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Bad plug wire effects?

 
Old 01-12-2019, 09:29 PM
  #31  
docmirror
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Originally Posted by Hey_Allen View Post
The explanation I was given, and how I've read elsewhere, is that the Oxygen sensors were detecting O2, rather than the combustion byproducts of it.
Both are true. It measures the free O2 in the gas stream, AND all those gases are byproducts of combustion.

At perfect stoichiometric ratio of 14.7:1, the free O2 is about 4% of the various gasses of the combustion event in an Otto cycle gas engine. That produces a reference voltage which is sent to the fuel injection ECU. The ECU is constantly adjusting the pulse width to maintain the proper ratio. Now - for bonus points, the ECU actually doesn't hold the ratio exactly static. There is a periodic variance built in to burn off the surface of the catalyst so that the cat converter will have a significantly longer lifetime( > 100,000 miles in most cases). The ECU typically will run slightly lean of 14.7:1 until it runs in burn-off mode, when it enrichens the mixture slightly so that the catalyst in the converter is refreshed.
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Old 01-13-2019, 11:59 AM
  #32  
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is it possible that a misfire, or a combination of misfires (all 8 cylinders at the extreme), could be misinterpreted by the knock sensors
and erroneously pull back timing? wondering if a poor ignition condition could lead to false knocks?
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Old 01-14-2019, 12:15 AM
  #33  
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Merc:

I put on new Beru wires today, and..my "leaving a light" and "Highway load RPM" rumble are gone.

Lets see if it sticks for a few days..but..this was the last part of the ign system I had not replaced yet.
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Old 01-15-2019, 08:48 AM
  #34  
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FWIW: new plug wires have made a significant and noticeable difference! idle was darn good prior; now incredibly rock steady.
more performance at 3k and again at 4k when flappy kicks in. I fought this for a long time, especially since I needed other parts
of higher priority. the wires are not cheap, but like a lot of other bits, most likely the last set I will buy. thanks roger!
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Old 01-15-2019, 09:13 AM
  #35  
Chuck Schreiber
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Merc,
Glad to hear!

Cross it off your list. On to the next project!
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Old 01-15-2019, 09:20 AM
  #36  
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Just to add a data point. I've had many cars that had stumbles, rough running and a '90 that would actually stop running after it got hot. All issues taken care of with new plug wires.
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