CIS questions
 

I searched and couldn't find an anwser to this. It's a 79sc euro. Here's the deal:

The car runs well only if the control pressure is set to something like 2.0 bar warm. It will start well at 1.0 bar cold. Anything higher and it has a lean misfire at low throttle, like it has a vacuum leak. System pressure ~5 bar. New fuel pump, new accumulator, new injectors, new injector lines, no visible rust in tank, recently changed fuel filter. The fuel distributor is not gummed up, and the barn door moves easily. No hot start problems. I have tried to find a vacuum leak to no avail.

I am at a loss. Any ideas? Also, does anyone happed to have the control pressure specs for a 79 euro? It has to be a euro because the us and euro fuel distributors are different for 1979. Thanks,

so how did you set the warm control pressure at 2.0 bar, being that warm pressure is not adjustable? pull off the vacuum hose?

Have you set the CO correctly using a proper gauge? You may be too lean.

I carefully drilled through the brass cap on the bottom of the WUR. The WOT diaphram can be adjusted by a 3mm nut under that cap. On my WUR (I don't know if this is true for all others), only the atmospheric compensation is destroyed by cutting through that cap. The WOT function still works. Because the adjustment only affects the inner spring you lose some WOT capacity at low pressure.

I got the idea from one of your earlier threads.

As far as the pressure goes, when I bought the car it had been set to 2.0 bar through extreme pin knocking. It ran well warm, but was rich cold. Cold pressure was around 0.5 bar at 50 F, so it flooded the engine every time it started. I drilled and tapped the pin and brought it back up to correct (I thought) spec cold and 3.4 bar warm, but it ran like total crap. So I lowered the cold back down to something reasonable and put the warm back to 2.0.

If 2.0 warm is correct, then that's fine. But according to my cis book that's too low. I don't have any porsche factory literature so I don't know what the real pressures should be.

I have checked the mixture a million times using the push-pull method and my homemade exhaust gas analyzer (3-wire o2 sensor in a pipe). I can richen it up and it runs a little better, but at the expense of idle hunt.

Keep the ideas coming! No suggestion too rediculous!

did you buy it like that? check the WAR and the fuel head numbers, make sure they are both compatable....i had a similair problem, car would run good at 1.0 bar and wont run in spec... turns out the head and regulater for the same car, change WAR to correct head, runs like a champ...

The pressures should be in a range, and that range varies with temperature. The WUR is temperature dependent. At 20 deg. C(68 F), the pressure should be 1.95-2.55 bar (28.3-40.0 PSIG). Get the P-T graph for your car....you are shooting blind.

Adjust the control pressure to when the engine is warm when it should be steady. Your system pressure is good, so your could start circuit may be problematic. You might also have an internal or external air leak. 2.0 bar warm control pressure is too low. The lower that pressure the richer your car will run, but you report knocking ...so somehow it's leaning at off idle RPM. You never want to compensate for poor operations or bad components at idle....find the problem and fix it.

Mobile Wrks: It's not critical to match the WUR to the Fuel Distributor (fuel head number?). The fuel pressure can be in a range. That's what we should care about. I've got a later WUR (from an '80+ SC) on my '79 SC and it runs wonderfully. Flow to the injectors is determined by plunger position and the pressure differential at the fuel distributor. The WUR is just a glorified back pressure regulator with a somewhat predetermined P1-vs-T...that's it!

I'm working on a smarter electronically variable WUR that will be used primarily for turbo applications, but it can be used for NA SC's too....soon we can get rid of that crusty aged WUR. WUR

Dont know what models these are for, but maybe could help.
http://forums.pelicanparts.com/uploa...1113393878.jpg
http://forums.pelicanparts.com/uploa...1113393892.jpg

Thanks for the help guys. I know that I need the proper numbers for my car, I was kind of hoping someone with the right literature would post them. I've got the generic graphs but wasn't sure if they matched, as others have posted that earlier SCs has lower pressures.

I have the proper fuel distributor for the car. I also know that this fuel distributor was used in the 2.7L engines. It makes sense that Porsche would lower the control pressure to make up the increase in displacement. I'm leaning to this conclusion because I've spend 2 months looking for an air leak but cannot find it. I've pulled the throttle body and checked it, replaced all the hoses, manually checked the AAV for closure, checked the distributor diaphram, checked the barn door, inspected the airbox with the throttle body off and pop-off valve open, pulled and resealed the pop-off valve. I put a xenon lamp in the airbox last night in the dark, looking for cracks in the airbox. I can't think of anything else.

Rondinone,

I have 2 charts for 79 cars. If built through Dec 78, your CCP @10C should be 1.6 - 2.05 bar. Warm should be 3.2-3.6 w/ vacuum line attached; 2.7-3.1 w/ line removed.

If built from Jan 79 on, CCP @ 10C = 1.15-1.6, warm 3.2-3.6 w/ vacuum and 2.7-3.1 w/o vacuum.

This is from the Bentley. I honestly don't know if the figures should be different for a Euro. I am assuming you are using a fuel pressure gauge. Are you checking warm w/ vacuum on or off?

You know, it 's possible your WUR is kaput and cannot be adjusted by the pin knocking method because of some other problem area, like the bimetallic strip.

This is not setting the CO properly. You're fiddling with too many things and CIS systems don't take well to fiddling!

Sorry to sidetrack, but I have a related question:
On those graphs they compare temperature to pressure. Where is the temperature reading taken, ambient? At the WUR? Engine temp?

I have a CIS pressure tester hooked up to my car right now and I'm trying to make sense of it. I have the factory manuals, a CIS book, and posts from this board but some of the details are contradictory. Yes, I am a bit slow.

Ambient temp in celcius degrees.

Thanks

Thanks. The wur seems to warm and lean properly, but I've never had it at those values. Let's see if I can do something with the proper pressures. I didn't know Bentley had this much detail. Guess I know what's next on my shopping list.

Story of my life.