islaTurbine

What are the typical causes for elevated fuel dilution numbers in UOAs? Obviously leaky/old fuel injectors and vacuum leaks could cause it. But what other culprits could there be? Weak fuel pump? Failing AOS?

My numbers previously hovered in the high 1’s prior to installing new 996.2 injectors, and they’ve been climbing ever since that install. It now appears to be affecting the additive package in my oil so it’s time to act. The engine has been smoked multiple times with no visible leaks. New Bosch O2 sensors, new Beru plugs, new Bosch coils, new Bosch MAF.

hardtailer

First thing I would do is put those original injectors back in there and see what the subsequent UOA's tell you.

islaTurbine

Unfortubately those were tossed months ago. They appeared to be original to the car (1998/1999) and I figured they weren’t worth keeping around.

hardtailer

That's a shame.
In that case I would go back in there and remove the new injectors and test them or have them tested. Most probably they'll perfectly fine but re-doing the whole r&r of them will require you to re-visit your/the mechanic's work and that in itself will show what went wrong and is causing the fuel dilution of the oil.
Hindsight is 20/20 but for the future you could consider, also for 20y old parts
-never change a running system
-parts quality is never higher than during the actual manufacturing period of the vehicle they are used in

philbert996

Were the fuel injectors new OEM Porsche?

islaTurbine

Bosch OEM. Bought during the pandemic and I struggled to find them in stock at that time. I’m honestly suspecting the AOS at this point. I’ve been considering upgrading to Skip’s UAOS soon as my AOS is 7 years old and has 35-40k miles on it.

jdbornem

It seems like a strange suggestion to me to never replace 20 year old injectors, that largely, have been recommended here to be replaced. Plus, we're not comparing parts quality to when brand new. The comparison is between new injectors in 2022, and 20 year old injectors with many many hours and heat cycles on them. If new injectors are worse than that, then there is a significant new part production problem! It's pretty cynical to expect that all new (Porsche or OEM) parts are automatically even worse now, than the 20 year old worn parts currently on the car.

Practically, you might also double check for vacuum leaks. Do a smoke test. Replacing injectors requires reaching around the top of the engine, it could be that something was left loose, or a vacuum line broken.

Did you buy the Bosch injectors from a reputable dealer? I think I've read cases of counterfeit parts from ebay and Amazon

hardtailer

Read closely what I wrote. Both wording and meaning is different from what you took it for...

ZuffenZeus

Uhh, not sure about that statement. For example, Porsche implemented a 6305 IMS bearing after the 996 generation had ended thus unofficially admitting that it was a superior choice over the 6204 single and even the 6204 dual row. All short block replacements did not include the older bearings. I could list a bunch of other parts that were improved because of poor quality and/or performance after the manufacturing period.

Personally, I think the problem with OEM injectors is the amount of knock-offs that seem to be genuine BOSCH but end of being copies and subpar to say the least. That's why it's important to purchase replacement parts from reputable companies like LN Engineering, FCP Euro, Pelican Parts, etc. And when in doubt, purchase genuine OEM from your local Porsche parts department.

hardtailer

Comparing part number (incl. its revision) per p/n is how I mean it as well as quality in the sense of how well the original spec is met by each and every individual item of said p/n produced by the parts manufacturer.
And it's not about finding the exceptions to this statement.
The value is in taking it into consideration when replacing parts. Nothing more nothing less.

This is not contradicting what you pointed out BTW.

ZuffenZeus

I think it's important to be specific to owners especially new owners that don't have experience with the good, bad, and ugly with parts associated with these engines. For some other makes, it's a standard practice that owners should seek out NOS parts. However, that's not a good practice with these engines. Another example, Porsche recognized problems with coolant expansion tank caps. They leaked under pressure. After a few revisions, they finally got it right. But if someone were to purchase the exact caps that were sold during the manufacturing period, it would be a problem that could lead an owner in the wrong direction thinking something else is causing the leak with the cooling system. They had similar problems with earlier versions of the RMS. In 2005, Porsche moved to Polytetrafluoroethylene and that stopped the oil leaks. I think you get my point and I'm not trying to be argumentative. Just think it's a better message to tell owners to purchase parts that are proven to work and in some cases, that may mean aftermarket.

Porschetech3

You have been considering installing the UAOS for some time... JUST DO IT !! ..lol

There is no downside to installing the UAOS, in fact it should have been designed that way from Porsche...

I recall a while back you had reported that a manometer reading was nearly -9inwc on start-up that slowly went down to -5inwc after some seconds. That is a sign the AOS diaphragm has a small tear ( failing).

The possible scenario from failing AOS to fuel dilution in UOA.... .is as follows....The failing AOS will cause a lean condition while cruising which will cause the fuel trim to adapt to more injector open time to compensate ( which produces the correct mixture) , but after the trim has adapted this increased injector time is reflected also in cold starting which the increase in injector open time will cause a VERY rich mixture when cold..( like an old school choke that is over-chokeing).. this can lead to fuel dilution after a while of doing so..

islaTurbine

Yessir I’ve just been putting off the inevitable purchase for various reasons. Really I was just hoping I could make it to Black Friday for a holiday deal.


Order submitted. Thanks Skip.

Porschetech3

Got it !! Thanks !!
It will take a couple of weeks though, I am sold out at the moment...George has been very busy and his small CNC machine that usually does the UAOS's has been tied up on a large-long running job...That little machine has been so busey that he actually bought a new machine to help out on the work load...He is suppose to start on them this week and then send them to be Annodized...so will take a little time... Please be patient..

BRS-LN

Usually poor fuel injector performance, a fouled/ failing MAF, aftermarket intake or exhaust are responsible for high fuel dilution.
In the cases where these have been rules out, the driving factor is usually mechanical in nature, with combustion byproducts and raw fuel being allowed to bypass the critical seal between piston rings and cylinder walls. If the above conditions are present, they can create a lack of ring seal that can further drive the issue.