DEC Customer Concerns

Customer Questions and Concerns

Here are a few letters and emails from customers who had certain expectations that were not met. Please read the commentary below so you have a better understanding of some of the issues regarding DEC vs Aftermarket vs Factory converters.

1. General Fitment & Cosmetic Issues (shipping dings & scratches) - here are a few emails I received from a BMW M3 customer.........

Question - Steve, I have a question. I have received the DEC cat and am pleased with the workmanship. However, the exhaust end of the converter, there are two pipes, but only one has the flange fitting. The other pipe appears to be a sleeve fitting, the female component. I am pretty certain that the OEM exhaust is a double flange joint. After finding Borla exhaust would be 6-8 weeks and Billy Boat is $800, I settled for an Ansa exhaust. It is on the way. I am concerned about the disparity in the cat/exhaust joints. If the exhaust is double flange fitting, how does one make the connections. Do I have the proper converter????? A. Richards

Response - on many BMW models (E28/E24/E30/E36/etc), the muffler uses a double flange connection but the catalytic converter uses 1 fixed flange and 1 floating flange. The floating flange side gets the larger of the 2 o-rings I sent you which slips over the outside of the pipe. The pipe on this fits inside of your muffler. You have to re-use the old steel floating flange. Having 1 fixed and 1 floating makes installation a lot easier and takes into consideration production variances.

Question - After taking all the exhaust system off of the 1995 M3 (automatic) today, I find that the DEC Cat Does Not Mate To The Manifolds! It is off by almost an inch. The superior tube is off and I notice evidence of hammering and bending at its first bend. They still did not get it right. I have no intention of going to the considerable trial and error effort of getting some kind of a fit. It was my understanding, and I did ask for a bolt on fit. I am not satisfied with the product and wish to return it for a full refund. A. Richards

Response - DEC catalytic converters are built as "bolt-on" units and the alignment tested in factory jigs before shipment to the customer. The marks you see on the outside of your header pipes (the scratches, not the mandrel formed bends) are merely cosmetic scratches from UPS or Fedex handling and should not affect performance or fitment. Minor cosmetic damage is NOT grounds for returning or replacing a catalytic converter. If the damage were severe enough as to affect fitment, I should have been notified immediately to have DEC send a replacement unit and file a freight claim with the carrier.

The customer must allow the manfacturer (DEC) at least one opportunity to replace a damaged or poor fitting unit. Any potential customer that does not agree with this course of action should simply source an original factory converter through a local auto dealership.

2. "Check Engine" indicator

This is another chronic problem that's prompted many a phone call. The "check engine" light is triggered by one of the rear ("monitoring") oxygen sensors. These sensors have a platinum coating at the tip that is very sentitive....oil and antifreeze contamination along with other malfunctions upstream at the engine can cause erratic signals at the rear sensor(s) and cause a "Catalyst Below Efficiency" fault code to trip.

Customers should refer to Items #7 and #8 on the Troubleshooting page to work through this problem.

And one last comment....change your sensors at least every 100,000 miles. While the rear sensors (on OBD2 cars) can trigger annoying fault codes, a bad front sensor ("regulating sensor") can produce excessively rich conditions and melt the ceramic bricks inside the converter.

3. A Few Notes on 1993-1998 BMW 8-cyl Converters - I was recently blasted by an irate customer who was very disappointed with the DEC converter I sold him. Folks interested in purchasing a pre-99 BMW 8-cyl cat should read and understand the differences and why they exist between the factory unit and DEC's converter. All OBD/2 BMW cats have received these updates and will therefore appear different from the factory converters.

Please Read and understand both of these situations before purchasing a DEC catalytic converter.

A. May 2004 Email from Gary T. ('95 540i)

Steve,

This letter is to notify you that I am returning the DEC catalytic converter that I ordered from your company last week. I am very disappointed with this part for the following reasons....

1) Your web page is very clear that DEC catalytic converters are mandrel bent, this is not the case on the unit that I received. All the bends on this unit were the type of bend that reduces the pipe diameter by the 15% or so that you claimed restricts exhaust flow. This is not what we discussed when I ordered it and is unacceptable.

You're right....according to the manufacturer, the bends on the 8-cyl cats are too tight for the use of mandrel dies. This was news to me and I have now amended the website to read "Most DEC cats have mandrel bends". I'll let DEC know that the first sentence in their 2002 catalog ("All DEC catalytic converters are fabricated from mandrel formed components....") is misleading and should be clarified.

(Note - it would be interesting to see a back to back dyno comparison of HP & torque of DEC vs BMW's 8-cyl cats. I think the cat and not the piping is the bottleneck in the exhaust system on the 93-98 8-cyl models.)

2) The original exhaust system for my 1995 BMW 540 is 2 1/4 inch diameter.The DEC unit measured 2 inches in diameter (much less where the pipes were bent). We used a micrometer in multiple locations to determine this. This also is unacceptable.

The factory BMW exhaust is double walled accounting for extra thickness....the inside should be close to 2".

3) Here's the icing on the cake for me. The new catalytic converter is approximately 7 inches wide and 9 inches long with a one inch wide "flange" or flat piece that goes all the way around the cat and is where they probably spot weld the top and bottom together. Instead of having this flange be horizontal or at a slight angle to fit in the recessed area where the old cat was someone at DEC decided to have this flange run vertical so when we dry fitted the new unit the flange pointed straight up and down. The lowest point of the flange was now 1 1/2 inches below the original cat and would bottom out the first time I went over a high parking entrance. Since the warrantee in voided if the cat is damaged this seemed ridiculous to design it this way.

BMW has historically had a problem V8 cat brick failures and DEC was able to resolve this by putting a stainless steel mesh around the bricks to keep them stable. Reliability is significantly improved. This solution required a "pancake" shaped cat instead of an "oval" one. The exhaust tunnel was designed by BMW for the use of the oval shaped cat. In fact, when you lay the DEC cat in place and line it up with the manifold flanges, you'll see it sits in the tunnel at an angle (ie, the welded seam is not at the 12 o'clock position). This asymmetrical fit might be disconcerting to some but it does allow for maximum ground clearance. The outer shell of the DEC cat will hang approx 3/4" lower than the factory unit.

(Note - if anyone is not comfortable with this design change, they should stay with the factory BMW cat. BMW eventually changed their design with the later V8's (9/98 & later) which resolved the issues of the earlier converters.

4. Steve, in fairness I must add that you handled all aspects of this transaction with a professional attitude and worked with me to get me the parts on time and I appreciate this. I'm writing this letter so you have some documentation to give to DEC. I'm not sure how your description of their quality of work came about but as a business owner I would hate to have my reputation tarnished by inferior workmanship by another supplier.

Gary....I know I tried talking you into the factory cat as I do all of my customers but most people are more interested in the substantial cost savings. Performance wise, the DEC is probably very close to stock and it should last longer but only you will be able to make that determination after you get your new BMW cat installed.

5. I have contacted my credit card company regarding this item plus shipping that I am disputing. They tell me I should expected a full credit (no restocking charge) for the catalytic converter plus shipping within 30 days of your receiving the returned part. DEC should have UPS pick up this part at their expense. Please let me know how you want this unit shipped.

As these differences between DEC and BMW converters were not properly explained to you (they will be detailed to all future customers through your letter & response), I have had DEC issue a call tag for pickup of your converter.

B. October 2004 Emails & Phone Calls from a '95 740i customer & his mechanic

A customer purchased a replacement set of converters for his 95 740i in April 2004 and they experienced a full meltdown with severe blockage 6 months later. Meltdown does not happen without some condition in the engine or fuel management system causing unburned fuel to be released and ignited in the exhaust. If the situation is not corrected, the replacement converters, DEC or factory, will experience the same failure. THIS IS NOT A WARRANTY SITUATION! Replacement converters will be charged at full retail.

The customer had the situation diagnosed by a local BMW dealer. Here's the email I received with the initial diagnosis........

Steve, I just received a call from BMW and here is their response:

"RICH, WHAT HAS HAPPENED IS THE CATALYTIC CONVERTERS ARE HALF THE SIZE OF THE FACTORY PARTS AND WILL NOT EVER KEEP UP WITH WHAT THE VEHICLE PRODUCES LIKE THE FACTORY PARTS. JOHN HAS CHECKED THE VEHICLE AGAIN AND BOTH THE CATS ARE BAD, VEHICLE IS RUNNING FINE."

Are these the wrong size for my 1995 740IL BMW: DEC-1451 and DEC-1450. Please confirm and let me know what I need to do.

The DEC supplied cats are in fact smaller than the original BMW ones but this does not affect flow due to the "venturi effect". There are 2-3 companies in the US making catalytic converters for companies like DEC, Miller and others and they have a few standard sizes to choose from. DEC and other companies use these cats and fabricate the pipes and flange connections to fit the various vehicle applications.

When the customer was advised that his meltdown would not be warrantied, he and his mechanic came back with another explanation........

Steve, the mechanic says the car is running rich because the oxygen sensors do not thread as deep into the pipes as on the factory converters and the sampling of exhaust flow is inadequate for proper control of the fuel management system.

DEC and just about every other aftermarket cat company buy their O2 sensor bungs from the same suppliers. The factory cat may allow the sensor to go a few mm deeper into the exhaust stream but the sampling is the same 5mm or 10mm off the inner wall of the pipe. With meltdown, we're talking about the difference between an AFR of 10 or less vs an normal AFR of 13-14....you're not going to see that magnitude of air-fuel ratio difference due to sampling points within the pipe.

Both of these accusations (undersized converters & inadequate air/fuel sampling) cast dispersions on the performance standards of DEC and the whole aftermarket catalytic converter industry (approx 2 million units per year). An in-house converter comparison on the dyno (BMW factory cat vs DEC aftermarket) would be interesting but the results (which one produced better hp/torque numbers) would be limited to the samples and model tested.

(Note - if you're going to have a local BMW dealership do the converter replacement on your car, DO NOT give them a DEC or any other aftermarket part to install. If anything goes wrong, it will be blamed on the part you brought in and you'll most likely be charged additional labor cost.)

C. March 2005 Email from a satisfied '95 740i customer - just to show you not all the feedback is bad........

Dear Sir,

I recently purchased a DEC cat for my 1995 740i from you. It has been on the car a month or more now with no problems. I wanted to offer some feedback for your site for those considering the purchase of a DEC unit (at a considerable savings vs the factory unit).

I recently replaced both O2 sensors and obtained the nuts and gaskets from the dealer separately so the only thing I bought was the DEC unit for the left side replacement. My reason for the replacement was that the thing sounded like a dishwasher full of rocks due to the internals becoming partially separated and rattling around. I read quite a bit on the web including the postings on the Ultimate Garage site and after speaking with Steve, I decided to place the order. I think his approach of offering all the customer info, both good and bad, instilled a sense of confidence in doing business with Ultimate Garage not found with other sites.

I would classify myself as an advanced home do-it-yourselfer. I have my own lift and many tools to work on cars properly. I can do most anything and have been fiddling around with BMW's and Porsche's for over 20 years. I know all the pros and cons of aftermarket parts and have been burned many times by poor fit and or poor service life. The fit and quality of construction of the DEC unit is first rate. It slid into place with the same level of fit I would expect from a factory unit. I could not discern any noticeable difference in the underhang or ground clearance of the new unit. It provided good clearance to all the surrounding shrouds and surfaces. It runs quiet, does not make any cool down noises ( ever shut off a 911 Porsche after some hot licks) and it cannot be seen to underhang at all.

All up it took me 2.5 hours to do the install including the time to drill and retap a broken stud in one of the headers; yes Virginia, I heated the p**s out of it with an Oxy-Acet Torch before wrenching it. Please feel free to post this info with the other info on your site to offer a another view from a very satisfied customer of DEC and of the Ultimate Garage.

Sincerely, Tom Kinney