billzorn

my 2008 997.1 cab has 84K and is running well, no codes thrown, no misfires. but the plugs have never been changed that i know of. i'm considering replacing the fuel injectors to lower bore scoring risk, and wonder if lowering the engine for that makes it easier to replace the plugs?

jchapura

C2S Coupe 997.1
I did lower my engine about 40mm when changing my fuel injectors. Apparently, there's another trick that suggests removing the electrical connection to the coils to allow more free movement of the cable bundles that are above the fuel rails.

Regarding the spark plug change, which I did during a separate maintenance event, I did those without lowering the engine and while the car was on my QuickJacks.

Both jobs are a tight squeeze for a subset of some of the items; small hands are a distinct advantage.

JAGMAN1

I’ve been doing the occasional oil analysis to look for fuel in the engine oil. I use that to predict whether the injectors need changing. YMMV…

billzorn

doesn't that tell you you should have changed them before the metals showed up in the analysis? i'm not sure mine need changing after more research, i don't have direct injection. it would be nice to have full data on which cars get scored.

jchapura

There's a consensus value for how much fuel in the oil is too much, for DFI and port injected engines.

​​​​​ What is your fuel dilution/contamination value and was it assessed with a Speediagnostix-like test (GC rather than flashpoint) for fuel percentage/contamination?

billzorn

just got a kit, haven't tested yet. i guess my point is that analysis can't tell you when it's time to change injectors, it can only tell you they've failed in the past and that failure has caused damage. there's a case for preemptive replacement with normal analysis in cars at high risk, i'd think.

jchapura

I wouldn't agree with your damage statement only because you might catch the injector issue early enough before bore scoring occurred.
I would agree with preemptive replacement as is case with other components like the water pump, battery, serpentine belt, etc.
Most agree that much of the benefit of used oil analysis comes from the trend analysis of the multiple results over time.

billzorn

perhaps i don't understand what these tests show. there is fuel dilution and contamination with increasing values prior to scoring of the cylinder wall? i thought they were a sign it had started. i wonder what causes this without the scoring?

Wayne Smith

Fuel dilution is to a large part based on trip length and ambient temperature. Short trips while running rich with clearances not to temperature push gas into the crankcase. If you don't get the oil hot the fuel doesn't vaporize and escape.

On a 997.1 follow proper warm up procedure (drive off immediately after starting but keep the revs below 3000 and keep the throttle soft and avoid bogging) and change the oil every 3000 to 5000 miles.

Fuel injectors causing bore score is for the 997.2 with direct fuel injection. This is only if the pattern gets screwed up due to dirt. Injector cleaner with PEA helps. I don't see the advantage of changing the fuel injectors in a 997.1.

Petza914

Yes, you would see fuel dilution in the oil analysis before you'd see metal increases from it washing the cylinder walls. This is one of the reasons to do UOA, along with silicon levels from dirty air filters or vacuum leaks, metal wear, and viscosity reduction to determine what mileage interval you should be changing the oil you use for your particular engine and use case. A single analysis won't tell you much unless there is really bad news. You need 3 at the same mileage with the same oil type before you can start making decisions.