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Originally Posted by AFB24911S
I have read the Bosch book, Jim's Basement CIS Primer, and the excellent CIS Troubleshooting for Dummies thread. Here we go, the fear-inducing injection system!
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Very good!
The problem is - these sources mainly explain the function of each component, but mostly they do not cover up how they interact on particular operation conditions and how they will affect other CIS components in case of failure. This in depth understanding you only get on practising on CIS systems...
In consequence you have to take care on every single CIS component on engines like yours as they might have more than a single problem.
Of course, there's are troubleshooting tables from CIS Primer and other sources. But again - this won't show you how to proceed in detail on problems. Furthermore several issues on CIS engines overlay other issues and mimic the behaviour of non existant issues. This confuses most of people working on them and they bring in other issues to solve former issues instead of sorting out the original problems. It's a complex system at first sight... but not if you got a deeper understanding ... then it's pretty simple.
Lots of things has already been written yet by others. You first should work these suggestions before proceeding with other ones. That's also one of the main problems on solving issues on a CIS: People tend to jump between several issues and components instead of solving one problem at a time.
Quote:
Originally Posted by AFB24911S
My car:
1977 Porsche 911S Targa, original engine & stock cylinders, cam, etc., CA market, but now with an 11-blade fan and the EGR circuit cut off.
The problems:
Cold start - cranks for about 5 or 6 seconds before starting. It coughs within the first half second as if it wants to ignite right then, but then it keeps cranking until it starts.
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Takes too long to start. I suppose that the fuel pressure build up requires that time. Leads me to a bad check valve at the fuel pump. That coughing at first crank may be caused by the rest of fuel (and pressure) resides in the fuel lines and the fuel accumulator from last run.
Quote:
Originally Posted by AFB24911S
Warmup - between minute 3 and minute 15 of driving, which is also right up until about 180°F oil temp, it bogs/hesitates at low revs under load.
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Mixture and probably ignition timing incorrect. May caused by many reasons: vacuum leaks, misadjusted sensor plate height, not fitting control pressure, worn injector valves, bad fuel distributor, too low fuel system pressure, bad ignition and timing ... almost everything is in question then.
Quote:
Originally Posted by AFB24911S
Running - lots of body shake at idle, rough even at 1,000-1,100 RPM. During normal driving it makes decent power and I am getting about 20-23 mpg.
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See the list a line before.
Quote:
Originally Posted by AFB24911S
All of these problems have persisted since I bought the car about 5 years ago, but a collapsed suspension, messed up seats, and other issues took precedence. Now, I'm finally getting to the fine tuning.
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Any flaws in my game plan? Other, better ideas?
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Seems to be a decent plan. Conclusion: In such issues you have to take every CIS component in suspect.
Quote:
Originally Posted by AFB24911S
Then, I'm going to check the cold start valve. First to see if it sprays in a nice pattern, then to see if it leaks when it shuts off. I've got six gorgeous plastic volumetric cylinders for that.
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The problem is its reachability. It sits on the backside of the airbox in the bottom case. Very poor to reach. I recommend the following: Go and check out the connections of the TTS. Put in a push button (normally opened) in parallel to the TTS to mimic the TTS and engage the CSV manually. Then start the engine and let it run, push the button then (to inject fuel) and see how the engine reacts: When the CSV works and injects fuel the engine will show it in two ways:
If it runs better => mixture is not rich enough. If it stalls or starts surging => mixture is too rich.
If nothing happens then the CSV is bad/clogged.
Such a push button at the CSV is also extremely useful to determine whether the mixture is lean or rich when cruising or accelerating. Pressing the button on such situations gives the engine some extra fuel. So you get a much better feeling what the engine needs. On accelerating extra fuel let's the engine revs better/quicker? => mixture too lean. If if bogs and stalls, mixture is too rich/rich enough. Also on cruising, starting etc.
But: Be aware of back fire which can happen anytime!!!
Therefore never do such "experiments" without a fire extinguisher in place, as well in the car!!
Carry 2 with you: A bigger and a smaller one... Push the button only short times like 0,5-1 sec or so. You get the idea...
The AAR does not closes completely like a valve. There's always a tiny hole and some leaking air through it:
As this is measured air behind the sensor plate that is no issue!
The AAV must be checked with a vacuum pump the apply vacuum on the control plug to engage it. When the throttle closes the vacuum increases and the AAV must open to give the engine a little extra air to burn the already created mixture for two reasons: To prevent banging in the exhaust and to keep the revs above 1500rpm when changing gears to make gear changes smoothier. Otherwise passengers will nod their heads....often overseen. When the engine rpms drop too quick/fell immdiately to idle rpm when releasing the throttle this clearly leads to this.
One of the most important things and most overseen: The sensor plate height in conjunction of (my description) the injection begin. This means the sensor plate height has a huge effect on the mixture overall. It's height must be adjusted meticously as Porsche/Bosch specified in the manuals. Why is that? The sensor plate height defines the working intervall from being lifted from idle up to WOT. The lower the sensor plate is adjusted, the more way the lever will travel. This enriches the mixture overall. Vice versa if the sensor plate is too high. This will lean the mixture overall. So first of (if all other things have been worked as mentioned before) make the sensor plate height adjustment is correct as specified!
Then in conjunction to this - check the injection begin. This is the point where the sensor plate switches on the fuel pump by being slightly lifted due to the sucked air when engine starts and idles.
These two settings always must be seen in conjunction!!
Also check that the injector valves all spray the same fine moistured pattern and - very important -they spray all the same amount of fuel!! (less than 5% difference each). Otherwise some cylinders run too lean and too hot which may causes valve tickering due to prolonged valves from heat and in the end may cause serious engine damages like broken rocker arms, holes in pistons etc...
You already know the fabulous video series about the 911 2.7 CIS from Klassikats?
https://www.youtube.com/playlist?list=PLkWFofpgz2OgF9FdliKnlzuY0pygqRkMj
Heavily recommended to watch, even more than once. If you better know the CIS the more time and effort you save. Watch all the videos to the end!
Good luck! Curious what you will find out...
Thomas