F20 with H23 intake = 2 problems

[Locutus]

Hi!

I know, the F20 engine is not quite familiar in the us, but this is basically an F22 engine, with smaller displacement.

So what was swapped:
- H23 intake (complete)
- 60mm exhaust system with stock cat
- P28 ECU
- OBX cam gear
- custom ebay exhaust manifold

The setup is working, and its doing a fine 170PS at 6800RPM, with 190Nm at 5000RPM.

The problems:

1. There is a sharp flappering sound, wich exactly begins at 4000RPM (i guess where the intake manifold changes to the other profile) Unforunately i cant diagnose it, since it only happes under load, and i have no access to a dyno pad now, to look at the intake while running the engine on load.

2. If the FPR valve is connected with vacuum to the intake, the idle rpm is whacky, goes up and down sometimes, especially when the motor temperature is lower. It even causes sometimes so low rpm-s, that the motor is stalling. If the FPR valve's vacuum is disconnected, the idle RPM is perfect, but it consumes a good 2 liters more..

Any ideas?

[deevergote]

The P28 has been tuned, correct? It's not stock?

Are there any noticeable performance issues when the sound occurs, or does the car still accelerate smoothly?

Make sure your base idle and ignition timing are set properly. These threads will help:
http://www.cb7tuner.com/vbb/showthread.php?t=146239
http://www.cb7tuner.com/vbb/showthread.php?t=146242


If your oxygen sensor is old, replace it. Replace it with NGK/NTK or Denso ONLY. No Bosch sensors.


Check the FPR to make sure it isn't faulty. Or simply replace it.


With the information you've provided, those are the only questions I can think of that might steer you in the right directly. Perhaps someone else could offer more assistance.

[Locutus]

Hi!

Thanks for your fast response.

Yes, the P28 is tuned, it was fine setup weeks long, to reach this level.

And no, there is no performance drop. It accelerates like hell up to ~7500rpm. Also the CO2 emissions are fine, ive got it checked just some weeks ago. So i assume it cant be the oxygen sensor, since it would ruin the emissions, or?

[visualpoet]

Have you taken the plenum off to make sure all four butterflies are secure? It's a stretch, but I can see where a loose butterfly plate could give you some noise when they open up.

[deevergote]

I would think that something loose in the intake manifold would result in a noticeable performance drop... of course, so would a bad o2 sensor (though the excess fuel consumption made me think o2) I did consider something loose inside, though... It IS possible.

But you're right, if emissions are alright, then it's likely not the o2 sensor. Was this problem happening at the time that you had the emissions tested?

Was everything working properly for a while, and then started to make this sound? Or has something been changed, with the sound following imediately after?

Is your IAB system wired to the ECU, or is it operated by vacuum?

By your description of the sound, the only think I can think of is that the IAB valves are opening and closing rapidly... which could be an issue with the wiring or vacuum that operates them.

The FPR issue has me stumped. It's probably something simple, but it's not something I've ever encountered.

[visualpoet]

I would think that something loose in the intake manifold would result in a noticeable performance drop... of course, so would a bad o2 sensor (though the excess fuel consumption made me think o2) I did consider something loose inside, though... It IS possible.

But you're right, if emissions are alright, then it's likely not the o2 sensor. Was this problem happening at the time that you had the emissions tested?

Was everything working properly for a while, and then started to make this sound? Or has something been changed, with the sound following imediately after?

Is your IAB system wired to the ECU, or is it operated by vacuum?

By your description of the sound, the only think I can think of is that the IAB valves are opening and closing rapidly... which could be an issue with the wiring or vacuum that operates them.

The FPR issue has me stumped. It's probably something simple, but it's not something I've ever encountered.

My thought was that if one of the IAB butterflies is slightly loose, it could be held secure against the inner IAB plate wall in the closed position, but then flutter around when they open. No real change in the performance, but if one is loose, the screws could work out and create major havoc in the engine when they eventually fall out and get sucked in. I've seen a loose butterfly plate on a carb do it before.

[deevergote]

Ah, very good thinking. I was imagining all 4 failing at once... but just one loose one would make sense. It wouldn't make much of a difference in how the car feels, but it would make noise.

It is also something that could fall into the engine and cause serious damage... so that would DEFINITELY be something to check into! Fortunately, the plenum is fairly easy to remove to do so!

[Locutus]

Ok i will try to remove the plenum, to check if its something with the valves. Sounds easy enough to check that.

Btw, this flappering sound is there some 1.5 year now... unfortunately i didnt have the time, to go on with this project. The whacky idle just started last winter... oh thats also almost a year now , i first tought its the cold days, but it didnt go away...

The RPM fluctuations is by the way not so, as described in other topics as failing IACV, so that the RPM is going higher and higher. Mine is going lower.
For example, i near at a red light, so i press the clutch and put it into empty gear. While the car is still rolling, the RPM is stable. Once the car is stopped, the rpm drops to 250, and back 750. And so on, for a good 15 seconds. After that, it suddenly restores to normal idle, around 900. This happens for some 2-3 times a week, at most.

[PR CB7]

clean all of your idle sensors
you can adjust idle w a screw on the TB

if you say that the problem has been there for more than a year now..........

when u did the intake swap, did you swap plenums, or the whole intake

[Locutus]

clean all of your idle sensors
you can adjust idle w a screw on the TB

if you say that the problem has been there for more than a year now..........

when u did the intake swap, did you swap plenums, or the whole intake

The whole intake was swapped. And there wasnt any problem with it, at that time. Both problems only began later on.

The IACV was already cleaned, it had nothing wrong. The vacuum hoses are also replaced with all new ones.

[PR CB7]

The whole intake was swapped. And there wasnt any problem with it, at that time. Both problems only began later on.

The IACV was already cleaned, it had nothing wrong. The vacuum hoses are also replaced with all new ones.

any sharp piece or loose IAB will create a drag at WOT, take it all apart if you can

check it out, clean it while your at it, ITS been more than a year now