kylelovesbass

Hey guys, posted this in another forum but was told this may be the best place for it. I've done a ton of searching on here and troubleshooting already and this problem is driving me mad. I've found a few other threads with a similar problem but all were unresolved. I'm not one to ask for help unless I've done all I can to solve a problem, your help is greatly appreciated!

I have a 92 Civic with a D15B7, all stock, 325,000 kms. The car is in very good shape, no burning oil, engine is super clean on the inside. Bought the car a few thousand kms ago and it has had this issue from day one. Warmed up idle is a little rough but not too bad, cold idle is fine except for the pops. When I start the car from cold, it idles where it should but then after about 10 seconds the popping and puffing begin to happen from the exhaust. I can feel the rpms drop a little when this happens. I also put a piece of paper near the pipe and it pushes it back at each pop, so pressure seems outwards. Occasionally the popping goes away for a little while when the car is warmed up, but it's usually just random. The car runs beautifully otherwise, starts right up, smooth powerband (although a little rough still from idle to about 1500rpm), good power, never misses a beat. Gas mileage is what it should be, about 28-35mpg depending on city/highway. CEL is not on, no codes.

Here is the huge list of things I have tried/tested to solve the problem which have made no change at all, I am out of things to test with my limited car knowledge. At least I've learned a lot so far:

-Compression is at 170-175psi all cylinders
-Don't have a leakdown tester but turned engine over slowly by hand and leakdown level seems good
-CTS tested with ohm meter
-New spark plugs, wires, cap, rotor
-Plug gaps checked
-Old spark plugs looked pretty good, doesn't look like it's running too lean or rich. If I had to guess, I'd say things could be a little lean
-O2 sensor bench tested fine, swapped in another known good one just to try
-IAC bench tested, cleaned
-Entire distributor swapped with another car
-Fuel injectors removed and cleaned
-Listened for injector pulses, seem steady on all
-Valve clearance checked and adjusted as needed, wasn't far off at all
-TPS checked and adjusted slightly, reads .5v-4.5v as it should although it has a little drop out around 2v, don't think this would cause this problem though
-Fuel filter replaced
-New PCV valve
-No exhaust leaks
-FITV cleaned and checked, works fine
-Tried grounding the engine better using jumper cables from engine right to negative battery lead
-No vacuum leaks now , smoke tested, found a couple tiny little leaks
-IAT tested fine
-Mechanical timing checked, timing belt is lined up properly
-Ignition timing checked with timing light, was perfect. Tried adjusting timing way off in both directions as well, still pops
-Used timing light to see if spark ever drops out, seems steady
-Alternator checked, solid 13.8-14v

All I can think of at this point is a randomly sticking exhaust valve, but if that were the case I would imagine the popping should happen right away when I start the car, but there's always at least a 10 second delay before the popping begins at cold start. Also, I would imagine a sticking valve would cause issues above idle speed, but the car seems perfect throughout the rpm range. Don't really want to have to remove the head and do a valve job unless I know for sure it's the problem.

Also seems like this could be a lean misfire, possibly due to fuel injectors not functioning as well as they should be. I removed the injectors and cleaned them properly and they seemed great, but who knows. May try to swap in some known good injectors soon. I also smoke tested for vacuum leaks before, but there were only a couple tiny leaks which were fixed.

Please help, this problem is driving me mad and I don't want things to get worse if this is a symptom of a bigger problem that could develop.

Also, here is a video of the exhaust sound:

https://www.youtube.com/watch?v=tr-B...ature=youtu.be

TomCat39

You've gone over everything with a fine tooth comb.

2 things stick out for me. One is your gas mileage. I have the same motor meshed with a DX gear ratio transmission (Canadian CX/US DX) and my lowest MPG is 34 MPG. I'm averaging just shy of 39 MPG (38.8). And my best was a long highway trip running up mountains at 120 KPH which was 44 MPG. Your 28-35 seems low to me. But then again, I don't do heavy downtown type city driving, mine is more country road, highway with just a bit of in city super stop and go driving taking care of errands. Which is also a lot of turn off and start up going from store to store to store.

In your list I didn't see you mention if you inspected your catalytic converter. There isn't a secondary o2 sensor on the D15B7 to monitor how well it's working. I was thinking maybe it's partially clogged and would take a moment or two (10 seconds maybe?) to create enough back pressure to affect idle. Clogged just enough to affect idle, reduce mileage a little bit but not enough to affect the rest of the cars performance to be noticeable. It's all I could think of that you haven't already done or looked at.

Sucks to have to pull the cat off so you can look through it to see how clear the honeycomb is, but it seems like it's the only thing left that hasn't already been touched.

Maybe someone else has a better idea. :/

kylelovesbass

Thanks, appreciate the help. I had the same idea, maybe the cat is a little clogged, but I thought you would have a noticeable drop in power because of this. I suppose I'll be unhooking the cat and having a look! I guess I can run the car for a little in the driveway and see if it still pops without the cat hooked up, will be pretty loud though haha. I'm pretty sure the cat is super old, there was no mention of the previous owner changing it.

My average mpg for a mix of city and highway driving is about 29 mpg (and I drive like grandma), I thought that was a little low too.