Ok this is a weird one and I am not even sure if it is a problem but I noticed it and thought to ask the more knowledgeable to see if this is something that is wrong and can be fixed.

During idle (cold or warm) there is generally even exhaust pulses but randomly about every 2-3 seconds there will be a larger exhaust pulse. Its louder (nothing like a backfire but you can hear it if standing near the outlet) and there is a single burst of higher exhaust volume. The engine and exhaust system will shake when this happens as if the combustion in that one pulse was larger than normal.
Now with this said the car runs just fine as far as I can tell but I would think if everything is running to spec then the exhaust should be smooth and even.

As of now there is a brand new dizzy, alternator, FPR, and main relay, Plugs are maybe 6 mo old wires are new. Any help is appreciated and I've searched extensively and haven't found anything close to this issue.

Edit for info: This is a 90% stock 89 Si only mod is tanabe catback with random tech cat. Timing set to spec wIth timing light last week.

 

interesting, do you think you could give us a video?

 

Ill try to get one tonight.

 

Ok too dark to get video but recorded the audio you can really start hearing it at about :35 and its gets more clear from there on http://youtu.be/uE1_SRuz794

 

My car started doing that after I took it out of storage sitting nearly a year. I started replacing vacuum lines and have some more to do. The rest of my ignition system is practically new and timing was dead on. In my case I must have a leak somewhere as I had to up the idle to prevent stalling too.

 

So you were able to fix it with vac line replacment?

 

i can't watch the video but i'm fairly sure what you're describing is a misfire. it's not a larger pulse but rather a total lack of a pulse.

 

I didn't get a chance to replace them all, but the few I did had no effect. My car is now off the road as I got an inspection ticket for oil burning. I'm pretty much doing a full teardown and rebuild now and if it still happens after, then who knows.

 

Would a misfire cause a sudden increase in exhaust volume. I can actually put a piece of paper by the outlet and it moves when one of these off pulses happens.

 

Bump for some help.

 

like i said, you probably have a misfire problem, the engine shaking and exhaust "puffing" both support this. i think you are hanging up on the perception that there is a stronger exhaust pulse, which is most likely just an illusion. fix your engine miss and both problems will be gone.

 

i had a problem almost like this. was on a 87 prelude but same problem. it ended up being that my valves needed some asjusting. so i took my valve cover off and asjusted to spec and added some fuel injector cleaner to my gas. Walla problem solved. could be a missfire but doesnt sound like it. in my case i guess one of the intake valves was opening a tad bit too much and causing a cylinder to intake more gas than the others thus giving it a more powerfull combustion therfore causing the pulses that you are hearing.
just dont forget to do the usual like clean/check cap and rotor regap spark plugs and check ur wires resistance.

 

if i were you. run some injector cleaner, and do what others are telling you. the injectors could always use a good cleaning. besides that it's not really too bad. i've heard way worse.

 

Thanks for the pointers guys. I'm gonna run through the recommendations and get back to you with results.

 

Did you ever solve this issue? My 90 hatch with d15b1 has the exact same issue. all ignition parts are brand new as well as new injectors and fuel pressure regulator. timing is good and no vacuum leaks. compression is good across all cylinders. kinda driving me nuts.