Carb tuning with O2 sensor

[Ted Guldemond]

Does anybody out there have any experience with carb tuning ie: jetting using one of the after market O2 sensors (air/fuel ratio monitor). Specifically where can you install the O2 sensor on a merc. exhaust manifold or riser before the water dumps in?

[txtaz]

No pro here, but why do you need an O2 sensor with a carb? The air/fuel mixture is controlled by the jet size not an injector. Do you have an ECM?
Wes

[Rootsy]

no need for an O2 sensor if you are running a carb, other than to "tune" the carburetor...

easy to do with aftermarket SS riser tubes... hard to do with stock merc exhaust...

you MAY be able to utilize the existiing threaded hole in the manifold... but the thread is going to be wrong and it is going to be deep.. the O2 sensor needs to be right in the exhaust stream too... and using the hole in the manifold will put you at the front or rear... instead of in the mixed (average) stream as in the riser...

O2 sensor really HATE being damp or wet... as in they tend to go kaput...

[Traveler]

I've been messing around with mounting a wide band on a Merc 350 mag MPI. I tapped into the elbow using the threaded hole that's already there then route the exhaust gas through a tube and back into the exhaust below the diverter valve. It seems to get a decent reading but I'm not absolutely sure of the accuracy. I've designed a spacer with a port for the sensor that will mount between the elbow and manifold but have yet to build it. The plan for next year is to remove the Merc ECM and run DFI.

[Ted Guldemond]

My goal is just for tuning to optimize jetting. My compression ratio is such that I want to make sure there are no lean spots. But come to think of it with marine gas at $ 3.50 plus, leaning out my cruisers 454's might not be a bad idea. Where is the O2 sensor located on the newer marine engines with fuel injection?

[farmer tx]

Why not install a pyrometer probe in each riser and get a dual pyrometer guage for the dash? Lean condition will be VERY evident with high exhaust temp.

[GEOO]

I run Stainless Marine Exhaust, Here's where I installed mine.

http://www.donzi.net/forums/attachment.php?attachmentid=843

[mrfixxall]

[QUOTE=Ted Guldemond]My goal is just for tuning to optimize jetting. My compression ratio is such that I want to make sure there are no lean spots. But come to think of it with marine gas at $ 3.50 plus, leaning out my cruisers 454's might not be a bad idea. Where is the O2 sensor located on the newer marine engines with fuel injection?[/QU


OTE]their rrrrrrrr none

[farmer tx]

Ck this out.http://cgi.ebay.com/ebaymotors/NEW-ISSPRO-PYROMETER-R3607-TOP-OF-THE-LINE-THE-BEST_W0QQcmdZViewItemQQcategoryZ46100QQitemZ800458 5717QQrdZ1QQsspagenameZWDVW

[Mr X]

A pyro will get you in the ball park, and ONLY at wide open throttle, but not NEARLY as close as an O2 sensor.

To jet it perfectly thru the entire throttle range you need an O2 sensor and preferably installed on both sides.

[Ted Guldemond]

Mrfixxall are you saying there are no O2 sensors on new fuel injected marine engines?

[Ranman]

Mrfixxall are you saying there are no O2 sensors on new fuel injected marine engines?

That is correct. There are no O2 sensors on the Merc fuelie motors.

[Ted Guldemond]

Forgive my ignorance but how does the processor modulate fuel dispensed from the injectors ie:pulsewidth ?

[Traveler]

I can field this one. An O2 sensor provides a modifier to the base table to add or subtract fuel when operating in closed loop mode. Without the sensor the system always runs in open loop and uses the base table.

[Ranman]

I can field this one. An O2 sensor provides a modifier to the base table to add or subtract fuel when operating in closed loop mode. Without the sensor the system always runs in open loop and uses the base table.

That's how I understand it. If changes are made to the engine to enhance breathing, etc. A new base table must be created and implemented as well for fuel management.

[mrfixxall]

merc dont run o2s yet ,, the pc stays in open loop and fuel is figured out by a cts and a map sensor..............thay are trying some new stuff out in calf i forget wht thay call it but im sure it wont be long..if your trying to install o2s you can try to tap the center oF the intake manifold...but im sure you wont get a accurate reading...

[Ted Guldemond]

Thank you for the info. I was thinking of taking a 1 or 2 inch riser extender and modifing it to allow the O2 sensor to extend into the main channel and thus be exposed to the common stream of exhaust gases for one bank of cylinders. I would only leave this on long enough for tuning. Would the readings in this scheme be useful enough to warrant the effort?

[BUIZILLA]

I'm not so sure an o2 is gonna be very beneficial in a marine environment, especially non closed cooling, where the block temp stays so low.. Closed cooling at 190* + I can see it, but at 145* water temp, it would seem to be a wasted effort. Most EFI systems don't go into closed loop until 145-155* anyways.

JH

[Ted Guldemond]

How about jetting the old fashioned way, plug color? Only I'm not thrilled about an abrupt shutdown at higher speeds or WOT.

[mrfixxall]

also pyrometer isnt gonna work either because of water cooled exhaust temps to iffy hot cold hot cold,,,,, if you want to spend some big bucks on egt system to see what each cylinder is doing ....we use a auto meter set up that will measure temps from idle to wot ..