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2007 V8V manual, sometimes a miss at idle

 
  #1  
Old 04-15-2019, 08:26 AM
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2007 V8V manual, sometimes a miss at idle

I have a 2007 V8V manual trans car that has just passed 50K miles. The car is running fine and not displaying any warning messages.

I've noticed that over the last month or so I feel a slight miss fire at idle when at a stop light.
Happens with the can in neutral or with the clutch depressed
This does happen every time when idling.
Slight miss with maybe a few seconds between.

Anyone with a similar experience?

My past experience with other cars has been plugs/ignition.
 
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Old 04-15-2019, 10:11 AM
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Originally Posted by boxercupdave View Post
My past experience with other cars has been plugs/ignition.
That would be my first guess as well. You say no warning messages, but are there any stored codes?
 
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Old 04-18-2019, 10:58 AM
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Today I finally connected my Autel 802 scanner and it reported the following.

MIL Status 0
Codes Found 0
Monitors N/A 0
Monitors OK 9
Monitors INC 0

Trouble Codes Menu
No Codes are stored in module

Pending Codes Menu
P0420 Catalyst system efficiency below threshold bank 1
P0430 Catalyst system efficiency below threshold bank 2

Note that after buying the car in 2014, I later found out that the original cats have been replaced with RCS units, so this might be a reasonable pending code if 200 Cell cats?

As none of the findings indicate an issue upstream I think I may attempt a plug change.

Dave
 
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Old 04-18-2019, 12:33 PM
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It makes things harder if there isn't a code. I'd think that the knock sensor would pick up an ignition related miss but maybe not. I'd still look at the ignition system but based on the O2 codes you may be looking at the ECU correcting for a bad O2 or cats. You could watch the fueling correction in real time and see if the ECU is making some drastic corrections.
 
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Old 04-19-2019, 12:08 PM
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Which of the real-time items should I view? The 802 allows me to run a graphic of each real-time. More are available but I think these are the ones to view.

SHRTFT1
LONGFT1
SHRTFT2
LONGFT2
O2B1 S2
SHRTFTB1 2
ODB2 S1
SHRTFTB2 S1
O2B2 S2
O2B1 S1
SHRTFB1 S1
O2B1 S2
 
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Old 04-19-2019, 01:01 PM
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I'm not completely familiar with the differences between the various long and short term fuel trim data streams, it's probably for the two cylinder banks. The FTs are fuel trim, the O2s should be reading the sensor voltage. Look for fuel trims as described here:

https://www.obd-codes.com/faq/fuel-trims.php

O2 sensors should not run from one extreme to the other (0.1 or 0.9V) or be pegged on either end.
 
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Old 04-19-2019, 01:12 PM
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If not later today it's be Monday. Plan to take it out to get it warmed so it comes out of closed loop and then look at the trims and the S1 and S2 O2 sensors for both banks. Fuel trims also. This will be good exercise for me to get more familiar with using the tools.

Dave
 
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Old 04-19-2019, 02:54 PM
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Good luck. If it's not in fuel trim or O2 voltage, take a look at some of the other sensors:

MAF
There are a bunch of misfire ralated codes, MISFIRE and NM are the first to look at
Crank and cam sensor sync SYNC
Throttle position TP

There's a pretty long list. Check out this on the DB9

https://aston1936.com/2016/04/11/liv...i-code-reader/
 
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Old Yesterday, 01:10 PM
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With your Autel your able to go into vehicle on board test, select Ford and 1 of the 2 selections for modules will allow you to look at misfire data for each of the 8 cylinders.
 
 
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