G.I.G.

I've heard about fuel trim levels here a lot, and I'm wondering what number or what range is ideal for our cars, specifically .1's. I have an iCarsoft that can provide some live data, and if that doesn't work I can try to track down a Durametric, but I don't even know what I'd be looking for.

Another question I've had when this subject comes up is what do you do if your fuel trim level is off in one or more cylinders? Is the remedy always to replace the fuel injector, or is there anything else that can be done to improve the fuel trim without replacing the injector(s)?

silver_tt

Tony is right about everything in this video except fenster means window in German, not glass.

silver_tt

And before you smoke test the engine I would just measure the vacuum with a manometer because it takes less than 30 seconds to do. It will let you know if your AOS needs to be replaced, which is a common problem.

DFI engines will run significantly higher vacuum so it will differ between a 997.1 (~4-6" H20) and 997.2 (~15" H20).

G.I.G.

Thanks, that was an informative video. If I understood the overarching message, it was not to worry yourself about short term fuel trim values, and to look/diagnose using the long term values. So if the RKAT values are within 3% +/- that you should be good, and if they exceed 6% +/- they're not so good and it will most likely trigger a CEL. So I'm left with the same question: if you have no indication that your fuel trims are outside the margins of where they should be, and you have no CEL, why would you check fuel trim levels at all unless you suspect a problem? I've had the same question regarding cam shaft deviation and why anyone would replace properly operating chain tensioners if you don't hear any paddle slap at startup and have no other indication that the tensioners are failing. My Indy who knows Porsche's extremely well (worked for PCNA, then the local Porsche dealership, then to the Indy) said that there is no need to proactively change fuel injectors nor chain tensioners on these cars if there is no indication of a problem. I feel like those of us who frequent Rennlist sometimes have solutions looking for problems.

Charles Navarro

By the time the fuel trims are so far off that you throw a CEL, you've likely already caused damage to the engine. It doesn't take much effort to look at those values if you own a Durametric.

G.I.G.

OK, good to know. So if I understand that video correctly, the RKAT value is what you should be looking at, and you don't want them to exceed +/- 3%? What would require corrective action, in your opinion, and what would the corrective action be (injector replacement, etc.)?

silver_tt

Agree. Tony also mentions this in the video. Talking a port injected 2000-2008: the RKAT adjusts to +/-6% before a CEL is thrown at 6. But anything above +/- 3% is cause for concern and won't CEL even though it could be causing damage. If you do oil analysis this should show up as higher fuel dilution and port injected cars generally should not be running high levels of fuel dilution at least compared to DFI engines where you can easily see over 2% on some engines in some circumstances.

For timing chains and tensioners you can measure in software to have a good indication of when it needs to be replaced. This hits close to home for me because I almost destroyed an engine due to timing chain "stretch" (the tensioner was extended so far it was literally about to come out of the housing).

Last thing I will say is that a "good" oil like Driven DI40 holds less fuel in suspension than other oils. It will also prevent timing chain stretch, which is of particular concern on DFI engines because of soot, for several reasons. Also it is a good idea to only run Top Tier gas and use a fuel additive with PEA (Techron, Driven Injector Defender, etc) on the last tank of gas you burn just before your oil change.

Charles Navarro

Checking the crankcase vacuum with a manometer to verify you have 4-6" of h2o would be the first thing I would do since it's so easy to do followed by smoke testing the intake. If you have any exhaust leaks, however unlikely, I'd correct those as well. Most of the fuel trim related issues we see come from vacuum leaks, oil fill tube and aos vent tubes being the likely culprits.

CarreraSFan

Experienced bore score on my 2005 997S at just over 46000 miles Car was located in Missouri (cold weather). Used for weekend driving and HPDE. Stock except for Fabspeed intake and complete exhaust and tune.

silver_tt

I am sorry to hear that. Which cylinders were scored? Any other details or pictures how bad? Do you plan to rebuild? I know a very good Porsche indy in STL if you need it, done a lot of major work on my cars.

CarreraSFan

Actually all cylinders showed some evidence of bore score when the motor was torn down. I received the car back earlier this year after having Flat Six Innovations (Jake and company) build it into a 4.0 with a few special pieces. Still being broken in but it is incredible.

silver_tt

That's a great outcome and prudent decision. Flat 6 is a premium product but let's just be honest, you get what you pay for; especially when it comes to engine rebuilds. There aren't even a handful of people I would trust to do that work but Jake no question would make the list. I was just watching Hartech's TikTok a few days ago and Lee was honing out steel liners before installing closed deck Nikasil cylinders. That is just fantastic work on Hartech's part so kudos to them. If my wife was still in London and I lived there I would have Hartech do it. But that person that owned the engine and took a swing and a miss on their first rebuild attempt with whoever decided to install steel liners is lucky they didn't ruin their block. And that someone exists with the expertise to hone it out and do it right. There are many ways to do this wrong. If you look at the Hartech vs Flat 6 approach they are nearly identical from what I can tell. Anyway, strong work.

Once it's broken in take it to Ozark International and then please send me pictures

This can happen to these Lokasil/Alusil cylinders at any mileage. It has been 10+ years ago but I owned a stock 2002 911 C4S for many years in STL that I used as a daily driver and track car at Gateway International and other tracks. Back then the big scare was IMS not bore scoring. When I sold the car to move to a 2002 911 TT I don't know that it didn't have bore scoring (I never thought or knew at that time to check) but if it was the case there were no signs of it. It never burned a ton of oil, tail pipes looked fine, etc, etc. Would never know for sure though because it's gone and it would need to be scoped.

CarreraSFan

I totally agree that there are a hand full of people in the world that I would trust to rebuild these motors and none of them are what I would consider as inexpensive. As you say, you get what you pay for. Locally I did check with Reid Vann to see how they compared with FSI but they told me straight up they could not do the work that Jake was going to do for the quoted price. Since I had no intention of selling the car, cost became secondary to performance and I haven't looked back. I too track at Gateway and I'm looking forward to tracking at the Ozark track. It does appears to be quite technical. Appreciate all the comments. Thanks.

Steveyruss

Lots of talk in this thread about the cooling system and lubricant that can contribute towards bore scoring. Not much said so far on fuelling. I think ensuring that the injectors atomise the fuel properly could well be another factor in this otherwise it could mess with the lubricant in the cylinder. Personally, I've just had my injectors cleaned after an engine rebuild and as well as overhauled the cooling system (new low temp senor, new coolant pipes including crossovers, new water pump ect) I've changed my oil type. Likely, it's multiple systems involved here and you need to make sure the systems are all running to their optimum. Personally, I'm making sure I'm on top of it all.

silver_tt

I would never clean injectors after a rebuild and would only replace them. Seen too many cleaned injector stories gone bad only to trash the engine all over again. You are absolutely right that if the injector isn't spraying properly and the fuel doesn't atomize it can fuel dilute the oil or worse cause it to wash off the cylinder walls.