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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8622
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Eclipse: the manifold, or the second converter which..o2 sensor..pipe

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on this 01 eclipse, I have code p0421 warm up cat efficiency low. Would that be the front converter which is part of the manifold, or the second converter which is after the second o2 sensor? The second converter was removed and I don't know when it was removed, but there is a pipe welded in where it used to be. The car has some stalling issues and the 0421 is the only code.
If you have the manifold with integrated converter that looks like this:
then you will only be concerned with the manifold converter (pre-cat) with regards XXXXX XXXXX check engine light.

On vehicles that have the manifold mounted pre-cat, the larger post-cat under the vehicle is NOT monitored and incapable of setting a check engine light. Be aware if your manifold does not look like above, the story is a bit different, but from your description you have the in-manifold pre-cats.

Having the post-cat eliminated on this type system again will not set a check engine light, and it also will not affect drivability/stalling etc.

Inspect your throttle body first thing and clean it up as necessary; this is the #1 cause of stalling on this vehicle.

Regarding the actual P0421 code, 90% of the time this is a faulty manifold/pre-cat. You will need to monitor the O2 sensors to verify they are working, if they are the manifold will need replacement.
Customer: replied 6 years ago.
I monitored the o2 sensors, and the cat is doing absolutely nothing. The temp was actually cooler after the manifold cat than before. So, to install a new cat where the old one used to be would be a waste of money?
Very good. Yes as long as your front and rear sensor are nearly matched in output, that cat is kaput.

Installing a cat where the missing one was would not be a waste; it would bring your emissions down where they are supposed to be, it would restore the lost back pressure and at the most basic, would clean up the odor from the vehicle that the missing cat likely created.

However... installing a new cat where the old one was removed will not correct the check engine light; remember the oxygen sensors are situated just ahead and just behind the manifold pre-cat.... any changes after that point would not be detectable by the computer since there are no oxygen sensors after the post-cat. The pre-cat/manifold would still need to be replaced to correct the check engine light.
Customer: replied 6 years ago.
Ok. one more question, is the manifold for that car the same as the one used on the 2002 mitsubishi eclipse 2.4L?
No problem.

It depends on the emissions rating on the vehicle; any California emission Eclipse 2.4L produced from June 2000 through May 2005 will interchange. You can check the build date on this car and/or the donor by looking at the door jam sticker where the VIN and curb weights are listed. At the top of it will read "OCT 01" or similar. As long as both vehicles are within that range, you will be fine... that is the range that used the pre-cat manifold pictured above.
Customer: replied 6 years ago.
ok. so there's not 2 different styles of precat manifolds between 01 and 02?
No there is an early 2001 and late 2001 manifold, then 2002-2005 which is identical tot he late-01.
I apologize, I typo'd that last response which made that confusing, it should have read "June 2001 through May 2005" will interchange, as long as both are within that range you are fine.

For interchange help, here are the part numbers and break down:
Production date June 2000 - May 2001 Part number MR552684
Production date June 2001 - May 2005 (Actual production stopped in February though) Part number MR597478

You must have a matching date range between the donor vehicle and your car for it to work; if production date is not available or you can not confirm California emissions etc, I can verify this by VIN if you can provide both VINs as well.
Customer: replied 6 years ago.
OK. No chance though that the stalling could be caused by this in your opinion?
It isn't terribly likely. Remember the code is coming on because the computer is seeing a similarity between the front sensor and the rear sensor; If the converter were physically clogged it could cause this to happen, however you would be more likely to see a O2 sensor range malfunction instead of a catalyst efficiency problem (little sense as that makes, that is simply how the computer would interpret the reduced flow).

If the converter were clogged to the point of causing a stall, you would definitely be able to feel a difference in power driving the vehicle as well.

What are the circumstances that it is stalling? Is there any notable event/moment that it started, or did it just slowly get worse?
Customer: replied 6 years ago.
it doesn't seem to do it when it warms up. it only stalled a couple times. most of the time it doesn't die. it stumbles like it's going to die. It isn't constant
What is the idle at cold/hot?
Does the engine bog down when you try to accelerate from a start? How about while at cruising speed?
Customer: replied 6 years ago.
it didn't when I drove it last. The person who drives it all the time told me that it just died on him when he came to a stop. it started right back up. the check engine light was on, and the only code that I got was p0421
And they didn't indicate that the light had been on previously?

Do you have a vacuum gauge you can check the manifold vacuum with the engine running?
Customer: replied 6 years ago.
The light was on previiously with 2 egr codes and the 0421 code. I changed the egr solenoid and it's been a week and the egr codes have not come back, but the 0421 code did. just yesterday it stalled on him. Last week I checked manifold vacuum and it was 21 if I remember right.
Okay, sounds good so far.

The thing with the P0421 is that it can take weeks to occur; because of the way the test for it works the required driving time, temperature, etc, as well as the repetition required, sometimes it can take up to a month for this code to set after a problem is caused (or light is reset). The absolute earliest I have seen was about a week and a half.

Odds are this code was present for weeks prior to the EGR repair and just had not failed enough times consecutively to trigger the light. Short of filling the tank with diesel, there is nothing that could have occurred in the past week to bring the converter from 100% good to failed, it just doesn't break down that fast.

Was the battery disconnected or replaced during the EGR repair?
Customer: replied 6 years ago.
no. the battery was not disconnected. The 0421 code was present before the egr repair. I knew when I did the egr that the cat was shot too. I am just hoping that the stalling that happened to him was related to the cat failure.
Ah okay, I understand now.

I would not put any wagers on the cat being the cause of stalling, -especially- with a 21inHg vacuum reading. The amount of these cars that are on the road with bad cats down here is very high (there is no emission testing where I live). The cats fail prematurely on this vehicle, usually around 110k, but I have seen a few around 90k, and due to the cost (especially of the later model) they are rarely replaced here as no one wants to spend the money with the vehicle operating fine.
While it is possible it could have failed in such a way to cause a stall, it is not common and would absolutely be reflected in a low manifold vacuum reading, which you do not have.

Personally I would put my money on a idle quality issue that is causing the stall (be it dirty throttle body or malfunctioning IAC, etc) that may have been amplified with the now corrected EGR flow. Remember the EGR is supposed to be introducing inert gas into the mixture... this was not happening while the EGR was malfunctioning and may have set some skewed fuel trims that need to correct themselves now that there is correct EGR operation..
Doug and other Mitsubishi Specialists are ready to help you
Customer: replied 6 years ago.
If this were the case, would it be normal to have some stalling with no trouble codes or pending codes present? I did monitor the fuel trims today and they were ok at -4 short, and 8 long, but then again when I saw it today, it wasn't stalling on me or even hesitating and like I said the only code I got was the 0421
Absolutely. Stalling issues on this car almost never set trouble codes unless someone has started messing with the base idle trying to "fix" things.

Your trims sounds pretty good. Have you pulled the intake hose off and checked the throttle body condition yet? I'd be curious to know how clean/dirty it is.
Customer: replied 6 years ago.
I will do that tomorrow morning and let you know what I find.
Sounds good, keep me posted.
Customer: replied 6 years ago.
will do. thanks for all your help.
You're welcome!
Customer: replied 6 years ago.
Ok. the car is here. it's idling rough like it wants to die. when I remove the vacuum hose on the throttle body labled E, the idle goes up and the engine smoothes out
It sounds like you may have one of the vacuum lines reverse; it would appear you are applying EGR opening vacuum at all times... this would be most likely an issue with incorrect hose routing. Check the hose diagram on the under side of the hood and make sure nothing is reversed
Customer: replied 6 years ago.
wanna job? thanks again.
Was that it?
Customer: replied 6 years ago.
sure looks like it.
Nice! If you need anything else just let me know.
Customer: replied 6 years ago.
it actually looks like the vacuum lines were routed correctly. could it be a problem with the vacuum control valve? or possibly the new egr solenoid?
It isn't terribly likely, but it is possible. Does the egr solenoid open and shut correctly with voltage applied?
Customer: replied 6 years ago.
I think I figured it out. tell me what you think. According to alldata, there is supposed to be a hose with a restrictor in it. That hose is not there, but a regular hose is. I have another mitsu with that hose. I put the hose on it, and it seems fine now. Could that have been the problem?
If you do not have the restricter in place, you are definitely going to have a problem; this restricter is used to reduce available vacuum below a level the engine is capable of regulating.

If this is not there (it should have a white stripe on the hose) this will create EGR malfunctions. Start with swapping that over... you may find you need to replace the vacuum valve as well as this restricter also prevent garbage from going through there (it typically clogs at the restricter first). Not necessarily the case here, but something to keep in mind.
Customer: replied 6 years ago.
I don't know why it was missing, but I have put one from another car in and it is running much better. Thanks once again
No problem, keep me posted if it acts up.
Customer: replied 6 years ago.
I just got back from a test drive and it would appear that I spoke too soon. When I came to a stop, the car just died. It did start back up. When started back up, it acted like it wanted to die.

And I assume this problem was not present before the EGR problem? If not, did it occur when the EGR problem occurred, or after the repair?
Customer: replied 6 years ago.
it apparently wasn't present until after I put in a new egr solenoid. a few days after I replaced that solenoid, this started, but no egr codes returned. I had it sitting idling for a good 30 minutes, and it idled fine. it wasn't until after the test drive until it acted up
Hm, if the hoses are routed right, this doesn't make too much sense.
Is the solenoid passing air at rest, and holding vacuum (sealed shut) with 12V applied? Can you resistance check the coil on the solenoid, it should be about 30ohms.

Does the engine stumble it's way down to a stall or does it just drop off entirely? Did we ever check the condition of the inside of the throttle body just to be certain it isn't gunked up?
Customer: replied 6 years ago.
I actually tested the solenoid before I installed it, and it passed the vacuum test and the ohm test. I just looked at the TB, and it doesn't look too gunked up, but inside the intake it looks pretty wet
That is OK past the throttle body, don't worry about that. If there is anything other than silver inside the throttle body, clean that sucker out until it is spotless... any black line across the center line where the plate closes can pose a problem.... use brake cleaner to clean it out, if anything other than silver remains, use a pick or scotch brite to get everything up.

Beyond that there really isn't anything probable that could have occurred from replacing the solenoid. Unless the system has been inop for a long time and the valve is occasionally sticking open, that is about all I can come up with.
Customer: replied 6 years ago.
Ok. I will keep you posted
Customer: replied 6 years ago.
ok. i had it idling just now. it was idling fine. I goosed the gas and it it revved fine, but came back down and started stumbling bad.
Can you reproduce it fairly consistently? If yes, disconnect the EGR valve hose and see if the problem goes away.
Customer: replied 6 years ago.
i think with the egr valve hose disconnected it has gone away
Make sure.... take a test drive (you will likely set a check engine light for insufficient flow) and see if you can reproduce the stall. If you can't, it sounds like the valve is sticking. There may be some carbon buildup on there and when it opens during normal driving it isn't closing all the way when returning to idle. Only other possibility would be the vacuum valve, though these rarely fail (and I don't believe it could in such a way to cause this issue anyway)
Customer: replied 6 years ago.
well... I replaced the egr solenoid again, and the problem was gone. ran great until today. Apparently it's doing the same thing again. It seems as though the egr solenoids keep going bad. I have already put in 2 new solenoids and each one lasts about 4 days. is it because they are napa parts, and not oem? or do you think there is something about the car damaging the solenoids?
Interesting.... Put a Mitsubishi solenoid on there and see if the problem persists.

Mitsubishis do not get along with a lot of aftermarket parts (typically igniters, cam/crank sensors, anything hall effect). This would be the first case I've heard of aftermarket solenoid failure, however it wouldn't surprise me too much. They are so inconsistent we won't deal with anything other than factory equipment now.

The only probable causes for failure would be heat failure or fatigue from duty cycling. The solenoid uses battery voltage, so the odds of an over voltage failure are ruled out. The only electrically associated component to the solenoid is the driver in the PCM.... and again it is battery voltage so and over volt failure is out. Considering it works OK for a few days, I would wager that if it is a failure from duty cycling fatigue, it isn't going to be PCM related but rather component weakness as a malfunctioning driver should result in abnormal behavior for those few days as well.

My only concern is that the solenoid was bench testing OK (unless it had not been tested again after the failure). This part makes me a bit suspect of the driver however it would not explain why it works OK when you put a different solenoid in.

Lets start by going back to OEM solenoid and re-evaluate after that, as the only other reasonable item is the PCM which is considerably more money and not terribly likely.
I have a feeling I may be adding a new item to the "don't buy aftermarket" list.

Please keep me posted!
Customer: replied 6 years ago.
I will definitely keep you posted. I have a date with the thing tomorrow afternoon. Again, I really appreciate your expert opinion regarding this issue. thanks.
It's my pleasure, I'll be glad to get to the bottom of this (probably not as much as you though).

This certainly does explain why it was clearing up with the hose detached. Most dealerships should have this solenoid in stock, so hopefully you can get this squared away quickly and we can start the 4 day countdown :)

Take care