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.

That would be my first guess as well. You say no warning messages, but are there any stored codes?

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

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.

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

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.

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

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/

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.

I did as J doubleU recommend and went into the misfire section under Ford and reviewed the 4 types of data available for each of the cylinders and no misfire data as available. All show 0.

I also went back and reviewed the data for the following;
ECT 183 degrees F
SHRTFT1 -1.6%
LONGFT1 -3.1%
SHRTFT2 -1.6%
LONGFT2 .8%
MAP 5.7 psi
O2B1 S1 .765v
SHRTFTB1 S1 3.1%
O2B1 S2 .0.75v
SHRTFTB1 S2 3.1%
ODB2 S1 .095v
SHRTFTB2 S1
O2B2 S2 .045v
SHRTFTB2S2 it reads 99% and the graphic shows a steady trace, no movement like SHRTFTB2 S1. Al other traces increase and decrease except this one that stays the same.

Great work! It's odd that the sensor itself is reading very clean but the short term trim is so high. It might still be a cat on it's way out or it may be a dying sensor that is responding slowly. I'd swap the secondary O2 sensors from banks 1 and 2 to see if the high reading follows the sensor or the cat.

Any luck so far?

I will get back on later this week if time allows. First step is to replace the one sensor that has a fixed output then move on to other possible causes.

This week my main task is working on my wife's Miata. Timing belt, water pump, cam and crank seals etc...

I'll be tackling that same job in my NA , but I've got another 10,000 miles before I have to worry about it :)