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Old 06-07-2009, 07:38 AM   #11 (permalink)
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I think there's something else going on here:
Car is currently running on 89 octane due to good wife believing she heard knocking. "OK Honey, I will put in only 89 octane till we figure out what the noise is".

Edit:
I think the higher octane is enabling greater ign. advance - and the fuel management map limits lean burn when there's more advance.

Higher octane will allow more advance, as the knock sensor dynamically contributes to advance settings. I suspect the ECU is programmed to disallow lean burn when advance exceeds some predetermined amount. Of course ECU is designed for 87 octane but with 89 the advance will be more than generally expected so lean burn is disallowed more often.

This would fit with less lean burn occurring in wet conditions - the water 'mist' in the intake air also reduces knock, allows more advance, and so probably places more restrictions on lean burn.

I'll be testing for this by using different octanes, but at ~475 miles/tank that testing will not be rapid.


Last edited by brucepick; 06-07-2009 at 04:31 PM..
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Old 06-10-2009, 01:57 AM   #12 (permalink)
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So what factors contribute to lean burn? I have a CA model HX and I drive 70 miles round trip, lately since the NBA finals have started I've driven a bit faster to get home

But normally I am driving at 60-65 a 17-20 Throttle position. Best tank I've got was 42mpg with tires at 44psi. Still haven't had a chance to drive 60-65, no ac, for the whole tank.
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Old 06-10-2009, 12:35 PM   #13 (permalink)
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Quote:
Originally Posted by brucepick View Post
I think there's something else going on here:
Car is currently running on 89 octane due to good wife believing she heard knocking. "OK Honey, I will put in only 89 octane till we figure out what the noise is".

Edit:
I think the higher octane is enabling greater ign. advance - and the fuel management map limits lean burn when there's more advance.

Higher octane will allow more advance, as the knock sensor dynamically contributes to advance settings. I suspect the ECU is programmed to disallow lean burn when advance exceeds some predetermined amount. Of course ECU is designed for 87 octane but with 89 the advance will be more than generally expected so lean burn is disallowed more often.

This would fit with less lean burn occurring in wet conditions - the water 'mist' in the intake air also reduces knock, allows more advance, and so probably places more restrictions on lean burn.

I'll be testing for this by using different octanes, but at ~475 miles/tank that testing will not be rapid.
The knock sensor will not advance ignition timing. A properly running engine will have no difference in spark advance between 87 and 89 octane fuel (provided the engine is designed to run on 87). The knock sensor is there to pull spark IF and ONLY IF it detects knock, to avoid damage to the engine in the event of something going wrong, such as bad fuel. If the engine were to continue advancing spark until it detected knock, and the knock sensor were broken... every failed knock sensor would result in a destroyed motor. That being said, if there is something wrong with the car, and it's knocking, i could very clearly see there being a rule saying, In the event of timing retardation due to knock, do NOT enter lean burn, as lean burn would greatly aggravate knock.
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Old 06-11-2009, 06:28 PM   #14 (permalink)
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Further developments.
The car now will enter and stay in lean burn well below 65 mph.

The morning of June 8 I heard an exhaust leak up front, so I took it to Monro Muffler (franchise). Cat converter/exhaust manifold combination was OK but they replaced everything behind it. I also removed all the remaining lower grill block which was mostly on the cat converter side of the grill as I didn't want them to get in a twist over it.

With those changes, it now goes into LB and stays there just as I'd earlier worked out. Warmed up, TPS below 20. Will stay in LB unless TPS goes over 32.

I don't know yet if I'll need to replace the lower cat-side grill block when the weather gets cold or rainy. We'll see. For now I'm a very happy camper because it will run in LB at the drop of a hat. Unfortunately I'll never know if the cure was the exhaust fix or the removal of the grill block.

Sorry for the red herring info earlier.
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Old 06-11-2009, 06:35 PM   #15 (permalink)
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I don't think the grill block would effect it. I would re-install the block.

There was probably a problem in that the EGR not functioning properly due to the exhuast leak. This might throw the fuel trims way out of line, (not enough exhuast in the intake air), throw the check engine light you were seeing, and prevent lean burn.

Mind you, that's all supposition from a computer engineer, not an automotive one... YMMV, etc...

Throw the grill block back in,and see what happens? Only costs you a bit of time, and some skinned knuckles worst case?

-Steve
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Old 06-11-2009, 06:37 PM   #16 (permalink)
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Quote:
Originally Posted by CA_HX_5Spd View Post
So what factors contribute to lean burn? I have a CA model HX and I drive 70 miles round trip, lately since the NBA finals have started I've driven a bit faster to get home

But normally I am driving at 60-65 a 17-20 Throttle position. Best tank I've got was 42mpg with tires at 44psi. Still haven't had a chance to drive 60-65, no ac, for the whole tank.
Do you have the LB gauge set up on your ScanGauge? I'm assuming you have one as you're reporting TPS data. Right now I'm seeing LB anywhere between 55-75 mph. Probably higher, as long as you don't exceed 32 TPS. I never tried because I hate those on-the-spot interviews with the men in blue.

If your tires are sound and rated 44 psi or better, consider putting them up to 50, cold.

As for a/c, I've (sometimes) been switching it on and off manually, on the a/c button. I leave the temp slider at max cold and switch the compressor off when it gets pretty cold and back on again when the chill is gone. (apologies to BB King)
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Last edited by brucepick; 06-11-2009 at 07:01 PM..
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Old 06-11-2009, 06:45 PM   #17 (permalink)
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Quote:
Originally Posted by stevey_frac View Post
I don't think the grill block would effect it. I would re-install the block.

There was probably a problem in that the EGR not functioning properly due to the exhuast leak. This might throw the fuel trims way out of line, (not enough exhuast in the intake air), throw the check engine light you were seeing, and prevent lean burn... Throw the grill block back in,and see what happens? Only costs you a bit of time, and some skinned knuckles worst case?

-Steve
not enough exhaust in the intake air??
Hmm. Does it have EGR that pulls from post-cat converter?

Even aside from the intake air bit, I'm sure that the leak just aft of the cat messed up the O2 readings. And I bet that leak was building for a while and finally became clearly audible.

OK, I have to admit to CRS syndrome; I'm now past 55 and I don't mean mph. I"m PRETTY sure I ran it for about 40 mi. with the grill block back in and had trouble keeping LB. But I will put the lower grill block in for tomorrow's 60-mile ride up to work and we'll see how it goes. No inconvenience at all - it's sections of foam pipe insulation bundled together to fit the grill openings. Easily removable and reinstallable.
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Old 06-11-2009, 07:04 PM   #18 (permalink)
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I am glad to see this thread, I am wanting to talk to more people with CA spec hx's. Since I have installed my mpguino, Ive been watching my instant mpgs and my gallon/hour reading to try to get a better feel for whether or not I am in LB.

Before I had any instrumentation I got two or three tanks at 49 mpg average. Now, my mileage has gotten worse. I try to maintain the best instant mpgs all the time and in the end I think it is killing me. So now lately I have been sucking it on my instant mpgs while I accelerate for the sake of getting to cruising speed a bit quicker and holding a much higher cruising instant mpg.

Help me out, what am I doing wrong?

I have that $20 digital voltmeter kit from australia in the mail, that will let me watch lean burn a LOT better.

Also, just FYI my car has a "faulty" ECU that throws a code occasionally similarly to yours Bruce, except mine is for a 02 sensor reading slowly. There is a TSB for it and apparently the ecu just needs to be replaced with an updated version. Its like $600 so I just deal with the light coming on every 1 to 2 months.
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Old 06-11-2009, 07:24 PM   #19 (permalink)
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Quote:
Originally Posted by LeanBurninating View Post
... Help me out, what am I doing wrong?

I have that $20 digital voltmeter kit from australia in the mail, that will let me watch lean burn a LOT better.

Also, just FYI my car has a "faulty" ECU that throws a code occasionally similarly to yours Bruce, except mine is for a 02 sensor reading slowly. There is a TSB for it and apparently the ecu just needs to be replaced with an updated version. Its like $600 so I just deal with the light coming on every 1 to 2 months.
Shoot, I wish I knew! The occasional ECU code sounds scary. Hopefully that's not what's messing things up. $600 - ulp!

It's very sensitive to throttle position which I watch constantly on the ScanGauge. Without that monitoring I'm sure LB would happen much less often. When needed I can also watch intake air temp, coolant temp, and other stuff that might not matter.

Tell me about the $20 voltmeter kit. Link??

You may know from other posts that I'm watching LB on the ScanGauge. That costs >$20 though. And it only recognizes LB for a gauge readout but not for its mpg calculations. If the MPGuino was as easy to install as the SG I would have one already. I just don't feel like hacking into the wiring on this beast right now.
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Old 06-11-2009, 07:45 PM   #20 (permalink)
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