Hello everyone! Newbie here!

Van in question: 1999 E350 XLT SuperDuty 138" W/B, 5.4 V8.

Strange problem... About a month ago, I replaced the stock exhaust (muffler + tailpipe) with an aftermarket replacement. Went on without a hitch. Van was quiet again.

The van ran fine, same power as usual, no problems...

Then a week ago on the highway, I pull out into the oncoming lane to pass a slow moving vehicle. As soon as I pull out, oncoming traffic appears at the crest of the hill ahead. There was enough room to pass, but it required a heavy throttle.

I step on it, not WOT, but close... And the motor did not respond! It just continued along at the same rpms, no acceleration!

OK, so I pull back in behind the slow vehicle because there was no way I could pass.

Since then, I've tried WOT a few times and same thing.

Otherwise, the engine seems to drive fine, has normal power from a standstill, normal acceleration on the city streets and highway is normal. The only time this happens is when I floor it.

I have a code reader, no error codes returned.

Transmission feels fine too, shifts fine, except for one little item. I noticed this a day or two after the failed passing out on the highway.

When stopped at a red light in gear, foot on brakes as you would when waiting for a green light... There is a new sound coming from the transmission, doesn't sound 'smooth'. If I shift to N, the sound goes away. Tranny fluid isn't burnt, still nice and pink, doesn't seem to be losing any either.

This sound seems to be intermittent, wouldn't seem like a noise that doesn't belong to most folks but after all these years of owning the van I know it is a brand new sound.

Any ideas about the possibilities?

I don't think there's anything serious going with the engine, because it runs perfectly fine except for a WOT situation.

Maybe it's a sensor, a faulty signal being sent to the computer and causing a fuel/ignition map mode that won't allow high rpm?

Any ideas / suggestions?

Any specific sensors to check, or any other obvious things? Or maybe it could be the new aftermarket exhaust system? The tailpipe is only 2" ID, I think the stocker was at least 2.5".


BTW... Great forum you have here, everyone seems nice and genuinely helpful!

 

WOT the heck?!!

My first guess is a nearly plugged cat.

If you RPM's don't increase, the that seems to rule out transmission.

Since the cat is near the transmission, maybe that's where the noise is really coming from. Or you had a small leak at the exhaust manifold, and with the increase in back pressure, the sound is now louder.

Oh, and now that I went back and reread your post, you mentioned that you now have a smaller exhaust pipe than stock, and that will also increase back-pressure, even if the new muffler decreased it. The easiest way to know is to cut the pipe before the cat. You'll not be able to tell the difference in flow at the tail pipe.

What's the mileage and how often is it driven?

 

Good one!

WOT = Wide Open Throttle.

Common term in the snowmobile, ATV, and moto-cross bike world. Sorry about that, I forget it might not be universally used in all motorized applications.

You might be onto something about a possibly plugged Cat... My 79 Ford van had a muffler that plugged up, similar symptoms but worse. It was hard to get any acceleration out of it.

On this truck it didn't happen gradually though, just a few days before it had normal power just like usual.

Do symptoms of a partially plugged cat appear suddenly, all at once? Or should I have noticed it gradually creeping in?

How does one go about testing for a plugged cat? Is bringing it to a dealer or mechanic the only way?

 

I'm not that old. I figured it out rather quickly.

They are extremely sudden. I say it's my first guess because I figured it would be worse than what you have. So it's a hit and miss whether it's the cat.

My 88 RV just went all of a sudden on an major US road of all places (and right where I only have enough shoulder to get it inches off of the driving lane.) Only would idle. It died whenever the throttle was pressed even the slightest.

You got me on that one. I assume flow can be measured at the tailpipe, but I don't know what you should have, even if you can get your hands on a flowmeter.

My fix would be to make sure you have a small length of pipe with an ID just slightly bigger than the pipe's OD in front of the cat, and 2 U-bolts, and cut it.

Maybe someone else will 'pipe' up here and either tell you how to check, or offer a better guess.

Also, I'd think it would throw a code by this point. Have you went out to an empty place and just hold it to the floor for a long time to see if you get a code then? On my 2000 when my 2nd COP went out in 2 weeks, I had to take it out and floor it for 2 miles to get a code so I knew which cylinder the bad COP was on.

 

check the TPS as it may have developed
a bad spot at the wot spot

 

Check this under the heading EXHAUST BACKPRESSURE CHECKS

http://www.aa1car.com/library/converter.htm

or another webpage says

"To test for a plugged converter, drill a small hole in the exhaust pipe right before the catalytic converter. Install a temporary hose fitting and attach a long rubber hose and a 0 to 10 pound pressure gauge. With the gauge inside the car, drive up a hill or accelerate and read the pressure. Normal is 2 to 3 pounds, restricted 4 pounds or higher."

 

Hey, that's a good idea... I'm going to try that when I drive north this weekend.

Yeah, I had two COPs go bad... Felt both of them fail, returned stored codes as soon as I plugged in the code reader!

Thanks for your suggestions!

 

Hey, another good suggestion... Thanks!

I have the factory shop manuals at home up north, I'll look up the TPS when I get there! There's probably a way to test it with a VOM. I suppose it's one of those devices that won't generate an error code.

 

Wow, never heard of that one before! I just may end up trying that after exploring other possibilities.

Reason being, I'll just leave it as a last resort if other possibilities prove to not be the cause just to avoid having to weld up the hole!

Thanks for the link, I'm going to check that out right now!

 

Make sure you're air filter housing is still latched. My dad has this happen on the PA turnpike a while back, his air filter had come loose from the rest of the intake and the MAF wasn't reading the air flow.

 

That article at the link you posted is excellent! Very informative! Thanks!

It's given me some things to consider and check, as it discusses related items that could be causes of cat failures.

At this point I'm still not sure the Cat has failed though, I'm also going to verify the TPS as MHG suggests.


You guys are great!

 

Great! I'll check that... Thanks!

I'll also check the ductwork leading from the airbox, MAF housing & wire/connector etc.

Now that you mention it, it's probably time to clean the MAF sensor too. It's been a while. Last time I had a good look at the actual MAF element, it appeard to have some extremely fine dust particles on it. I blasted it off with some canned air and a solvent I use when working on sensetive electronics... But that was about 200,000 kms ago, and haven't checked it since. Thanks for the reminder!




Hey, any of you guys into ATVing, or snowmobiling?

Just wondering.

 

A friend of mine has had dirty MAF's but he had only idle, and it would not throttle up.

 

Hello everyone... Hope you had a great weekend!

Well, here's an update on what's going on with my van.

I live approx. 115 miles from where I work. So on weekends I get to go home, this entails a 2-3 hour ride.

During this trip, the truck started out with the same symptoms as the last time I posted. I did have the OBDII code reader connected for the entire ride.

Roughly halfway there, I started noticing the power drop. It began to fade to the point I could just maintain highway speeds but had none of the normal power even for accelerating to highway speeds from stops.

When I finally got home I checked the code reader for logged errors. It returned two... #1131 & #1151. According to the manual these are lean conditions.

First I thought fuel filter... But it's too soon, changed it last spring. So after checking the air intake tract & air filter, I thought I may as well swap out the fuel filter. Thank God I had another on the shelf in the shop!

Switched to the new filter, test drive, and all is normal!!!

I couldn't even blow through the filter I took out! It was almost completely clogged!

I suspect something must be going on at the gas station I fill up at, have been going to the same station for decades.

I'm going to ask next time I go to see if they know anything. Maybe other customers have also been asking why their fuel filters are clogging prematurely.

Thanks everyone for trying to help out, I really appreciate it! The willingness to help out is what makes forums great!

 

Did you ever run it out of fuel, or run it real low since the last filter change? I've seen them suck up crap when running them empty.