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Running issues after exhaust header / cat change [solved]
2002 Civic LX ~138k miles on 2nd engine (used engine w/ 30k miles)
Couple days ago on the way home started sputtering, flashing CEL, barely made it home, visual check indicated a large crack in the Exhaust manifold. Great, put a cheap steel pipe mated to a catalytic converter for a nice expensive fix.
Pulled the old pipe to see if it was repairable- crack goes all around the center, into the oxygen sensor, so I decide to replace the part.
New Cat/Exhaust manifold installed, torqued (Center nut couldn't reach with torque wrench- no leaks detected there but possibly it needs another 1/4-turn?), connected to sensors and exhaust, start up:
chug, chug, chug then ran ok,
then ran not so ok
then threw P0302
tightened connections stopping leaks at the oxy sensors and let car sit overnight.
Next morning, starts up ok, then chug, chug, chug, dumping fuel and smoking out the tail pipe but no code, no flashing CEL
I don't see any more leaks from inside the engine compartment but obviously something is wrong. No other components were changed, other than a little bit of a rough idle the car ran fine before this incident.
When it is misfiring/chugging, turning on the a/c may make it die, really low idle.
I have not pulled any plugs or coils to check them yet, but would they get damaged from driving 1/2 mile in 'flashing CEL' mode?
re: Running issues after exhaust header / cat change [solved]
The old cat was fine it was the manifold that was cracked. Now I'm getting random misfires. It seems like it's not getting enough fuel or there is a leak somewhere. It hesitates to start and once it start it hunts for idle sometimes wanting to die if I touch the gas pedal.
re: Running issues after exhaust header / cat change [solved]
Update: no start
the fuel pump is new this year and I can hear it power up when the key is turned
the spark plugs and coils look fine no unusual corrosion
re: Running issues after exhaust header / cat change [solved]
I'm taking the pipe off and putting it back on again. Is there another forum I might check where the cool Civic guys hang out who might be helpful in diagnosing this mess?
re: Running issues after exhaust header / cat change [solved]
remove plugs. air the cylinders. you might be flooded
check the plugs, if they are around 100k miles or more, change them.
remove filter to make easier to start
how old are the o2 sensors?
any remaining engine codes?
you can also just remove the downpipe under the cat to see if that helps start, reconnect later
if things that have been bolted down for years are suddenly removed, they tend to do weird things - suspension parts tend to break right after you put new parts, like antiroll bar endlinks, top mounts, etc.
we also see engine sensors failing right after timing belt changes. mine did so (camshaft, crankshaft sensors did fail right after - maybe connections got some grease, don't know why, just that they do.)
the usual with most cars i have owned...
(This is not normal, but fuel pump, injectors could be at fault too, some debris got in there. Coils usually don't fail either)
re: Running issues after exhaust header / cat change [solved]
try honda-tech forums also. some old members in there.
over the decades, I have found the weirdest reasons for the problems my cars had.
the weirdest was a clunk noise anytime the car would be subjected to G's.
It was a glass coke bottle (yes, I am almost as old as you, before PET bottles) that got under the rear seat and would hit the walls...
re: Running issues after exhaust header / cat change [solved]
Throttle body appears okay, pretty clean inside . The engine is relatively new as far as miles go if the installer is to be believed. I think my next move would be to smoke test it to see if there are any Hidden leaks. From my BMW experience, leaks in gaskets and vacuum lines are the primary cause of misfires
re: Running issues after exhaust header / cat change [solved]
check the air intake body? it's plastic... hard to see, since it's sandwiched between engine and firewall. Some anecdotal cases where it was actually cracked.
only instance i removed it was when i changed the head gasket, but i removed the whole head with the intake in it, don't know how much a pain it is to remove the intake alone.
re: Running issues after exhaust header / cat change [solved]
Originally Posted by CivicChoice
Are they? I thought 135 was optimal so not that far off?
That’s the minimum compression that’s considered acceptable. They’re typically in the 160-180 range.
Just want to check something that wasn’t addressed earlier: are there any other engine codes? Are your sensors OEM? I want to emphasize this especially because aftermarkets don't cooperate with Honda's. I don't care that a voltmeter shows if they're working - they aren't.
re: Running issues after exhaust header / cat change [solved]
Smoke test shows no discernable leaks.
as far as I know the sensors are OEM they have been working fine the whole time
the only codes were p03 random misfire codes
while the car is down I will adjust the valves to see if that helps
re: Running issues after exhaust header / cat change [solved]
Valves adjusted, they were all about 1/4 turn too tight on the adjuster screw.
Start er up, chunky idle then blowing thick smoke out the tailpipe after about 1 minute.
Issue... valve cover bolt would not torque, appears stripped. Now I'm looking at a tap and die?? It wasn't leaking smoke there but could this be the issue?
re: Running issues after exhaust header / cat change [solved]
rerun compression check after valves adjusted
cyl 1 150
cyl 2 155
cyl 3 143
cyl 4 170
new plugs
the engine fires right up idles around 1100 then 30 seconds later it almost stalls revs up and start blowing smoke out the back again
leakdown cyl 1 9%
cyl 2 7%
cyl 3 30%? Would not pressurised over 80 and leak to 58
cyl 4 4%
Cylinder 3 has been the questionable one
head gasket?
Leakage appears to be from both valves, positive pressure from both intake tube and exhaust pipe, no coolant bubbles
Last edited by CivicChoice; Aug 8, 2021 at 06:48 PM.
re: Running issues after exhaust header / cat change [solved]
so far, looks like the main issue was the cylinder losing compression, and the valves were the culprit?
head gasket will let combustion gases escape to the coolant in these cars. It will push the coolant then to the expansion reservoir and coolant will leak from there.
If your reservoir is full and you lost coolant in the radiator (combustion gases will expand and not pull the coolant back) then you have a blown headgasket.
If your reservoir is normal levels and you are not losing coolant on the radiator, then the head gasket is likely still OK.
if no gasket, run the engine a little longer, maybe it just is adjusting the ECU idle.
How much smoke are we talking about from exhaust?
If a lot, potentially the valves might need new seals? (You will need to remove the head, though...)
Remove the camshaft and check the rocker arms first? LX should be easier than EX (no VTEC rocker arms, they are slightly a pain)
re: Running issues after exhaust header / cat change [solved]
I'm in the process of pulling the head off the car and I'll have the valves work and get a new head gasket since it's off there. It looks like a lot easier job than pulling heads from a Subaru which I have done with the engine in the car. I will report back the results
re: Running issues after exhaust header / cat change [solved]
So I got the head off with the help of a YouTube video, whoever decided to put a nut on the bottom of the intake manifold that could not be accessed I cursed their ancestors and offspring as sadists.
So it's off to A1 Cylinder Head in Jurupa to rebuild this week.
re: Running issues after exhaust header / cat change [solved]
Update: got the head cleaned up and new valve seals, couple new valves and re-installed everything.
Fires right up, but bounces rev limit at ~4000 repeatedly and sets P0335 . Not sure where to go from here, the P0335 threads I have read are no-starts
Diagnostic testing of the sensor : power and ground OK, no pulse from sensor during crank rotate. Oh goody, get to take the car apart again and throw more money at parts.
Last edited by CivicChoice; Sep 4, 2021 at 07:00 PM.
Reason: additional info
re: Running issues after exhaust header / cat change [solved]
Car has an AEM intake on it, am putting it back to stock, pulled a stock unit from the pick-your-part in San Bernardino. No particular reason except it should be quieter and not look like crap (cone filter rubs on the underside of the hood) but I did not realize I needed a
Genuine Honda 17228-PLC-000 Throttle Joint Rubber
to connect the tb to the intake/filter box dammit I prolly could have found one for no charge at the parts place, live & learn... am going with ridiculous price OEM sensor once I get to it since I do NOT want to do this again soon. Next time I need to pull splash shields since almost all of mine are missing
Running issues after exhaust header / cat change [solved] 
