Missing above 4000 rpm——help please

[KyleW87]

I ran through and read posts I could on misfires, but couldn’t find anything. I’ve got a 2008 gt with 48,000 miles. The car runs great at low rpms, but when you get on it then it’ll miss above 4000 rpms. Throws misfire codes for both random and cylinder 6. I have replaced fuel filter, plugs, coil packs and injectors. Still is doing it…. Anyone have this before?
The car also smells like urine after so could it all be the cats being bad? It has had a catylitic insufficiency code that I have cleared. Could clogged cats cause the misfires? Or could this be a timing issue and need new cam phasers? I am at a loss.

thank you guys/gals for the help. It’s appreciated.

 

[msvela448]

The car also smells like urine after so could it all be the cats being bad? .

Maybe your car is pissed off?

Dad Joke?....... Or did you mean Rad Joke?

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[KyleW87]

Maybe your car is pissed off?

Dad Joke?....... Or did you mean Rad Joke?


Haha, literally pissed off yes

 

[pass1over]

i've been chasing a returning to idle issue on my '12, and have read that if your exhaust smells really foul after a WOT run, it could be a symptom of the o2's going bad

 

[msvela448]

A bad catalytic converter usually has a Sulphur-like smell to it... So it is possible you have bad cats... But a misfire is usually fuel or spark related... I'd also give the MAF a good clean with some MAF spray, and while you are in their clean the throttle body.

Lastly, the OEM Motorcraft coil packs are the only way to go. Aftermarket and autoparts store replacement coils are notorious for failure and bad performance. Spend the money and go get a set of coils from a dealership... Or order them from Tasca Parts.

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[Dino Dino Bambino]

I ran through and read posts I could on misfires, but couldn’t find anything. I’ve got a 2008 gt with 48,000 miles. The car runs great at low rpms, but when you get on it then it’ll miss above 4000 rpms. Throws misfire codes for both random and cylinder 6. I have replaced fuel filter, plugs, coil packs and injectors. Still is doing it…. Anyone have this before?
The car also smells like urine after so could it all be the cats being bad? It has had a catylitic insufficiency code that I have cleared. Could clogged cats cause the misfires? Or could this be a timing issue and need new cam phasers? I am at a loss.

thank you guys/gals for the help. It’s appreciated.

Clogged cats could cause all the symptoms you've described. To find out if the ceramic medium has broken down, raise the car and bash on the cats with your fist. If they rattle like a can of marbles, they need to be replaced.
At only 48k miles they shouldn't break down though and that would suggest there's another underlying problem. Therefore once you do replace the cats you'll need to clear existing fault codes, drive the car for at least 10 minutes so that it's properly warmed up, scan the ECU for new codes, and go from there.

 

[KyleW87]

A bad catalytic converter usually has a Sulphur-like smell to it... So it is possible you have bad cats... But a misfire is usually fuel or spark related... I'd also give the MAF a good clean with some MAF spray, and while you are in their clean the throttle body.

Lastly, the OEM Motorcraft coil packs are the only way to go. Aftermarket and autoparts store replacement coils are notorious for failure and bad performance. Spend the money and go get a set of coils from a dealership... Or order them from Tasca Parts.


Thanks. I cleaned MAF and throttle body as well. I did the red MSD coil packs. Think that could be the issue over stock?

 

[KyleW87]

@Dino Dino Bambino I ordered headers and high flow cats. We will see what happens. I bought that car from a guy who drove it pretty hard so I’m hoping it’s nothing hurt internally. I’ll have them check vacuum when they put the headers on as well. Might as well put new o2 sensors in as well?

 

[Juice]

Why would you order new exhaust without diagnosing the issue?
The pcm is pointing to a potential issue with #6 cylinder. A new set of plugs, and swap coil packs on #6 and any other cylinder. If the misfire follows the coil, buy one coil. A compression test would not hurt while you are doing plugs.
Catalytic smell is NOT from a bad cat, it is from bad combustion. (That rotten egg smell used to be from an EGR stuck open at idle)
You said you had p420/430 codes, catalytic converter efficiency below threshold. This means the catalyst is not able to do it's job. And just replacing the cats only covers up the issue. Was your catalyst code on the same bank as cylinder #6? That would tie the issues together.

 

[KyleW87]

Hey Juice. Catalyst code is on bank 2. I replaced all the plugs and wires and the problem still remains? Can rev the car past 6,000rpm when it’s in neutral, but under load it misses as soon as you hit that 4000 range. I don’t know a lot about variable timing, but could it be an issue with the cam phasers or chain causing that? Any other suggestions? Cylinder 6 is on the drivers side second from front of the car correct? I’ll pull the plug and move it around.

 

[Juice]

I would have done a compression test
Did the #6 plug look any different than the others?
I would expect codes other than misfire if there was any mechanical issues.
Out ofcuriosity, has the trans been removed recently? A crank relearn may not be a bad idea to perform.

 

[KyleW87]

Thanks Juice. I’ll get a compression test as well. The crank relearn has to be from a mechanic shop?

 

[Juice]

You can do a crank relearn from an sct x4 tuner, or Ford IDS. I dont know if forscan can do it, I have not seen that for my coyote.

 

[Dino Dino Bambino]

@Dino Dino Bambino I ordered headers and high flow cats. We will see what happens. I bought that car from a guy who drove it pretty hard so I’m hoping it’s nothing hurt internally. I’ll have them check vacuum when they put the headers on as well. Might as well put new o2 sensors in as well?

Adding headers/high flow cats plus new O2 sensors might alleviate the symptoms but they won't treat the disease (the cylinder 6 misfire) that could have damaged the driver's side cat in the first place.
As Juice suggested, move the plug first (to no.5) and see if the misfire code moves with it. If it doesn't, move the no.6 coil and repeat. Finally do the injector if you have no joy with the other two.
A compression test on the no.6 cylinder would at least confirm that there's no significant leakage of combustion gases past the piston rings or the valve seats.

 

[GlassTop09]

Hi KyleW87,

After 1st doing all that has been suggested (swap plug, coil & injector from #6 cyl & another known good cyl & end up not successful in finding cause of misfire) but before actually doing a compression test I suggest to pull the valve cover on B2 & inspect the cam followers on #6 cyl...especially the 2 cam followers on the intake valves...to ensure that they're still intact & are still under the cam lobes & on the lash adjusters & the camshaft cam lobes themselves are still good. This 4.6L does have a tendency for cam followers to fail (usually the cam follower roller needle bearings fail which will loosen the cam follower up & can then either break or come out from under the cam lobe\off the lash adjuster) & if 1 of the intake cam followers on #6 cyl has broken\come out this will throw the engine crank velocity patterns off on that cyl & cause the PCM to set off the very misfire codes you're seeing & engine can start misfiring when under enough load due to not enough air intake during intake stroke thru 1 open intake valve. The engine will still run fairly decent w\ only 1 of the intake valves operating in the cyl as long as the other intake valve fully closes & stays closed.........
The only thing that keeps these cam followers in place is the valve spring tension & lash adjuster pintle when pumped up against the camshaft cam lobes (why is noted as "zero lash") so if the needle bearings fail in cam follower roller, cam follower itself breaks or lash adjuster pintle loses pump up they'll come loose & can be spit out\broken....regardless of mileage on engine.

I've had 1st hand knowledge\experience of this happening as laid out on my car........

A cyl compression test or a cyl leakdown test won't show this up if both intake valves are fully closed & seated during this testing so it is a good practice to do before doing any internal cyl pressure testing to make sure that all the upper valve train is intact (don't assume that all is good just because you don't hear any strange noises coming from the valve covers....put actual eyes on them) to verify\eliminate upper valve train failure as a cause of the misfire. If the upper valve train is still in good shape & intact you'll already know from this finding that the issue is internal to the cyl after doing all the other stuff & not successful in finding the cause of misfire, then IMHO I would go straight to a cyl leakdown test on #6 cyl to determine if the issue is either head related (bad valves, valve seats) or cyl related (bad piston, rings or bore) due to the fact your engine only has 48K on the clock (low mileage) & only 1 cyl is identified showing an issue. Then after finding the actual issue in #6 cyl I'd run a bore scope in #6 cyl to assess the cylinder bore condition in block to determine if it is still good before considering doing any type of physical cyl compression testing.......

This is my suggestion of process & why to consider once all the other stuff mentioned prior comes up empty.
Your decision in the end..............

I hope this helps & you find your issue external of the cylinder.........

PS--You also may consider to do a smoke leak test on intake side to verify/eliminate a potential vacuum leak on #6 intake manifold runner to head O-ring or #6 injector IM side O-ring as well. Most likely is not your cause of issue but as I've already mentioned....don't assume that it isn't.

 

[KyleW87]

GlassTop09. Thank you for the awesome and extensive response. I was considering putting in the Ford hotrod camshafts….so that would be a good time to have a closer look. I’d have to have a shop do what you suggested as my mechanic ability ends after the basic stuff. I’ve never gotten inside to have a look at that stuff before. Thank you again!

 

[Ekis]

Fuel filter or fuel pressure?

 

[GlassTop09]

GlassTop09. Thank you for the awesome and extensive response. I was considering putting in the Ford hotrod camshafts….so that would be a good time to have a closer look. I’d have to have a shop do what you suggested as my mechanic ability ends after the basic stuff. I’ve never gotten inside to have a look at that stuff before. Thank you again!

Since you're thinking bout installing cams............

I'll make another parts suggestion for you to consider to add to your cam install & that is to replace all the original cam followers (24 in all) w\ the newer upgraded cam followers (FoMoCo #3L3Z-6564-A) as these have the improved oil squirt hole design & are made of better materials so stronger than the original ones. The new oiler design was done to eliminate the oil starvation issue of the cam follower roller needle bearings (which is the main cause of cam follower failure in the 4.6L\5.4L Modular engines) & w\ this new design the oil loss thru the PCV valve is greatly reduced....almost to the point of nil....due to the oil being directed at the cam lobe\cam follower roller contact point instead of pointing up at the cam lobe itself which greatly reduces the amount of oil being slung up into the air space off #8 cyl (where the baffle entrance opening to the PCV valve is located in B2\DS valve cover) cam lobes & overspray from #8 cyl lash adjuster pintles (the large holes in the original cam followers) along w\ slightly improved oil pressure\volume delivery to rest of engine components. These parts were developed after the production run of the 4.6L\5.4L engines had ended so no 4.6L\5.4L engine came w\ these installed from factory & IMHO is a highly recommended engine upgrade component to add w\ a cam install or to do as part of an upper valve train refresh project. New follower design is the bottom one in picture:


I didn't mention the lash adjusters as from all my research Ford didn't refresh\upgrade this design thus are pretty bulletproof but these can only be replaced when the camshafts are removed & in your case (low mileage engine) IMHO can be left alone if the engine maintenance has been kept up regularly & good quality oil used (no varnish or sludge deposits present)....unless you want to change them anyway during the cam install. So if you do change them I'd suggest to get the Ford Performance M-6529-3V kit (has all 24 cam followers & 24 lash adjusters in 1 package) as this will be the far & away cheapest price you'll find (either part bought separately will cost more than this kit does) & you'll want to use only Ford parts here.

Something to consider to upgrade\add to any cam install on these 4.6L 3V's........if budget allows.

 

[KyleW87]

Thanks again GlaasTop. I’ll add it to my parts list. I am gonna do new springs too. I wonder if it’s got a weak spring as well. If it was often pushed to hard they were likely damaged too. Can’t hurt to upgrade it all.

 

[GlassTop09]

Here is a good video by FordTechMakuloco on why you should replace all of these whenever you go into the valve covers....and his take on the new design cam followers:
Ford F-150 5.4L 3v Triton Engines: This is Why You Always Replace the Roller Followers! - YouTube

Note that the owner really had 1 bad & another 1 getting loose on #2 cyl....on a fresh timing job done........ Owner wised up & had Brian to replace everything up top but the other shop should've done this up front so be aware of the thinking to reuse these........... I've been there, done that......& paid the price.

Enjoy!