The issue with my van has me and 2 other mechanics stumped.
Over the course of 2 days, my van went from running alright, to having absolutely no power going up hill (like, had to drive in 1st/low gear, and even that only produced 15 mph) and did not want to accelerate much on flat land. It idles fine (maybe a bit of a nearly un-noticable tremble, but smooth nonetheless) and slow pedal pressure revvs the motor, but a quick press has lag.
I got a code P0171 (bank 1 running lean) and have looked into vacuum leaks and manifold leaks, visually inspecting everything and using a rubber-hose stethoscope as well as the carb cleaner spray trick. Couldn't find anything. I changed the fuel filter, thinking low fuel pressure, didn't help. Code reader shows approx 40 psi at idle, 1500, and 2500 rpms during live test.
Long term fuel trim on bank 1 shows 25% at idle, 1500, and 2500 rpms.
LTFT on bank 2 is normal (about 10%)
I tested the resistance of all 8 injectors, they were all 12 ohms.
COP's all brand new Accel's.
I cleaned the MAF with MAF cleaner, even though it didn't look dirty.
I removed the O2 sensor from bank 1 to see if a clogged cat was causing too much back pressure, but the hesitation still persisted.
Any thoughts?
Any insight would be very appreciated.

 

Really would be helpful to post the year, engine and even the mileage when your asking questions

Assuming that you changed the COP's then you Might have a 4.6 or 5.4 engine???

Here's a Link to sensor tests and general overall tutorials.

Reading and testing is less costly than throwing a ton of parts at it.

On page 2, there's a test for troubleshooting Codes P0171. Might get you somewhere's with that alone. Funny, just looking at the list of problems, the fuel pump comes up?

Question, did you or any mechanic do a Compression Check?
Reason I asked, if it's not some sensor, fuel pump problem, something internally in the engine could had failed

Let us know how you make out.......

 

I agree

Ford Truck Enthusiasts Forums - View Profile: Vizzle

 

OOPS posted in wrong thread so I removed it..

 

Upstream O2 or down stream? Pull the up stream only, and bank 2 is usually the culprit, in spite of what the code says.

...and what the others said. year, engine, mileage.

 

Remove the exhaust from the engine and look into the pipes.
Take pics. Report back.

I bet its your cats.

I applaud your lengthy, thorough diagnosis actions lol

 

That's not the correct way to diagnose a problem with a suspect plugged cat, the proper way is to use a "Back Pressure Gauge" in place of the upstream O2 sensor, which would take 5 minutes, and not hours to remove the exhaust components.

 

I suspect most people don't have that tool but it does sound great.

Removing the front of the exhaust is easy if it's not rusty.

 

What range of pressure at the O2 port would be considered normal? Very clever method to troubleshoot a blocked Cat.

 

The one I "borrowed" from a ASE mechanic friend, was just self reading, remove O2 sensor, using the correct adapter, attach long hose, start up, idle, and hit the gas pedal to the floor several times, and the gauge will read in the green (good) or in the read (bad) Then let the thing cool down for a while,as the adapter will get very hot for a long time.

LINK

Guest the OP has not check this........so side tracking is OK

 

Harbor Freight has a Vacuum/fuel pressure tester for $16, $12 if you have a 20% off coupon. Good little handy tool to have.. It comes with some adaptors but I don't know if one of them fits the O2 sensor. If not, then you can go bay a shop and pickup an old 02 sensor they are throwing away and make an adapter for free.

Here is a couple of videos. The first one shows a great homemade adapter that is good for high temperatures. In this video he says no more then 1 to 2 lbs at idle and no more then 4 or 5 psi at 3K rpm. He also says check the specs, so perhaps different cars vary on the amount of proper back pressure..

This video shows you how to diagnose the problem with a good scan tool hooked up along with using a gauge to test back pressure.
This guy says 1.5 psi at idle is bad.. Other videos say 0 to 1 psi is ok.


This video shows you how to check back pressure using the port on the DPFE sensor. If you have one then you will not need to remove the O2 sensor..
This guy says no more then 2 psi at 3k rpm. That a good car will read 0 at idle..

 

annaleigh, as always, thanks for posting up visual info for the subject we're discussing.

I think the 3rd video with the "quick" check thru the DPFE is more app for our vehicles.

 

Thanks for the kind words Wildman. Everyone here has been so helpful when I need advice so I have to return the favor. On top of that I learn too!

If you noticed in thew caption about testing from the DFPE, it says if you have a 3 cat system and only one of the upstream cats is plugged, you may not see the back pressure at the DFPE and still need to check at the O2 sensor..
So that would mean that in a 3 cat system, both front cats, or the rear cat, would have to be clogged to get the back pressure reading at the DFPE.

Lets say someone had their front cats replaced but not the rear one and now a few years later they have a blockage again. .
So how would you check the rear cat?
Perhaps with a infrared thermometer, and read the temperature in front and back of each converter?
I also think most 3 cat systems have 4, 02 sensors. One at the front of each main converter and one at the rear of each main converter.
If you use a vacuum/pressure gauge and check the back pressure at the front of the converter and it shows to be clogged, it could possibly be the rear one, not the front one. So in the case of a 3 cat system it would be best to check the back pressure at the rear o2 sensor also.

Now my 1990 Town Car had 4 cats but I have no idea if it had 1, 2, 3, or 4 o2 sensors because I never had to work on it...

Anyway,, here is a series of videos by Walker Exhaust Systems that is well worth watching "in order". IT covers many different aspects

You might want to go directly to YouTube so you watch each one in order.. it is called 13 Steps for Diagnosing Emissions Issues

 

I'm betting money on the exhaust, ha to be majot restriction somewhere, possibly a melted cat..