BoostedTT91

My 02 civic started bucking one day, mostly would be under light throttle conditions. After trying to figure out what it could be for a bit, I figured it could be the EGR valve so I took it off and it was very dirty. Cleaned it out completely and still did it. If I unplugged it, it wouldn't do it anymore so that was the problem. Wasn't able to buy a new one right away so I just left it unplugged since it worked fine without.
About 2 weeks later, going home at night, it started bucking very hard and the check engine light start to flash at me. This would happen after about 5 minutes of driving once it got completely warmed up.

Would a bad EGR cause this much of a problem?
On a side note, I have had a check engine light on for about a year that comes and goes on catalyst efficiency so I assume my cat is going bad. Since they are so expensive to replace I left it go. So trying to figure out is this bucking being caused cause my cat is plugged up now after all this time or is it still the EGR. Any thoughts?? Im limited on funds so don't want to throw $ at something that isn't the actual problem.

ezone

Not while it is unplugged.

And it may not even be a valve problem. If it just misfires a cylinder at steady speed that's usually not a problem in the valve itself.
Serious bucking might be a bad valve though, I've felt them act like a galloping horse at times.

You haven't checked for new fault codes yet?

It should have a lot more than just a cat code now. It's going to have codes for the unplugged EGR.......what else does it have stored? (misfire?)

BoostedTT91

I'm going to check the codes in the morning again, im at work right now. I don't have a scanner, just flash the codes. Dumb question, but will it flash multiple codes?

yes it was happening while the EGR was unplugged. It would happen for like 1 minute then stop. I have a 15-20 min ride into work and it happens once each time for a minute or less and then doesn't do it again. I plugged the EGR back in today just to see if it would still do it under heavy throttle instead of light throttle like it did b4 with it plugged in and it still did.

So yea ill check the codes in the morning and yes im sure it will have the cat code, egr code and misfire code. Would a clogged cat cause these symptoms?

ezone

Get a real code reader or phone app + dongle (google Torque scanner app?). You can find cheapies under $20. The phone app can give you a decent amount of live operating data too.

Or stop at some local parts stores (autozone) and see if they read codes for free.
Get the actual code numbers, not their descriptions and shopping lists.


Clogged cat would not have symptoms like you describe.

BoostedTT91

ill run to autozone and have them scan it and see what it says. The only thing I know that was sure causing light throttle bucking and cut outs was the EGR, but nows its worse so not sure what could cause this. Ill post the codes tomorrow and we can go from there. Thanks for your help ezone!!

BoostedTT91

So driving home just now I checked and it starts acting up soon as it fully warns up so basically once it goes into closed loop it starts

ezone

It's probably been in closed loop a lot longer than you think.

Closed loop can begin as soon as the primary O2 sensor is hot enough to become active.........closed loop can begin in as little as 15 seconds from a cold start.

Best way to know if it's in open or closed loop for sure is with a scanner data list.

Did you get fault codes checked yet?


Get the codes before you try this: If you want to eliminate loop status and O2 sensor feedback, simply unplug the primary O2 sensor, erase adaptive memory (battery disconnect for 10 min.) and give it a drive. PCM will stay in open loop/base fuel map with no primary O2 sensor input/fuel trim correction.

BoostedTT91

Checked the codes and I have alot.
Code 12- Egr valve
Code 67- catalyst efficiency
Code 71,72,73,74- misfire in every cylinder

ezone

You know why it's got the first 2 codes.

If it were me, I'd want a lot of live operating data on screen while it's acting up. Maybe take a recording of the events on screen for later review.

Gotta figure out what can make it misfire and run bad only after warmup, and figure out if it is something to do with the PCM inputs, or PCM outputs, or is it caused by something completely unrelated to the PCM...

BoostedTT91

Yea unfortunately don't have that option at the moment. Might just be forced to sit till I can buy a scanner.

Wankenstein

Hehe..you said dongle.

Colin42

The bluetooth ones are less than $20 on amazon

BoostedTT91

Seems to only happen under heavy load. My trip to work involves going up a few big hills which is when it always happens. Drove it around today for a bit on all flat roads and it didn't act up at all

BoostedTT91

Had AutoZone scan it today and their computer came up that the exhaust manifold was the problem. I can't imagine that would be the issue.

Colin42

what was the actual code number?

Slumpertcivic

Heats up and expands enough to create and exhaust leak is possible.

Seems you should be able to clearly hear any leak big enough to confuse the O2 Sensor.

BoostedTT91

So I came home and checked the exhaust manifold, no cracks anywhere or leaking I can find. I reset the codes and regapped my plugs cause they were out of spec to high and took it for a test drive up some hills under hard throttle and light throttle and it didn't do the hard bucking like before this time. The only code it threw now was misfire in cylinder 4

BoostedTT91

It still cuts out under light throttle from the egr valve which i know is bad cause it doesn't cut out under light throttle when it's unplugged. I bought a new downstream o2 sensor but I'm gonna hold off on putting it on for now. I don't believe that's the issue but not 100% sure yet. Working on getting a scanner to see the data live

ezone

A clogged cat will usually only limit air (exhaust) flow (restriction) and cause a power loss...that's like a ceiling or power limit ---and that varies with how much you push the gas pedal. I've not seen one cause bucking.

A cat code (P0420) does not necessarily mean the cat is clogged nor does it mean a restriction, it simply means the PCM determined it has lost efficiency.

I can't either....unless they saw the P0420 cat code.
There isn't any code that is defined as "exhaust manifold is the problem".


Do you remember reading this statement:
Get the actual code numbers, not their descriptions and shopping lists.


Besides....If you have an EX with VTEC the cat is not in the exhaust manifold. It's further back under the engine compartment.



You have a code reader?
How wide were the plug gaps? What did you set them at now?
And what brand and type of plugs are in it now?

You could mark the coils 1-4 then swap #4 coil with another (maybe #3), then drive it and see if the miss code changes to whatever cylinder you swapped that coil with.
You could swap #4 spark plug to another different hole (maybe #2) at the same time and then if the miss code moves.....you may know which part caused it, coil or plug depending on if the code shows up as cyl 3 or cyl 2



Why downstream sensor?
How about the upstream sensor?

If you think the EGR is still questionable you could unbolt the EGR valve and slide in a thin piece of cardboard (cereal box), bolt the valve on again---the blockoff (cardboard) will make sure it's completely disabled

BoostedTT91

P0420 is the code that has been on for quite awhile. Its on for awhile and then goes over for alittle. It's been like that for probably like 10 months now.

Yea not really going by AutoZones "this is what is wrong " suggestions based on your codes but that's just what they said.

I would think if the cat was clogged I would notice a constant lack of power or issue, but it's since that's not the case im thinking that's not the issue either.

Their is ngk Iridium plugs in the car and they were at .050" so I brought them down to .040"
I'm gonna see if it just stays with just 1 cylinder misfire now instead of all cylinders like it was before and then I'll swap the coils around to see if it changes.

Unplugging the egr should do just the same.

Slumpertcivic

If the diaphram inside the egr valve is blown out it may be causing issues even when unplugged, hence the blockoff insert.

If you had high oil consumption like me, the bucking could be the result of the excess oil interfering with combustion cycle. My son wants to slap a dual fuel sticker on it because he is convinced it’s running on more oil than gas now.

Besides adding oil in now and again, the P0420 kicking in randomly was the second sign that I had let the oil consumption issue go on for too long and now the inside of the cat likely looks like a heavily fouled spark plug all inside those passages.

BoostedTT91

Ok well I'll try making a block off plate for the egr and see if that changes anything. I do go through alot of oil but it's due to the oil pan leaking.

Colin42

How bad is the oil pan leaking? Couple drips overnight?
The majority of it is probably going out the exhaust

BoostedTT91

Solved the problem. Turned out to be the spark plug gap. I regapped the plugs to the correct gap 3 days ago and it hasn't done the hard bucking or check engine light flashing. Still does the light cutting out under light throttle but I know that's due to the egr