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Old 05-12-2000, 09:08 AM   #1
Tim Prudence
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Member#: 216
Join Date: Aug 1999
Location: san diego, ca USA
Angry Help! Still some detting!

I'm running 5 psi non-intercooled, from a small IHI turbo off a 94 Legacy. I have my fuel pressure set at 50 psi (at idle) rising 1 pound with every pound of boost. The AFC is giving 10% at 2000, 15% at 3000, 18% at 4000, 20% at 5000 and 25% from 5500 up. O2 sensor voltages look good, always between .850 and .865 at WOT. The ITC is retarding timing 3 degrees at 2400 and 5 degrees from 4000 up. I get no detonation at WOT.

I do get some detting (sometimes very BAD) when shifting gears. It only happens right when I'm shifting, and only when I'm shifting hard. My guess is that the fpr is raising fuel pressure fast enough with boost. Does anybody have any other ideas, or any ideas on how I can rectify?

Please help!

PS - Has anybody figured out the ITC check engine light problem? I haven't had my check engine light turn on until I hooked up the ITC yesterday.
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Old 05-12-2000, 09:29 AM   #2
Tyrmeltr
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Member#: 667
Join Date: Dec 1999
Chapter/Region: SCIC
Location: Los Angeles, CA
Vehicle:
2013 Impreza WRX 5D
Plasma Blue Pearl

Post

I don't understand Tim, you should be fine. This is very strange. I also don't think your lack of an intercooler is hurting you at 5psi. I'm running stock '98 ECU and Fuel sometimes to 14psi (short bursts, intercooled of course) and no det. I usually run 5-7 psi though. My motor (EJ22G w EJ25 DOHC heads) is smaller with lower compression, and this probably allows me to get away with a little more naughtiness. It runs quite rich until you're at W.O.T. and like 4500-5000 rpm's, then it leans out BIG TIME, but still does not det. 90% throttle and I can go all the way to the limiter (6750), whitout any lean out. What year is your car? Have you talked to other turboed owners of the same year? What has Ed at iSR had to say about all this? I am very interested at this point as to what your problem is.
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Old 05-12-2000, 09:36 AM   #3
Tim Prudence
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Join Date: Aug 1999
Location: san diego, ca USA
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I have a 99 some it's got a tendancy to run lean at upper revs. But this is not my problem. Fueling seems to be adequate, it's only shifting gears... almost always at 4000k to 4500k

Yesterday after I got the ITC hooked up, I was so happy that I had no detonation I was flying around one sucluded road by my house. Totally smooth and quiet all the way up to 6250 in second gear, then I threw it into third and let out the clutch <PING PING PING PING!!!>. I let off the gas immediately, but I thought I had already toasted my engine. Thing is, if I shift real easy and the go to WOT no detonation. It's so weird!
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Old 05-12-2000, 10:55 AM   #4
Bassem
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Location: PA, USA
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Tim,

I'm no expert here, but doesn't the fpr use the manifold pressure to dictate how quick to rise the fuel pressure? At 6000 rpm, you are running 1000 revs/sec which is 250 cycles/sec. So each cylinder at the moment you lift of the throttle is still sparking at that rate. If your fpr dumps the gas pressure too quickly (due to sudden closing of throttle) and you still have more air than the stock ECU expects in the manifold, you will be running lean for those 100 cycles (assuming you shift in less than 0.5s). And perhaps thats why detting occurs.

However, when you shift slower, your MAP decreases slower, and hence your fpr meters down slower, and so you still carry enough gas between gears to minimize detting.

Just trying to use common sense, but again, I need someone to back me up.
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Old 05-12-2000, 11:27 AM   #5
Tim Prudence
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Location: san diego, ca USA
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No...

The detonation happens when I'm shifting IN to gear, not out of gear. But the principles are basically the same. When I'm out of gear, there's no boost, so fuel pressure is decreased. When I put it in gear and step on the gas, boost seems to be rising faster than the fpr can accomodate.

At least that is the theory. But I still have no idea how to correct this?

Another idea that might be possible is this:
My BOV valve is venting to atmosphere. Every time I lift throttle to shift, the engine experiences a very rich condition. The ECU sees this an attempts to react by leaning out excessively. The detonation I hear is what's happening when I catch the tail end of this.

I guess I could test this by shifting very slowly (to allow ECU to stabilize from BOV venting). If detonation still occurs then it's due to the limitations of the FPR, and I have no idea what to due. If it doesn't occur, then it's due to the rich condition caused by BOV venting. If that's the case then I will need to figure out how to use the deceleration function of the AFC in order to solve that problem (I should probably figure that out anywhere so that I don't kill my cat).

What do you guys think?
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Old 05-12-2000, 01:42 PM   #6
josh
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Hey tim

I cannot offer too much on the detonation part, but your ITC is what is causing the CE light. Mine flashes around 3k RPM, or if I decelorate quickly with the clutch engaged. The ECU is seeing a misfire due to the intervention of the ITC unit. Ignore it. I have had mine in for a few months, and no illeffects. That is with the dials all on +5 degrees.

On the detonation, I think you and Bassem are on to something. I think Shiv might have experienced this as well, not sure tho.
Shiv? you out there?

josh
 
Old 05-12-2000, 01:54 PM   #7
Tim Prudence
Scooby Specialist
 
Member#: 216
Join Date: Aug 1999
Location: san diego, ca USA
Post

My check engine light is not flashing. I hooked up the ITC last night, pulled back timing in a few spots and everything was fine. This morning, on my way to work, the check engine light came on and stayed on.

My detonation has subsided for now, I think because it is so warm outside. I'll see later tonight when the air is denser. I had my friend spend some time looking at the O2 voltage while I was shifting gears, and he couldn't see any momentary lean readings....

So far the problem is only happening around 4500 rpms, this corresponds to the torque peak is where cylinder pressures are the highest. I have a feeling that my fuelling is ok, that I just need to pull back timing a little more in this range. But it's weird that I can zoom through that range and no detonation, but when I shift into it there is detonation. Maybe when I shift right into that touchy zoom, the knock sensor doesn't have enough time to do its thing.
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