He folks, my 06 van has been a fine running steed since I purchased it about a year ago and then suddenly last week is started running very poorly, serious loss of power, a rough idle and lots of random stumbling. No codes at all and nothing seems out of the ordinary with ForScan hooked up so I'm thinking it's got to be something outside computer control. How common are melted cats on these vans? The exhaust is all stock as far as I can tell and it's never been loud but it's unusually quiet since this problem begun, so I'm wondering if one of the cats has clogged up and is basically forcing exhaust gasses back into the motor making it run lean. I was also gonna check fuel pressure but is there a test port on these motors? Anyway.. any help or suggestions would be appreciated, hopefully I'll have some time this weekend to do more than plug in the scanner.

 

A 'quick' check would be to pull the exhaust loose enough to see if that is the problem. Sometimes, if you feel the pressure at the tailpipe while someone revs the engine, you can tell if the exhaust is blocked.

I haven't seen a cat melted but I have seen blocked cats from too rich a fuel mix and just plain age. jim

 

Very common in my experience. My 2007 E350, my previous van was a 2003 E250, and my recently owned 2000 Ford Contour- all developed bad cats. Every one of them I rodded out and drove tens of thousands more miles.

However idle quality has never accompanied a bad cat for me. And the stumbling has not been random- it's been very very predictable; always stumbling under load at medium/high rpm.

Keep us posted.

 

Yeah.. I have seen aftermarket cats fail and when they do the substrate breaks loose and rattles around inside which is very obvious, but I got nothing like that now just the quietest exhaust of any vehicle I have ever owned LOL... the hum from the tires at hwy speed is louder so I may have to "fix" that anyway.

So what about testing fuel pressure? I had the doghouse off and there is some weird *** looking device hanging off the body above the rear of the engine that looks to be inline with the fuel rail. Is that the FPR with a test port on it?

 

Well it isn't a melted cat, I cut the exhaust off just behind the cats today and it's a lot louder with the same stumbling and misfiring so I'm back to thinking it's something electronic that the computer hasn't picked up on yet.. maybe a cam or crank position sensor?. If this were an older truck I would have swapped the TFI module already but does this truck even have something like that?

 

With no lights on I would clean the MAF Sensor and Throttle Body, the TB will bite your fingers off if the Battery is connected...........'fair warning'

 

Thanks.. I'll give it a try.

 

if you cut it behind the cats then you missed the point of the experiment...

 

I know what you were thinking but a melted cat would be more audible with the whisper quiet muffler removed, you're likely to hear some hissing from a melted cat, but that wasn't the case it got much louder and there was no change in the way the engine ran so that was enough for me to check that off the list.

 

Turns out it was..... spark plugs. I did also change the cam sensor in a desperate attempt at logic but it made no different at all and even with that sensor disconnected the engine ran no better or worse.

What I removed were NGK plugs that had been in there for some time as whatever they used for dielectric grease had turned to orange/black crust, and from everything I know about Fords the only plugs that last in these motors are OEM originals so I replaced them with Motorcraft plugs and the truck is back to it's smooth running self again. I was dreading having to do this job based on everything I have read on these motors but it went well and actually removing the plugs was no worse that doing the same on an old Windsor motor.. it's just all the extra work involved with the COPs and of course doing it in a Van versus a pickup truck which means it was a 4hr job not 30 minutes.

 

Behind or before ???

 

Hmm, be prepared to have that problem come back again eventually. Plugs are never the problem. And I do mean never. I've run several brands of mid grade plugs for 300,000 and 400,000 miles (no I'm not joking) without issues. NGK are not chinese knock-off plugs and should never cause you issues. I've run NGK in several vans for hundreds of thousands of miles. It's MUCH more likely that you had a misfire on cylinder 1, 4, 5 or 8 due to the intake manifold leaking coolant into the plug hole and your procedure of replacing plugs dried out the boot and coil enough to cause it to run smoothly again. So you may have an intake manifold leak. Odd that you wouldn't get a misfire code, but I'm still suspecting that before a plug failure that should also cause a misfire code.

That said, I've often found that the leak is so minor that replacing the coil, boot and plug will stop the misfiring and with the more even and smooth firing, the manifold will not leak as much and you'll be fine for quite some time before it happens again.

Cutting the the exhaust behind the cat, as Im50Fast said, is missing the point. I pull the downstream O2 sensor and test drive when I'm looking for a plugged cat because what ALWAYS happens is the upstream cat falls apart and plugs the downstream cat. Pulling the downstream O2 right in front of the downstream cat will allow exhaust to bypass the plugged cat without screwing up mixture like pulling the upstream O2 would, and is much less invasive than cutting off pipes.

Checking for a MAF failure is as easy as unplugging the sensor. If the van runs better with it unplugged, then it's very likely a MAF issue. You can run with it unplugged but it will idle poorly and use more gas but otherwise it will have plenty of power and run smoothly at highway speed. MAF issues can come up with no check engine light, so that's not a bad idea to check on that before major projects.

 

I read about the leak issue into the plug cavity and have seen it on other non Ford engines so was wondering if I was gonna find any but I didn't.. all plugs and boots were bone dry with no signs of oil or coolant. And I have to disagree about the plugs because my experience is the exact opposite of yours, I spent most of my life so far with 87-96 F series trucks and those old pushrod motors just seem to eat any plug that isn't a Motorcraft copper, and these fancy platinum plugs are just useless in those motors sometimes only surviving a month. No in this case the problem was the plugs, the motor idles smooth as glass now and has all it's power back and I changed nothing else.

OK I see your point and yes that makes perfect sense if you were presented with the issue out of the blue as a mechanic at a shop would be... he doesn't get the back story or know what preceded the current state of operation. But I drive this truck every day and there were no noises, if a cat had come apart I wouldn't need to do anything to know about it, the metallic rattling sound of the lose substrate would be more than obvious even before it got bad enough to actually break up and partially or completely plug the exhaust. Been there and done that a few times now so I know exactly what that sound is, at the time I was thinking specifically a melted cat like what used to happen to the old pellet cats in the '80's, but I don't know if exhaust temps can even get high enough to actually melt one of these newer cats so the whole thought process was probably misdirected anyway.

I cleaned the MAF which didnt look terribly dirty and it improved the idle slightly but didn't eliminate the bigger problem so I moved on.