comegetme

Yes. All values are in range except 280 HC (multiple times the allowable value) at 25 mph only. On this or another forum it was said that this is an indication that the root cause is not the cat, as a failing cat would typically fail on all exhaust gases. However, the car seems to get stronger with the cat removed, prompting me to replace it to eliminate the possibility of a clogged cat, even if it is just part of the problem.

comegetme

I'm not convinced that the minuscule 4.5% difference in diameter makes a difference. I am concerned not only that I'm paying an additional $50 for nothing, but also that I am missing something about those 2 almost identical options, and I am not understanding the explanation of the Magnaflow technician, whether or not they have the same shape, dimensions, and bolt patterns, and why the model with downpipe is paradoxically less expensive than the one without.

To be honest, this whole aftermarket cat industry with their 49-state, CARB, and 50-state versions seems to be an intransparent, shady, hard to understand business, especially considering that 90%+ of mechanics seem to either refuse, or violate the law with their catalytic problem "fixes". (And 90%+ of California cars of that generation seem to get fake smog tests, as a result of that intransparent mess.)

eghatch9295

iTrader: (1)

with passing nox, i seriously doubt that your cat is the issue.

comegetme

Point well taken, and consistent with some other cases. However, on CA->Fed VX conversion won't pass smog - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com the "experts" say that "only 9% co2 with 8% 02 @ 2500 rpm" is indicative of a failing cat, while "if the cat was working well expect over 14% co2 and 1% 02". The presumably failing values of this guy in 2010 are very similar to my values. His problem disappeared when switching to a CA ECU, an observation that found no explanation in that thread. My car has an additional problem of extreme loss of power. Every case is different, all this is more art than science, and not everything can be explained. I'm continuing performing all tests that were suggested on this thread. Swapping the cat and/or the ECU might be one of my tests, while I am waiting for the tools for the compression, leakdown, and vacuum pressure tests that I ordered.

comegetme

Following up on my previous post: Another data point is 1995 VX Smog Sad Face - Fuelly Forums where the owner reduced his HC, initially 250, by 90% by replacing this cat. It appears that all his other emission values were in range. This was a CA car. His HC value was very similar to mine. It was discussed in this thread that the cat failure may have been the result of another root cause worth fixing. However, whether the damaging root cause condition is still there or was just historic is unknown, and I guess in either case replacing the cat if the cat were clogged, would be the first step to be able to properly test all the other components. In summary, and putting all suggestions and data points together, I am currently following a multi-pronged strategy of probably replacing the cat (and be it just for testing or having an additional cat available in the future for test purposes), AND doing the engine compression, intake, vaccum pressure, and fuel pressure tests.

eghatch9295

iTrader: (1)

with your lack of power, there is an underlying cause other than a cat.

94eg!

iTrader: (2)

The real problem is.....that just like medical doctors....nobody really knows what they are doing. And time is money.

Chrisfrom1986

iTrader: (1)

What "testing" did you do? Did it include a compression test?

TomCat39

Love it, lack of power and EVERYONE goes for the first most basic test.

comegetme

I unscrewed the connection between the manifold an the catalytic, while waiting for my tools for the compression, fuel pressure, and vacuum tests to arrive. Probably the same that the dealer did. Hard to compare as it's loud, and I don't have tags so I don't want to drive it beyond my street.

comegetme

While I am waiting for the engine, fuel pressure, and vacuum gauges to arrive, I took out the catalytic. It was surprisingly easy for me as a total beginner. I sprayed all bolts with PB Blaster the day before, and bought a 3/8" and 1/2" socket set, and a 1/2" breaker bar at Harbor Freight. Constructed a little ramp with wood that I had lying around, and drove the car onto the curb with the front wheels (I'm on a cul-de-sac with no traffic). The rest was easy.

I meant to buy a 6-point socket set, but realized that I mistakenly got a "Hi-Viz" 1/2" set (more little teeth in a circle). I have yet to learn what the difference is, but it worked perfectly.

I am ready to install the new Magnaflow catalytic, but I have a hard time figuring out if I need a gasket between the catalytic and the downstream exhaust pipe, and if yes, which one.
Parts diagram https://www.hondaautomotiveparts.com/auto/jsp/mws/prddisplay.jsp?inputstate=5&catcgry1=CIVIC&catcgry 2=1992&catcgry3=3DR%20VX&catcgry4=KA5MT&catcgry5=E XHAUST%20SYSTEM&vinsrch=null shows part number 13 (GASKET, EX. PIPE (47.5MM-48.5MM) (ISHINO)). I'm not sure if this is the gasket for my configuration.
O'Reilly and Autozone have several gaskets, but you can just search by engine size, not by submodel (VX), which is a pain.
https://www.oreillyauto.com/shop/exh...92/honda/civic
https://www.autozone.com/gaskets/cat...nverter-gasket
https://www.autozone.com/gaskets/cat..._0_0_1382_7633
https://www.autozone.com/gaskets/cat...71_0_7008_7633

It appears that a "ring" or "donut" is commonly used for exhaust connections; but I feel it should be a flat metal gasket with 3 holes for the screws, like the one between the manifold and the catalytic with 4 holes, or not?
The original catalytic did not have a gasket at this location. It was metal on metal with 3 screws, when I took it out. Is that ok?
O'Reilly or Autozone customer service was of no help whatsoever. Your help is much appeciated.

comegetme

Here are the old and the new catalytic. I will keep the old one in storage in any case, in case I ever need to troubleshoot performance or smog problems in the future. The problem is, if I replace several parts between smog tests (e.g. catalytic, ECU, etc.), I don't know which one fixed the smog issue. Every smog test and re-test is $50 plus $10 state certificate.

eghatch9295

iTrader: (1)

annnd, it wont fix anything.

comegetme

I don't assume it will necessarily fix anything, but it did in many performance and smog issues of VX owners. We discussed that. Can you help with my question about the gasket?

eghatch9295

iTrader: (1)

you sure there isn't a donut gasket stuck in the original downpipe?

comegetme

Because of the geometry of the pipe, it is hard to visually inspect the upper surface of the downpipe flange when working from below. When the cat was out, I didn't specifically watch for it, but I did not notice anything. And I'm sure that the metal flanges touch each other - so if there was a donut, it is still inside the pipe - I'm not sure what function it would fulfill if it is completely inside the pipe.

Having that said, I hope the donut did not move from its original position into the pipe, and caused the sluggishness and lack of power?!!! (see next post)

comegetme

POWER IS LARGELY BACK AFTER REPLACING CAT!!!

I put in the Magnaflow cat, test drove it around the block, and the power of my VX is back!!!
It feels now similar to the other VXs that I had.

Caveat: Shortly before victory, I noticed that I forgot to insert the backside heat shield. This must be inserted before screwing the downpipe and lower flange of the cat together, and before screwing the exhaust pipe to the frame with 2 screws, to have the flex in the downpipe. Tried to detach the exhaust pipe again from the frame, and I can't get the screws off any more. The heads are rounded. I got them off and on before, I used the correct 12mm socket, and there was no slippage or anything. Bummer! I'm not sure why I rounded them!!!
The screws go into threads that are part of the steel hanger on the frame, so I'm not sure how to remedy the situation. I guess the only way is to cut of the screw head? I am inclined to bring it to my mechanic on Tuesday to deal with the screws. I crawled like 20 times under my car for this freaking cat, I have enough for the moment

Because of the lower flange of the cat touches the downpipe flange, but I didn't put all screws in, I guess there is also a slight chance that exhaust currently escapes through the gap thus resulting in the regained power; and not the cat, but the downstream exhaust or muffler was clogged.

Because of the missing heat shield, I did not drive it to the freeway to complete my test of returned power, as I'm afraid of the heat damaging something. I'm petty confident though that the power is either completely, or largely, back.

The next step is smog (again), and a strategy question arises again: Do the next smog test ($50 + state fee) with the original fed ECU, or swap in my CA ECU. On the one hand, I would like to know if it passes with the current ECU (which I ultimately want to use), after fixing the cat. On the other hand, I would rather not spend a gazillion times the $50 for a trial and error game, and I'm tempted to play it safe and swap in the CA ECU for the smog test.

As far as the old Honda cat is concerned: I'm not skilled at evaluating cats, but visually I didn't see anything. The upper filter is slightly darkened, which I would expect from something after having 191k miles worth of exhaust blown through; the lower filter looks almost 100% white and clean (I find that quite amazing). Piciures attached.

Any advice on the worn screwheads that I need to get off to insert the heat shield, would also be much appreciated.

comegetme

Regarding the gasket: It appears that many cats come with a triangle shaped soft metal gasket for the end with 3 screw holes and flat flanges as in the following pics. My flange is flat on the mating side.

https://i.ebayimg.com/thumbs/images/...bzJ/s-l225.jpg
https://img.go-parts.com/catalog/bra...ll/4C19F8D.jpg

Unfortunately my Magnaflow didn't come with any.

I am noticing that the donut style seems to be typically used on flanges with two (not three) screw holes.

mk378

Check for leaks by having someone stop up the tailpipe with a rag while the engine idles, and you listen under the hood. Leaks before the cat are especially bad as they will fool the oxygen sensor.

Use a matching set of parts, 49 state or California. Don't mix parts from the two versions.

Chrisfrom1986

iTrader: (1)

If you use the ca ecu you'll need a 4 wire o2 sensor, the federal ecu uses a 5 wire wideband sensor. Don't smog it until you make sure there aren't any exhaust leaks or you'll be likely to fail.

comegetme

I agree with the common consensus to only use the right parts for the model. However, my idea to use a CA ECU for smogging is based on numerous reports from VX owners having similar problems, where swapping in a CA ECU fixed their problems - if not the root cause, at least their smog problems. While honda-tech is a forum for Hondas in general, VX specific issues are often discussed at length on fuelly.com and ecomodder.com. I have a 1992 VX, most if not all of which came with a 5-wire sensor (CA and federal models). Honda switched to 4-wire for the CA model starting 1993. It is commonly believed that for 1992 models, the 3 CA/fed differences (ECU, wire harness, O2 sensor) are reduced to 1 (ECU), which means you can convert back and forth between CA and fed configuration by swapping the ECU alone. For whatever reason, some owners passed smog with the CA, but not with a fed ECU (although in principal, a fed VX is capable of passing smog in CA). I personally am still deliberating how to proceed in my case.

comegetme

I did some extensive testing on the freeway after replacing the cat, and discovered that full power was not yet there.

While I was still waiting for my diagnostic tools, I brought it to yet another mechanic (#6). The mechanic discovered that the timing was at 1 ("one"), while it should be between 14 and 18. He said he adjusted it to 14 which was the maximum he could go, as the timing belt jumped or something was wrong. He said the car had full power after setting timing at 14. I am currently having timing belt, tensioner, and water pump replaced, for a total of $550.

I am curious why a total of 5 mechanics / smog test professionals, 4 of which I asked for a full diagnosis of significant sluggishness of the car - 2 regular repair shops in the neighborhood, 1 smog test professional, one smog+repair shop owner, and the dealership - did not detect that timing was at "one" ??!!! The smog result paper from the 1st stop says "ignition Timing - PASS - 16 BTDC" (although it can currently mechanically only go to 14, and was at 1). I guess this is fraud, or at least the services paid for were not provided. I would have thought that the second mechanic (the fool) might have fooled with the timing, but the last place the car was at was the dealership. I would think that when asked for a full diagnostic, this quick, basic check would be the first they would do, or at least not omit from their "multi-point diagnosis". Or is it possible that the current shop is ripping me off to make an extra $550 after quickly adjusting something else that made the power come back? He showed me the timing setting at 14 after his adjustment, and it is at the limit. I'm lost and unclear who is ripping me off at this point. The car was not driven between the times when the various "diagnostics" happened, except for the distance between the mechanics, less than 5 miles.

I acknowledge that this is primarily a DIY forum, and having that said, I cannot wait for my own diagnostic tools to arrive.

94eg!

iTrader: (2)

Mechanics don't know the in's & out's of every vehicle. Especially older ones. They make a lot of assumptions.

Just make sure this guy had the "service check connector" jumped when he checked & adjusted timing. The ECU alters timing all over the place if that 2-pin connector under the passengers dash isn't jumped with a paper clip.

comegetme

I don't think I can verify if he did that, or get back to him and ask if he did. Mechanics don't like it if the customer is overly controlling. I already tried to steer him into checking certain things, to which he replied he is ASE (?) certified and knows exactly what he is doing. He seems to be nice and smart, and has 30 years of experience. But then again, the fool who added the second catalytic had all of that too...

I'm not sure when exactly the ECU would alter the timing all over the place, but it is my understanding that (setting aside adjustments, for the moment), the timing can be read out easily with a timing light. Obviously it was extremely far off. (Or are you saying that the ECU needs to be jumped only for reading out the timing?) If it was not in the range, AND could not be adjusted to the proper setting, and/or it went all over the place, I assume and HOPE that is was a good idea to replace and re-install the belt/tensioner/water pump. Also, if it really gained full power after setting to 14, that would have been the first time after thousands of miles, so again to me that would indicate that the repair being done is useful.

Just for clarification, are you saying it is theoretically possible that the timing was 16 at the smog shop and at the dealership, and after less than 5 miles of driving (and the same symptoms persisting), it shows "1" because of action from the ECU, and cannot be turned beyond 14 at the distributor? If yes, there is something I need to learn. If no, I am tempted to demand my money back for the smog test. If the smog professional skipped the mandatory timing check and just put in 16 on the sheet, it would have caused me several weeks of money, work, and trouble that I might have otherwise quickly solved.

94eg!

iTrader: (2)

I'm not saying he screwed up, or you didn't get the timing "more better" than it was before. I cannot say for sure how the ECU adjusts timing at idle as I have only ever checked/adjusted it per the instructions which specifically instruct you to jump the service connector. If the car "feels" better and isn't detonating I'm sure your mechanic is on the right track. Sorry my suggestion probably made a mountain out of a mole hill.

I'm not sure about local laws or California smog, but it could be worth it to fight for a free retest.