Is it too much timing or not enough that creates surge @ idle?
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From: W.P.B. Florida
Is it too much timing or not enough that creates surge @ idle? I've done a search & found that some guys say you need more timing at idle to help stop surging with a cam.Others say the cause of the surging is too much timing. Which one is it & how much do I add or subtract?
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From: Schiller Park, ILL Member: #317
Re: Is it too much timing or not enough that creates surge @ idle? I've been struggling with this myself. Maybe someone can chime in with a good explanation.
Let's expand the question too...
Is there a recommended set of parameters to work with? Like for a cam of the XXX/XXX duration with XXX LSA start here ____? Or add/subtract in increments of ____?
<img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
Let's expand the question too...
Is there a recommended set of parameters to work with? Like for a cam of the XXX/XXX duration with XXX LSA start here ____? Or add/subtract in increments of ____?
<img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
Re: Is it too much timing or not enough that creates surge @ idle? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by ChrisB:
<strong> Typically a surge at idle will be from too much timing - or more commonly from too lean a mixture.
Chris </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Assuming the O2 sensors are working properly how can the idle A/F be lean or rich when the PCM sets it at 14.7:1?
John
<strong> Typically a surge at idle will be from too much timing - or more commonly from too lean a mixture.
Chris </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Assuming the O2 sensors are working properly how can the idle A/F be lean or rich when the PCM sets it at 14.7:1?
John
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From: W.P.B. Florida
Re: Is it too much timing or not enough that creates surge @ idle? ChrisB .. There are a lot of people that agree with you but also a lot that say just the opposite about the timing. I have to ask the same question as JNorris did above about the lean condition.
Has anyone cured the surging or hunting with more timing? How bout less timing? If so ,how much?
Has anyone cured the surging or hunting with more timing? How bout less timing? If so ,how much?
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From: College Station, Tx
Re: Is it too much timing or not enough that creates surge @ idle? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Assuming the O2 sensors are working properly how can the idle A/F be lean or rich when the PCM sets it at 14.7:1</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">
There could be a leak or bad o2 issue causing a problem - but that aside, just because the car is at 14.7:1 doesn't mean that's where the idle is most stable. 14.7:1 is just stoich - but it doesn't have any special connotation for power, stability, etc.
Rich and lean themselves aren't absolutes anyway - they just indicate relative conditions. Being at 14.7:1 could easily be too lean for best idle, power, etc. (infact it probably is).
Depending on where you are starting from will also have an effect on whether you need more or less timing - if you are at 5 degrees then yeah, you probably need more. Conversely if you are at 20 I would probably try backing off. Larger camshafts will need more timing, higher compression, less.
Lean condition is probably the #1 cause of hunting at idle - it will be especially noticable as you load down the engine more - you can have a solid idle with lean/high timing condition, and as soon as you load down the engine (kick on the AC) it starts to hunt/surge.
As for the final answer, the easiest thing to do is just try it out - you aren't going to hurt anything adding/pulling out a few degrees of timing here or there, so why not test it out?
Chris
There could be a leak or bad o2 issue causing a problem - but that aside, just because the car is at 14.7:1 doesn't mean that's where the idle is most stable. 14.7:1 is just stoich - but it doesn't have any special connotation for power, stability, etc.
Rich and lean themselves aren't absolutes anyway - they just indicate relative conditions. Being at 14.7:1 could easily be too lean for best idle, power, etc. (infact it probably is).
Depending on where you are starting from will also have an effect on whether you need more or less timing - if you are at 5 degrees then yeah, you probably need more. Conversely if you are at 20 I would probably try backing off. Larger camshafts will need more timing, higher compression, less.
Lean condition is probably the #1 cause of hunting at idle - it will be especially noticable as you load down the engine more - you can have a solid idle with lean/high timing condition, and as soon as you load down the engine (kick on the AC) it starts to hunt/surge.
As for the final answer, the easiest thing to do is just try it out - you aren't going to hurt anything adding/pulling out a few degrees of timing here or there, so why not test it out?
Chris
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From: College Station, Tx
Re: Is it too much timing or not enough that creates surge @ idle? You would have to put the car into PE mode at idle (set the TPS to enable WOT to 0 for low rpm's) - the o2's will still read, etc. but learning will be disabled. You can then use the PE vs RPM table at low rpm's to adjust the a/f ratio. (If it works like LT1's you may need to change the values in the open loop table also at some point - in LT1's it goes with the richer of the two).
Chris
Chris
