as the AP1 ecu cannot be reflashed. They described it as updating the software, but I don't think that's what they did.


All vacuum hoses have been checked, as well as the vacuum pump, the mechanic is sure the vacuum is ok. I will ask him to double check, I was helping him for the 10 hours we worked on it last saturday.
It does the same with the tank full, however, a malfunctioning fuel pump could give less than the required s2k lph. We'll see to that as well, thanks for the advice.

crisskro

Still no fix, waiting on a stock fuel pump and both o2 sensors (ryan!!!!!!!!!!)

Symptoms: out of gear, I rev it to any RPM, let's say 4000 and keep it there. Everything is ok for about 5-10 seconds, then I can hear the exhaust pop like minor multiple misfires and the RPMs drop to 700, and in the next two seconds it shoots back to 4000 RPM, then misfire and back to 700rpm etc. Cold or warm engine, same thing.

The car pulls strong from all RPMS up to 9000, without misfiring, no smoke, oil consumption is normal.

• I have no CEL related to misfires, I do have a failed secondary O2 and the CEL is on. However, this error is unrelated as the sensor has broke recently and my original problem was there before this happened.
• I have replaced sparkplugs, IACV, coilpacks, crank position sensor, cleaned throttle body, checked the throttle position sensor and it's ok, ran fuel injector cleaner (redline), valve adjustment, the air filter is new, the cams line up properly, the vacuum seems to be in order, cleaned the evap canisters.
• mods (updated): big bore throttle body, de-cat test pipe+catback, lightened flywheel, injector o-rings that go on the block may be bigger than oem (1mm?), walbro 255lph fuel pump, ecu is stock.

Not many things left to check, fuel pump + filter and knock sensor will be next on the list to check. Maybe when the engine was swapped they broke the sensor then replaced it with an aftermarket one that is over-acting.

BlackFox

Still the same here.

Was able to exchange sensors and injectors with another s2k owner, without succes.

Still waiting for my pwjdm intake gasket, the only culprit I still suspect.

If that doesn't change the problem, then I don't know what will.
Car will drive good one day, and shitty the next.
Apparently clouds of grayish smoke when shifting in high rpm, haven't seen this myself however. (Testpipe installed)

Injector cleaner made the engine run better and it didn't stall. But as soon as I refueled without it, it ran worse.