Bad Cats and Misfire

[OHFord]

I recently purchased a 2004 Eddie Bauer Explorer with a 4.6L V8. I pulled the codes and I'm getting code 420 which from what I have read means one or more of my cats aren't working right.

I am also getting two codes that say misfire in cyl. #4 and misfire at less than 1000 rpms. I tried to do some research about how to fix the problem and I found that sometimes the plastic intake manifold can crack which leads to coolant misfiring the plugs. But from what I could tell the problem usually only happens in vehicles 2002 and older. Since mine is a 2004 I wasn't sure if this was possible.

Also it seems that if the manifold cracks its near the front of the engine, but I am getting a misfire in the rear of the engine. I checked my coolant level and it is low, but I can't tell if where it's leaking.

Right after I purchased the vehicle I replaced all the plugs with motorcraft direct replacements, so those shouldn't be causing the problem. Is it possible the coil pack is bad. If so I thought it would misfire at all rpms.

Can anyone give me advice on where to start to diagnose the problem. I'd hate to spend the time and money replacing the manifold if that's not the problem. And I'd prefer not to spend the $90 to have the dealership tell me what's wrong with it. But I'd like to get the problem fixed so it doesn't damage the new cat I evenutally get put on. Thanks in advance.

 

[swetrid]

Coil pack will usually show up under a load. If you have coolant leaking don't replace the intake manifold.

 

[OHFord]

Thanks, that makes sense about the coil pack. If it's not the coil pack, do you have any thoughts on how I can diagnose the misfire?

 

[OHFord]

Update: I did some investigating tonight and there is no coolant leaking into any of the spark plug holes so I've ruled out the broken manifold. The only thing I can think of is a bad coil pack or a leaky head gasket. I changed to coil pack with another cylinder to see if the misfire code changes.

Could the bad catalytic converter be causing the misfire? I have a hard time believing the cat went bad so early but I guess it could happen. Has anyone else had this happen or have any advice?

 

[n2epv]

Bad coil packs on my '04 probably causing weak spark. Started and idled great, but skipped under load. I've replaced 2 so far at 78K miles and plan on the other 6 plus new plugs this summer.

You could always swap #4 with another coil and see if the code changes cylinder #. Very easy to remove/replace, just don't drop the bolt!

 

[matt0248]

A bad cat can cause a misfire. But it is usually due to the cat being plugged and causing too much back pressure. Generally this happens under load, but it could have at any time. Misfires though can damage cat's by overheating them to the point they melt internally. You could have a leaking fuel injector on cyl #4 causing that cylinder to flood a bit during start up and would continue for a few seconds.

 

[Bummed Out]

Hey guys I am having the same issue essentially. I replaced the manifold, plugs, checked all coils, harnests and fuel but still have a misfire in 7. I know as a fact that my cat is done-for, BUT i dont want to replace the cat and then find out that the misfire is still there... So, lets say I fix the cats, but still have the misfire, what else can it possible be, and is it even worth replacing them before fixing the misfire since my cats are prob bad as a result of the misfire?

 

[matt0248]

Hey guys I am having the same issue essentially. I replaced the manifold, plugs, checked all coils, harnests and fuel but still have a misfire in 7. I know as a fact that my cat is done-for, BUT i dont want to replace the cat and then find out that the misfire is still there... So, lets say I fix the cats, but still have the misfire, what else can it possible be, and is it even worth replacing them before fixing the misfire since my cats are prob bad as a result of the misfire?

How do you know the coils are still good? Did you swap coils from the opposite side of the engine over to see if the misfire followed the coil? you can also do this with the fuel injectors. If these do not narrow it down then the next thing to do would be to do a compression test on all cylinders to see if mechanically everything is ok.

 

[Bummed Out]

matt0248 thanks so much for the response!!!

indeed i did all those things, swaped the coils - and it still showed 7, checked the injectors, and even did a compression test and it was fine.. big time stumped!!!!!

 

[YoungMounty]

Sorry if I misread something but I don't think I read anything about you checking the spark plug wires to make sure they were good? Won't take long to check and could be a simple fix.

 

[JoshMcMadMac]

matt0248 thanks so much for the response!!!

indeed i did all those things, swaped the coils - and it still showed 7, checked the injectors, and even did a compression test and it was fine.. big time stumped!!!!!

It is probably down the harness, then. Start checking it out, starting at the coil.

Sorry if I misread something but I don't think I read anything about you checking the spark plug wires to make sure they were good? Won't take long to check and could be a simple fix.

There are no spark plug wires on the 4.6L.

 

[YoungMounty]

It is probably down the harness, then. Start checking it out, starting at the coil.


There are no spark plug wires on the 4.6L.

Haha well that for sure isn't the problem then!

 

[JoshMcMadMac]

Haha well that for sure isn't the problem then!

No worries, man...it is not uncommon advice for folks that are not as familiar with the 4.6L.

 

[jayton]

Sounds a lot like the problems I had with mine. I replaced all the cats, plugs & boots, and leaky valve cover gasket, and the problem was still there. Mine was showing misfires on 5&6. Swapping coils didn't change it.

I never did get it figured out and about a year later the engine spun a bearing and chewed up the crankshaft.

Maybe the wiring harness has a short? I don't know if my spun bearing was related to these other problems, but if I were in your shoes, I would be paying that $90 for the dealership to hook it up to that fancy machine. The machine they have is not the same as the $50 code reader you can buy at the auto parts store.

 

[Bummed Out]

JohnMcMad.. - Thanks for the response from you and the others, I did check the harness' as well, and the light flashed on it and it worked!!!

Jayton - Thanks for taking the time to respond! Indeed sounds like we have/has the same issue!!! I would pay the 90 to the dealership, but are they able to $100 pinpoint the problem? My mechanic friend as a legit code reader, beyond the capacity of those auto zone readers and it said cylinder 7 and that was all it said.

So heres where im at since last positing? replaced the rear cat (one of the frnt ones was fully emptied and all the debris was on the rear cat), and now im down from 20lbs to 6 lbs of pressure (so theres another problem, that is, why still back pressure when should be about 2lbs?). But the mechanic who first checked it is gonna check it one more time, so have you guys a checklist, beyond what we have already said, that i can have him look at with his tools/resources to see if he can find the issue?

Also, FYI the misfire happens usually in the first few thousand RPMs

Thank you brethren.

Jason

 

[stal005.0]

Still possible u have an intake leak from the gasket. If u r low on coolant and do not see a leak it is going some where. Have u pressure tested cooling system to rule out any external leaks.

In my shop this month we have been working on a 5.4l with a misfire on cylinder 3 as the ford factory scan tool told us. After replacing coil, plug, injector and doing top engine clean still a misfire. Performed compression test and found cylinder 7 with very low compression compared to other cylinders. Pulled heads to investigate and found ring broken scoring cylinder wall. Scan tool told us 3 but was actually 7 causing problems. So just cause scan tool says a cylinder the computers are not 100% all the time as we learned.

I would look deeper into the low coolant problem and find out where u are loosing coolant from. And with this misfire and new cats do not run a lot u will be buying new cats again.

Also make sure compression test was done properly and not giving u inaccurate readings.

These phantom misfires are always fun I hope you find the problem and hopefully it's not like this poor 5.4 and I look forward to finding out the cause.

 

[rhaynes]

http://easyautodiagnostics.com/index_ford/index_of_articles_1.php

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