Here is an interesting development in my Aero reno process. Since I got it I've done a bit of work and got the engine running very well... but I could hear what I first thought was a knocking sound, kinda like a rod knock. After driving a few days with it I concluded it wasn't a rod knock as the sound was worse under load and changed pitch slightly when the engine warmed up. So I kinda left it at that knowing that the motor was fine but not knowing the source of the knock. Well, today I decided to look under the van while it was running. After contorting myself to several different locations I narrowed it down to what I thought was the catalytic converter. I thought I must be on crack as it didn't seem possible for a CAT to make a knocking noise. I hammered it with a rubber mallet to see if anything rattled.. nothing. After staring at it for 10 minutes I decided to pull the oxygen sensor out (ahead of the CAT) and take it for a spin. Soon as I fired it up.... NO knocking sound! Just a bit of exhaust noise blowing from the oxygen sensor hole. Then I took it for a spin and it felt fairly normal until i FLOORED it.... woa definately more power up high.. climbed much better up the rpm's (butt dyno).

Questions:
- this is the first encouter I've had with cat problems, has anyone else encountered a similar scenario / symptoms? I thought they "rattled" when they went bad, not a knocking noise.
- Now that I've felt what the motor should feel like, I'm thinking I might just do a high-flow cat but keep the 2.25 diameter exahust.

Opinions / experiences appreciated. I'm not sure where to go from here. I know if I buy a cat from an exhaust shop then I'll pay a premium. I'd rather get a high flow cat from Bear River or e-bay? .. opinions on that would be great also.

** side note, the knocking sound was not really really loud, but more than noticeable. At one point I thought I might have been a cracked manifold or exahust gasket. I would describe the sound as if it were between a mild engine knock and a pulsing / dronning exhaust leak. I was surprised to find out that pulling the oxy-sensor would make it go away.

Thanks

 

I think my cat is plugged also But I'm going to change the fuel pump first. I have two vans that have no power up high. I would just get a stock cat replacement. They are cheap these day's.

 

chea stock replacement = good... and if you have a 4l 2wd, stock everything is good enough to brake lose the tires... at least it was in my mom's bone stock 100k 2wd 4l...

these vans have a nice power setup... low end tourqe, and highend power.... i like that... too bad the auto tranny won't let us vitalize the high end power more... oh well.

 

I have a 4.0 AWD. I just got home after a drive to get some groceries... just plain wow, what a difference from before.... transformed the engine. I didn't have anything to compare it to but now I know it will tow my trailer with ease. Now to figure out a replacement CAT.

Overall I'm pretty pleased with how this van is turning out. I'm still not far into it money wise and it's starting to show it's potential. Running list of things done so far:

- Cleaned sensors (MAS, IAC)
- All intake gaskets
- Valve cover gaskets (motorcraft)
- New injector o-rings and cleaned injectors (soaked em over-night)
- New plugs (champion copper.. oops, oh well they work well right now)
- New plug wires
- Trans filter / synthetic trans oil
- New heavy duty battery
- Wheel bearing (minty piece from junk yard)
- Synthetic 5w30 + filter
- Mint carpet from junk yard ( front to back < $25, putting in this weekend )
- Replaced all cracked plastic from junk yard
- Found missing interior pieces from yard (cig lighter, ash-tray etc)
- New flex pipe in exhaust
- Coolant flush
- Cleaned intake as best I could by hand including throttle body
- Sea-foam treatment via the intake
- Motorcraft carb cleaner treatment according to ford's TSB here
- New front brake pads and rotors
- Washed

Running like a champ (without oxygen sensor that is)

Small vibration remains in front end under heavy braking, I think it's control arm bushings, more investigation required. Otherwise... she's gold.

 

plugged cat is a possibility, though I have not seen many plugged Aero cats. Good design, strong and solid. About the only thing that can plug them up is either a seriously out of tune engine, a blown head gasket, a major oil leak, or a physical impact to one of the cats. None of those are common in my experience. You would notice a major power loss long before the cats plugged up.

If you decide to proceed with a cat, take a look at our selection, everything we have is all stainless steel, and all of them are high flow. The selection on eBay sucks. Most of the cats sold there are not cats at all. Also don't buy anything that costs less than $40 before shipping. Cheap cats are not made to last, and are not considered to be high flow either. Once you get into the higher priced stuff, you will find that what we offer is a better product for the money no matter how you look at it.

I am still running the original cats on my '94 Aerostar, but my parents '92 has had the cats replaced, and of course we used our own product. Excellent flow and performance. Also easily passes emissions tests, and continues to do so each year. We had a case were the cat had managed to get hit, so we had the shop rebuild the entire exhaust, 2.25" all the way.

If you have a 3.0L, go with a 2" system, better low end torque and still larger than the smaller parts of the stock system. We went with 2.25" on my parents 3.0L and found it did have an adverse effect on the power off the line. Once it revs up a bit, it has plenty of power, but you have to really mash the throttle, and thats not good for gas mileage. If you have a 4.0L, 2.25" is great.

If you decide to buy a cat from our online store, just mention that you have an Aero in the notes field at checkout. BTW, we are not listing all the sizes we have, because our 2.25" and 2.50" standard body converters (900 series) are out of stock and being supplemented by an alternate brand. The alternate brand is the same price, and pretty comparable, but is not fully stainless.

 

I have a 4.0 which I believe is 2.25" ? I'll measure tomorrow unless somebody knows off-hand.

 

During the process of trying to get this resurected van running properly, I did do a sea-foam treament through the intake as well as three bottles of motorcraft carb-cleaner through the intake (according to ford's TSB here) (followed by an oil change). Let me just say that the sea-foam let off a serious smoke show outta my exahust. My neighbours thought my house was on fire. I took it for a spin while it was smoking and people were stopping to watch. I'm sure that dislogdged some amout of carbon.... but having said all that... that knock noise was there before doing any of the above procedures.

 

ngrover,

What did you do with the HGEO sensor when you removed it? If you just left it hanging around, it would have sensed a lot of air, reporting a very lean condition to the EEC. This will definitely affect how the engine runs. Maybe that's why the engine feels stronger; the EEC has richened the A/F mixture.

 

Interesting you say that... the check engine light did come on the second drive after pulling the 02 sensor. I just ran out with my scanner to read the codes.. i got a P1131 which is:

"Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1"

Are you suggesting the CAT may not be bad? So far the only real connection I have is that by pulling the O2 sensor, the knock noise went away. And when under the van, I had thought the noise was comming from the CAT (which is how I even decided to pull the O2 sensor)... hmmmm... any other ideas as to what this might be if not the CAT? I hope I'm on the right track. Yes, according to my spidey senses there is a good gain in power after pulling the 02 sensor, I seem to be able to "wind it out" a lot longer.

Any chance the O2 sensor is bad? It is pretty dirty but I don't know what is normal. That might not explain why I thought the knock was comming from that area though?

 

no harm in changing it if you haven't already.

 

O2 sensor allows the engine to run on Stoichiometric closed loop fuel control via injector pulse time adjustment. At the moment your running off fuel tables direct via the computer. A new o2 sensor is a good idea, Like changing out the jets in a carbed engine.

 

Actually, the computer can run on a stoichiometric ratio without an O2 sensor (uses speed density calculations, which are spot on if the injectors perform exactly as designed.) The O2 sensors secondary function is to verify the fuel trims are correct, and also to ensure that the fuel mixture is constantly cycling between slightly rich and slightly lean for emissions purposes. Its primary function is fine tuning the mixture and allowing the computer to compensate for leaks, plugged injectors, misfires, and differences in the combustion efficiency one each cylinder.

I vote that you replace the O2 sensor. If the element is dirty, it reduces the contact surface area and that directly affects the accuracy of the reading. This will result in a low voltage condition, which the computer interprets as lean. This will cause a chronich rich condition. Poor performance and sluggish response would be the results, since you are no longer running stoichiometric. A new sensor may improve performance. Even if the sensor does not improve performance, it will prevent the new converter from being damaged by an excessively rich mixture.

The units we have listed on our site that I would recommend if this were mine depends entirely on how much you want to spend, how you want it to sound, and whether you want a basic replacement or a performance oriented replacement.

The least expensive route is to replace just the affected converter(s) with the part# 505, which is a smaller bodied compact converter and would be suitable if you installed two of them.

The next step up would be the #905, which is a standard bodied cat. You can use just one to replace both converters, but that would result in an almost raspy sound. Sticking with the OEM dual converter setup helps keep the van quieter.

The ideal converter, which can be used in a signle or dual converter arrangement would be the
#1005, which has a larger body and is more suitable for larger vehicles. The larger cross section produces a deeper tone, and flows a lot better than the smaller cats do.

If the van were mine, regardless of which price level, I would choose the dual cat setups to keep the sound level down, because the boxy body of an Aerostar tends to drone and resonate. The dual cats really help minimize the effect. As far as the installation, the cats should really be welded, not clamped. This results in a better looking longer lasting job. The heat shields should be facing the transmission to protect it from the heat as much as possible. If you do use clamps, don't use the common inexpensive kind of exhaust clamp, use these clamps

http://store.summitracing.com/partde...5&autoview=sku

One of these times, I want to develop a direct bolt in assembly for Aerostars that is less bulky to ship. I want to build a unit with a detachable y-pipe that connects to the rest of the system with a flanged joint. I would make the y a smoother transition, which results in increased torque and hp. The problem is the only real market I would have for it is either you folks here, or the younger rice burner crowd who happens to buy vans.

 

Learning a lot here. I was reading about 02 sensors until late last night ... oh man I'm tired.

The van doens't smell as though it's running rich.. but it's hard to say what's really going on. In anycase the van was designed to run with an functioning 02 sensor so I'm sure that although it's running much better it's still less then ideal.

Plan of action (thanks to the input):
- Replace the 02 sensor
- Test drive, if it doesn't feel as good as it does without one then...
- Replace the CAT with a #905 from Bear River.

It could be that both the CAT and the sensor are fouled up. My 02 sensor is a very dirty brown and one of the slits on it is halfway plugged up. Perhaps the 02 sensor has been causing it to run rich enough to foul the CAT?

So question then, if in theory the van can run at stoichiometric ratio without a 02 sensor, can it also do so WITH an 02 sensor that is danding outside the exahust and reading outside air? It threw a code after pulling the sensor... does that mean the ecu ignores it's readings?

 

So if I put a pressure guage in the 02 sensor holes before and after the cat, what kind of pressure drop should i expect?

 

You can run at stoichiometric ratio via the fuel tables, however without feedback adjustment. If you hook up the o2 sensor outside of the exhaust it will read lean, since compared oxygen on both sides of the sensor will be identical. That means you will be adding fuel, the injector pulse time will be increased & you'll be running black plugs very shortly. You are actually better in this case running with NO o2 sensor. You will get a CEL though. Also even a leak in the exhasut system before the convertor can affect the o2 sensor reading & cause incorrect fuel trim adjustment.

ATB Aeroman.