kylelovesbass

Hey guys, first post here. 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 is 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, good power, never a backfire or misfire. 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
-O2 sensor bench tested fine, swapped in another known good one
-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, this shouldn't 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.

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

kylelovesbass

Anyone? I'm doing more research, 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 fine, 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.

Freemananana

iTrader: (3)

You would have better luck moving this topic to the 1992-2000 subforum where they know these cars. Try reposting it there.

kylelovesbass

ok, thanks, sorry don't know the forums well here!

98vtec

I am in this situation now with my h22. does not like a leaner idle than 14.2 or it "pops" as you are referring to. I have tried switching to a "better" injector which did not fix the problem although they appear to be doing a better job overall.

it has a new distributor in it but did it with the old distributor even after converting to external coil.

I have messed with individual cylinder fueling and adding 5, 10, 15% to each cylinder does not help (i was hoping giving one cylinder more fuel would at least help me pinpoint a problematic cylinder since it idles nice and smooth with richer idle mixtures.

compression is perfect

next is to try a valve adjustment. i dont believe this to be the problem but i guess it doesnt hurt to see if i maybe did it too tight.

In all my other setups, i have never had this problem so its a bit daunting that a healthy engine with new EFI parts are causing it.....but i have seen some weird stuff before so I dunno lol

this is not an all motor topic so i am going to move it to Tech/misc

fcm

I do not see where you said you checked fuel pressure.

What kind of gas are you using? 94.

kylelovesbass

Ah, haven't checked fuel pressure. I don't have a gauge but I'll pick one up tomorrow. Using regular cheap gas, will try a little premium when the tank gets low and see if that makes any difference.

And thanks EFI, it seems that this issue has something to do with a lean burn. I'm learning how to read spark plugs and it looks like things might be a bit lean.

holmesnmanny

sounds like cat is plugged .. to test disconnect the oxygen sensor connector ignore the check engine code ...remove oxygen sensor from exhaust pipe... see if it runs better

fcm

" The car runs beautifully otherwise, starts right up, smooth powerband, good power"

^^ not a symptom of a bad/plugged cat. 94

kylelovesbass

Yeah I don't think it could be a bad cat. I'm going to start the car up today with the CTS and O2 sensor unplugged (should keep it in open loop and make it run richer I think??) and see if that makes a difference. My thinking is that the car is too lean at idle for some reason when it goes into closed loop. I also smelled the exhaust when the car is at operating temp and it seems lean I guess, doesn't smell as strong as I think it should. I'm pretty sure this car is in open loop and running rich as it should for the first 10 seconds or so at cold start because it always runs perfect at first, the pops never start right away. I'm just trying to eliminate the possibility of a sticky valve because that's not fun to fix lol.

I haven't tested fuel pressure yet but that's next on the list. I don't know if that would be the problem because it runs so well above idle.

I also disconnected and plugged the vacuum hose going to the fuel pressure regulator while the car was idling, which as far as I know should have raised the pressure and richened the mix, but this didn't have any effect.

Really appreciate the help here so far thanks guys

fcm

Pulling the vac line will raise the pressure, however, A/F ratio is controlled by the ECU/ECM with info from sensors, like the ECT sensor. 94

kylelovesbass

So I started the car up without the CTS and o2 sensor plugged in (was hard to start but it did) and the pops and puffs went away. The car idled a little higher and smoother. I'm assuming that I have forced the car to run richer by doing this, so it seems like the issue is a lean mix at idle. Basically at this point I'm just happy that this doesn't seem to be a valve issue. I still haven't figured out what the problem is, I guess testing fuel pressure would be next.

I also tested the MAP sensor. I'm not sure if I did it right because I couldn't find a very good guide online. I probed the light yellow wire closest to the firewall and grounded the other wire on my multimeter, not really sure if that's the right wire to probe but seems right. With the car off and ignition on, I got about 3v. At idle it was about .8v, but as I increased the rpms over 5000 I couldn't get it much higher than 1.5v. I don't know if I did this test right so I'll have to do some more research. Also, unplugging the MAP doesn't have any effect on the pops.

kylelovesbass

Ordered a fuel pressure tester from ebay, should be here in like a month from China by horseback. In the meantime, I hooked up a voltmeter to my o2 sensor to see what might be going on with the mix. I noticed that the voltage would drop very low (.1-.2v, lean mix) which seemed to correspond with the exhaust pops and little dip in rpm. The voltage was mostly around .7v at idle.

Going to change my fuel filter now, don't expect it to fix anything but who knows when the last time it was changed and it's a few bucks.

Guess I can live with this issue for now, I'm pretty sure it's not a valve problem at this point and a lean mix at idle shouldn't hurt the car. Will keep updating this, I WILL find the problem lol. Hope this helps anyone else having the same issue.

kylelovesbass

YES! I think I found the problem. Swapped in the fuel injectors from my Integra which runs perfect and the popping went away. Idle was nice and smooth like it should be. Going to buy some new injectors, I might just have one bad one but I think I'm just going to replace them all. Will post if this solves the problem for good which I imagine it will.

I found this thread where a guy had the exact same problem with his S2000 and it was the fuel injectors, good info here on the same issue:

http://www.s2ki.com/s2000/topic/659930-misfire-thread/

duh702dc2

I have this same problem I posted a thread but nobody had any input on it. Heres the link I even put up a video. Check it out guys I'd appreciate it .

https://honda-tech.com/forums/showthread.php?t=3203547

98vtec

I've tested 3 sets of injectors on mine

kylelovesbass

So I got new injectors, installed them and the problem got WORSE. WTF!! I knew something was up with the injectors I got, so swapped them into my integra and it ran poorly as well, lots of pops/puffs from the pipe. Turns out that they sent me two injectors that were the wrong flow rate, good thing I had swapped the good Integra injectors in from before or else I would have probably never solved this issue thinking the problem was something else.

Anyway, two of the new injectors are going back but this problem is SOLVED. I put two of the correct injectors into the Civic along with two of the old ones for now and the car runs smoothly as it should. One or two of my old injectors is clogged causing the misfire exhaust pops, at least two seem to be ok for now.

This took me like 2 months to figure out lol. Glad I learned a lot. Hope it helps others.

Not4Sale

Man this sounds like my issue, car runs fine but has a rough idle, not much surging but rough. don't have a cel . haven't had time to really check out, but you've given me some ideas