Can a bad COP cause a P0174? With truck running (can hear/feel an engine miss at all RPM levels) I can unhook the connector going to the #5 cylinder COP (drivers side, front cylinder), and there is NO Change with engine harmonics/rpm's. Unhook any of the other 7 COP connections, and I get a noticeable stumble/miss.

However, there is no CEL, just a pending code. Even after driving for 20+ miles.

ALL COP's are of questionable service/brand. Injector is firing, I get a pungent un-burnt gas smell at idle. Breakdown and replace all COP's? Have gone over all vacuum lines multiple times (I know, I know, go over them again). Compression Test that cylinder?? Brand new intake gaskets installed while swapping in new to me engine by ex Ford Techs. Techs say swap in new COP's, but not wanting to spend that much if not needed. Thanks.

 

I went with these ones over two years ago. No issues since. You can usually get a deal on buying the set (I got them half price from NAPA on sale).

 

Your all over the map with guessing.
Code 174 tells you the long term fuel trim table for bank 2 has shifted rich more than 25%.
Usually it's due to a vacuum leak in the intake tract, however a misfiring cylinder might affect the amount of air in the exhaust gas where it would be detected by the Oxygen sensor..
A missing cylinder should set a code. If no code the cylinder is not misfiring. The reason is the way a misfire is detected. The crank sensor measures the rotation time for every cylinder every time. If it too slow as measured against the average, it's called as a misfire by the computer and code set for that cylinder.
To see what your dealing with, you need to look at the live operating data with a Scanner and service by that data result.
What you need to see.
1. Where are the long term fuel tables.
2. Misfires and the mode 6 test 53 record of misfire counts of each cylinder.
Do not clear codes or power down the computer because you lose all important data for troubleshooting.
Unless you go about it in this manner, it's all guessing.
Pulling connectors off coils, injectors and sensors is not a very productive way to troubleshoot because the system reacts in ways you might not expect.
Good luck.

 

Those coils are the worst you can get.
Made in China and garbage.
Some people have luck like a clock shows the right time twice a day even it it's not running.

 

Right On Bluegrass, Need to check data, missfire counts, a vacuum leak at the manifold or PCV hose that crumble's is very common and will cause a missfire on a cylinder were the leak is closest, swap a coil from a firing cylinder to no.5 and see if the miss moves to a different cylinder. Then you know at least the COP is good or not.

 

I would not swap coils to a different cylinder until you get a CODE and know which cylinder is the problem.. Your still guessing at #5.

 

Thanks for all the suggestions/info guys. Bluegrass I have poured over several of your post on the dreaded P0174 and P0171. I don't have a live data scanner, so I may have to order one to get that data. As Bluegrass and others have stated, I am leaning towards some sort of vacuum leak. The explanations provided make perfect sense, but the disconnecting of the COP's has/had me stumped. I will go over the PCV lines AGAIN and see if I am missing something. I traced out the EGR plastic lines and they look fine, but I may just change them out, not a huge cost for 1/4" vacuum hose.

Thanks Guys, I WILL report back on what fixes this issue.

 

Should I be able to see spark on the spark plug tip, if I remove the COP, insert a NEW motocraft plug into the COP, connect the two pronged connector to the COP, then start it?

I know this is extremely old school, but in my thinking, I should be able to see spark (in my garage, no direct sunlight). Discuss..............

 

 

my 2002 5.4 motor had two small 1/4 inch vacuum lines on the drivers sided--- EGR and close to the exhaust manifold.. They got hot/ brittle/ cracked and I got the 171- 174 codes from that... about 8 inches long I think.

 

Promised I would come back and update when I got this thing figured out. Well here goes:

So, had a junkyard motor installed by my ex-Ford Tech shop. They were not thrilled with my engine choice, but I am just trying to get the vehicle in running condition to sell. Could not sell it to someone with a possible headgasket problem (as diagnosed by the above mentioned shop. Could have been head gasket or cracked head they said). Engine is a late 1999 with the aluminum intake, PI headed motor, 112,000 miles. Installed new plugs, intake, throttle body, IAC, and EGR gaskets. All looked good. They FORGOT to swap over the COP's I had in the original engine, and left the ones that came in the junkyard motor. I have been running ARA Parts brand COP's with zero issues for over 4.5 years, but they didn't get swapped to the junkyard motor.

They knew I was doing this on a tight budget, and told them to get it swapped out and running, and I would fine tune anything. Picked it up and on the way home it threw P-0171, 0174, and one for cylinder 4 misfire. Searched hi and low for a vacuum leak and found a split in one small line. Fixed it and cleared all codes and none returned after driving for 35 to 40 miles, but had a dead miss. Started unhooking COP connections one at a time. 1 - 4 caused the motor to stumble noticeably at idle. #5 (front drivers side) there was NO CHANGE in engine idle. 6 - 8 did exactly like 1 - 4, with a very noticeable idle stumble. Swapped COP's around and #5 STILL showed no change in idle when it was unplugged, but very noticeable with all others. Still NO CODES. Remember post about one bad COP causing "ghost failures" with other COP's. Shop had already sent my old motor off to have the heads looked at, so my old COP's were a no go. Ordered 8 new COP's from ARA. They were cheap enough, and I had good service from the others, so what the heck. Installed new COP's.......still #5 no change when unhooked. Swapped in a new connector......still no change .

Did some more internet reading/searching, came across someone who seemed to have had the same issue as me. Ran his tank down to around a 1/4 tank and added seafoam, Techron and another brand injector cleaner to his tank and drove it. After about 30-40 miles it was purring like a kitten!!!!!! I figured why not give it a try. A little under a 1/4 tank, added B-12 Berryman Injector cleaner (12oz), Lucas deep fuel system cleaner (large bottle, 16oz???), and Techron (20oz). Went less than 2 miles and mine was idling perfectly!!!! Drove another 20 to 30 miles running errands in traffic and NO CODES, and smooth as silk idle!!!!! Got home popped off COP connection on number 5 and stumble, stumble, stumble!!!!!

In my opinion, it was a plugged/stuck injector, along with the vacuum leak and possible bad COP's. Hope this helps someone!!!!

 

That's one of the reasons I started adding a bottle of Techron on every other fill up. Plus I use 89 or 93 octane. The ethanol blend gasoline sucks. Slowly destroys older engines. But there is nothing else available. The federal government has to stop subsidizing farmers. We end up using more oil growing the corn, transporting it to ethanol factories, producing it, then adding it to our gasoline. And the **** is less productive gallon (ethanol blend) vs. gallon (straight gasoline). What bull***** Bush Jr. and the Republicans spewed saying that the ethanol would decrease our dependence on foreign oil. We have plenty of oil here, but US companies sell it to other countries because they can make a larger profit. Plus we have deals with foreign oil producers that allow us to have military bases in their countries (Saudi Arabia).

 

As a continued follow up to this issue, I wanted to see if my problem was MORE Injector or COP related. Call me a glutton for punishment, but I could not leave well enough alone. Dug through my just removed COP's from my junkyard motor, grabbed the two that LOOKED (very unscientific) the worst, and swapped them in on different cylinders on 5-8. Never was able to generate a single miss or stumble when swapping around, driving, then unhooking COP's.

So, to anyone chasing missing, stumbling, or general not running good problems, I would definitely look at injector issues. Have put a full tank of doctored fuel (Berryman, Lucas and Techron) through the truck and it is still running strong. I believe my whole problem was Injector related (plugging, general crap in the system), but the new COP's helped ease my mind.

Have a buyer lined up for this Friday .........if he gets his bonus check........and it will be AS IS, NO WARRANTY SALE!!!!!!