I have a 2006 Ford F-150 Fx4 with the good old 5.4.

During a drive it just here and there would seem to lose power or stutter like a bad coil pack or plugs.

Codes for multiple cylinder misfires showed up so we figured the loss of power and the misfires were related.

Changed the plugs and boots (3 or 4 had carbon arc on them from bad boots)

The misfire codes cleared and it runs and idles (although still feels like a miss (mi misfires per the scanner), but won't really rev above 3500.....

Initially thought cam phasers, but I don't hear any audible ticking at all coming from the front. Then maybe plugged cat.....

A friend has a snapon scanner, and only code it sees was a p1184 (Oil temp out of range), a wheel speed sensor code (which probably is right and it needs to be changed)

This snapon is pretty robust, I am really at this point just trying to diagnose what the issue could be.

We did verify the can bus ground and the obd port is good to the PCM.

Any test I can run with this scanner to try and hone in on the issue?

 

Monitor all 4 O2 sensors the front sensors should switch between .1 and .9 volt and they should be smooth like rolling hills (put the scanner in graph mode) and the rear O2 should be steady around .7-.8 volt with occasional dips lower than .4 after the cats are warmed up. If the rear mirrors the front or stays low then the cat is bad. Also both long fuel trims should be pretty equal if one side is way off then the cat is partially plugged on the rich side IIRC. Most likely you have a restricted cat from the misfires. It doesnt take much to melt one down on this gen truck

 

Check your individual cylinder misfire data in Mode $06 while it's running and the symptom is present. Any misfires that are detected will be reflected there long before a code sets.

 

Awesome, I will get going on that and post what results I find.......Thanks again for the help!

 

snaps of o2sensors. Hopefully data makes sense to someone.

 

From those graphs I would say both cats are bad. Loosen the exhaust pipes at the manifolds and drive it to see if the power comes back. If it does then that confirms bad cats. Also it's possible for parts of the brick to clog the muffler too.

 

I see two functioning converters. Nothing there that would indicate a misfire issue or a fault with the cats.

Go check the data I told you to check.


I will say that, if you do have a misfire, those converters probably won't be good too much longer.

 

No, those cats are definitely bad. The second pic is a dead giveaway that recording was taken at higher RPM due to the frequency of the front O2 sensors switching and both rear sensors nearly mirror the fronts. A functioning converter doesnt switch that fast. Those converters cannot store enough oxygen to burn the HC and CO. If they could then there would be no oxygen left in the exhaust at the monitor sensor causing it to read .7-.8v most of the time.

 

What are the long and short fuel trims at idle and 2500 RPM?

 

Gentlemen may I respectfully join/comment on the discussion - to prompt more analysis in hopes of not misguiding the OP. O2 sensors and oxygen presence and CATS and voltage measurements representing them can often get confusing. If i understand the last sentence above - it leaves a misleading impression. Oxygen 'PRESENt' at an O2 sensor will cause voltage reading to be LOW (.1 volt). If NO OXYGEN is present - it means the CAT MEDIUM was successful in absorbing it / and consuming it to the extent NONE voltage reading would be HIGH at O2S2.


I agree with @projectSHO89. Cat Below Efficiency codes are produced when, DURING CAT MONITOR test conditions (Cat temp normal, & Light cruise 40-60 mph), the switch ratio between downstream O2 - to - upstream O2 rises above 60% to 75%. While the required test conditions are unknown here - I do see switch ratios LESS for downstream - by SOME percentage. Even in second picture, the ratio appears OK. Switch rate shown must be a function of time/division setting on the scanner as it isn't controlled 'directly' by RPM. I would feel all different about this if cat mid-bed temperature was known and if the test was done at idle - where downstream should basically be steady at .6 to .7 volts.

 

All those tests were done with the truck just idling. If there is any more data you need to help diagnose, I can certainly pull that a post if it helps.

I will say there were no misfires at all (checked via the scanner).....

projectSHO89:
that being said, the truck did have several cylinders with misfires..... I fixed these with new boots (old boots were arc'ing out)

Is there any harm in doing as 70f100longbed mentioned and taking the cats loose and testing it by driving it?

 

IF, IF, IF -- diagnosing requires considering lots of factors. If those readings were at (or near) idle at light engine load [WITH cats up to 'operating' temp], there WAS too much downstream O2 switching going on.

"Inferred" Mid Bed Cat Temp can be read at OBDII PID #0907, equation for ºf = A*256+B. Has to be > ~1000º to begin operating very effectively.

Having said that; I never recommend replacing parts immediately based on DTC's, but I DO place lots of weight on DTCs as part of diagnostics. That PCM is much closer to the situation than we are. You can't monitor cats all the time, and it does. If your PCM was not successfully passing the Catalyst Monitor test, you would have a P0420 or P0430 within two drive cycles. "Catalyst Monitor Status" can be monitored at OBDII PID #095D, bit:0 for completed this drive cycle true/false.

As for other testing, @projectSHO89's direction is still best. Run a Mode $06 test report. You can't feel ALL misfires. That report will give misfires 'BY cylinder' for current drive cycle ---- AND --- for last 10 drive cycles. It will also give cat switch ratios for latest Cat Monitor run -and- max limit for setting DTC. $Monitor Id MID:$21 & 22, TID:$80. And Freeze Frame data is always helpful to analyze conditions presented at the instant DTC is set.

 

All tests were at idle and i let the truck warm up for quite a bit of time, then ran those tests.

 

Long and short fuel trims on both banks at idle and 2500 RPM will be helpful. I'm standing by my statement as both cats being bad.

The following pics were made today from a truck I'm working on. Its a 2006 F150 4.6 with 255K miles. It came in with a dead misfire on #8 and lean bank 2 codes. Coil and spark plug fixed it. I cleared KAM and drove it 10 miles then made these recordings. The bank 1 cat was replaced 20k miles ago and bank 2 is original.

This is at 2500 RPM


This is at idle right after the 2500 RPM run


This is at idle after about 5 minutes


Notice the steady voltage of bank 1 cat at idle. Thats an efficient cat. Bank 2 isnt as efficient and it wouldn't surprise me if it came back in a few weeks with P0430. fuel trims on both banks are near 0.

Here is the plug which demonstrates why coils and plugs should be replaced at the same time for misfires. Had I only replaced the coil it would have surely misfired again

 

There's a reason that spark plug anti-foulers still get sold in the auto part stores, you know. I don't think anyone has used one on a spark plug for a long time.

I'd certainly agree that the cats in the first example and the #2 cat in the second are a long, long way from being pristine. However, they do not appear to be "bad enough" to fail the on-board diagnostics due to exceeding the switch ratio limit and to trip a cat efficiency code. A completely dead (inert) converter will cause the downstream O2 waveform to look exactly like the upstream with a tiny time lag.