Kanthinar

I have searched for the last 3 weeks on this forum for advice about where to start. There is a very strange noise that occurs near 5000 RPMs and up on my car. I will do my best to give as much detailed information as I can to the problem and the noise itself.


My 8 is an '07, 6 speed with 110K miles on it, and no cat simply a straight pipe (I purchased the car that way). I just replaced the spark plugs, the coils, and the wires about 2 months ago. This strange noise started I would estimate about 3-4 weeks ago.


When the engine is first started, this noise does not appear to be there. The best way I could describe it is it sounds as if the engine is fighting itself. It reminds me of a valve float noise; a tapping sound. My brother said it sounds like a jack hammer but you cannot feel through the petal or the car itself. The sound is directly tied to the RPM's because as they increase so does the frequency of the sound. Also the engine takes longer than normal to accelerate to the red line when this noise is present. Again this only happens when the engine is fully warmed up and under load. If I rev the engine while in neutral with no load the noise is not there.


The engine also seems to be running extremely, EXTREMELY rich. This started occurring when the noise started as well (at least that's when I really took note of it). When at a red light I will depress the gas petal and there is momentary pause before the RPM's begin to rise. There have been a few times when I've almost stalled the car.


I'm new to rotary engines, and I've read all the "new owner" forums. Any advice would be greatly appreciated, as I'm at a loss.


I do believe the rich exhaust (richer than usual) and this noise are directly related. I know rich exhaust is a result of not have a cat installed but I've had this car for well over a year now, taken great care of it, and it never had this pungent an aroma or acted this capricious.

Loki

iTrader: (1)

I'd suggest pulling the sparkplugs to see what's burning. Since they're fresh, they should have some light brown and black on them, but no oil, gas or other substances. If one spark plug looks out of ordinary, we can pursue that lead further.

Since it happens only under load and above a certain RPM, I'm tempted to call what you're hearing knock. Unfortunately, it's a bit hard to judge just from the written description. Are there any check engine codes? I imagine you have at least one for the missing catalytic converter, but are there others?

Kanthinar

I pulled the plugs when this first started and the combustion in all chambers appears to be fine. Last weekend I replaced the clutch and while I had the car up I pulled the plugs again to see that they were still burning fine with no gas or oil residue.


Actually there are no error codes present. Each time after I drive a check to find no code, or even pending codes. As for the engine knock noise, that could very well be it but I have never actually heard engine knock myself so I have no idea what it sounds like.


One thing to note, when I started the car after letting it sit for a few days with the battery disconnected (from installing the clutch) it ran great the first time. I shut the car off for probably 5 minutes and then the problems began to return.

paimon.soror

iTrader: (15)

also, get us a reading of your fuel trims if you can. Either buy, or find someone who has, a live obd2 scanner (like this or something similar: ) and see if you can monitor your STFT and LTFT. If its rich, that will tell you.

Kanthinar

I own the Actron AutoScanner Plus CP9180. I have just completed running the car. The knock was not present throughout the RPM range under load.

My scan tool can read 20 frames of data and the values are as follows:

ST FTRM1% 0.0
LT FTRM1% 0.0
The calculated load% 100
RPM 5836
Speed 63 MPH
Fuel Sys 1 OPEN

Now at some point along my Journey the values of ST FTRM1 and LT FTRM1 do change to the following

ST FTRM1% 0.0
LT FTRM1% 3.9
The calculated load% 10.1
RPM 2850
Speed 28 MPH
Fuel Sys 1 OPEN

If you need something else let me know. I will take a drive to get it to replicate the knocking. I'm assuming its engine knock noise but I do not know what it sounds like.
If you need any other sensor readings let me know. I have recorded all the possible sensors.

Again I'm not sure what the nominal values are or should be. This level of sensor control is all new to me but I am learning.

Loki

iTrader: (1)

Hrmmm. Nothing there jumps out as crazy. Do you think you could record the noise?

Kanthinar

I will have to locate my recorder and figure out a way to rig it so there is no wind noise. On my second trip out I have some very different reading with the scan tool:

ST FTRM1% 11.6
LT FTRM1% 0.0
Fuel sys: Open

Then 15 seconds later:

ST FTRM1% -5.8
LT FTRM1% 6.4
Fuel System Closed

The engine had begun to make noise at this point. I can get more data but I did not think the fuel trims would vary so drastically. In one freeze frame they are reading
0.0 and then varying by as much as 8.0 points. Is this normal?

paimon.soror

iTrader: (15)

my recommendation if you want us to get a good idea of your fuel trims (its hard to tell right now, but nothing is jumping out), but if you can try the following:

go out on a nice stretch of flat road... use cruse control....

sustain 4000rpm, wait 10 seconds, and get us what you see for stft and ltft
then go sustain 5000rpm, wait 10 seconds, get us what you see for st and lt
go sustain 6000rpm if you can, wait 10 seconds, get us what you see for st and lt

you can use this procedure to get vids too as based on what you said, i suspect you will start hearing the noise at 5/6k

If you dont, that tells us something, that it is load based. but we will cross that bridge when we get there.

Kanthinar

Thank you I will do that in the next few days. Again I apologize as I'm new at diagnostics with the tool.

paimon.soror

iTrader: (15)

Not a problem at all. Good luck, hopefully we get something in the numbers to help you out.

Noises are the hardest thing to diagnose because everyone hears the noises differently. Even a recording may not tell the whole story.

Other experts may chime in and have better ideas, but hopefully what I provided will get us moving in the right direction

Kanthinar

The issue was compression loss all along. Sorry about the long delay. I had a rotor 1 misfire after pushing it hard and decided to pull the engine to rebuild it since I have the place, time, and money right now. The rotor housings are some of the worst I've seen. I'll post pics when I get home.

Kanthinar

So this is the OBVIOUS problem with my engine. I've already conceded that I need 2 new rotor housings but the big question....do I need a new intermediate iron??

9krpmrx8

iTrader: (46)

Yes.

Kanthinar

I figured that I had too but I wanted another opinion just to be safe. Amazingly enough the rotors and the e shaft are still in great condition. Thanks for all the help.

Now I'm strongly debating buying a remanufactured engine assembly and putting off rebuilding this till another day. The cost to rebuild is rapidly increasing and I'm sure the value of a rebuild is long gone. Still will be a fun side project none the less.

9krpmrx8

iTrader: (46)

Great condition as in you checked them with the proper measuring tools?

Kanthinar

Yeah. I'm a machinist/tool and die builder so I have (or have access to) all the tools I need. The only tool I do not have is the go/no go gauge for the corner seals so I ordered a gauge plug of the appropriate dimension and modified it to match the SST.