philip77o

Hi, this winter I did the venturi delete, injector seals replacement, oil pressure sender replacement, vacuum lines replacement. I removed the useless narrowband and installed an autometer wideband. Today I started the car for the first time since November with fresh 91 fuel and 20w50 oil. I started the car, the wideband bounced between 8-9 for 4-5 seconds which I believe is the sensor that gets heated. And then it went up between 14,6:1 and 15:1 on idle 900 rpm and vacuum/boost gauge at -15psi. I let the engine run to normal operating temperature but I kept getting 14.6 AFR

I didnt want to go take a ride to be sure I make no damage... Idle should be at 12:1 or 13:1 if I'm not mistaking ?

fejjj

Idle should be 14.7

Yours looks to be spot on.

Carlsbergas

My idle ratio jumps from 14.7 to 15.0 all the time since my o2 sensor is in working in closed loop. Well thats what joshua told me. While cruising it stays at 14.7 at 17psi its about 10.8-11.4

philip77o

Alright looks like I'm good then. I'm gonna go for a test drive tomorrow. This one might sound a little stupid but which side is lean and which side is rich ?

Thank you !

Tom M'Guinn

Right, for idle and cruising, it should target 14.7. At wide open throttle, you want to see somewhere between 11.5:1 and 12.5:1 depending on fuel quality, ignition timing, boost levels, etc. Whatever you target, it will bounce around a little above and below the target, which is perfectly normal.

You should re-install the narrow band sensor so the DME can adjust the mixture on the fly to keep it close to 14.7 unless you are using the wideband as a simulated narrow band for the DME. Otherwise, you will run directly off the maps with no closed-loop adjustments, which only results in unnecessarily high emissions and poor gas mileage (and potentially fouled plugs, burned cats, etc.). If you have a big cam or other reason to target a richer mixture, then you are still better off running the motor in closed loop but with a richer target.

Tom M'Guinn

Lower numbers are richer, e.g., 11:1 is rich. 16:1 is lean.

Sixline

We are assuming he put a wideband in place of the factory narrowband.

If that's what you did, like Tom said, put the factory narrowband back in and weld in a separate bung for the wideband. Make sure it is roughly 3 feet after the turbo and pointed down so water doesn't collect on the tip. From what I have read, putting a wideband in the factory narrowband location will drastically shorten the life of the sensor as it is just too hot.

philip77o

I installed the wideband's o2 sensor somewhere near the starter area. About 36" from downpipe. The factory o2 sensor is still in place. Is that what you mean ? I also welded the o2 bung 10oclock to keep the sensor away from moisture.

Sixline

Yup that's what I mean.

Did you get a chance to make a run under boost?

Also, someone correct me if I am wrong, the car should idle richer on cold start up until the DME senses a certain temperature has been reached.

Tom M'Guinn

These two statements seems to conflict? At any rate, yes, it can't go into closed loop immediately, as it needs the O2 sensor to heat up first. That usually takes 10-20 seconds I'd guestimate. As soon as the O2 sensor is warm on my car, it starts targeting 14.7:1.

Sixline

My guess is he had a narrowband AFR gauge.

Tom M'Guinn

Ah, perhaps....

philip77o

Yeah I meant I removed the narrowband gauge and installed a wideband. I had exactly this one.
I have not had the change to test the car yet there's too much puddle and pothole on the road

Cyril

From John @ Vitesse Racing

The following AFRs should be observed once the engine is fully warmed up.

Idle: 14-15:1 AFRs
Part Throttle, light cruise: 13.5-14:1 AFRs.
Under load/boost 1-7psi: 12-12.5:1 AFRs.
Boost 7+ psi: 11.5-11.8:1 AFRs

The above is based on 100s of 951s we prepared for street/track.

(note: the car will run in the 11-12:1 afr when warming up . )

Tom M'Guinn

At idle and cruise, the O2 feedback system will always try to bring you back to 14.7 (if working) so the actual maps would need to be very rich to get consistently into the mid to high 13's while cruising at normal freeway speeds. On some maps John disables the closed loop system, so I wonder if the numbers listed above were for that kind of map, with his chip board, his injectors, etc? Running significantly richer just creates more smog, is harder on the cat, get worst gas mileage, etc... Absent drivability issues from performance parts, there's really nothing to gain going richer than 14.7 for highway cruising (maybe as part of temp management on a track) on a street car. Maybe John will chip in....