erietdyk

Alright, I'll start from the beginning. I had an exhaust leak when I bought the car, and I thought it was the manifold/cat, so I replaced that. During the removal/install process, I decided to be a ricer and run it without the manifold. Not the problem. The rear flange from the midpipe completely separated, and was basically running open manifold. It ran fine for a week this way, but always had a CEL on that I didn't know what it was, but I assumed O2 from running it without the manifold on.

Today, I installed a new-to-me midpipe that I picked off a junker and welded up the flanges on for higher strength. After the install, it had a SERIOUS lack of power (0-60 in stock 1/4 mile times), and it started making this woosh sound, which happens at high RPM in neutral, and pretty much all the time above 1500RPM under load.

http://www.youtube.com/watch?v=aoNY9uhgKiY

I've never dealt with this problem before, so I have no idea what it is. The cat is brand new, and it's blowing exhaust out the tailpipe with ease, so it's not a clogged exhaust. No vacuum lines are disconnected, and they all look to be in great shape. I'd test them with some carb cleaner, but I don't have any and all the auto parts stores are closed at this time. I've got a code, #65 Secondary oxygen sensor heater wire (black wires), but I don't see how that could cause a lack of power or throw it into limp mode. Besides, it's had that CEL on for the entire past week; of which it's been running perfectly.

Any input appreciated.

erietdyk

Oh, and the car has had a tune up, minus oil, oil filter, and PCV valve within the last few weeks. I've got them, just haven't tossed em on yet.

Former User

Have you recently checked for codes? Any new ones?

Check whether 7.5A dash fuse 15 is blown.

erietdyk

Will do, and I'll get back to you.

erietdyk

No such luck. Every 7.5A fuse under the dash is perfect. Swapped a new fuse into 15, still did nothing.

erietdyk

And no new recent codes.

s10murray

i've got a bone stock 97 coupe civic and it needs some gitty up and go but i'm going to focus more on suspension because one day i plan to engine swap for a b18

erietdyk

Mine had gitty up and go. It took out my 2011 Sentra SE-R with BRM Exhaust. Now, it's anemic, and I have no idea why. Nothing aside from the mid-pipe was changed, and it was a perfect condition part.

motegicivic

Do a compression check, might have a burnt exhaust valve.

grumblemarc

iTrader: (4)

I could be wrong but it sounds like a serious vacuum leak. Pop the hood and have someone else rev the engine while you pinpoint the source.

erietdyk

Doubtful, considering it drove fine for me for the past week.

It definately doesn't sound exhaust related, that's for sure. I've checked for vac leaks everywhere, it's just odd it's all happening as I put on that new midpipe.

grumblemarc

iTrader: (4)

Like I said, get under the car/hood and have someone else rev the engine. Or get under the hood and yank on the throttle cable.

Former User

How old are the plugs, wires, cap, and rotor?

Have you checked the ignition timing?

With the key in ON(II), does battery voltage reach the secondary O2 sensor plug? What is the resistance of the heater element?

erietdyk

I got it up on a hoist in some light at a buddies shop. Once I could actually see, the problem was abundantly clear. My muffler had bulged out, and it was filled with dog food and dryer lint. Mouse must have made a home out of it while it was out of service for the couple weeks my exhaust was disconnected. Sawzalled the muffler off, and it runs just like it did before the midpipe was installed. Now I just need to find a new muffler, get a new spring bolt kit for the flange, and I'll be laughin'.

Plugs, wires, cap, and rotor are all new within the last couple of weeks. I haven't checked the timing, as I don't have a timing light. I also haven't checked to see if battery voltage is hitting the 2nd O2 heater wires, or the resistance of the heater element, as I don't have a multimeter. I assume I'll be able to find a frayed or broken wire somewhere, and that I'll just have to replace it. Don't feel like spending $200 on a new O2 if I don't have to.

Former User

Good job solving the problem.

I guess this test...

...may have been misinterpreted?

motegicivic

[QUOTE=erietdyk;47539632]Doubtful, considering it drove fine for me for the past week.



You said: "I decided to be a ricer and run it without the manifold."

Right you mean just open on the engine?

If you ran it like that you can burn an exhaust valve.

erietdyk

Definitely. Lesson of the day: Always do diagnosis yourself rather than letting the service manager at Canadian Tire do it for you. I had him stand behind it and hold his hand over the tailpipe; he said it was fine.

[QUOTE=motegicivic;47540550]Yes, no manifold, straight out the ports. Understood that that CAN burn an exhaust valve, it didn't. It running for the past week fine proved that. Lotsa people telling me that, though.

Former User

This^ is almost surely a myth.

Blacknight117

iTrader: (1)

Has to be, how `bout those people who run open headers..

erietdyk

The "myth" is that the valves being so close to cool air after the engine is shut down can warp or crack them. The burning part came from engines not running properly without back pressure. Their tuning was all incorrect for running without a manifold. Running without a manifold is perfectly fine; just like zoomie headers or ITB's on the intake side, but the engine has to be properly tuned for it; least that's what I've been told by all the muscle guys.

Running (an) open header(s) Is completely different than running no header(s) at all. One at least has some amount of backpressure; an amount that the engine can easily deal with on the tune it was given before opening the header(s), while the other is coming straight out of the head(s) without any manifold(s) at all. If properly tuned, it can easily run and drive this way, but without a tune it's damaging to the valves.

Former User

I believe that this^ too is a myth. A few old anecdotal stories having little or no scientific support was likely propagated without anyone questioning the source.

erietdyk

Well, it does have a bit of theoretical support. By removing the manifold completely, you essentially eliminate back pressure. By eliminating back pressure, you've increased the flow of that engine drastically; enough so that the stock fuel map can't handle it, and the engine runs lean. We all know that running lean means running hot, and all that hot gas (and probably flame) has to escape somewhere. Again, all theoretical, but all logical.

Former User

I'm highly skeptical about the backpressure idea:

https://honda-tech.com/forums/showth...t=backpressure

erietdyk

Well, seeing as how an increase in backpressure creates a decrease in flow and power, a decrease or elimination of backpressure should create an increase in flow and power, logically speaking.

Backpressure is in every exhaust system, even one that doesn't exist on a vehicle running straight out the head; the port would create a small amount of back pressure, but nothing significant. Backpressure is an obstruction in itself, as it disrupts flow. It's great for 2-strokes, but 4-stroke engines have no need for it. The old adage "backpressure is the enemy of horsepower" is true on naturally aspirated engines such as these, and almost any engine running without manifolds.

Now, if an engine is tuned to work with a specific manifold to aid in scavenging, and you suddenly take away that engines scavenging effect and give it a lot more flow, it's not going to be able to adjust and will run lean. I've seen first hand what running lean can do to pistons, so I don't doubt it could do the same to an exhaust valve.



It's good to question everything, as that's how you learn, but I wouldn't doubt that running an engine without it's exhaust manifold could do some serious exhaust valve damage.

Former User

Backpressure has absolutely nothing to do with exhaust scavenging. That's the myth. Removing the manifold reduces the velocity of exhaust flow and it is this reduction that decreases scavenging.