F355 Head Scratcher

This is the exhaust gasket 2 inches from the Front O2 sensor on bank 1.
No amount of tightening on the bolts is going to seal it air tight.
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Mystery is solved, so I am done with this thread.

LTFT bank 1 at +12%: It's because the two air leaks into the exhaust near the O2 sensor leading the sensor to see a lean condition, and the ECU is trying to enrich the injectors on that bank.
LTFT bank 2 at -10%: It's because the broken knock sensor on bank 1 giving false signals to the ECU leading it to retard timing, making incomplete combustion, giving rise to a rich condition read by the O2 sensor, which tells the ECU to lean out the injectors on bank 2.

The under-load hesitation is the false retardation of spark on bank 2 leading to misfiring and incomplete combustion on bank 2.
No CEL is set by the ECU because ... it is causing the spark retardation on purpose, so no CEL is set.
The rear O2 sensor signal is not steady is "probably" the high flow cat converters going bad. I have a set of stock converter that will get installed with the engine out to verify this. There really is nothing else that can cause the varying rich-lean signal on the rear O2 sensors.

 

How long have you had the car? It sounds like little proactive maintenance was performed, simple things like replace old hoses or old sensors for good measure etc. Sounds like your inspecting it well for things to correct and once done it should run like a top again. Well done!

 

Eric, it's not my car. Period.

 

I'm not so sure those arguments are correct. The first one is plausible, but depends on how bad the leak is. It assumes that by making the mixture richer the reduction of O2 in the combustion products is balance by the additional O2 in the air leaking into the exhaust, thus the O2 sensor see the correct amount of O2. I think that could happen. It's the negative LTFT that I question more. Incomplete combustion would result in excess O2 in the combustion products and that should also trigger a lean condition and LTFT should go positive for that side as well. The O2 sensors don't measure how much fuel is in the exhaust, they only measure O2. A lean condition yields to much O2, a rich condition yields too little O2. Incomplete combustion yields too much O2.

I recall a while back you had a car with a misfire, resulting in unburnt fuel in the exhaust (incomplete combustion). One of the symptoms you reported was that LTFT kept increasing positive. Different cause but same scenario.

 

Looks like the piece that broke on my F355 last year. I think it was either not available or part of a larger expensive set, so I just bent a straight piece of hose. Miro came up with a ready-bent solution.

( EDIT: just found the thread: https://www.ferrarichat.com/forum/threads/fuel-leakage-disappears.596718/ )

 

Time to salvage that car. Ketel is going to have to work hard to pay this bill. Are you at 5 figures yet?

 

I have a ready bent solution. I don't remember where I got it. I think it was a BMW fuel vent hose from an E30 M3.

Got it.
https://www.pelicanparts.com/catalog/SuperCat/0543/BMW_0543_FULFUL_pg1.htm#item2

Part #: 13-53-1-726-960-M9

 

I was just going to ask if this was Ketel's car. Sounds like Mitchell with finally have that car sorted out. Just in time for a Fall Stooge!!

 

It will be perfect when mitchel finishes with it.

 

And the thing put up one more fight before giving in.

The hole where the knock sensor bank2 screws in inhaled its thread forcing me to fix it with a Timesert.
The after market cheapy MAF sensor died right out of the box and refused to idle.
The factory heat exchanger boot clamp ran out of travel and coolant leaked out under pressure. Add 2 hours to the battle.
The car started up ... on one bank. The whole day to trace the problem down to a broken wiring splice inside the engine wiring harness. Fun with the engine in.

I will light a match under this thing if it gives me anymore crap.

 

Add to that hot and smoky Bay Area weather. Good thing it’s not your car. It would be gone.....

 

I,know you found the problems Mitchell but what’s you take on a slight vacuumed leak at a pressure regulator, would that not allow less fuel into the rail resulting in a lean condition??
When I checked my stock fuel pressure reg there was only about 5psi from all or nothing so not much variance I thought.

 

Maybe I got that backwards Now that I think about it.

 

Slight vacuum leak at the pressure regulator would close the diaphragm a little more, resulting in more restriction of flow, and create more fuel pressure at the rail, for a slightly richer condition.

 

I was not sure I thought maybe from my testing the vacuum allowed more return to tank flow
But thanks
Ps
Engine still out, will have to delay to winter, work getting in way of fun, again ha ha

 

My test of the intake manifolds is to spray brake clean at their bases. If there is at change in idle, there's an air leak - and I had one but it told me where it was and a friend made a nice, single, gasket for the 2 poet manifold whereas the factory has a gasket for each port in 8.