F355 Off throttle exhaust burble and rough idle sometimes - Ferrari Life
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post #1 of 29 Old 05-04-2015, 07:20 AM Thread Starter
 
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Off throttle exhaust burble and rough idle sometimes

Ok guys, please tell me if I am on the right track.

Just purchased, 96 355 spyder 37K. Major service done 2014. New Tubi headers and exhaust, CATS are OE and were replaced at 12K.

Issue: Slight burble in the exhaust at light throttle when cruising. Sometimes the idle hangs up for a second, then lowers with a slight miss sound. Almost sounds like a cammed V8 at idle. Doesn't always do it. Car revs and pulls great without any hint of missing. I haven't driven any other 355's but I feel the car is a bit flat at 3K revs and really comes on strong around 4K. I dont know if that is normal or not. Not a lot of torque below 4k. But that is subjective as I dont know how it is supposed to run.

What I have done:
1. New plugs and wires
2. Fixed SDL TC
3. I was getting a misfire on two cylinders and redid the connectors. Cleared up codes and missfire.
4. Cleaned MAF and idle control
5. Checked other connectors --- seem fine.
6. O2 sensors are all new
7. Reset ECU a couple of times....seems to help for a little while

I am getting CAT efficiency codes for both banks. No other codes. I have ordered some Evoflow Cats and hopefully that will fix the codes.

From my research, I am thinking the timing is off slightly. I read an old thread on Fchat in which an owner had very similar issues and it was finally corrected with a timing adjustment. Of course that means engine out and I was hoping for a few more years before I had to do that.

The car runs and drives great, but the burble and rough idle drive me crazy. Any thoughts? Should the car have that burble at idle? Most people would probably not even notice, but unfortunately I do. I am wondering if timing can be verified with the engine in?
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post #2 of 29 Old 05-04-2015, 07:27 AM
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When I left of the throttle in my 98, I also get a burble, however, I have no rough idle - it purrs like a kitten. I believe the burble is related to the exhaust pressure (and I don't have a muffler - just pipes)
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post #3 of 29 Old 05-04-2015, 07:30 AM
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As a suggestion, you may want to send your injectors for cleaning and testing. If your timing was off - I would expect consistent results - not intermittent.
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post #4 of 29 Old 05-04-2015, 07:40 AM Thread Starter
 
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As a suggestion, you may want to send your injectors for cleaning and testing. If your timing was off - I would expect consistent results - not intermittent.
Thanks. I ran some cleaner through them but maybe some deeper checking is in order.

What about being a bit flat around 3K? I think I am kidding myself about it being intermittent....seems like I notice it every drive at some point. Mine purrs then coughs a bit, then purrs, then coughs.
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post #5 of 29 Old 05-04-2015, 07:48 AM
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Much, much ground to cover...
-No torque below 4K? Normal, a Toyota Corolla has more grunt.
-Above 4K, hold on, as this is where the fun begins
-Timing? Ignition timing is non-adjustable
-Burbles on coast down-I'd be looking for exhaust leaks with a smoke tester. Some "burbling is normal.
-Idle quality; oh, where to begin other than a compression and leak down test
-Erratic idle-> IAC motor, ignition wires, injectors

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post #6 of 29 Old 05-04-2015, 07:53 AM
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Quote:
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-Burbles on coast down-I'd be looking for exhaust leaks with a smoke tester. Some "burbling is normal.
I'm getting ready to do this Dave. I really, really how my headers are not toast (yet). I want to drive the car and don't know what I would do for headers other than GP and I don't want to lose the entire drive season.

I have a feeling this is not going to end well....
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post #7 of 29 Old 05-04-2015, 08:21 AM Thread Starter
 
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Much, much ground to cover...
-No torque below 4K? Normal, a Toyota Corolla has more grunt.
-Above 4K, hold on, as this is where the fun begins
-Timing? Ignition timing is non-adjustable
-Burbles on coast down-I'd be looking for exhaust leaks with a smoke tester. Some "burbling is normal.
-Idle quality; oh, where to begin other than a compression and leak down test
-Erratic idle-> IAC motor, ignition wires, injectors
I am glad to hear about the no torque below 4K. That was leaning me towards an improper belt change where the cams were close but not dialed in. I guess I have gotten used to the variable timing (vanos) in modern cars and forgot how old school felt. Shift at 8K and it never gets below 4k.

As I said in a previous thread. I do have some exhaust issues that I am going to sort for good when I replace the CATS. I have some leaking post cat.

IAC and injectors are easy enough to play with. Compression/LD was good when I bought the car. At least that was what i was told by the mechanic I hired.

I am thinking electrical. When the car was having some top work completed prior to me getting it shipped, an oil leak around the filter threw oil all over the motor. They had to replace something around the oil filter housing and "clean" the entire bay. I think this is what caused my my missfire issues early on. Maybe I need to go through the connectors again.

Thanks for the replies. I really appreciate the help. I wish you guys were closer.

ernest
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post #8 of 29 Old 05-04-2015, 08:30 AM
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To answer your question above - you could verify timing with the engine in but it would be crude and you could only see if the factory marks line up. However, I've done testing and found a 7 degree swing for lining up the marks (one side of the mark to the other). Again, based on intermittent issues - I doubt it's timing.

You say "good compression and LD" - that is very subjective depending on who is evaluating the results and the results can vary based on how the test was done. If you want to do these tests, I can help you but the LD is not the easiest to do in the car. It's doable but a bit of a PITA. If you want to try, you can borrow my tools.
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post #9 of 29 Old 05-04-2015, 08:55 AM
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Intake manifold bolts loose or gasket disintegrating? Light torque on bolts often means they vibrate loose. My techs torque mine at every annual.

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post #10 of 29 Old 05-04-2015, 12:30 PM Thread Starter
 
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Originally Posted by dave rocks View Post
To answer your question above - you could verify timing with the engine in but it would be crude and you could only see if the factory marks line up. However, I've done testing and found a 7 degree swing for lining up the marks (one side of the mark to the other). Again, based on intermittent issues - I doubt it's timing.

You say "good compression and LD" - that is very subjective depending on who is evaluating the results and the results can vary based on how the test was done. If you want to do these tests, I can help you but the LD is not the easiest to do in the car. It's doable but a bit of a PITA. If you want to try, you can borrow my tools.
Thanks for offer. I am going to keep checking the easy stuff before I go into the LD. I should be able to see things better when I drop the exhaust to replace the cats in the next few weeks. Vaccuum lines, connections, etc.

Little by little it is getting sorted.
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post #11 of 29 Old 05-04-2015, 01:54 PM
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Do you have a good OBD2 code reader that can give live data? If so, check the MAF value, O2 sensor values, short term/long term fuel trims and injection timing values as well. If you can share that stuff with us, we can help you with more calculated answers. Otherwise it's a bunch of guessing, which isn't my favorite way to pass time or fix cars.


I agree with Taz though, just off the cuff. Exhaust leaks or intake plenum coupling boots causing vacuum leaks are very likely causes. What did the plugs and O2 sensors look like? Discolored, sooty?



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post #12 of 29 Old 05-05-2015, 07:55 AM Thread Starter
 
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Do you have a good OBD2 code reader that can give live data? If so, check the MAF value, O2 sensor values, short term/long term fuel trims and injection timing values as well. If you can share that stuff with us, we can help you with more calculated answers. Otherwise it's a bunch of guessing, which my favorite way to pass time or fix cars.


I agree with Taz though, just off the cuff. Exhaust leaks or intake plenum coupling boots causing vacuum leaks are very likely causes. What did the plugs and O2 sensors look like? Discolored, sooty?
Yes, i have been checking live data. I need to figure out how to send it as a file. I haven't run MAF value or injection timing. I will add those.

B1S1 - runs from .04V-.7v
B2S1 - same as B1
B1S2 - .075- .110 mean .12v
B2S2 - .025-.055 mean .044v
STFT B1 - .0-.8 mean .2%
STFT B2 - -1.6%-1.6% mean .5%
LTFT B1 - 1.6%
LTFT B2 3.9%

I would think my post cat sensors should be a little more stable, and perhaps the cats are bad. Hope to fix that soon.

Plugs and O2 sensors looked good. Car really runs good. Just a little idle issue. I am thinking leak.
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post #13 of 29 Old 05-05-2015, 08:58 AM
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Definitely a tad of funkiness on Bank 2 (5-8). Fix your exhaust leaks, reset the adaptive values and then look at LTFT. Out of curiosity only, what type of code reader/software are you running?

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post #14 of 29 Old 05-05-2015, 09:38 AM
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Yea, you need to focus on taking care of your leaks. The ECU is trying hard to sort out the mixture but just can't quite get it. The Bank 2 readings are far enough out of spec to be a problem. Have you checked the operation of the exhaust bypass valve? Are you certain it's opening up when it is supposed to? Some of the most common issues I've come across on 355's with cat efficiency errors are an improperly operating by pass valve or dead catalysts.



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post #15 of 29 Old 05-05-2015, 10:25 AM Thread Starter
 
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Thanks guys. I am using a Kiwi bluetooth unit with Dash Command app.

So, I am looking for reasons that bank 2 is lean, correct? Unmetered air. Maybe I have an intake plenum/vaccuum leak on bank 2? That could cause an erratic idle, possibly intermittent. Could be as simple as a bad rubber hose. I need to brush up on the diagrams for rubber lines. That along with exhaust leaks and new cats.

I have had the by pass valve off, and it seems to be functioning. It sounds like it opens around 3-4K rpms, under throttle. I have moved it by hand while the car was running and heard the sound change, so I think I know what i am listening for. But, this is my first Fcar owned or driven, so go easy on me.
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post #16 of 29 Old 05-05-2015, 10:28 AM
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Ernest- Opening schedule on the F355 varies depending on which gear you are in, apparently to get by the Euro noise test.

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post #17 of 29 Old 05-05-2015, 05:53 PM Thread Starter
 
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Curious how it knows what gear I am in? 6 spd.
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post #18 of 29 Old 05-05-2015, 07:40 PM
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Ernest- It only has to know whether you are in 3rd or not, so some kind of microswitch, I guess. Seems like it was 3000 rpm and WOT in all the gears but 3rd, where it was 4000 rpm. Forget where I found that. 5.2 US F355s have a temperature sensor that tells the bypass when to open.

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post #19 of 29 Old 05-06-2015, 12:06 AM
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5.2 US F355s have a temperature sensor that tells the bypass when to open.
Yes, thermocouple downstream bypass valve.
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post #20 of 29 Old 05-06-2015, 03:22 AM
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Curious how it knows what gear I am in? 6 spd.

Probably more likely by knowing the signals from the RPM sensor and the Speedo sensor.

If you are going to tell someone how to remove a bolt you should at least know which way to turn the wrench.
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