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Written By: Dangling Fury

QR25DE Precat Issue FAQ


What is this “precat issue”?

The precat (or pre-catalyst) is a catalytic converter located in the stock exhaust manifold. The QR25DE tends to run a fairly rich air/fuel mixture so it is very likely that not all fuel is being combusted in the cylinders and instead combusted in the precat, which can cause it to break apart into small pieces. These substrate pieces get sucked back into the cylinder and damage the cylinder walls, ultimately causing increased oil consumption. It certainly doesn’t help that the precat sits so close to the engine. To the best of our knowledge all precats from 02-06 are of the same make/construction.

The FSM page below shows the location of the precat:



No one knows for sure what percentage of precats go bad, regardless, whether it's 5% or 50% the problem is a real one, enough to necessitate an official recall by Nissan. It is interesting to note that many more Sentras than Altimas are affected by this problem even though they have identical engines/precats. This leads one to believe that the driving habits of the typical Sentra SE-R owner (hard aggressive driving) ultimately contribute to precat failure, most report it between 30k and 60k miles.


What is the official Nissan description?

"Certain engine operating conditions may cause the pre-catalyst to overheat and damage the catalyst substrate. If pre-catalyst substrate particles enter the combustion chamber, they may score the cylinder walls, resulting in increased oil consumption. If the engine oil level is not checked on a periodic basis as specified in the owner's manual and drops below the low level, and the driver continues to operate the vehicle ignoring noticeable engine noise, engine damage may occur which could result in a fire."


What does the precat look like?

Here is an inside pic of a stock manifold right after the 4 primaries (which were cut off). This is a rare look at the top part of the precat since the primaries usually obscure a clear view. Normally the silver part that you see towards the bottom half of the catalyst is supposed to cover the entire surface, however, damage to the precat has caused it to disintegrate, and small dark gray precat substrate pieces were sucked back into the engine.



So what can I do about it?

1. Remove the precat from the stock exhaust manifold (don't worry, you still have another cat in the midpipe). Take the exhaust manifold off the engine and use a long screwdriver to break the precat into pieces and completely remove it, you're going to have to do this from the bottom of the manifold, it's the only way to access the precat. Once all the big pieces are out, scrape the sides to make sure all the small pieces are gone and use an air blower to ensure all particles are removed. Make sure you wear a 3M surgical mask the entire time so you don't breathe in any catalyst dust.

2. Or you can install a catless aftermarket header. If you get a "shorty" (tri-y or 4-1) like Hotshot or Nismo, you essentially replace the stock exhaust manifold and eliminate the precat but again, you still have that cat in the stock midpipe. If you get a "4-2-1" header like the DC Sports or AEBS it will replace both the exhaust manifold with precat and the stock midpipe cat, resulting in no cats at all.



removed the precat but I’m getting an SES light!

The QR25DE has two O2 sensors, one before and one after the precat. On ’02 and ’03 models, both O2 sensors are plugged into the stock exhaust manifold. On ‘04+ models the second O2 sensor is further downstream in the midpipe.

After removing the precat or installing a catless aftermarket header, the two sensors are now reading the same exhaust flow. The second O2 sensor must read a different exhaust stream and send that signal to the ECM to avoid a SES light. You can accomplish this three different ways:

1. Relocate the second O2 sensor behind the remaining cat in the stock midpipe, you will need to extend the second O2 sensor wiring and have a bung welded into the beginning of the catback exhaust. One note of caution, if the wiring is too long, the signal may be weakened to point where the ECM will think the second O2 sensor has failed, resulting in an SES light. The pic below shows the O2 sensor relocated to the beginning of a Stromung catback, before the resonator and after the midpipe cat:



2. Use a "ghetto sim” or anti fouler plug adapter to recess the second O2 sensor away from the exhaust stream. This is the easiest and cheapest method, however, it doesn't always work, especially if the second O2 sensor is still close to the engine. The pic below shows a ghetto sim installed on one of the bungs of a Hotshot header:



3. Get a Casper's O2 sim for the second O2 sensor so it sends a different voltage signal to the ECM. This method almost always works but you need to shell out $50 for the sim. Casper just discontinued their O2 sims so you'll have to look for a used one or go with option 1 or 2.



What about the official Nissan recall?

When you take your Nissan in for the official precat recall, here’s what the dealer will do:

- Reprogram the Engine Control Module (likely to lean out the air/fuel mixture)
- Test the pre-catalyst to determine if it needs to be replaced
- Inspect the pre-catalyst to determine if more extensive repairs are needed
- Install new heat shields
- Change your oil/filter

IMPORTANT: There are numerous instances of precats failing even AFTER the official Nissan recall procedure. The only 100% proven and effective solution is to remove the precat entirely.


What about state emissions testing if I remove the precat?

Catalytic converters work best at high temperatures, this is why the precat sits so close to the engine, it reaches its optimal temperature quicker, thus cleaning your exhaust for the first few minutes after startup. However, the QR25DE comes equipped with a second catalytic converter located in the midpipe. This midpipe cat alone will still allow you to pass emissions after the car has warmed up. If you have a visual inspection in your state (like California) an aftermarket header will obviously cause you to fail, so your best bet is to either use the stock manifold without the precat, or just swap in the stock manifold for the inspection.



QR25DE “Butterfly Screw Issue” FAQ


What is this “butterfly screw issue”?

All QR25DE intake manifolds are “dual stage” and come equipped with two runners in each primary. There are four butterfly valves (or power valves) in the lower half of the intake manifold, one in each runner. Below 5000rpm the butterfly valves remain closed to optimize torque, above 5000rpm the valves open to allow more air into the engine. For each butterfly valve there are two screws that hold them in place. These screws can come loose and get sucked into the engine, causing damage to the head, cylinder walls and/or precat. This issue affects all model year QR25DE engines except '06 which have redesigned screws.


Official Nissan description

"Nissan has determined that on some model year 2004 Nissan Sentra and 2004-2005 Nissan Altima vehicles equipped with the 2.5 Liter engine, there is a possibility that power valve screws located in the intake manifold may become loose. If this condition occurs the malfunction indicator lamp (MIL) may illuminate and unstable engine idling or power loss may occur. To prevent this from occurring, Nissan is conducting a Service Campaign to inspect and replace the power valve screws with new ones. In a limited number of cases engine damage may have already occurred; and, if so, more extensive repairs including repair or replacement of the engine or catalytic converter may be required."


What do the butterfly screws look like?

First is a pic of the butterfly valves with all eight screws in place:



Here is a pic of an unfortunate owner who found that one screw was missing:



Finally, certain '05 and all '06 model QR25DE engines have new revised screws:



So what can I do about it?

The fix is relatively straightforward: take apart the intake manifold and tighten the screws along with a very small drop of loctite on the threads of each screw.

Here is a great writeup:

http://www.b15u.com/sentra-specific-installation-guides-technical-info/9009-loctite-secondary-butterfly-screws.html

Below is a diagram from the FSM which includes torque specs for all the bolts and screws:



What about the Nissan Voluntary Service Bulletin?

Nissan will install new butterfly screws for you, but this only applies to certain ’04 and ’05 models even though it has been proven that ’02 and ’03 models have the same issue. ’06 models already have redesigned screws installed from the factory, only time will tell how effective they are.
 

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Sorry for the extremely late and random post, but My engine cracked a crankshaft bearing and subsequently destroyed some engine internals, which I have no energy left to spend fixing on this car. What is the exact damage a failed pre-cat can cause, and has anyone had any experience with Nissan actually taking responsibility for damage caused by the recall? My car died at 70k miles, out of warranty, and my local dealer's service manager is a complete ass, so I'm just wondering if this could have been caused by a known defect and if there's any chance Nissan will pay for the damage. Thanks!
 

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So I went to my local nissan dealer and asked them about the butterfly screw
problem and they told me that they could run my vin # and determine whether or not it had a product recall so i gave that to them and they told me that i was fine. I have a 2003 spec v but i understand that this problem can happen to my year car. It seems though that the official recall is only for 2004-05 specs, so im just wondering what exactly to do? should I loctite the screws anyway? Also about how much would it cost to have a place do that cause i am not under any type of
warranty and i know the dealer would charge a lot.
 

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actually the "fix" was suppose to fix the 04+ the problem was with 02-03's yes u need to do it. Just do it ur self its really not that hard. theres a how 2 on here also that will walk to you through step by step how to do it.
 

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Great write up. It took me about a little less then 2hrs to do mines.
Mines already had locktite on it too!
Well, at least i have peice of mind now.
 

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actually the "fix" was suppose to fix the 04+ the problem was with 02-03's yes u need to do it. Just do it ur self its really not that hard. theres a how 2 on here also that will walk to you through step by step how to do it.
so the 04 05's dont have the issue?
 

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Hey Guys,

My engine makes some interesting ticking noises. Dealer claims its a Rod Knock and I should get the engine replaced. I'm wondering whether I can somehow prove that Catalytic Converter was the cause of damage and have them replace it for free.

Car is 2003 with 54k miles. Out of warranty, but emission equipment is guaranteed for 8 years or 80k miles.

If anyone has access to VIN database, can you check whether my VIN has gone through recall already? (Dealer didn't see any current ones open for my car, but they might've missed this one since its already old.)
 

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I have an 07 remanufactured QR25deT engine that came with a b15 i just bought. Should i still double check the butterfly screws?
 

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So what do guys who don't want aftermarket exhaust do with the pre-cat issue? Do they hollow it out? If they do is there any additional noise or CELs?
 

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I got a 03' se-r and the engine surges passed the 4500rpm, replaced cam & crank sensors, had codes P0507 & P2135, cleared DTC's, performed the re-learn, vehicle drives normal till you go pass the 4500/5000 rpms and it surges and no DTC's present.

my question is would the secondary butterfly's be the cause of this problem?

thank you..
 

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I recommend everyone do the butterfly screw fix I bought mine second hand and the guy said he did it. I got bored tonight and took it apart all four plates were very loose luckily all screws are accounted for.
 

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Is the intake gasket a reusable one or do we need to have one on hand before we get into it?
 
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