Any 930 Turbo Owner.. Please Read!

[TurboRuf]

First I’d like to start out by saying this forum has been the best source of Porsche technical information I’ve ever come across. I can’t thank the countless members enough for the help they have given during my restoration.

Now on to the question… for over a year now I’ve tried to get a straight answer on this but have been unsuccessful. I’m simply trying to understand the proper, or most direct, way to connect vacuum on a US turbo distributor. Preferably on an engine with smog hardware removed. This sounds simple however it has baffled even the experts.

I’ve searched the entire archives and posted several questions in the past without ever getting a definitive answer. Hopefully we can clarify this once and for all.

If you could each go out to your 930/911 turbo and follow the vacuum lines from the distributor to where they terminate we could solve this mystery. Not only would I appreciate it but also I’m sure countless other board members would. Once you have traced these two vacuum lines, report your findings back to this forum.

The diagrams posted below will hopefully help clarify a few things. According to Porsche the RED hose was used for distributor Advance. A BLACK hose was used for retard. This would be consistent with the photos listed below that a fellow Pelican member emailed to me. If I’m reading these photos correctly… from the distributor the advance line runs to the thermo time switch. The thermo time switch then connects to the upper right port on the throttle body. The distributor retard line connects directly to the lower left port on the throttle body. Does this sound correct?

Tell me your findings and hopefully we can solve the mystery!

[RarlyL8]

What year is this engine?
It looks like it is California smog equiped.

Everything I see looks right until you get to the distributor. The red and black lines are swiched (or labeled backward).

The black line should go from the retard pot (labeled advance) to the unvented thermo valve (thermo switch) to the bottom of the throttle body.

The red line goes from the advance pot (labeled retard) to the full throttle retard control (cutoff valve). The cutoff valve has three connections.
(1) between the thermo switch and the bottom of the throttle body
(2) splices into the hose between the blow off switching valve and the blow off valve housing
(3) splices into the hose between the WUR and the air cleaner.

I am in the middle of a 930 CIS crash course myself due to a turbo swap gone bad. The information I just regergitated is from my tracing of the 930/63 engine plumbing that was on my '78, the 930 shop manual, and the Bosch CIS manual. All of the smog crap has been removed from my engine. You can get rid of most of this stuff if you wish. A Euro distributor will simplify things and give a more agressive timing curve.

[RJ Gilliam]

Wow what an answer....RarlyL8 you amaze me.

[TurboRuf]

Rarly,

Very informative… thank you for the clarifications. I've had so much misinformation on the subject my head is spinning.

>What year is this engine?
>It looks like it is California smog equiped.

My engine is an 85 ROW with US distributor.

The engine in the pictures I’m not sure about. It was California smog equipped though. The images where emailed to me by another member.

>The red line goes from the advance pot to the full throttle retard >control (cutoff valve). The cutoff valve has three connections.
>(1) between the thermo switch and the bottom of the throttle >body
>(2) splices into the hose between the blow off switching valve >and the blow off valve housing
>(3) splices into the hose between the WUR and the air cleaner.

Are all of these items and connections necessary for the red advance line? I don't have a cutoff valve and the blow-off housing was removed. I now have a C2 Pop-Off valve and long neck intercooler pipe instead.

[RarlyL8]

You have an ROW engine with a California distributor.

You don't need any of this advance stuff. It is only on the engine for smog control devices.

I'm not certain, but you may be able to simply disconnect the advance vac line from the distributor pot and cap the pot and the throttle body. Give it a try. The advance vacuum line pulls from either the air cleaner or the same throttle body port as the retard line, depening on the switching controlled by the cut-off-valve that you no longer have.

With the mods you have it would be worth the money to trade your California distributor and some cash for a US/Japan/Euro unit (preferably Euro).

[TurboRuf]

Rarly

>You have an ROW engine with a California distributor.

Long story but it's true.

>You don't need any of this advance stuff. It is only on the >engine for smog control devices.

This is good information. I was told the distributor needed to advance on startup. This just added to my confusion.

>I'm not certain, but you may be able to simply disconnect the >advance vac line from the distributor pot and cap the pot and >the throttle body. Give it a try.

I'll give this a try and let you know how it works out.

>With the mods you have it would be worth the money to trade >your California distributor and some cash for a US/Japan/Euro >unit (preferably Euro).

I agree, that would certainly make life easier. My problem is the distributor has been modified for the twin-plug RSR cap and rotor. It would be tough convincing someone to trade.

[TurboRuf]

OK, now were getting somewhere!

I found the California diagram and it confirms everything Rarly said. I plan to plug the ports tonight and give it another go.

Rarly, on the Thermo Valve... does the CARB port go to the TB?

Thanks again for the great response.

[expat]

Jesus RarlyL8...bloody applause to you

The guy comes up with a good question and you hit it with certainty, specificity and explain it easy enough for anyone to understand.

I'm not sure why but I feel really impressed. THIS BOARD ROCKS!

Mark

[RarlyL8]

My engine does not have the thermo valve with the threaded port end. It looks like this thing screws directly into your intake.

There are 2 thermo switches (valves) on the California 930. They are #6 and #8 on your diagram. #8 is used to block vacuum retard on the distributor until the engine warms. This switch/valve is unvented. #6 is striclty an emission control device regulating vacuum to the aux. air valve.

The California distributor might need advancement upon startup in your modified application. The advance vac line Ts into the same throttle body vac line used by the vac retard, between the thermo valve and the throttle body.
When the engine is cold the thermo switch/valve is closed. This shuts off vac to the retard pot. At the same time the 3-way cutoff valve in the advance line is open allowing the advance to see vacuum from the same source on the throttle body.

How much advance do you need on start up? I don't know. That depends on the ambient temperature and the fueling that the WUR is giving. This is why I suggested plugging the line. It may be that simple.

EDIT: your cold start problem may not be related to the above items. You have a new WUR that should be shooting fuel in via the 7th injector. The entire system is pressure dependant. If your fuel accumulator is not holding the pressure will bleed down and cause stumble upon startup until the pressure returns. You can check this very simply by pushing your finger down on the air metering plate. If the plate is rigid you have pressure, if not you don't. Hit the key to turn on the pumps - the plate should immediately go rigid. The WUR gets its fuel and pressure from the fuel head.

[TurboRuf]

The plot thickens!!!!!

I went back to review some of the conversations I had with Steve Weiner of Rennsport Systems on this subject. Steve has been extremely helpful in the past and very knowledgeable when it comes to 930’s.

Our conversation read something like this:

Question:
>Since my vacuum canister has an upper and lower port for >advance/retard can I assume it's a California distributor?

Answer:
“All of the USA Turbos, '85-on had that.”

Question:
My vehicle has all of the smog equipment removed, would it make sense to simply plug the lower vacuum canister port (retard)? From what I'm reading the lower port is strictly to help lower emissions?

Answer:
“Its there for ignition retard at full boost, too. You need to keep it.”

Question:
Finally, when the car hits boost is the ignition supposed to advance or retard?

Answer:
“It will retard on-boost, and allow full advance off-boost, for better throttle response and low-end torque. The 78-79 Turbos do not have that lower port on the advance can and they operate differently altogether.”

Wow, did that ever clear things up. So Rarly, it sounds like we are both right. I’m glad I went back to the archives.

I still need to figure out if my distributor vacuum lines are run correctly and if I’m using the proper Thermo Valve.

[RarlyL8]

I'm glad you were able to speak with someone knowledgeable about the post-'85 turbos. It was the ADVANCE line that I suggested you plug, not the retard. That one should be needed in any turbo application (retard on boost).

I tore the top end of my motor off this evening. My engine does not have that screw-in thermo valve. Unfortunately I didn't find anything that would obviously cause my high idle. Double check it again later.

A couple of you guys sang my praises for trying to help out with Ruffs vacuum troubles. I appreciate that but am a bit troubled that others didn't chime in and help out as well. I am learning this stuff right along with you all. There are many folks frequenting this board that are experts. We could sure use the help.

[TurboRuf]

Rarly, your input is always greatly appreciated. You have always taken the time to help clarify my questions, for that I am grateful.

>It was the ADVANCE line that I suggested you plug, not the retard. That one should be needed in any turbo application (retard on boost).

Thanks for the correction.

I tore the top end of my motor off this evening. My engine does not have that screw-in thermo valve. Unfortunately I didn't find anything that would obviously cause my high idle. Double check it again later.

Sorry to hear that you didn’t find anything. The PET guide can be somewhat misleading at times. It looks like they show both Thermo Valves for all of the 930 years. I’m sure it’s one or the other depending on the year.

I have learned a lot on this board over the years and continue to each day. I also expected more experts to respond. We have such a diverse range of people that frequent this board, it’s a shame more people didn’t contribute. Generally the more people that respond the clearer the picture becomes when trying to troubleshoot.

I’ll keep everyone posted on what I discover.

[RarlyL8]

I have noticed something and would like the mechanics among us to confirm this.

The 930 shop manual has three (3) schematics for 930 CIS configurations. This is for every year, '76 to '89. That's just not possible. There is no doubt that every single year had small changes in the system.
I really think this is fact and causing so many of the headaches.

Ruff - you say your distributor has been modified for use with twin plug heads. Was the advance curve modified? The push me-pull you vac/retard game might be hurting the function of this unit. You might need a specific non-standard vac setup to run this unit optimally.

[TurboRuf]

Rarly,

I don't believe the advance curve was modified. It's very similar to the Andial distributor conversion.

[stephenshane237]

Just a quick question for those who understand this part. After warm up both hoses to the distributor have vacuum at the same time and boost at the same time, what stops the lines from working against each other?