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2007 f150 catalytic converter issue
11-24-2015, 10:23 AM
Post: #11
RE: 2007 f150 catalytic converter issue
No problem, I'm here till Saturday anyway.

Replacing one cat versus both becomes a matter of your time / expense. Since most cats are part of the front pipe or Y-pipe they are often done together just for that reason. Another reason to do both is they have been in roughly the same service for the same time so there's a good chance the other will need replacement soon.

Short story: I've been working for the same fleet shop since 1997 and the owner is always looking to save a buck. I started similar diagnosis issues with changing the O2 sensor figuring they were just old (average failure was 130k miles) only to spot a trend where a month or two later I got the same readings. (P0420) I then started welding in single cat replacements to get by annual inspections only to spot another trend. You guessed it, the P0420 came back in a year or so. Since then I have been doing cats as a set (3 cats in a y-pipe) and everything is good several years later. Average age in this fleet is near 15 years old pushing 250k miles. Now the boss has a different outlook where my time is also worth money.
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12-06-2015, 11:03 PM (This post was last modified: 12-06-2015 11:12 PM by salamander.)
Post: #12
RE: 2007 f150 catalytic converter issue
Ok, did some more tests. I put a new fuel filter on to no avail. Didn't change anythimg, but at least we know its got a good filter now. Looking back at the data streams I did, the fuel pressure remains consistently between 37 and 40 psi..only seen it drop to 37 one time so I'm feeling good about the fuel system. Also cleaned the maf sensor for good measure.

Hooked up the vacuum gauge today and went driving. Here are my readings- 22 inhg at idle and when decelerating with foot off of gas. Cruising at 45 mph on flat road is 8-10 in. Light throttle during normal acceleration drops down to 3-5 and then picks back up close to 8. If you step on it at all as if passing someone or accelerating up a hill it will immediately bottom out at 0 inhg and might go up to 2 or 3 while the transmission shifts but then bottom out again until you let up on the gas.

We went up a long steep hill where we started at about 45 mph and as soon as the engine had a load on it requiring more throttle the vac dropped to zero and stayed there until we got to the top and was able to get off the throttle. Thats also when the truck stutters the most.

Pulled another code as well...the truck now has the p0430 so the bank 2 cat is now showing weak as well as the original bank 1 cat which is the p0420.

In summation, the stuttering issue seems to happen mostly after the truck is good and warmed up and it may be a bit more frequent now. We now have a code for each cat. Fuel pressure seems fine. Cant seem to find any indication (yet)of a faulty coil pack. Have not noticed any vacuum leaks although I havent tested the whole system. And the vac pressure is hitting zero on acceleration.

My daughter said "what do you think?" I replied "I think you need two new cats." What do Yall think? I hate to tell her definatively that the cats are the issue and then be wrong after dropping $300 dollars on new ones, but it seems that everything is pointing at the cats. That being said, I did not remove the muffler when I did the vac pressure test so there is still the possibility that the restriction could be in muffler. However it sounds hollow when tapping on it and if yall agree with the cat diagnosis I will run the vac test again with out the muffler just prior to removing the cats and welding on new ones.

I Know you can't say for sure without actually laying hands on the truck, But with the given information do you think I should feel confident telling her to get the new cats, or am I being hasty?
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12-12-2015, 12:03 PM
Post: #13
RE: 2007 f150 catalytic converter issue
Ok, back from vacation and wondering where you left off since this post last weekend?

The only thing I see out of the ordinary in your vac readings is they seem to be a little high at idle, although over 20" is normal on deceleration.

BTW, have you checked with the dealer to see if cats may still be under warranty? Some of these emissions parts could be covered up to 10 years / 100k miles.
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12-12-2015, 01:18 PM
Post: #14
RE: 2007 f150 catalytic converter issue
Hope you had a good vacation. Had not thought of checking with the dealer...would be worth a shot. Have not progressed any further this week, she waiting for another paycheck to get the cats.

To clarify...You said the only thing you see out of ordinary in vac readings is the idle being a bit high. Should I still be thinking there is a restriction with it dropping to zero upon acceleration?
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12-12-2015, 01:26 PM (This post was last modified: 12-12-2015 01:36 PM by Rupe.)
Post: #15
RE: 2007 f150 catalytic converter issue
Zero vac at partial throttle (1/3 or more) is normal. If the reading did NOT drop to zero then I'd say there's a restriction. (back pressure) What caught my eye was it's been a LONG time since I have seen anything close to 20 inches at idle. These days it's fairly common to see 16 - 18 inches due to retarded timing and other emissions related items. You can also get a high reading if you tap into the line after a check valve for the vac tank that runs the HVAC system. If there was no check valve then each time you drove up a hill the system would go to defrost. (the default)

Edited to add: if you still have the owner's manual there's a few pages covering the emissions warranty worth reading.
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12-12-2015, 07:16 PM
Post: #16
RE: 2007 f150 catalytic converter issue
ok, this is where I'm a little confused. I was thinking that if the vac goes to zero upon acceleration that it indicated a restriction. Would it be in my interest to cut out the converters, run a straight pipe, and see if it fixes the stuttering issue. Then I can always put the cats back on.

Where I'm coming from is she doesn't have to pass emissions here. So whether the cats are converting the exhaust gas isn't really an issue. Just trying to fix the stuttering on acceleration is first on the list. Hate to have her spend money on cats if it wont fix that issue.

So you think that problem might lie elsewhere?
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12-12-2015, 07:42 PM
Post: #17
RE: 2007 f150 catalytic converter issue
I see where this can be a little confusing, which is why I don't use that method too often. The key with a vac reading is "how soon" it goes to zero on acceleration. (and does it linger there) With a clogged cat it will head that way earlier in the game so it's a matter of knowing what "normal" is with a particular vehicle.

Here's a thought to ponder: If you manually put the trany in 1st gear and tried to drive say 30 mph then you know the rpm is up a little and the engine is trying to move air, right? Work the throttle and if the cat is clogged the vac will stay low (below 10"?) when the throttle is closed and when you step on the gas it will probably never go all the way to zero due to the restriction.

Another thought to ponder: Rather than cut out the cats (extra work) try driving with the O2 sensors removed. That should make enough of a leak to see if a reduction in back pressure helps.

Last but not least, it may be worth a set of spark plugs just to remove any doubt in that category. I can't tell you how many times I stumbled on that as a fix because someone didn't replace things with OEM to save a few bucks. Speaking of saving a few bucks, it sounds like you are covering your bases very well but I got to thinking about that idle vac over 20" and was wondering if there may be restricted air filter? Certainly worth a look or even a test drive without it for a few miles.
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12-13-2015, 04:26 AM
Post: #18
RE: 2007 f150 catalytic converter issue
Hmm...in reference to the high vac at idle- something that just occurred to me, but let me make sure I understand the vacuum system first.

While the engine is running it is sucking air through the upper intake mainly through the air intake into the throttle body but also through any other openings such as the vacuum tree. If the flow was restricted through the air filter it would thus suck harder through the vacuum tree, thereby increasing the vacuum pressure reading, correct?

One thing I noticed when she bought the truck is that there is a lot of fine sand in the engine compartment. It's like whoever owned it took it to florida and spent a week on the beach right before the bank took it back. I also noticed it has one of those K&N air filters but I did not take it out and inspect it or clean it. Could very well be clogged with that same sand. And if so, that would increase that vacuum at idle, right? I will check that out tomorrow.

Pain in the butt to remove the oxygen sensors without just letting them dangle in the air. (connectors are almost inaccessible for my hands) might be easier to just cut or drill a couple holes in the exhaust pipe forward of the converters to see if it helps having the extra airflow. Pipes are in good shape so it would be easy to weld a scab back over the holes.

Thanks for your thoughts, I get to wondering why I always seem to get these issues that are never simple! Seems like I get to play detective a lot on these vehicles, Lol.
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12-13-2015, 12:11 PM
Post: #19
RE: 2007 f150 catalytic converter issue
You seem to have a grasp of the vacuum in your mind so just imagine that air filter slowly being blocked with dirt and the fact that the K&N has less surface area than a stock filter so needs manual cleaning more often than an OEM replacement. OTOH, that can't cause an intermittent issue, which still may be related to plugs being fouled or the cats failing.

BTW, to clean those filters the MFG suggest you use their special package (read: $$) of detergent then dry in the sunshine. Afterward you coat the media with their special "juice" to hold the dust particles. In a pinch you can use any strong home cleaning agent such as laundry or dishwashing detergent, Fantastic, etc then apply a dose of WD-40 or Marvel Mystery Oil. If you use too much oil you can wrap it in a few paper towels for a half hour to drain it away. Lacking time / sunshine you can use a shop vac to suck / blow air through it to speed drying time. (low pressure / high volume) Be aware that normal 100 psi shop air may blow a hole in the filter material. The same goes for a garden hose on straight stream. Be gentle!
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12-14-2015, 12:19 AM (This post was last modified: 12-14-2015 12:21 AM by salamander.)
Post: #20
RE: 2007 f150 catalytic converter issue
I checked out the filter and it looks nearly brand new. I took off the plenum and made sure there were no mud dauber nests or anything blocking flow. Measured vacuum again and got the same reading at idle with air filter installed and with air filter and plastic ductwork removed. So maybe this truck just has high pressure at idle? I'm thinking I read somewhere 17-20, but having a hard time finding any actual specs.

I also removed the two 02 sensors from cats and drilled out a 3/8 hole in each pipe just in front of the cats but downstream from the #1 02 sensors to give extra exhaust flow. I figured I can weld scab on two holes to close them back up. Drove the truck like that and it didn't seem to help much. It drove good for first 8 or 9 miles and then started the periodic stuttering, "missing?" just like it has been doing.

I wonder if a 3/8 hole and an 18mm hole in each side is enough to bypass a restriction? I know its work, but would it be more definitive to go ahead and remove the two cats and temporarily replace with just a straight pipe? That would definitively give the answer to the cat question wouldn't it?

You mentioned possibility of fouled plugs. I spoke with a friend on phone who is a mechanic in another town and he mentioned the plugs also. He said it could be valve timing on the triton 3 valve design but if it was I should be getting an actuator code which I am not. So he is leaning towards an issue with plugs.

He suggested I wait and see if we can get a misfire code to show up. Then told me about the bad plug design and need to get the special triton broken plug removal tool. Just my luck. I read the TSB on these plugs and believe I have the mechanical ability to change them. 130,000 miles they are probably due for changing, so at some point I probably will invest in the special tool anyway. Wondering should I just go ahead and change them?

Then again at $15 a piece plus the tool...Do you know of a good way to narrow this down some more in regards to the plugs without physically pulling one or hoping for a misfire code?
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