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2007 f150 catalytic converter issue
11-20-2015, 01:59 AM (This post was last modified: 11-20-2015 07:39 AM by salamander.)
Post: #1
2007 f150 catalytic converter issue
hello all again, have a new question I need some help with. will take a bit to give all pertinent info, so bear with me!

Daughter just got a 2007 f150 5.4 engine with 130,000 miles. when we test drove it the truck drove fine if you ease into the gas, but if you put your foot in it and accelerated fast it would "stumble" and bog down but then pick right back up and go. My immediate reaction was it felt just like a coil over plug breaking down. (have replaced all 8 on my sons truck). she got a good price on it and bought as we felt we can fix this issue so I don't have any history to give on the issue.

Over the next two days, the truck hasn't done it nearly as much as that first day. The check engine light was not on but I went ahead and scanned for any codes yesterday and did not pick any up. I also ran some live data streams with my scan tool. about 3 hours later drove the truck again and this time I picked up a code P0420 -catalyst system efficiency below threshold in bank one-the check engine light still did not come on though. also the truck never stumbled and bogged down.

later that night as she was driving home the issue happened at highway speeds while accelerating hard and the check engine light finally came on. she drove to parts store and they scanned it and retrieved the same P0420 code.

I was reading elsewhere to look at the o2 sensors and that if the cat is working right then the upstream sensor will graph with wavy lines and the downstream with basically flat line...if the downstream is wavy then its a good indication that the cat is bad or going bad. So I looked back at all the data streams I did that day and when I graphed the o2 sensors both down stream sensors show extremely wavy lines.

I also read to look at fuel trim from the freeze frame and that high fuel trim would likely indicate a possible vacuum leak which could cause the code as the engine is getting to much fuel to compensate...the long term fuel trim on bank 1 was 6.3 and 7 on bank 2. Stft on both had values of 0... haven't had a chance to check for any vac leaks yet.

I would like to think that perhaps the cat is the issue, and belive that a bad cat may very well make it run like it is but I don't want to jump to uneducated conclusions...especially with the truck only bogging down occasionally now. Do yall have any thoughts on the best direction to move forward? I can post all the freeze frame data if would help...Really appreciate any ideas you have on determining if the cat really is bad or something else causing the code and the truck "stumbling" issue
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11-20-2015, 10:58 AM (This post was last modified: 11-20-2015 11:01 AM by Rupe.)
Post: #2
RE: 2007 f150 catalytic converter issue
You mention "both" downstream sensors reading wavy so I figure you have dual exhaust, which also means more than one cat, right?

You'd be correct in that the second O2 sensor should be a fairly constant reading. What goes on here is the front sensors read the mix and trim the system as necessary, within limits. The mix will vary lean / rich in small amounts every few seconds. The rear sensor(s) just report on the final result after the cat, which means if the cat(s) are doing their job (an after-burner of sorts) the reading should be cleaner and more consistant. The P042 usually means either the cat(s) are tired, although weak sensors can throw you a curve ball and replacing them might turn the dash light off for say 1000 miles.

The hard part here is the hesitation / stumbling you speak of. The only way a cat can do that is if the internal biscuit is breaking up and restricting the exhaust flow. You can try banging on the cat with a rubber hammer to see if it rattles internally, which is a sure sign, although not a perfect test. Another test that does seem to work better is to rig up a pressure gauge to fit in the forward O2 bung. I fabricated an adaptor using a broken spark plug and soldering / welding a threaded bushing to accept a 1/8" threaded hose. (grease gun flex hose is cheap) From there it goes to a 30 pound gauge. Depending on the space available I have a 90 degree fitting. The hose allows you to let the gauge hang out where you can see it.

Here are some numbers to work with for a good system...
0 psi at idle
2-3 psi at 2000 RPM with light throttle jabs
5 psi with hard throttle jabs.

These are max readings for a good / normal system. A restriction will give you near 30 psi very quickly when you jab the gas.

Obviously you may set other codes by having the O2 sensors out of the pipe but the test only takes maybe 20 seconds so maybe not. Try to work quickly so the pipes don't get too hot, then you can switch sides.
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11-21-2015, 03:17 AM (This post was last modified: 11-21-2015 03:19 AM by salamander.)
Post: #3
RE: 2007 f150 catalytic converter issue
thanks Rupe, Definitely gives me a starting point. I like the idea of the pressure gauge. Will give that a whirl as the hesitation and bogging down is the #1 issue.

We will know for sure if I put the pressure gauge on exhaust, but I'm wondering if the hesitation is a completely different thing from the catalyst code as it was doing it before the code came up. It is also not doing it as frequently...seems to me it would stumble on acceleration nearly every time if there is indeed a blockage?

Wont be able to test for another day or so. If the cats don't pan out as the culprit, what direction would you suggest starting in first to diagnose most efficiently? Fuel...ignition...o2 sensors?
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11-21-2015, 11:15 AM (This post was last modified: 11-21-2015 11:35 AM by Rupe.)
Post: #4
RE: 2007 f150 catalytic converter issue
Still could be fuel pressure with either a failing pump or partially clogged fuel filter and would be worth doing the filter first as cheep insurance. Neither will set a code unless you are on the gas long enough (5-10 seconds) to set something oddball. I know some of the older GM vehicles would give you CEL for extended wide open throttle driving in the mountains.

A bad cat can give intermittent issues. What happens is the honeycomb may be cracked in the center and as things warm up the alignment of the two parts change. The old sign was hearing an odd sound fron the tail pipe as if someone stuffed a potato in the end so it makes a loud "wooshing" noise. I still hear that out on the road from time to time but I have never been able to hear it from the driver's seat. That's why I like the pressure gauge test, which I have only been using for a few years. It will tell you what's going on without leaving the garage / driveway so no chance of getting stuck on the road.

Edited to add: the O2 sensors will not change much in the way it runs because the ECM will just stay mid point in the mixture as a default. IOW, maybe a slight roughness in the idle or slight decline in power, but that's about it. Most people wouldn't notice unless the dash light came on.
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11-23-2015, 01:18 AM (This post was last modified: 11-23-2015 01:55 AM by salamander.)
Post: #5
RE: 2007 f150 catalytic converter issue
Here's where I'm at now...I removed the two upstream sensors one at a time and checked the pressure via an adaptor I rigged up from an old temp sensor housing drilled out and a piece of brake line welded to it to hook up the pressure gauge. The results where spot on with what you said should be expected...6psi was the absolute max with the pedal floor boarded. Idle was 0psi and short hits on the pedal were 2-3.

So we can safely assume that neither one of the cats are causing the stumbling/hesitation on acceleration, correct?

I started to change out the fuel filter but couldn't get the one clip off and she had to leave in a hurry so will get that changed in next couple of days. Seems strange that the first day the vehicle would hesitate and "cut out" like that constantly when accelerating but the last few days it only seems to do it at highway speeds and mainly when going up a hill. I tried to get it to do it the other day for a couple hours..constantly getting on the gas and it would not stumble until we were on the freeway going 60 mph up hill.

One thing I noticed just now- replaying the data from the scan tool. when I was streaming data and the truck was running good my short term fuel trim never went above 4 and was mostly in the -3 to +3 range. One time on the freeway though, I hit the record button just as it started stumbling and the short term trim at that moment was +12.8 and then went back down to normal levels as the issue cleared up. Relative fuel pressure read 38 which I believe is in normal range. Would that mean the engine was actually getting that much fuel or the sensors were just calling for an overload? would the sensors be calling for that drastic change because of pump cutting out for a second and them not sensing any fuel?

Pulled each one of the coils and checked them over with ohm meter and they seem to be averaging fairly close to each other and to a new one. misfire data on scan tool consistently shows system ok on all cylinders. ( Got a new Bosch 1300 and am still working through the manual so its possible I may miss something?) And of course there are no misfire on such or such cylinder codes coming up.

Given these bits of info, do you think I should concentrate on fuel system? On an aside...My obd1 trucks (87 and 90 f150) stumble and fall constantly when an O2 sensor goes out-they run like crap! Would that be because they only have one sensor instead of 4 like the newer models where one "makes up" for a failing one? So you feel that the sensors are probably not at fault on this issue, correct?

Thanks again for the advice Rupe, appreciate yall taking time out of your days to do this!
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11-23-2015, 06:19 AM
Post: #6
RE: 2007 f150 catalytic converter issue
I had a van that was doing very similar things. To nail the problem down, I found a long hill. I drove up the hill hard and at the same time lightly applied the brakes. This put enough stress on the engine to make it set a code. "Lean Fuel." Changed the fuel filter and the problem was solved.

Please keep us posted to what you learn.

Thanks for using the forum,
Garner

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11-23-2015, 10:31 AM
Post: #7
RE: 2007 f150 catalytic converter issue
I'm with Garner here. Get the fuel filter changed and see if you can get an actual fuel pressure reading. Also sounds like you have a fair assortment of tools handy so might be worth rigging up fuel pressure and manifold vacuum then going for a ride. Note the readings before it gets hot then compare when the problem kicks in.

Note: newer vehicles have slightly low vac readings anyway so you are trying to see what "normal" is before the issue and note the difference during the loss of power. If you see "0" vac early in the throttle then it's an exhaust restriction that is changing as it warms up. What I'm driving at is your numbers for backpressure were at the max level already so it's not a stretch to think they coundn't wander farther with time and heat. A brand new cat will have trouble reaching 1-2 psi at full throttle / load. (power braking against the trany) Combining slightly elevated numbers with the P0420 (lazy cat) code still has me leaning toward a cat issue but since they are expensive and a royal pain to change we'd like to make sure.

BTW, I'm leaving on vacation after Thanksgiving so Garner is in charge for 2 weeks. Good luck!
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11-23-2015, 08:35 PM
Post: #8
RE: 2007 f150 catalytic converter issue
Thanks Garner and Rupe, I will be getting the new fuel filter on probably thanksgiving morning. let me make sure about the vacuum test...

I can just tee into the vacuum tree on the intake and run a long enough hose into the cab to observe the gauge while holding it. Then what I'm looking for is to see if the vac pressure bottoms out when the stuttering and hesitation occur. And that would be indicative of the cats' insides moving and swelling with heat and thereby causing the restriction and probably also the loss of power/stumbling on acceleration. All this sound right?
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11-23-2015, 11:15 PM
Post: #9
RE: 2007 f150 catalytic converter issue
Yeah, you have the right direction. My point was to notice what "normal" is at idle, light throttle, and say 30 - 40 mph cruise. Obviously it will drop as you lay into the gas. For instance, if it's say 16" at idle, 8" light throttle, and 14" at 40 mph normally but after warming up the numbers go drastically downward (because you have to lay into it) trying to maintain speed, then you will have a clue. Typically the idle vac doesn't change much as long as it is possible to idle. IOW, if part throttle (light on the gas) becomes near zero you have a restriction. This is where it's hard to do the exhaust back pressure test because the pipes are too hot work near.

Oh, make sure you are on manifold vac and not on the reserve tank, which has a check valve so you wont see the drop.

BTW, I have rigged a gauge to the windshield or wiper arm with tape if the hose isn't long enough. Whatever works!
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11-23-2015, 11:40 PM
Post: #10
RE: 2007 f150 catalytic converter issue
Something I forgot on that last post...lets say a restriction is indicated, what then is the procedure for determining which cat or both is at fault? I was thinking that the passenger side would be the one since the p042 code was on bank one, and bank one also had the slightly higher readings on psi test. But maybe both are bad...how would one go about deducing that?

Sorry to keep throwing questions out right before you go on vacation!
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