13.5 AFR on 14b @ 13psi??

[boostforfun]

Just did some exhaust work on my friends car, then put wideband on, its reading 13.5 at 13psi pull in third.

The car is a bone stock 90 FWD except K&N filter, 7cm exhaust housing on 14b, evoIII o2 housing, 3" turboback exhaust with dynomax muffler.

The car had no resonator, and was creeping to 16-17 psi, but was really droney, so we put a 30" glasspack in it to help with drone. Now it only spikes to 13psi.

However, after the glasspack install we put in a AEM wideband, and discovered that it is reading 13.5 AFR at 13psi on the top end.

I told him to do no more pulls until we can get this sorted out. I am taking my logger over this weekend to look at it.

Any initial ideas on why so lean? It must be fuel delivery. I am going to recommend to him a fuel filter change and rewire the pump. But still... that seems REALLY lean for that amount of boost, even with the 7cm ported housing and ported E3 o2.

Another thing I remembered; I guess it has the lower honeycomb removed from the MAF

 

[Ghost1984]

I'm not an expert but assuming with all the exhaust mods you have it might be running a little lean because more air is being forced in and only have a stock fuel system with no tuning device might make it run a little lean, but I'm not sure since I think the stock fuel system can handle around 15psi.

 

[boostforfun]

Yeah, it confuses me because I had my car (90 AWD) with 3" exhaust, E316g, stock computer, injectors, and pump, and the same wideband. It was running 12.3:1 at 16psi on the e316g.

Im starting to suspect a pre-turbo exhaust leak. I will put logger on it to monitor knock.

Any other ideas?

 

[SpawnedX]

Boost leak.

 

[boostforfun]

Maybe... but my brain is having a tough time figuring out how air leaving under pressure would create a lean condition under load. Seems like that would make it rich.

I understand how a vacuum leak at idle might make it register lean.

I'm probably not understanding right.

 

[Ghost1984]

From what I understand a boost leak will cause the car to run rich.

 

[DSMDirkah]

^^^x2

The MAF reads the air entering the engine.. The air leaks out before combustion.. The ECU still adjusted for that missing air.

You are on the right path with changing the filter out and fuel pump. These cars are getting older now..

 

[TurboAnything]

How is your intake tube? a leak after the MAF would lean you out.

 

[Absit]

What are your IDCs looking like? Fuel pressure?

 

[williillii]

Im gonna guess clogged fuel filter, then post maf/pre turbo leaks, then bad o2 sensor in that order. Its really actually HARD to make these cars run lean in a stockish setup.

 

[boostforfun]

going up on Sunday to iron this out... Starting to think it is the sensor, as it is progressively getting more wacky. Its all over now, hanging around 17.ish when cruising, taking forever to warm up and work, and giving odd readings.

Going to put logger on it anyways and see what is going on, then prob get new sensor.

 

[williillii]

Take it out of the exhaust and wrap it in a rag thats saturated in gas...that will tell you if its able to read full rich.

 

[DSMDirkah]

going up on Sunday to iron this out... Starting to think it is the sensor, as it is progressively getting more wacky. Its all over now, hanging around 17.ish when cruising, taking forever to warm up and work, and giving odd readings.

Going to put logger on it anyways and see what is going on, then prob get new sensor.

The way I test wideband sensors (that is what you are talking about right?) is to hold a lighter up to them while they are on. It should read full rich. This way is much safer.

The regular narrowband o2 sensor has nothing to do with WOT operation of the car as it is in open loop.

 

[boostforfun]

The way I test wideband sensors (that is what you are talking about right?) is to hold a lighter up to them while they are on. It should read full rich. This way is much safer.

The regular narrowband o2 sensor has nothing to do with WOT operation of the car as it is in open loop.

Right, i was talking about the wideband. I am suspecting that the car may not be running all that lean, but that the sensor is going bad.

I will test the sensor when I get there.

 

[DSMDirkah]

Another thing that will throw everything off is if there are any exhaust leaks. This will throw the sensor way off and can be a pain. You will see it more in idle and cruise loads where the sensor will peg lean just because there are EL's and outside air is entering the exhaust stream.