Hello,

I have a question for some of the technical experts that frequent this site. I really appreciate the help.

Here goes:

I have a 2007 F150 Supercrew 4x4 with a 4.6L SOHC (2 ports) and 109,921 miles. For about a month I have noticed a mild misfire at low RPM/idle that is worse when the truck is cold, but which goes away at higher RPMs, when the truck runs fine. The truck throws no codes/presents no trouble lights. The basic code scanner I have lists no misfires during the last operating cycle. The spark plugs and COPs were changed in December 2014 at 99,198 miles with Motorcraft parts.

Here's a list of the stuff I've done recently trying to fix the issue:

1. replaced the fuel and air filters with Motorcraft parts.

2. cleaned the MAF sensor and the throttle body with appropriate aerosol cleaner.

3. run fuel injector cleaner through two tanks of gas.

The throttle body on my truck is p/n 7T4E-EC, so it does not have a separate Idle Air Control Valve, or I would have cleaned or changed that, too.

Has anyone else experienced this problem? If so, how'd you address it or what might I try next?

Thanks again.

 

Compression test.

 

Maybe do a suck test on the EGR. The 4.6's have a tendency to goober up the EGR ports. Did you remove the TB to clean it, or just squirt some cleaner in the intake?

 

Hi, thanks for the reply. I did not remove the TB, but that's next. Appreciate the advice.

 

There are several possibilities that come to mind:

1. Un-commanded EGR flow due either to an EGR system that's partly open or a fault EGR flow sensor.

2. Individual cylinder with a low-grade misfire.

You'll need a more advance scanner to investigate either. An Android phone/tablet plus an OBDII Bluetooth adapter plus the Torque app would work.

For the first, you'd have to look at the output of the DPFE sensor or the MAP sensor (I forget which your engine has) and see if EGR flow is registering.

For the second, you can look at the individual cylinder misfire counts (Mode$06, TID$81, PIDs$A2-AA). That way, you can see if the misfires are attributable to a single cylinder which will make your troubleshooting a whole lot more effect or if you have to check all of them.

 

Hi again and thanks for all of the advice.

This morning I removed the throttle body, as advised. FYI, it is MC p/n 7T4e-EC (Standard Motor p/n S20040) and looks like the one is this link:

http://www.ebay.com/itm/like/291488268676?lpid=82&chn=ps
The EGR pot set-up on this TB is different than the model that I am familiar with; this one has no IAC (I've heard it called the 'fly by wire' model). It looks to me like cleaning the EGR ports on this TB will require removing the valve itself (I think that it's MC p/n CX2095 and looks like the one in the link below), which I tried to do but the thing was so rusted and corroded that I was afraid I'd bust it or bend the pipe that it connects to; it's soaking in WD40 now.

%7C54&Model=F-150%7C666&Year=2007%7C2007&ie=UTF8&n=15684181&newV ehicle=1&s=automotive&vehicleId=1&vehicleType=auto motive

Unfortunately, I don't have access to a better code reader, which it sounds like I need, but as follow on to PROJECTSHO89's comments, if there was a low grade misfire in an individual cylinder, would it be less noticeable at operating RPM? The last time I had a misfire, which ended up owing to a bad COP, it got worse as the RPMs increased.

Again, many thanks for the help.

 

WD40 isn't particularly useful for that, switch to PB Blaster or Liquid Wrench, or any of the other "rust-busters".


It depends on the underlying cause of the misfire, which is often determined after the fact. Usually a weak spark caused by a COP is most commonly encountered when the system is stressed the most. That's just after the transmission has shifted into overdrive (if auto) with mild to moderate throttle. Dropping the transmission out of OD and giving it more throttle makes the symptom disappear since the system is no longer operating at its peak stress level.

The BT adapter and the app will total about $25-35, assuming you have an available Android device.