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Discussion Starter · #21 ·
I have spent a bit of time contemplating what course to follow. One specialist suggested some actions based on a "lean burn" hypothesis, where the motor runs one or more cylinders on a lean mixture (for some reasons). This is somewhat in line with the initial thinking of the local OPC. The issue with this is unfortunately that the specialist didn't indicate any specific actions without having my car in store.
I have landed on the following: The probability of the injectors being "off" is low since I have no error codes. This leads me to conclude that I have carbon build-up on the inlet valves and the inlet plenum. This can be manually fixed, and several recent Youtube videos demonstrate how.
The logical reasoning is:
With carbon build-up on the inlet side, the diameter of the plenum itself reduce which leads to a drop in air pressure (and air density) which in turn will influence the air flow to the cylinder itself, or at least produce a difference between cylinder banks. This could lead to a lean mix. I am pretty sure that the air presure sensor/air temp sensor cannot capture this since they are mounted in the wrong place in the inlet body.
I will report back any findings.
 

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Discussion Starter · #22 ·
I have now been fighting with the engine bay of the Cayman for two days (first time effort), and have at last been able to remove both the intake plenum and the two intake runners, which allows me to gain access to the inlet valves - both sides.
The OPC was reporting a delta in the exhaust values from the two cylinder banks (I do not know which bank produced the "off" values) and based on my preliminary findings, I observe a definite carbon build-up on the back side of the valves on the right-hand side and almost none on the left-hand side. I have no idea why, but really pleased to find it like this. I am pretty sure it will influence the running characteristics of the car. I will post more when I get better pics. Will spend a couple of days cleaning as I need to get access to the alternator pulley in order to turn the enging manually so that the valves close prior to cleaning, and this has to be done through the torpedo wall behind the seats.
 

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Discussion Starter · #25 ·
Finished cleaning. What a f..... job. Glad I had a vacum pump to get the dissolved carbon out. Also, having both an inlet valve- and brake cleaner fluid was nice. The latter dissolved the carbon "butter" while the former softened the hard carbon into a soft "buttery" sludge. Removing the engine parts was not that hard; making a "pattern" so that it is possible to mount again is key (to me it was at least), but the mantling was a bit of a pain. Getting the intake plenum back together with the intake runners, oh!
This is the best sequence:
1). Do the left intake runner first ( behind the driver). Tighten the bolts front to back 30nm torque.
2). Do the intake plenum, in a back to front movement (throttle gasket first).
3). Centre the plenum gasket (left one only) and the bracket, and fasten the one bolt.
4). Fix the left hand side electrical wiring, one vacum line behind the plenum and the oil separation tube.
5). Position the right hand plenum gasket and bracket.
6). Position the right intake runner, incl screws, but do not tighten yet.
7). Fix gasket and bracket with one bolt. Then tighten the intake runner bolts, front to rear 30nm.
8). Fix all remaining electronics (vacum lines, temp sensor left hand side only and pressure sensor (top of intake plenum) and the sound imposer tube.

Will test the car later this week.
The cleaned valves in pics.
 

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Well done, Jarl-Inge! Looks like a real dog of a job... Nice results, though - I hope that this will solve your (and then possibly my) issues. One thing I found interesting is that the buildup doesn't seem too excessive compared to, for instance, the picture below. Granted, it's a M96 engine from a 996, but should be representative. The walls are covered but the valves look almost squeaky clean, big difference to your engine. This engine ran rough but did also throw a number of codes so not 100% comparable.

Looking forward to hearing the result of your tests!

Liquid Fluid Snout Macro photography Metal
 

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Discussion Starter · #29 ·
Good news! Have tested the car, and I have been given a new car again. It is just beyond belief. No hesitations anywhere to be found in the rev range, smoother down shifts (this was a big surprise) and 5-10 more horsepower (feels like it anyway, especially down low). I am just so happy. This was always a kind of wildcard job, with no guarantee of any fix - but when the limited? build up of carbon I had made the engine run so poorly, then to all of you with same type of issues and having done the initial steps I did (or similar), it is definately something you should consider.
 

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Good to hear. So how many hours do you think it would take to do this for a first-timer, given the instructions/lessons learned from above?

I experience hesitation when the car is cold, but seems to be fine once warmed up. New plugs for 80K maintenance didn't affect it, so I'm thinking an intake clean is needed.

How many miles did you have on your CGTS?

This is one of the downsides of DFI. Fuel detergents don't do much to help prevent this buildup.
 

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Discussion Starter · #31 ·
I agree; even though I think the 9A1 engine is definately amongst the worse DFI engines affected due to the positioning of the injector, it doesn't do much for the intake chamber and the valve seating. I will probably consider a catch can having seen my engine up close.
My car has 19' km (12' miles).
You need to set aside about 3 days (as a first timer), and browse Youtube for good examples (have a look at Jeff Richardson and his white Boxster S; gained a lot of insights from him). Have a good look at the tools required, thrx pipes, general pipe set, triple square pipe for the alternator pulley, tools to scrape the carbon loose, vacuum pump++. I bought a borescope to make sure I was able to fix the valves in the top-dead position (i.e. closed). This is vital as you do not want to experience hydro-lock, but still made me nervous when starting the engine. Apart from that, just think logically and do a pre-dismantling video so that you know which wire goes where.
 

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Discussion Starter · #32 ·
Sorry, I skipped NOT with regards to the 9A1 engine. Not amongst the worst affected DFI engines.
 

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Thanks, I appreciate you sharing your experience. Mine is 103K km so I'm guessing it's past due for some cleaning. Also, after doing some homework I realize that my previous experience with the M96 engine does not apply at all since it is port injected. You learn something every day...

What is the vaccuum pump your refering to? And what kind of chemicals did you use?
 

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Discussion Starter · #34 ·
Thanks, I appreciate you sharing your experience. Mine is 103K km so I'm guessing it's past due for some cleaning. Also, after doing some homework I realize that my previous experience with the M96 engine does not apply at all since it is port injected. You learn something every day...

What is the vaccuum pump your refering to? And what kind of chemicals did you use?
The vacum pump is just a simple pump for extracting the carbon liquid once it has been liquified by the intake cleaner. You can buy it at Biltema (Sugepumpe for kjøretøyvæsker).
The chems used: Intake cleaner CRC and ordinary brake cleaner (Biltema).
 

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Attached is a post from a guy who had done a walnut shell blasting job. The intakes looked brand new afterward. He had designed and 3D-printed a vacuum adapter to keep the shells from flying everywhere. He said he'd send the stl files upon request.

 
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