Hi guys I'm looking for a little bit of help. I recently adjusted the valves on my 2000 civic hx (d16y5), and drove it after and everything seemed fine. Got up the next day and now the car has a random miss at idle, while driving mid range, and when letting off the gas, it gets worse as car heats up, and is not consistent. Cel is not on to tell me which cylinder. I fear I may have made an exaust valve to tight and burnt a valve, I have since gone back in and adjusted them slightly looser but I fear I may have already burnt the valve as there was no change. Can some body please walk me through identifying if this is the problem?

I don't think it's related to spark or fuel, I think I've covered my bases there.

I do not have a compression tester before anybody asks.

Things I've tried:
1. Spark plugs (#4 had oil on the threads but I have not been able to recreate that)
2. Plug wires
3.swaped injectors with known working used ones with new seals ( I can feel them pulsing as they should).
4. Checked for vacuum leaks with carb cleaner, got nothing.
5. Swapped injector/pump relay with known good used one ( pretty sure fuel pressure and injectors are fine).
6.tested ignition coil with normal results.
7. Did not replace cap/rotor but did inspect and looks fine. (Spark sounds really good when I pull up the boots)
8. Re-ajusted valves to slightly looser spec (still within spec).
9. Checked timing.

 

did you happen to remove the timing belt during the valve lash adjustment? Double check the timing again. TDC at crank pulley first...then TDC at the cam sprocket/gear.

 

Nope didn't mess with timing, I matched up the cylinder 1 tdc mark with crank marks and everything looked good. Only turned motor counter clockwise. I do have an update though, got a compression tester and I'm getting 135 ish on each cylinder. Does this rule out a cylinder problem, or should I try to do a leak down test? I'm honestly leaning towards vacuum again. Not sure why this ECU refuses to throw any codes.

 

135psi is a bit low. When I rebuilt my motor, I was getting around 190.

 

I'm coming up to 250k on the motor, has probably never been rebuilt. So I'm thinking it's just showing it's age a little bit. They are all showing the same, and I think the chances of each cylinder having the same problem has got to be slim to none right? My valve adjustment couldn't have possibly lowered compression on all cylinders right?

 

Here's another update. Just found a decently large crack on my exhaust manifold that extends all the way to the O2 sensor. Could this be confusing my O2 sensors?

 

I would redo valve lash. You could have it too tight. For the .009"-.011" I use the .010" so if it's a touch tight it's right for the .009" and a touch loose it's right for the .011" end of the specification. I do the same thing for the .008"-.0010". I use the .009" to set.

I also recheck after I torque the nut to spec to be sure it didn't turn the adjuster screw. Then move onto the next cylinder.

I'm sure you did valve lash after the car sat for a day so the motor was stone cold...

 

I just drove it with both O2 sensors unplugged and it seems like I'm no longer getting the miss at idle or while driving, but it does still buck when I let off of the accelerator.

I'm gonna get this thing welded up and I'll give an update later.

 

I was so convinced at first that that was what it was, you know obviously since that was the only thing I touched, but I've gone back and rechecked then multiple times and I don't think that's the problem anymore.

Found that crack in my exhaust and the thing seems to drive better without the O2 sensors, other than the bucking it does when I let off the gas.

 

I was posting while you were it seems. I didn't see the post with the cracked manifold. That would indeed cause problems especially being right by the sensor. Running it without the primary O2 sensor will keep it running in open loop so it's running rich constantly. Not only is your fuel economy going to take a big hit but you could cause cylinder wash over time ruining the piston rings.

 

Yeah, that crack is an unfortunate feature on those manifolds and yes, it will eventually cause the car to run poorly. Usually shows up as a high positive long term fuel trim, in some cases eventually throws a lean mixture code. The aftermarket manifold/cat combos seem to hold up better than the original.

 

Hi guys I'm back unfortunately lol. I threw on an aftermarket exhaust manifold and the problem continues, I'm thinking the afr sensor may have bit the dust as it still runs like hot garage with it plugged in. Has anybody bought the $60 one for the hx on rockauto? Has to be the 5wire wideband, most are super expensive so I'm hoping this one can at least handle the job for a short while. Also is anybody aware of a way to test a wideband sensor?

There is also a strange issue with my dash lights and interior lights flickering, Ive checked the alternator and I'm getting like 14.4, and Ive also checked fuse 15 and getting same power there. What else can cause a flickering issue like that, and can that possibly be the source of the overall problem?

Edit: also it does mis every so often with the sensor unplugged, but totally drivable and almost not noticable, with it plugged in it's not really drivable. Could I be getting bad power to the sensor, does anybody know what numbers I should be looking for?