After realizing I have a bad U-Joint, I go and get a new driveshaft. My exhaust has been acting funny. I'm getting random "puts" in the exhaust. "Puts" , "Boomps", whatever you want to call it. They arn't that loud, so I thought it could be an exhaust leak.

I take my exhaust off, and my left (when looking at the rear of the car) muffler falls off. Rusted to hell. The other side is looking bad too (holes, leaks, the works).

So I replace my driveshaft and start her up (without the exhaust and cat). I'm still hearing the "puts".

I was searching on this and I think this is called 'afterburing'. What causes this? And what is the common failure that creates this?

 

Mine does it every once and awhile too. I thought it was normal.

 

I never really noticed it before. It isn't loud like a backfire.

I don't *think* this is normal.

 

It sounds like you're describing a slight idle misfire.

It's no biggie as long as it doesn't miss under load.

 

hahaa... same issue

 

well lets just say its a RX-7 trade mark!!!

 

What kinda RPM range are these happening and what kinda exhaust do you have?

My car will do little backfires a lot but only really good ones comming off WOT at 7 grand.

 

Did they do this when they were new, or is it an age thing?

 

i don't know if they did it when they were new, but every rx7 i have been around has done this including mine which seems to be a very happy motor.

 

my rx7 has a little lumpy idle sometimes that sounds like a slight misfire.. but after like 3 mins it goes away and smooths out at about 800rpm.


this is on a new rebuild with 650 miles or something on it

 

Yup mine does that to it kinda pisses me off i wish i could have a humm instead of a humm plop hummmmm pop pop hmmmm.

 

I like it. I makes me remember theres nothing reciprocating in there.

 

clean your plugs, your leads, check your grounding.

My 7 was idling terribly - missing, hunting, idling high, idling low - instead of

purrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrrrrr,

it was

purrrrrrrrrrr brp brp purrrrr brp purrrrr purrrrrrrrrr brp prrrrrr brp brp brp purrrrrrrrrr,

with the tach bouncing around, sometimes down to 300, trying to stall - the whole car vibrated and the gear lever shook badly too - thought the engine was going to leap right off it's mounts.

I replaced the battery, set the TPS, checked for vac leaks, checked and set the idle adjust and rich/lean screws, grounding and everything else I could think of. None of that helped.

After plug cleaning, and lead connector degreasing, its purrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr brp purrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr. It even hot-starts now.

By the looks the plug-connectors on the leads just got coated in oil, and the plugs themselves were fouled after many flooded-hot starts.

There was noticeable corrosion on the front rotor's leading plug connector.

Now it hot-starts almost all the time, and the idle is way, way improved. Sometimes its the simple things.

It's not perfect, but close enough for me. God it sounds good

 

bad timing will cause those poping or burping sounds in the motor...

 

My timing is perfect and I used to get those.. There are a few threads out there about this and it's really common.

I say used to because after I got rid of the cats and did the Borla cat back I don't notice them anymore if they happen.

 

I've been hunting the exact same problem for quite a while. I checked my timing (perfect), set my TPS (on the $$), set my idle to 800RPM (+- 25RPM or so...), set my variable resistor (easy), changed my plugs (DAMN, they're spendy!), checked my plug wires (within range per the FSM), and it still happened.
I put a timing light on my Leading plug wires and found that while my front Leading plug was firing rock steady, my rear leading plug had a slight miss. (fails to fire a few times per 5 seconds or so) This coincides with the little "puts" in the exhaust. I put in my spare Leading coil and igniter (Yay parts car!), and found that the FRONT Leading plug was misfiring intermittently. Bought two used coils from an online merchane at a bargain price and found that BOTH of them misfired more than the coils I was using!
Moral of the story: After 15+ years, stock coils blow goats.

 

"Puts" in exhaust are normal for a rotary engine. It is the whole port VS valve issue. Seen as though ports are designed differently than valves in piston engine, they can let unburnt fuel into the exhaust, thus making the "puts". This is especially evident when hammering the motor to redline and shifting. You have all the ports operating and it lets a significantly larger amount of fuel in to the exhaust...that is when the flames come!! This explains why a 1.3 liter motor in a car that only weighs 2800 lbs on average can get as little as 10 MPG if driven hard. This also explains why the FB RX-7 is having such a hard time passing smog in its older age. As your rotary engine gets older, it will be harder and harder to keep smog legal (at least in CA). You gotta make sure your engine is in tip top condition. All the above maintenance recommendations will ensure your car lasts a long time and passes smog. When driven hard, a significant amount of fuel doesn't even burn in the combustion chamber, it burns in the exhaust (which does you no good, unless you like pyrotechnics!)

Kurt G.