First, the specs:
2006 MCS automatic, 47,000 miles, 15% pulley, JCW intake, JCW 380 injectors, one-ball exhaust, RMW tune (pre-cam and header), RMW cam, RMW street header, Brisk 14LGS plugs.

Have had the cam and header installed for about 5000 miles. Initially, everything ran perfectly, except for an occasional "random misfire" code every few weeks. Then, a couple thousand miles ago, started getting yo-yo type symptoms at full throttle between 3000-4000 RPM... then at about 4200RPM steady full power would kick in and everything would be fine. Under all other conditions (anything less than full throttle) performance was perfect as before. During the "yo-yo", boost would stay around 4-5psi... then at 4200RPM it would kick up to 13+psi and the car would GO.

I suspected the bypass valve - so replaced with a Detroit Tuned BPV - did this instead of stock "just because"... and figured the more "on/off" nature of the DT BPV was aligned with my driving style and mods.

After installing it, the "yo-yo" type feel went away, but still had the "surge" of power at about 4200RPM. Boost reads about 7-8psi until you hit that point- then immediate jumps to 13+psi as before. I just started monitoring throttle position via the ScanGauge - with the pedal fully depressed, TPS reads about 27-31 until the car hits the magic 4200RPM point, then TPS immediately jumps to about 87 when the surge hits. So, if I'm interpreting this correctly, even though I have the pedal fully depressed, the throttle body is only opening partially until this RPM point, then it's jumping to essentially WOT.

Car isn't throwing any codes at this time.

Any ideas?

 

Clean the coil terminal posts and install new plug wires. The first clue was the P0300 code.

 

I doubt this is the case, but that sounds a lot like when DSC gets activated in my car when I'm trying to launch from a light in wet conditions. All the power gets cut and I instinctively react to the loss in power by pressing in the accelerator more. Before I know it I suddenly get this huge surge in power when the ECU stops overriding the throttle sensor and uses the current position.

Not sure how it's related, but if you have your throttle mashed and you're not seeing full on with your Scangauge, I suspect there has to be something wrong with the drive-by-wire system... according to your diagnosis, the ECU is overriding your input.

GotMINI

 

Had some terminal connection issues a while back with the current wires - but those have been resolved since a recent new plug install and some mods to the wires. Haven't thrown a misfire code in over a month. But have this surge symptom consistently, every time I drive. I can't make the car *not* behave this way.

I have some extra OEM wires I can throw on there and test - and will do so. But I don't understand the concept behind how this would cause the specific issue I'm seeing here... what we're feeling isn't a misfire. Dan Zipkin rode with me when I did it yesterday, and it stumped him. I wish it were so easy... It's very consistent - low boost and maybe 70% torque delivery until a very specific RPM, then ZOOOM. Accompanied by part throttle turning into full throttle at that same point...

I know what you mean with the DSC - I've had that happen before - but that's not what's happening here. Still, I agree that it sounds as if there's some drive-by-wire issues..

 

I replaced the BPV with a DT just as you did. No help. My symptoms are a bit different.
> I have yo-yo and a flat spot from about 2800-3200 (pretty consistently) from there on up, it seems OK.
> On occasion, I start the car and it just goes immediately into "limp" mode. Once I restart, it seems fine, but the SES light stays for 1 or 2 more starts and then goes out.
> After I have started up (successfully) unless I turn the DSC off, the first time I mash the accelerator the car just WILL NOT ACCELERATE until I let off the gas and try to modulate it (even then it sometimes is tricky). Once I get past the "first" WOT the car seems to run better. That first one, though, is just a mess!! I was thinking that maybe the MAP sensor(s) are to blame.

I have a 15% SC pulley, OBX header, with OE cat, Milltek catback, K&N Typhoon CAI, DTBPV, one-step-colder-than-OEM NGK plugs, Helix 9mm plug wires (about 15000 miles old) MCD coil, M7 180* thermostat, 380 injectors, and an OLD Fireballed (Mynes) tune. I am scheduled to take the car to MiniCorsa (Danny) a week from today so that he can try to diagnose and then my plan is to get an RMW dyno tune. Anyway, I hope Danny can find the answer.

And, BTW, the car was also doing some of this s_ _ t BEFORE I replaced the plugs, wires and coil, too!!

 

seems weird your boost gauge would suddenly jump with the magic number.where are you picking up your feed for boost gauge? cant get around the thought of rpms going up then boost not registering till 4200 or whatever unless say the pedal sensor was rubbish , it's input not being seen till till 4200 ? that's no good either . if you stomp the pedal your boost should jump as you spool up . this is a good one . be interested to see what it is . i can run on vacuum all the way up to good highway speeds and dont go to boost till the throttle change is major . what's your vacuum at idle?

 

Are you sure that your 15% pulley is not slipping? Sure it's tight?
Otherwise it sounds like a possible issue with ECU being unhappy with some of your mods, specifically the tune maybe.

 

ECU always overrides "foot" input. ECU has the final word always, not your foot.

 

[Otherwise it sounds like a possible issue with ECU being unhappy with some of your mods, specifically the tune maybe.[/quote]

Blimey,
Have you tried scalating this issue with the tuner to determine is this might or not be related with the tune

 

Good thoughts, guys... I'm gonna be troubleshooting some more stuff tomorrow... Boost and vac are via ScanGauge (via TMAP sensor).

Regarding the tune... yeah, I would suspect that too, except that all was well with current tune and current mods for a couple of months... then this weirdness started...

I'm pretty confident the pulley is on tight... again, the weird thing is the complete predictability if it... it behaves EXACTLY the same way, at EXACTLY the same RPM point, EVERY time. No randomness to it at all. Usually, only a computer will be that repeatable... so either (a) it *is* something with the tune (odd that it waited a while to crop up) or (b) some sensor is failing as is giving bad readings, which the ECU is responding to in a repeatable way, or (c) maybe the BPV is closing in a couple of "steps" vs. smoothly (I'll test this tomorrow), or (d) I'm still stumped.

Haven't talked with Jan about it yet - trying to rule out the obvious stuff first... already working to schedule a re-tune as soon as he has the remote tuning rig ready to go.... but if it's NOT the tune, then I need to get whatever it is fixed before then or the tune will fail... and I really don't think it's the tune... why would that go haywire now, vs. months ago?

 

Doubtful that the belt is slipping with that profile. Typically, the belt will progressively slip more as the rpm goes up, it will not have this signature. 'Suddenly get better at 4200rpm' ?? nah......... not the belt

 

Yeah, that's what I thought to... I changed the belt just in case (old one was stretched pretty much to the limit) but now have new belt with proper tension and no change.

Supercharger pulley slip seems unlikely for same reason... why would it *stop* slipping at *exactly* 4200RPM under full throttle?... doesn't make sense to me.

 

Yes, I stated belt, I meant belt and pulley, agree....not that.

I believe it is something going goofy with the TPS, the throttle by wire system.

 

Yeah, the final say so does indeed come from the ECU, but that doesn't denote to me that the ECU is always overriding your input... I imagine it intervenes only when necessary.

GotMINI

 

I guess what I mean is that the word "override" is not really applicable here.
The input from the gas pedal is only one of several inputs used to let the ECU know it's ready to open the TB. So, it is possible that either the ECU itself has been damaged or an input, i.e. sensor or connector, is NG. But it also could be mechanical.
How is it idling?

Added: Seeing you say that no codes are being thrown, then it really may be an ECU thing.

 

Idles OK. A little lope, but that came with the cam.

Yep - I'm confident that it's the ECU controlling fuel and throttle this way in response to how it's interpreting *something*.... just trying to figure out what that *something* might be...

Another way to look at the symptoms:
Drive at 80% or less accelerator pedal - "perfect" through whole RPM range
Drive at 100% accelerator pedal over 4200 RPM - "perfect" for the rest of the RPM range
Drive at 100% accelerator pedal below 4200 RPM - "retarded throttle" until it hits 4200 RPM - which some people might describe as a "flat spot" - but the spot where the power comes on feel almost like you gave it a nitrous shot...

 

sounds like it's lean , it was tuned to the stock stuff and now you have dramatically opened up the breathing

Hope to have the remote tuning project finished up next week

 

Sounds like you have VTEC to me, did you install an awesome madd tyte JDM VTEC sticker without telling us?!

Good luck sorting things out, looks like you're on the right track already.

 

Just seems odd to me that this started a couple of months *after* the cam and header install... ran fine for a long time...

 

it's colder out...........need more fuel

 

Hmmmm...... you might be onto it here...

though I was throwing "rich condition" codes several weeks ago... so I started watch SFT on the scangauge... I see it get quite negative pretty often (rich) and sometimes I see it go a bit positive, but never way positive...

 

Hmmmm, I remember asking about this problem almost exactly a year ago today. HERE
So, then people should be getting two tunes a year if they live where the weather changes from 100 degrees to -10? Might be the reason so many issues are coming up lately.
PGT, you still on board with the responses of that linked thread?

 

I don't think it would be that big of deal but his car was tune with a stock header and cam. It wasn't tuned for what's on there.

this is a problem we see all the time, people change parts without getting it retuned

 

You really think that running lean is causing all these issues? Don't think so.

 

I said this specifically about Blimey's car

4200-4600rpms is the natural tq peak for that application but you already knew that....right?