Frozti

Was getting extreme power loss on my 97 EX coupe the longer I drove. If I turned it off and back on after a drive it would struggle then run rough for a bit and power loss would still be there. Noticed I was burning coolant so I replaced head gasket.

Machine shop found the cam journals were fucked, last owner must have ran oil low so I got a new head on Craigslist and it runs much smoother now but my issue remains. Start the car in the morning it runs like new but after a while no power. I'm thinking catalytic converter clogged from burning coolant or something ignition or fuel related. No CEL. Coolant is holding now, no leak. Temps never go above normal, could something be overheating that isn't measured by a sensor? Or possibly a bad sensor? At this point any help is appreciated, I want it running well so badly...

97 civic ex 222k miles, purchased at 217k.

Parts replaced:
-99 ex head
-oem head gasket + china intake/exhaust gasket
-new injectors (ticking gone)
-new fuel filter
-pcv valve
-plugs
-many oil changes
-oil temp sensor
-more if I remember

TomCat39

Your fast check is to slap a test pipe on in place of the cat.

If I recall the D16Y8 has it under the car so should be a matter of unbolting and bolting in a test pipe. That will rule out clogged cat or confirm it if the problem goes away.

Frozti

I was thinking I would loosen the flange between down pipe and cat, stick a penny or two in and clamp it down so it's practically straight piped and test it that way. Or I could buy the test pipe I linked at the end of the post.

Is there a decent chance it's the cat? Can you actually clean one with lacquer thinner or is that a myth? My muffler sounds really worn, I wonder if there's blockage in there. I just don't get why it starts out fine and get's bad through out a drive, and why hot days make it worse. Like I said, my temp gauge shows perfection.

STAINLESS DOWN/TEST HIGH FLOW PIPE/CAT CIVIC/INTEGRA EG EJ EK DC D15/D16/B16/B18

mk378

Vacuum gauge test for clogged exhaust. Or you can completely unbolt the pipe from the front of the cat and test drive. The car will of course be very loud, if it also gets faster you know there is a problem.

Frozti

Could I unbolt the front of the cat then stick a penny in and tighten the bolts so it's open but not all the way open? Would this be quieter? I have to drive the car for a while before it's really noticeable and I'm scared I'll get pulled over for loud exhaust...

CandyRedRC46

It is still going to be loud as **** and awful sounding with the ghetto penny method.
How about this? Remove your cat. Look into one end, with light on the other end. Can you still see light through all of the cells or only some openings?

TomCat39

The front of the cat uses spring bolts and a donut flex gasket if I recall correctly. The penny trick I don't think will work.

mk378's suggestion of a vacuum gauge setup is the best one without disassembly.

Laquer thinner will not clean a cat and probably will damage the precious metals.

The only thing I've seen studies show to rehabilitate a cat is citric acid bath at 80+ degrees. But if it's clogged, the damage is already done and no cleaning is going to un-melt the cat honeycomb.

Frozti

I ordered a cheap test pipe. Don't care about legality since I really am using it to test. Do the aftermarket name brand cats pass emissions tests? Oem is expensive and they cut them out at the pick n pulls if they haven't already been taken. Or at least I thought...

Still don't know if its the cat but the test pipe was cheap so I went with that. Is there anything else that comes to mind with these symptoms? Longer I drive the mushier the throttle gets. By the end of a 30 minute drive I have half the power that I did at the beginning. My idle goes down like 100 rpms lower than what I adjust it to.

Frozti

Putting the test pipe in now, having some complications with stuck bolts, china bolts wrong size etc. I can see light through the cat, don't know if it's the muffler. The test pipe has two o2 sensor holes so I'll try it with both plugged then unplug the extra hole if that doesn't work to see if it's the muffler. Need to check dizzy rotor and bearing, too.

Edit: It's on, testing tomorrow. I also drove without the gas cap to see if gas tank was venting properly and it made no difference. Is there any chance it's a cracked block that expands as I drive from heat? I must figure it out.

Frozti

Didn't help at all. By the time I was almost home the throttle was mushy and powerband nerfed. When I turned it off and turned it back on again it struggled, as if something was pushing against the starter. On the plus side it's raspy and obnoxious and fun to drive. Going to unplug an o2 hole.

CX-Adam

Any CEL codes?

It could be fuel related or ignition related. Your OP says you replaced the fuel filter but the FPR could be sticking open or your pump may be worn and overheating thereby developing less pressure.

If you go to a parts store you can rent a gauge.

1. Relieve pressure
2. Install gauge @ fuel filter banjo bolt
3. Disconnect and pinch shut FPR vacuum hose and start engine (may need to prime the rail first). Wait a few second and turn off. Pressure should be between 38 and 46 psig.
4. reconnect vacuum hose. pressure should be between 28 and 36 psig.

If you're not within the ranges, first check the fuel pump.
If it's high, then check for pinched/clogged return then faulty FPR
If it's low, then check filter (done), FPR, leak (probably not the problem)

Note, there's bias in my response. I've had a lot of fuel problems as of late so this is where my head is at.

Frozti

I rented one a couple months ago. Only tested with vacuum hose applied. It was around 33psi. Only check engine code right now is for lack of o2 sensor in test pipe. Before this I've never gotten a code.