| Author |
Message |
DAVE SHEARS (Daveshears)
New member
Username: Daveshears
Post Number: 28
Registered: 3-2001
| | Posted on Wednesday, July 24, 2002 - 11:25 pm: | |
I live in California with strict smog rules and I own a 84 308 QV. My car passes smog perfectly but I have the exact burbble sound that Bill has mentioned. The car runs perfect other than that. |
Dr Tommy Cosgrove (Vwalfa4re)
Junior Member
Username: Vwalfa4re
Post Number: 194
Registered: 5-2001
| | Posted on Tuesday, July 23, 2002 - 8:52 pm: | |
I have a Tubi and a test pipe. I had the tubi for about 6 months before I put the test pipe in and during that time I never noticed the burble sound. Once the cats were off I heard it all the time. My O2 sensor is not connected either. When I drive it hard (especially on the track) I will shoot out a pretty impressive fireball from the exhaust pipes. Not all the time, though. The car runs great and the fireball thing has been going on for about 4 years now. I have never worried about it figuring the lack of cats, disconnected O2 sensor, continuous injection system, and the occasional hard throttle was responsible. |
Paul (Pcelenta)
New member
Username: Pcelenta
Post Number: 19
Registered: 7-2002
| | Posted on Monday, July 22, 2002 - 9:33 am: | |
this may be a dumb question, but if there is significant unburnt fuel igniting in the cats and or the muffler and not in the combustion chamber where it should be... wouldn't that indicate too much fuel or a rich condition...
Have you checked all of the exhaust joints and headers for any leaks? this can cause some of the pops etc..
|
David White (Dwhite)
New member
Username: Dwhite
Post Number: 26
Registered: 7-2002
| | Posted on Monday, July 22, 2002 - 8:21 am: | |
I have a 83 QV with a tubi exhaust it always burbbles on decel. From all my expiereces w/ webers and tuning. I agree with James S. lean mixture is the usuall cuprit to exhaust burbble.
Just an FYI, my car recently went through a major service and they did not mention the burbble, nor did it ever concern me. I also had the car checked by a f-dealer before I bought it and there was no mention of this situation. I would not be overly concerned, besides if you were running rich the plugs would be smokey or black not brown. Maybe it was set to lean and the person set it back to normal. |
bill v. (Doc)
Junior Member
Username: Doc
Post Number: 61
Registered: 9-2001
| | Posted on Monday, July 22, 2002 - 6:51 am: | |
James--interesting point. In this case, the mechanic who had serviced the car before I bought it indicated that he purposefully richened the mixture for smoother performance. In any event , it is running very well and i think I'll have a Ferrari mechanic in my area test drive and listen to it just to be sure. |
James Selevan (Jselevan)
Junior Member
Username: Jselevan
Post Number: 54
Registered: 6-2002
| | Posted on Sunday, July 21, 2002 - 11:01 pm: | |
I have been following this thread with interest, and a bit of confusion. In the old days (carburation), a burbling and occasional back-fire on trailing throttle indicated a lean mixture. Furthermore, engines seemed to run better, and perhaps with improved performance when SLIGHTLY lean. The compromise, however, was that the engine, and the exhaust valves in particular operated at a higher temperature. The added fuel of a slightly rich mixture provided cooling to the exhaust valves, but did little to enhance performance.
Once catalytic converters came to be, with their high operating temperature and suceptability to unspent fuel, an exaggerated fear of rich mixtures came to be.
Anyway, Billy's first post sounded like a lean running engine. When one experiences significant concentration of fuel igniting in the catalytic converter or exhaust manifold, it is not subtle (bang and flames coming out the exhaust). Burbling is subtle. Sounds lean to me.
Jim Selevan |
Tim N (Timn88)
Intermediate Member
Username: Timn88
Post Number: 1281
Registered: 6-2001
| | Posted on Sunday, July 21, 2002 - 9:22 pm: | |
All cars make a noise when you are off the gas and the revs are coming down, dont they? Also having a 14.7:1 air fuel ratio is all well and good in a normal car, but theres more power to be had going a little richer. |
Steve Magnusson (91tr)
Member
Username: 91tr
Post Number: 866
Registered: 1-2001
| | Posted on Sunday, July 21, 2002 - 9:57 am: | |
bill v. -- I was just curious if you have an open-loop system (K) or a closed loop system (K with lambda). The closed loop system (if it was working) would actually try to uncompensate any added richness so setting things a little rich would only affect cold running (unless it's a huge added richness).
Check your Owner's Manual -- it should have a fairly decent technical description and figure of the injection system which might give you some guidance if it mentions components that are related to decelerating (high RPM, high intake vacuum) conditions (I'm 50% sure there is an added gizmo for this condition on the K and K/lambda systems). I'd recommend that you at least get one of the amazon books (either Aird or Probst) if you want to DIY on a K, K/lambda, KE system. (Greg's note implies this may vary, but) getting the tamper-proof plugs off the KE units on my TR was not easy. |
Ken Ross (Kdross)
Junior Member
Username: Kdross
Post Number: 87
Registered: 2-2002
| | Posted on Saturday, July 20, 2002 - 3:12 pm: | |
Bill:
Ferrari's tend to run on the lean side. This is why your mechanic probably adjusted your FI to run a little rich. With that said, bring your car back to the mechanic and have him return the settings to stock. When he asks why tell him "BECAUSE I DO NOT WANT THE CAR TO CATCH ON FIRE!" As Paul has already mentioned, the burbbling and popping noise that you are hearing is the sound of unburnt gas. Consider yourself lucky that your cats have not superheated and caught on fire. Cat fires are very common in Ferrari's and cause a lot of damage. Once you return the FI settings back to the factory specs, you should remove your cats.
Ken Ross
1985 308 QV GTS |
Greg Rodgers (Joechristmas)
Member
Username: Joechristmas
Post Number: 393
Registered: 3-2001
| | Posted on Saturday, July 20, 2002 - 3:03 pm: | |
The mixture is adjusted by a small screw (allen I believe) between the fuel dist. and the mass airflow meter. There should be a small rubber plug in there that needs to be removed before adjusting. This adjustment is best left to someone with a CO testing machine etc. The 85' QV has Lambda sensor. |
bill v. (Doc)
Junior Member
Username: Doc
Post Number: 58
Registered: 9-2001
| | Posted on Saturday, July 20, 2002 - 1:36 pm: | |
Steve--I don't know which injectors the car has. I just got it and i'm a complete novice--as is likely evident from my simplistic questions. Would the injector type make a difference in this regard and if so, how?
Interestingly, the more people I ask about this, even experienced mechanics, the more confused I get. It's literally a 50/50 split on opinons. The key, I would guess, is how rich the mixture was adjusted to. I did check one of my plugs ( didn't have the time to check the rest yet) and it looked perfect--cocoa brown, dry, etc. As i mentioned, performance is great, with the exhaust grumbling being the one and only symptom. I'll likely have it reset anyway, just to be sure the car is OK. Any idea how much labor would be involved in resetting the mixture to stock? |
Steve Magnusson (91tr)
Member
Username: 91tr
Post Number: 865
Registered: 1-2001
| | Posted on Saturday, July 20, 2002 - 8:57 am: | |
bill v. -- is the injection on your 308QV K-Jetronic or K-Jetronic with lambda (or something else)? |
Mitchell Minh Le (Yelcab1)
Junior Member
Username: Yelcab1
Post Number: 239
Registered: 11-2001
| | Posted on Friday, July 19, 2002 - 10:23 pm: | |
I do not know specifics about the QV system, but on a BMW and Porsche (with MFI) that I have the FI mixture is adjustable by a mechanic with CO2 and CO exhaust measurement device. This is done by adjusting the air ratio at the Air Box. The adjusting allen screw is set at the factory and normally forgotten, unless you have a specific reason to adjust it. And when you do, you really need exhaust gas analyzer to even tell which direction to go, otherwise you are just shooting blind. |
Paul Newman (Newman)
Member
Username: Newman
Post Number: 276
Registered: 12-2001
| | Posted on Friday, July 19, 2002 - 9:13 pm: | |
I dont know how you adjust an FI mixture but he is correct in saying that this will destroy the converters. Unburned fuel causes higher temps in the converters causing the catalyst to melt and plug the exhaust flow. I would be concerned. The converters also rely on the correct afr of 14.71:1 to operate correctly. Above or below that, the dont clean up the emissions like they are designed to. |
bill v. (Doc)
Junior Member
Username: Doc
Post Number: 57
Registered: 9-2001
| | Posted on Friday, July 19, 2002 - 8:43 pm: | |
I recently purchased an '85 QV and, although it runs, starts, and idles perfectly, there is a distinct burbbling sound whenever I decelerate or downshift. When i asked the mechanic who has serviced the car about it, he indicated that he had purposely adjusted the fuel mixture to run richer than stock and that that was what the sound was about. He indicated that the car runs better and stronger this way and recommended that I leave as is. Next, I asked another well-respected Ferrari mechanic about this and he thought that this should not have been done in that the richened mixture may leave unburned fuel and could cause major problems with the cat. He strongly recommended returning the setting to stock.
What are your opinions about this matter? Should I leave it this way or restore the setting to spec? In addition, how does one adjust the mixture on an injected car? Is it easy enough for a backyard mechanic to do or should it be left to Ferrari mechanics? Once again the car seems to perform fine , but for the burbble. |