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Old 07-31-2003, 12:07 PM   #1
QUICKONE
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Default Car feels like its surging?

Has any one noticed a feeling sorta like surging when driving at low rpm in 3rd or 4th - not accecelerating? I have never owned a turbo car before so maby this is normal?
Thanks in advance
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Old 07-31-2003, 12:39 PM   #2
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According to others here this can be caused by the hose between the Intercooler and the Throttle Body coming loose resulted in there not being a good seal. Check that first. It is NOT normal for the car to surge like that.
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Old 07-31-2003, 01:17 PM   #3
QUICKONE
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Default Thanks!

Any one else?
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Old 07-31-2003, 03:39 PM   #4
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Default surging

Mine seems to surge a little at 3k rpm if I am trying to hold it steady and not accelerate or decelerate. It is really noticeable when the air conditioner is on. I thought maybe it was just an artifact of the adjustable valves kicking on and off (if the sti is anything like the honda the extra valves kick in or out depending on RPM).
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Old 07-31-2003, 04:33 PM   #5
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That seems to make sense. If you are driving steady, but right on the edge of the VVT changing the valve timing, it might be going on and off. I think it would feel like it is surging.
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Old 07-31-2003, 04:48 PM   #6
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Default Re: surging

Quote:
Originally posted by Burke
Mine seems to surge a little at 3k rpm if I am trying to hold it steady and not accelerate or decelerate. It is really noticeable when the air conditioner is on. I thought maybe it was just an artifact of the adjustable valves kicking on and off (if the sti is anything like the honda the extra valves kick in or out depending on RPM).
Just to straighten things up... Honda's VTEC doesnt have "extra valves". They have extra lobes on the cam that have bigger lift and duration. I believe it is the same concept for Subaru's AVCS.

Adam
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Old 07-31-2003, 05:16 PM   #7
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Default Re: Car feels like its surging?

Quote:
Originally posted by QUICKONE
Has any one noticed a feeling sorta like surging when driving at low rpm in 3rd or 4th - not accecelerating? I have never owned a turbo car before so maby this is normal?
Thanks in advance
Sorry for the ignorance, but what do you mean "surge"? Like the feel of a Honda's VTEC kicks in? If it is, then, yeah, I do feel in, especially accompanied by the whine of the turbo
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Old 07-31-2003, 06:37 PM   #8
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I think I know what you're talking about, I was just noticing this last night.

Cruising in 4th or 3rd gear some where under 4K rpm (break in and all) AC on, I get a sense of the power of the car fluctuating. Surging, and then dropping, surging then dropping (an ebb and flood of sorts.) It isn't significant, but I can feel it.

That is all.
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Old 07-31-2003, 06:55 PM   #9
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That is the compressor for the AC kicking on/off....same thing happened in my WRX. When the compressor kicks on, it robs a little HP from the crank.
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Old 07-31-2003, 07:34 PM   #10
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Default Re: Re: surging

Quote:
Originally posted by awilson529


Just to straighten things up... Honda's VTEC doesnt have "extra valves". They have extra lobes on the cam that have bigger lift and duration. I believe it is the same concept for Subaru's AVCS.

Adam
Actually the Subaru AVCS doesn't work like Honda's VTEC. Honda's VTEC, as stated before has an additional cam lobe that is shifted in or pinned in (not really sure how it's engaged). This system changed the cam profile on the fly.

The Subaru AVCS system advances or retards the cam timing. It doesn't do anything to actualy change the cam profile. It uses an oil line to the cams that advances or retards the cam timing.

Now Honda's my have something like AVCS in addition to the additional cam profile. I haven't been keeping up on VTEC technology.
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Old 07-31-2003, 07:42 PM   #11
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Are you sure it isn't just turbo lag? My WRX can be nailed to the floor in third or fourth and not move and then once the turbo spools at 3000 rpm, it "surges" (READ: Takes off like a bat out of hell). Also, with AC on, 4 cylinders will be 4 cylinders. Have you ever driven a regular WRX with the air on?
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Old 07-31-2003, 08:16 PM   #12
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It does it without the AC on as well but it is just more noticeable with the AC on.. It might very well be the valve timing changing (anyone know what rpm this happens at?)

It is not one big surge like when the turbo kicks in. It is an ebb/flow (back and forth) type of thing that only happens when you are trying to keep your speed consistant at one particular rpm.

Sorry about the ignorance on the valve thing. I was told that the vtec would dissengage/engage 2 of the 4 valves.
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Old 07-31-2003, 08:21 PM   #13
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I concur, it's not the AC compressor. The pulsing (surging) has a frequency of about 1hz.
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Old 07-31-2003, 08:29 PM   #14
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Quote:
Originally posted by x510x
The pulsing (surging) has a frequency of about 1hz.
We're not talking about the same surge, but what do you mean about the frequency?
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Old 07-31-2003, 08:42 PM   #15
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Could be the engine managing (or mismanaging some of have said) the timing.
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Old 07-31-2003, 09:56 PM   #16
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Default Re: Re: Re: surging

Quote:
Originally posted by Darwood


Actually the Subaru AVCS doesn't work like Honda's VTEC. Honda's VTEC, as stated before has an additional cam lobe that is shifted in or pinned in (not really sure how it's engaged). This system changed the cam profile on the fly.

The Subaru AVCS system advances or retards the cam timing. It doesn't do anything to actualy change the cam profile. It uses an oil line to the cams that advances or retards the cam timing.

Now Honda's my have something like AVCS in addition to the additional cam profile. I haven't been keeping up on VTEC technology.
Hey Darwood... Thanks for clearing things up for me. I was under the impression that the AVCS was similar to VTEC...

Thanks,
Adam
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Old 07-31-2003, 10:02 PM   #17
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Default Re: Re: Re: Re: surging

Quote:
Originally posted by awilson529


Hey Darwood... Thanks for clearing things up for me. I was under the impression that the AVCS was similar to VTEC...

Thanks,
Adam
No problem,

I've noticed alot of people mistake AVCS for VTEC.

Lates
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Old 07-31-2003, 10:30 PM   #18
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Quote:
Originally posted by spool1536


what do you mean about the frequency?

I was trying to apply some time aspect to the pulsing to show (for me anyways) it's not a one time increase power. The power comes and goes and comes and goes (repeat ad infinitum), and the time it takes for it to go from higher power to lower power and then back to high is about 1 second.
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Old 08-01-2003, 01:46 AM   #19
Mr. Grinch
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Default Re: Re: Re: surging

Quote:
Originally posted by Darwood


Actually the Subaru AVCS doesn't work like Honda's VTEC. Honda's VTEC, as stated before has an additional cam lobe that is shifted in or pinned in (not really sure how it's engaged). This system changed the cam profile on the fly.

The Subaru AVCS system advances or retards the cam timing. It doesn't do anything to actualy change the cam profile. It uses an oil line to the cams that advances or retards the cam timing.

Now Honda's my have something like AVCS in addition to the additional cam profile. I haven't been keeping up on VTEC technology.
Some valve parameters that can be varied:
- lift
- duration
- timing
- effective opening

Honda VTEC basically operates on oil pressure. First, there are two sets of cams and two sets of rocker arms. They are not joined, and the agressive set are loose so do not activate the valve.

Once the magic RPM is reached (usually around 5K) the oil pressure flips a solenoid that shifts a pin to lock the two rocker arms. The agressive cam and rocker arm now activates the valve. They can have their own timing, duration, and lift. But both cams are fixed, so this is considered a "stepped" variable valve system.

So with early VTEC, it was like you had an on/off switch, the difference between the two cams being so noticable.

Now Honda has i-VTEC. In addition to the two cam profiles, they now can vary the timing of each cam profile, computer controlled. This has smoothed out the power delivery a lot. The valve timing is now infinitely variable, but the cam lift and duration is still fixed for each of the two cams... "stepped" variable lift and duration, infinite variable timing.

I'm not familiar with AVCS but it sounds like it only varies valve timing, but I don't know how. Probably another method of shifting the cam phase.

For reference, consider BMW VANOS. This can't change the cam profile or duration, but does change timing. It uses a splined cam driver connected to the intake or exhaust cam. Oil pressure shifts the splined cam, which now shifts the timing of the cam forward or back. As RPM varies, so does oil pressure, and correspondingly the timing. This is infinite variable valve timing.

Valvetronic is BMW's version of variable lift. Using roller cams, they create infinitely variable lift. Tied together with Vanos, they get infinitely variable lift and timing. Not sure about duration.

I think Toyotas calls theirs VVT-i and now VVTL-i Porsche is Variocam and Variocam Plus. Variocam Plus operates similar to VTEC, using 3 cam lobes and floating tappets, locked together at RPM by hydraulic pressure.
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Old 08-02-2003, 05:10 AM   #20
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Are you SURE it's not the A/C? I've noticed something similar on mine, but I also notice that if the A/C isn't coming on at all it doesn't happen.

Perhaps the ECU is trying to compensate for the A/C?

I've yet to own a car that doesn't surge some from the A/C cycling on and off. Of course, it most commonly happens when the HVAC system is in defrost mode, which automatically cycles the A/C.

FWIW, anyway.

Zen
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Old 08-04-2003, 03:43 AM   #21
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If you drive w/ the AC off it doesn't surge.
If you drive with the AC "on" you really don't notice it. If you drive with the AC on "auto" then you feel it. Sounds like compressor to me.
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Old 08-07-2003, 02:22 PM   #22
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[quote]Originally posted by Burke
[b]It does it without the AC on as well but it is just more noticeable with the AC on.. It might very well be the valve timing changing (anyone know what rpm this happens at?)

It is not one big surge like when the turbo kicks in. It is an ebb/flow (back and forth) type of thing that only happens when you are trying to keep your speed consistant at one particular rpm.

Burke--
Right on the money. Took it to the dealer and took their Performance Tech for a ride. He said it def. shouldn't do that.

Last edited by QUICKONE; 08-08-2003 at 10:49 AM.
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Old 08-07-2003, 03:00 PM   #23
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Probably totally unrelated, but but I know of other cars (M3) that had similar surging issues. Turned out to be a combination of bad injectors and fuel pump.

They should be able to at least test the injectors / fuel pump and system, but I guess some inconsistency in the forced induction could be a factor too.
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Old 08-07-2003, 03:54 PM   #24
QUICKONE
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Default Problem solved???

My dealer just called It seems there have been throttle body issues. Sounds like a bad group of them or something. They had the regional rep on it and SNA and are next day airing one to my dealer. Should have it in and running tomorrow aftnoon.
Will post he results FYI.
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Old 08-07-2003, 04:32 PM   #25
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Does the STi have a separate throttle body per cylinder, each separately controlled?
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