Fuel Trim and oil dilution question

2004 C2 with recent rebuild (3.8 nickies, UAOS, injectors, maf, basically all components recommended by LN on a new build were replaced with new) I just received my oil analysis from speed diag after my first oil change since original break in oil using BR30, about 500 miles).I had a couple of readings that were yellow (borderline) indicating oil dilution/fuel in oil (viscosity of 8.5 and fuel dilution of 2.3). Speed diag recommended adding a injector/carb cleaner) but my injectors are new. I added the cleaner recommended to the gas anyway but I also am checking fuel trims again. Bank 1 RKAT is -0.19 % and FRA of .90 Bank 2 RKAT is -0.14% and FRA of .92 So it appears I'm running a little rich (dme taking fuel away).? I was also going to check the oxygen sensors but quite honestly I'm confused for the results I should be looking for? I will also check MAF. Questions: 1) Can someone help with the oxygen sensor readings I should be looking for before and after CAT? I have searched and read on this but i'm still not clear 2) Are there other conditions (other than dirty/clogged injectors) that could cause fuel leak? As reference, I rebuilt from bore scoring and noted when I scoped the cylinders that an injector was leaking, prior to rebuild) Speed recommended running the cleaner and then checking again at next oil change. I just want to make to try and make sure this fuel dilution isn't a result of some other issue before running the next couple thousand miles. Thanks Dan

I forgot one thing. Even though I replaced the AOS with new if failed. I replaced the AOS with the UAOS towards the end of that break in mileage. Not sure if a failed AOS could also contribute?

Looks like your RKAT ( close to idle) is OK the FRA looks to taking away a lot of injector time...( due to too rich) Check your coolant temp sensor to make sure it isn't reading cooler than what the engine really is, that will effect the fuel Trim very much.. Test your fuel pressure ... Also what injectors did you install? Part number?? What MAF Sensor did you install? Part number/brand? What tester software are you using, Durametric?? Nothing is wrong with your UAOS...

Thanks Skip. Never doubted the UAOS, but wasn't sure if the failing aos could contribute to fuel dilution some how! I will work on this list and revert. One question though regarding engine temp, do you have a recommendation on how to verify temp reading? Use a infrared temp gun? I will look back in my file to check actual part # and manufacturer of MAF and injectors. I have durametric and Launch X431. I was using my launch for this reading because it is easier to take on a drive but will double check with Durametric. I have found all readings before are consistent between the two.

The temp Sensor is Dual NTC .....meaning there is actually two NTC sensors in one body. One sensor is for the DME to see the temp and one sensor is for the dash display to see the temp. Using a simple DVOM you can back probe the sensors and they should read the same volts ( the lower the volts the hotter the temp..) Since this a new/fresh engine, you should test the "blow-by" .. I did a whole thread on how to test blow-by to determine engine health/ring seal....If the rings have not seated yet/correctly the blow-by will put more fuel into the oil... It's always worth a test to see what you got...

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A few more questions: Were the o2 sensors replaced? Brand? Have you done a smoke test and manometer test? Do you have a cold air intake or washable (oiled) air filter? Injectors were replaced, not rebuilt, correct? Also, you don't need the break-in oil in there any longer. I'd recommend switching to a conventional non-friction modified oil. What we are recommending after initial 20-30 minutes on break-in oil (cam/lifters) is this oil: https://lnengineering.com/15w-40-con...-1-gallon.html I'd stay away from synthetic for the first 3-5k miles to ensure the rings are fully seated. If you do change any components like the o2 sensors, maf, etc., you need to do a vehicle handover or system adaptation to reset the adaptation. This was supposed to be done before initial startup as well. Was this done before initial start up?

Skip, Thanks for clarifying on the temp sensor and will revert on the other points you made. Thank you! Charles, Thanks as well for taking the time to chime in. O2 sensors are new - I have to check on the brand It has been smoke tested and manometer tested (back story is the new AOS I installed failed, noticed high manometer readings during first 500 break in) and was replaced with UAOS) I have on the Fabspeed air intake currently. I'm going to switch back to the factory box but haven't done it yet Injectors were replaced with new (I have to check on manufacturer) Original break in oil has been changed (that's what I pulled the oil analysis on, BR30). I switched to one of the other Driven non synthetics that you guys were recommending at the time, HR5? I did a handover before starting the engine after rebuild. I did not do that after UAOS install. I'll start working on diagnosis as suggested and report back (when I can find time to work on it).

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HR5 is also suitable as it's a conventional non-friction modified oil. You need to get the Fabspeed air intake off there as soon as possible. It's possible if that filter was over oiled it could have fouled the MAF as well. That's a known issue. I'd recommend a 3.8 airbox and paper filter if it was my car.

Yes, having the new AOS fail ( the manometer reading should NEVER be high and can only be due to failing AOS) will cause a "lean running" which will " increase the fueling trim/injector time".. The after the UAOS was installed, the adaption should be rest. It will eventually re-adapt on it's on but will take while ( this is not ideal then dealing with fuel trims) .. Looks like the RKAT ( close to idle) has already "re-adapt"., but the FRA (which doesn't get used as much) has not yet "re-adapted". Clearing fault codes will sometimes reset fuel trims, but not always, it depends on the fault code. Fuel trims should be checked "before and after" clearing fault codes to confirm they have "re-set".. Like Charles said a "hand-over" will reset everything back to factory defaults, Fuel Trim included. Then monitor fuel trims closely to see that they STAY close to default/ideal settings. Like Charles said also, reinstalling the factory air box and MAF is a good idea to keep that from being a factor..

For questions on new sensors used: MAF - Bosch 0280218055 Oxygen Sensors - Bosch 16433 and 0258006541 (has cross reference to volvo XC 90 16541) Fuel Injectors - Bosch 0280156053 I will report back when I have time to start with some of the diagnosis suggested.