Will overlap cause a false rich or false lean condition?
04-30-2005, 09:08 PM
#22
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Changing your VE won't really help. Overall it may help you run leaner, but huge fueling gaps between the MAF table and VE table are 90% of the reason most people's cams run like crap. As for enabling PE at 0%, that's no good either. You might as well just run an open loop tune. At least your fueling would be more accurate too. Anyways, I did some testing tonight by raising my O2 switch points. No real noticable difference. I am not going to go too crazy with them though. I think I have taken my tune as far it can possibly go. It has been a wild ride though, and I ended up with awesome results. Oh well...stupid cam overlap!
04-30-2005, 10:33 PM
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At idle my LTFT are -1.6 to +1.6 which is a good indication that the PCM is happy with the feedback from the factory O2 sensors.
However, my WB O2 meter reads an AFR of 14.8 to 15.1:1 at idle. In my case the PCM is seeing a false rich condition because it thinks my real AFR of ~15:1 is a richer 14.7:1
When I am driving along at RPM above 1200 the WB shows an AFR of 14.7:1.
John
However, my WB O2 meter reads an AFR of 14.8 to 15.1:1 at idle. In my case the PCM is seeing a false rich condition because it thinks my real AFR of ~15:1 is a richer 14.7:1
When I am driving along at RPM above 1200 the WB shows an AFR of 14.7:1.
John
04-30-2005, 10:55 PM
#25
On my car standing behind it the raw unburnt fuel burns the hell out your eyes. I guess I have the same problem. Leaving from a stop some times it feels as if the cylinders get loaded up with fuel, then it bogs and barely runs for a sec. To fix it I have been reving it up to clear it out. WOT it feel fine but I think I need it to be retuned.
Mike
Mike
04-30-2005, 11:05 PM
#26
Originally Posted by JNorris
At idle my LTFT are -1.6 to +1.6 which is a good indication that the PCM is happy with the feedback from the factory O2 sensors.
However, my WB O2 meter reads an AFR of 14.8 to 15.1:1 at idle. In my case the PCM is seeing a false rich condition because it thinks my real AFR of ~15:1 is a richer 14.7:1
When I am driving along at RPM above 1200 the WB shows an AFR of 14.7:1.
John
However, my WB O2 meter reads an AFR of 14.8 to 15.1:1 at idle. In my case the PCM is seeing a false rich condition because it thinks my real AFR of ~15:1 is a richer 14.7:1
When I am driving along at RPM above 1200 the WB shows an AFR of 14.7:1.
John
05-01-2005, 12:05 AM
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I believe cams with lots of overlap do 2 things. They allow air & raw fuel to pass directly into the headers, AND they allow exhaust gasses to blow back into the intake. Which is why you get burn-your-eyes-rich idle, and choppy, surging idle because the manifold pressure is pulsed from the exhaust. Overlap = BOTH valves open at the same time. So it depends on which stroke the piston is on for which problem you get. I get both.
05-01-2005, 12:18 PM
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Those of you going through this "false rich/lean" thing...are both of your LTFT's within a couple of points of each other? ie( B1LTFT = +10% B2LTFT = +15%) 
05-01-2005, 12:34 PM
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Originally Posted by Q
Those of you going through this "false rich/lean" thing...are both of your LTFT's within a couple of points of each other? ie( B1LTFT = +10% B2LTFT = +15%)
05-01-2005, 04:05 PM
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Originally Posted by SmokingWS6
VE: If you idle below 1000RPM open up the primary(secondary if you have it) VE table and hilight all the tables in the 400 and 800 RPM section. Multiply that section by 90%, this reduces the fueling in those cells. If this helps clean up the smell you can keep it how it is or Mutiply by another 90% or so. a 20% reduction in idle fueling should help a lot
05-03-2005, 12:23 PM
#31
False Rich Condition I believe it's a false rich condition, because it is actually rich from cam overlap only at idle. It is reading oxy, however if it was a clean burn it would no longer be read as oxy (or not high enough to change things) as the burn creates carbon monoxide and other bad stuff instead of raw mix. So, false rich will cause PCM to lean mix out, but only so far, and you still get raw fuel/air pumped through exhaust (being read before and after cat through o2's). This is why o2's and cats are sometimes removed.
To back this up:
HP Books
Chevy ls1/ls6 Performance
By Chris Enderes
ISBN: 1-55788-407-2
Page: 124
Talking about calc pulse width on look up table:
..."base pulse width(rpm/load) x factor A x factor B = pulse width..."
Anyway,
"From this example, you can see how the control system makes adjustments. With parameter B as the level of oxygen in the exhaust, the lookup table for B is the point at which there is (according to engine designers) too much oxygen in the exhaust; and accordingly, the PCM cuts back on the fuel."
Reads lean (fuel/oxy) and the pcm leans it out, right.
To back this up:
HP Books
Chevy ls1/ls6 Performance
By Chris Enderes
ISBN: 1-55788-407-2
Page: 124
Talking about calc pulse width on look up table:
..."base pulse width(rpm/load) x factor A x factor B = pulse width..."
Anyway,
"From this example, you can see how the control system makes adjustments. With parameter B as the level of oxygen in the exhaust, the lookup table for B is the point at which there is (according to engine designers) too much oxygen in the exhaust; and accordingly, the PCM cuts back on the fuel."
Reads lean (fuel/oxy) and the pcm leans it out, right.
Last edited by Robert56; 05-08-2005 at 03:31 PM.
05-03-2005, 12:56 PM
#32
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Originally Posted by Silverhawk_02TA
Won't work. The PCM will simply dump in more fuel using trims to compensate for whatever you subtract from the VE table, since it's still using the "less than optimal" data from the O2's. The only exception is on cold starts, before the PCM enters closed loop mode. This is where the "multiply by XX%" rule for the VE idle cells comes in after a cam swap. It leans out the VE table in the idle area to help with cold starts and idle in open loop.
05-03-2005, 05:03 PM
#34
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Originally Posted by WS6FirebirdTA00
another user, dont know if u stated this or not but does adjusting the switch points help this out at all?
05-08-2005, 03:38 PM
#36
Here's a link from innovate, on the false lean reading from high overlap cam (it's towards end of video). They state cam will give a false lean signal and computer will add fuel? I wonder if that's in general, because the above post that I quoted is ls1 specific and states pcm will counter the false lean? No wonder this is a little confusing, the experts give conflicting information, maybe not, but they should spell it out better for the hobbiest.
Edit: Video is, LM-101: Logwork Tips and Tricks.
Video from Innovate on False lean
Edit: Video is, LM-101: Logwork Tips and Tricks.
Video from Innovate on False lean
Last edited by Robert56; 05-08-2005 at 03:47 PM.
05-08-2005, 05:07 PM
#37
There is no contradiction. Overlap results in oxygen AND fuel exchanged from the intake stroke to the exhaust stroke. Both O2 and unspent fuel are present in the exhaust.
The purpose of the O2 sensors to to gauge combustion in the chambers via exhaust gases - namely oxygen. It is an indirect method to evaluate the AFR. This works pretty well unless you have a lot of overlap or an exhaust leak. In which case the oxygen present in the exhaust is the sum of unspent combustion oxygen and the oxygen pulled in via overlap from the intake stroke (or exhaust leak) . The reading from the O2 sensors is lean from the added overlap oxygen. Additionally there is unspent fuel in the exhaust - but the O2 sensors do not read fuel.
So, there is excess O2 which causes a false lean read of the exhaust. There is also excess fuel (rich). But in both cases they excessive oxygen and fuel (at least partially)are due to the overlap and do not accurately reflect combustion.
Make sense??
The purpose of the O2 sensors to to gauge combustion in the chambers via exhaust gases - namely oxygen. It is an indirect method to evaluate the AFR. This works pretty well unless you have a lot of overlap or an exhaust leak. In which case the oxygen present in the exhaust is the sum of unspent combustion oxygen and the oxygen pulled in via overlap from the intake stroke (or exhaust leak) . The reading from the O2 sensors is lean from the added overlap oxygen. Additionally there is unspent fuel in the exhaust - but the O2 sensors do not read fuel.
So, there is excess O2 which causes a false lean read of the exhaust. There is also excess fuel (rich). But in both cases they excessive oxygen and fuel (at least partially)are due to the overlap and do not accurately reflect combustion.
Make sense??
05-08-2005, 05:51 PM
#38
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Originally Posted by Bink
There is no contradiction. Overlap results in oxygen AND fuel exchanged from the intake stroke to the exhaust stroke. Both O2 and unspent fuel are present in the exhaust.
The purpose of the O2 sensors to to gauge combustion in the chambers via exhaust gases - namely oxygen. It is an indirect method to evaluate the AFR. This works pretty well unless you have a lot of overlap or an exhaust leak. In which case the oxygen present in the exhaust is the sum of unspent combustion oxygen and the oxygen pulled in via overlap from the intake stroke (or exhaust leak) . The reading from the O2 sensors is lean from the added overlap oxygen. Additionally there is unspent fuel in the exhaust - but the O2 sensors do not read fuel.
So, there is excess O2 which causes a false lean read of the exhaust. There is also excess fuel (rich). But in both cases they excessive oxygen and fuel (at least partially)are due to the overlap and do not accurately reflect combustion.
Make sense??
The purpose of the O2 sensors to to gauge combustion in the chambers via exhaust gases - namely oxygen. It is an indirect method to evaluate the AFR. This works pretty well unless you have a lot of overlap or an exhaust leak. In which case the oxygen present in the exhaust is the sum of unspent combustion oxygen and the oxygen pulled in via overlap from the intake stroke (or exhaust leak) . The reading from the O2 sensors is lean from the added overlap oxygen. Additionally there is unspent fuel in the exhaust - but the O2 sensors do not read fuel.
So, there is excess O2 which causes a false lean read of the exhaust. There is also excess fuel (rich). But in both cases they excessive oxygen and fuel (at least partially)are due to the overlap and do not accurately reflect combustion.
Make sense??
05-08-2005, 06:42 PM
#39
Originally Posted by Bink
There is no contradiction. Overlap results in oxygen AND fuel exchanged from the intake stroke to the exhaust stroke. Both O2 and unspent fuel are present in the exhaust.
The purpose of the O2 sensors to to gauge combustion in the chambers via exhaust gases - namely oxygen. It is an indirect method to evaluate the AFR. This works pretty well unless you have a lot of overlap or an exhaust leak. In which case the oxygen present in the exhaust is the sum of unspent combustion oxygen and the oxygen pulled in via overlap from the intake stroke (or exhaust leak) . The reading from the O2 sensors is lean from the added overlap oxygen. Additionally there is unspent fuel in the exhaust - but the O2 sensors do not read fuel.
So, there is excess O2 which causes a false lean read of the exhaust. There is also excess fuel (rich). But in both cases they excessive oxygen and fuel (at least partially)are due to the overlap and do not accurately reflect combustion.
Make sense??
The purpose of the O2 sensors to to gauge combustion in the chambers via exhaust gases - namely oxygen. It is an indirect method to evaluate the AFR. This works pretty well unless you have a lot of overlap or an exhaust leak. In which case the oxygen present in the exhaust is the sum of unspent combustion oxygen and the oxygen pulled in via overlap from the intake stroke (or exhaust leak) . The reading from the O2 sensors is lean from the added overlap oxygen. Additionally there is unspent fuel in the exhaust - but the O2 sensors do not read fuel.
So, there is excess O2 which causes a false lean read of the exhaust. There is also excess fuel (rich). But in both cases they excessive oxygen and fuel (at least partially)are due to the overlap and do not accurately reflect combustion.
Make sense??
