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CIS Tuning and Diagnostics on my '81 SC

 
Old 03-15-2019, 01:16 PM
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thinkiwanta928
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Default CIS Tuning and Diagnostics on my '81 SC

I've only had the car a week so I'm way early on experience with CIS.
This morning, it was 45F and the car was parked outside overnight rather than in my heated garage. The engine fired very quickly upon cranking and immediately went to 2,000 rpm. Very shortly after, such as 7 seconds, the rpm's dropped and the engine rpm's moved around with the engine popping some. I think popping back through the induction system. (yes, pop off valve installed) After about 30-45 seconds, the rpm's were low, around 800, and the car didn't respond well to a slow increase in throttle. Still trying to warm up in the driveway, the engine was missing some but rpm's were rather constant around 800. After about two minutes, I backed to then end of the driveway and let it warm up some more before taking off. When driving, the engine did not like much throttle demand below 2,500 rpm's with the car missing, feeling like it is struggling for more fuel. Above 2,500, the engine pulled normally under moderate throttle to 3,200 or so when I shifted to the next gear. So, when cold, the engine doesn't like load below 2,500 rpm.

I've been studying the CIS system and need to pick up a fuel pressure gauge setup for diagnostics. I'll be documenting my work on this new thread and thought it would be helpful for a CIS owner.

When fully warm, the engine runs very well and drives/pulls well. A few times, when the temperature was around 70F, I noticed the idle moves up and down ever so slightly, such as 950 - 1050. I can hear the engine note change ever so slightly.
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Old 03-15-2019, 11:26 PM
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Starbuckslova1
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Id honestly recomend checking the cold start valve and maybe tune the cis

this may help


right to richen (CW). always turn it from lean to rich for final adjustment. if you do not have a way to check CO, here is how i set mine. turn it CW until it surges at idle then back off a tad. blip the throttle and if the RPM's dip down then come back up to idle, it is too rich. turn it CCW about half a turn then back CW a little less than how far you turned it CCW. blip the throttle again. repeat until it no longer dips down when the RPM's come back down. mine is set so it has just a hint of wanting to dip down when i let off the gas. drive it and check again. i later had mine checked and it was dead on 3%.

also check for vacuum leaks
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Old 03-16-2019, 01:12 AM
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pmax
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The CSV is working fine if the car starts fine.

Check for air leaks first.
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Old 03-16-2019, 11:09 AM
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thinkiwanta928
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Originally Posted by pmax View Post
The CSV is working fine if the car starts fine.

Check for air leaks first.
Thank you for your thoughts.
Yes, the engine when cold fires with very little cranking, meaning 1-2 seconds. It seems to me the Aux Air Valve, or CSV?, is working properly, but can be easily tested as the CISprimer says it closes as soon as there is 5-6 inches of vacuum, which would be quick.

As for the Auxillary Air Regulator, does someone have a chart which illustrates the relationship of the AAR, ambient air temperature, engine temperature, and when it closes?
I assume this is the device that drops the cold idle from 2,000 rpm to 1,100 or near,13-14 seconds after cold start, which seems like an awfully quick to drop to a normal idle rpm range?

Background on engine - has about 2,200 miles on it rebuilt by a well known Houston area fellow named Peter Baldauf and the machine worked farmed out by Peter to a San Antonio specialist, Jones Autowerks. In January of this year, Peter serviced the engine including setting the valve gaps. The reputations of both of these shops is impeccable thus Iíll assume the engine is very healthy.
Nevertheless, when diagnosing something amiss in how an engine runs, one always runs down a basic checklist which I will:
Check the spark plugs
Check the timing
Inspect the vacuum lines, testing where able, such as inserting a hand vacuum pump and testing devices for movement and that they hold a vacuum. (Note, previous owner installed VDO vacuum gauge in the console, very neat!)
Overall visual inspection of induction rubber pieces and seals lookin for leaks.

1) As far as digging deeper into the operation of the CIS, Iíd like to know an answer to the above question regarding the CSV.
2) Iíll run a fuel pressure test - books and the CISPrimer website state the cold fuel pressure by the Control Pressure Regulator, WUR, should be 1.6 bar at 10C and 3.4 bar at 40, but once again, there is no chart of what happens in between these ranges? Am I to assume that if it is 1.6 when 10C and increases to 3.4 bar when device reaches 40C that it is functioning properly?

Thatís enough for now. Thank you for your help.
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Old 03-16-2019, 11:55 AM
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theiceman
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You need fuel pressure gauges to check the fuel pressure warm up profile.
Compare to spec.
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Old 03-16-2019, 02:16 PM
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pmax
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The idle drop sounds quick, I agree. Try inspecting the half moon plate in the AAR using a small mirror. Maybe it's stuck in the cold temperature. The AARs I have tested take >1-2 min to close.

Last edited by pmax; 03-16-2019 at 02:33 PM.
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Old 03-17-2019, 10:21 PM
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Mark Salvetti
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I would read this thread: http://forums.pelicanparts.com/porsc...g-dummies.html

Contact me by email and I can send you a pdf of the Bosch CIS manual, as well as a manual on how to rebuild the fuel distributor.

Mark
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