Bad cat or not?

[searcherrr]

Flat out: I drove with cylinder 5 misfiring for 100 miles (possibly a little bit more) and that entire time the rear cat was getting fuel dumped into it causing it to glow lava red. I verified this and as soon as I'd let off the engine speed on the highway especially when I'd come to a stop the coolant temp would soar to the top of the gauge within a matter of seconds. Given this thought and now recently I think I'm getting half the gas mileage I used to now with a new engine and just the fact that the cat glowed for 100 miles do ya'll think its very likely the cat is no longer any good?

I've read where you can test the intake vacuum as an indication of build up of backpressure and of course you can also do the backpressure test itself shoving an air gauge before the cat. In any case I'd rather just do the intake vac test. I guess if I see it fluctuate significantly then its a pretty good guess that the rear cat is toast right?

[wiswind]

Your shop should be able to test for back pressure on the cat.
If not, they can most likely recommend a place that can.

[searcherrr]

I tested the intake vacuum pressure tonight using a vac gauge.

First at idle with no A/C:
The gauge remained in the green (normal motor as it says), but continuously bobbled back and forth from 17.5 to 18.5 in hg vac and sometimes dropping as low as 17in. I did this test in Park. I do not use the word continuously lightly either. It was "constant".

First at idle with A/C:
Gauge immediately dropped to 16 in hg and bobbled from that to 16.5 in hg constantly. As the A/C compressor would kick off and on it would jump back up sometimes up to 18.5 when the compressor went off, then down to 17 when it was on, and then as compressor remained on it would work its way back to bobbling 16-16.5 in hg again.

Each time the radiator cooling fans would turn off the engine again would try to stall and vac pressure would surge up to 18.5 briefly and immediately go back down to the 17.25 - 17.5 range staying there if A/C was off, but eventually always lowering to the 16-16.5 if A/C on.

FYI - Anything below 17 in hg on the gauge is "red zone" aka not right.

Given that we know I've replaced just about every damn thing in this van recently what conclusion could we draw from this test? The gauge says that the "hand should remain steady in green zone" and when I've done this test before in my 3000GT it does in fact remain completely steady at idle as it should be.

Wouldn't constant drops in vacuum pressure constitute a backpressure build up and possible "partially clogged" cat?

How can I test my O2 sensors when they are off if I decide to undertake the task of replacing the Ypipe? Is there a way?

Wiswind - What scangauge "setup" do you use? Brand/model#, connections, config etc..

[wiswind]

First off.....I have no clue how to use the vaccum data.

The ScanGauge that I use it this one
http://www.scangauge.com/products/

Mine is the original one....before the II one came out.
I set it in "Gauge" mode.....and then select the parameters that I want to display.
Take note that it will NOT read fuel pressure, Barametric values, or other values that are not monitored on the Windstar OBDII system.

It also does not monitor the fuel trim values.

It is a good, cheap item that is easy to use......and I have found it to be a good investment.
I can leave it laying in the car, which I could not do with a laptop.
One nice feature is that it will do a "freeze frame".....save the various data that you can read in Gauge Mode......at the time that the failure code is set.
So you can see coolant temperature, RPM, speed, engine load, etc.
Not that I would know how to use the data, but a good mechanic might find it useful in diagnosis of the cause of the failure.


As far as the oxygen sensors, I also do not know of a way to test them outside the vehicle.
I would say that if you do not have a failure code, they are good.
The OBDII system monitors the oxygen sensors......and wil give you a code, even if the switching speed gets too slow.
Oxygen sensors were a failure item years ago.....but, at least the ones on our Windstars, are very reliable.
I changed my upstream oxygen sensors at well over 150K miles......and saw NO CHANGE in engine performance and fuel economy.
My engine was running well before and after the change.

[searcherrr]

Wiswind - About to read your previous post.

When you replaced the ypipe with the walker one were the bolts for where it meets the header pipes fairly easy to reach or did it require removing other stuff to get to those bolts?

[searcherrr]

Originally Posted by wiswind

First off.....I have no clue how to use the vaccum data.

The ScanGauge that I use it this one
http://www.scangauge.com/products/

Mine is the original one....before the II one came out.
I set it in "Gauge" mode.....and then select the parameters that I want to display.
Take note that it will NOT read fuel pressure, Barametric values, or other values that are not monitored on the Windstar OBDII system.

It also does not monitor the fuel trim values.

It is a good, cheap item that is easy to use......and I have found it to be a good investment.
I can leave it laying in the car, which I could not do with a laptop.
One nice feature is that it will do a "freeze frame".....save the various data that you can read in Gauge Mode......at the time that the failure code is set.
So you can see coolant temperature, RPM, speed, engine load, etc.
Not that I would know how to use the data, but a good mechanic might find it useful in diagnosis of the cause of the failure.


As far as the oxygen sensors, I also do not know of a way to test them outside the vehicle.
I would say that if you do not have a failure code, they are good.
The OBDII system monitors the oxygen sensors......and wil give you a code, even if the switching speed gets too slow.
Oxygen sensors were a failure item years ago.....but, at least the ones on our Windstars, are very reliable.
I changed my upstream oxygen sensors at well over 150K miles......and saw NO CHANGE in engine performance and fuel economy.
My engine was running well before and after the change.

Yeah I'd have a better idea myself on the vac stuff if I could get my service manual CD-ROM to work, but its crapped out on me somehow. CD data is damaged. At least it got me through my engine debacle before giving out. I may be able to make a makeshift CD from files I backed up minus the EVTM information cause those are the only damaged files.

Yeah, I probably will not change out the O2 sensors due to no codes. I really believe its the rear main CAT. I found a way to test the O2 sensors btw after I posted. Its pretty simple if I have them off.

I'm gonna do another intake vac pressure test today with RPMs at 2500. I bought a new manual (OEM paperback) from ebay which I should get shortly. If anyone wants to help they can tell me what the intake vac (inches hg) pressure should be for the 95 Windstar 3.8L. If I keep it at 2500 RPMs (hey I wonder if cruise control will work in park just to hold the engine at rev? Dumb question?) for a minute or so and it doesn't hold steady pressure then I'm gonna be pretty convinced the CAT needs to go.

I have also found a link that shows pictures of what a fouled/melted cat looks like inside vs a good one so that'll help if I get it off.

I would love to have the ScanGaugeII (looked at it just now), but since I have pretty good clues already as to what is going on I'm going to hold off till I get some money coming in.

I think the easiest test would be to monitor intake vac pressure with the ypipe removed (ear plugs probably needed?) and if it holds steady then I know whats up immediately.

[wiswind]

I used a deep socket to get to the nuts that are on the exhaust manifold studs.
I soaked them with PBlaster.

I STILL ended up with 1 stud that the nut was frozen on....and the stud unscrewed out of the manifold.
I ended up replacing that stud.
I was only able to locate the studs at the dealership......about $5 each.
They have a different thread for threading into the manifold than for threading the pipe retaining nut on.

There is NO spring on the studs, as some vehicles have.
The flange goes onto the exhaust manifold.....over the studs....and a nut goes on each stud.

I put some high temperature anti-seeze on the threads....never know if you will be back in there someday.

Now, at the back....where the "Y" pipe meets the flex pipe, I needed to come up with bolts.....the OEM "Y" pipe had studs on the back part.....the replacement did not.
New hardware is easier to work with anyhow......

The only thing that I did not like about the replacement is the fact that the top of the converter heat shield is right against the oil pan.

When removing the oxygen sensors......soak the threads with some PBlaster, but ONLY the threads.....don't get any spray or fluids over the body of the oxygen sensor.
The sensor measures the oxygen in the atmosphere.....and in the exhaust.....and generates a voltage based upon the difference.
So....you don't want to seal the external part of the sensor from the atmosphere by getting some fluid into there.

If you look in the picture that I put the link to.....in your other post....you will see that the downstream oxygen sensor is mounted into the rear part of the rear-most catalytic converter.......the metal around the threaded mounting ring is thin....
When I was doing the replacement, I very carefully applied turning only pressure to the sensor, using a oxygen sensor socket......and the mounting ring came right out of the catalytic converter with very little turning pressure.
This would be a problem, had I not been changing the "Y" pipe assembly anyhow!!!!!

Use extreme care in making sure that you get the oxygen sensors plugged into the correct connectors on the vehilce.......it can be a mess trying to track it down if you get that wrong.
So I would label....label....everything....

[searcherrr]

Thanks again.

Well, I've ordered a back pressure tester this morning. With any luck I'll have it by Saturday or Monday and put all this speculation to rest. I thought about going to the well know muffler place to have it tested, but I feel they would say its bad just to get business. My trusted shop.... well I just don't want to bother them with it really cause since the van sat in their shop for 4 months waiting for the engine debacle to end the last time I brought it back they just told me, "You just need to drive it for a while." so I figure they may say the same thing to me again which is a lil bit of a pickle cause I don't want anyone else touching my vehicles except them.

It will be good to have the gauge anyway as I'd like to test the pressure in my 3000GT as well cause I think I've been running a rich condition for quite some time now.

Anyway, I'll know when I get the gauge.

Would I be safe just using a flare-nut wrench instead of an oxygen sensor socket? I don't even know what an oxygen sensor socket is!??!?

[wiswind]

An oxygen sensor socket is just a deep socket with a slot in the side.....so that you can use a socket....and have the wires pass through the slot in the side of the socket.
I got mine at AutoZone.

My sensor came out just fine, except for the rearmost one.....the one that turned out of the metal.....I had to work on it for a while to get the mounting ring off of the oxygen sensor.....without damaging the sensor.
It is still working in the new "Y" pipe to this day.

[searcherrr]

Now that ya mention it man I think I've seen those sockets before. Just not something you remember cause its used so infrequently.

Hopefully my exhaust pressure tester thingy will arrive today. I probably could've used my fuel/vac pressure gauge and found an adapter to fit the O2 sensor and the gauge hose, but I guess its too late now. lol

Wiswind - Are there any SPECIAL MAGIC BOLTS that must be used for the exhaust or will bolts from Home Depot or other local hardware store be ok? Certain type of metal to use? I know you said you had to go to the dealer for some, but I'm just wondering if I can find them elsewhere if its ok to use any kind I find. I may be lucky though if I do have to replace the ypipe cause the ypipe has recently come off twice due to my engine debacle with ATK recently so I'd think that they should come off pretty good.

Were you able to reach the ypipe bolts to the header pipes from underneath or did you have to loosen the nuts from above the engine first?

[wiswind]

I got the bolts at AutoZone....nothing special.
However, the exhaust manifold studs, I had to get at the dealership....they ARE special, I looked for them at AutoZone and Advance Auto (Advance did have exhaust manifold studs.....just not the right size/thread.

I got everything from under the vehicle.....just follow the pipe up to the exhaust manifold.....2 nuts on the studs.
You will need a deep socket to get the nut off of the stud.

Another nut by the transaxle, then the 2 nuts at the front of the flex pipe.
You will need to purchase 2 bolts with nuts to install the new "Y" pipe.
These can be gotten at AutoZone, etc.

If the original exhaust is fine.....I would leave it be.....it is stainless steel.
My original is just fine.
My flex pipe is a bit worn.......I have a new one ($99), but could not get the old one out of the pipe on the front of the muffler......so I left it be untill it really falls apart.

The rest of the exhaust......from the back end of the flex pipe all the way back is 1 unit.....replacement is in parts.
Rock Auto has a nice breakdown of parts under the "information" for the Walker parts.

[searcherrr]

Wiswind - Should I be using some type of sealant (threads) or ring for reinstalling the O2 sensors?

What do you think makes those exhaust manifold bolts so special? Different kind of metal? Coated with some David Copperfield magic fairy dust?

[wiswind]

When you get new sensors, there is a small amount of high temperature antiseze on the threads.
So, I would put a small amount of high temperature antiseze on the old sensors that you transfer to the new "Y" pipe.
Be careful to put it only on the threads.....and just a little.

As far as the OEM, they contain more "stuff" and work better, from what I have read.
It took quite a while for the OBDII system to finish the drive cycle test.....as the downstream oxygen sensors are the last thing to finish.

My Walker replacement has been doing fine, and I have passed 2 emission tests with it (Wisconsin emission tests every other year).

I replaced mine because the ceramic honeycomb was broken inside one of the catalytic converters.....Otherwise they were fine.

[searcherrr]

I have obtained the back-pressure tester Tuesday and tomorrow will be the first chance I have to test the exhaust pressure. I will be following instructions I found somewhere to do this correctly.

Also, note I confirmed today at 212 miles on the trip odometer after filling up with 19.197 gallons of gas that I am getting a WHOPPING 11 MPG. I TOLD THOSE SUCKERS AT MY TRUSTED SHOP IT DID NOT FEEL LIKE IT PULLED AS HARD AS IT USED TO! THOUGH ITS A VAN N ALL I KNEW IT WASN'T GIVING ME THE POWER IT USED TO. AND THEN THEY SAID JUST DRIVE IT A LITTLE MORE AND BREAK IT IN!?!?!??!)@(*$)*_+!+_ aRRGGghhHHH !!! I mean do you have to break in EVERY new car you buy till it gets you better gas mileage? I DO NOT THINK SO. NEW ENGINE should mean BETTER gas mileage to BOOT as far as I'm concerned.

Anyway, I'll prove it tomorrow and I will be very very surprised if I am wrong about the CAT needing replacement at this point.

[tripletdaddy]

Searcherr, could you tell me where you bought, what brand, how much, etc. your back pressure tester and what all it can do and how, etc,
Thanks