Hello; I beleive I Havea CIS issue with my 928

Porche928EURO · 03-17-2005, 05:41 PM

Basicaly the car starts right up and as soon as it does the car looses power.... and the engines slowly shuts down....
So what I beleive is happening is I have a out of balance fuel situation...
the cold start pressure regulator is doing its job to release fuel to start the engine... once completed the the primary regulator is failing .... Please correct me if this sound wrong... I am a new 928 Owner this car is a 1980..... never owning a Porche before I am learning quickly...
I need to check all vacum hoses which this possibly could be a big part of the problem I have already found failed vaccum hoses...... I need to check the air Ring wich regulates by accuating a rod to the mechanicle regulator to tell it how much fuel to let go by, to the injection system wich is constant all the time...
Where would I tap in to the system with 2 fuel pressure regulator to measure the two fuel pressures?
and do you know what theses pressures should read?
is one pressure to the Cold Start regulator and another to the Primary regulator?
anyinformation would be excellent......
Thank you
Phil
I do know this the fuel pump does sound excellent and of course the fuel pump Relay is working...
I have also checked all of the fuses to make sure they are all non corroded...

928ram · 03-17-2005, 06:26 PM

2 things to check before digging directly into fuel injection:

Fuel filter; if you don't have a history of recent replacement get a new one.
Catalytic converter; your problem sounds as much like a clogged cat as a fuel problem.

Any more history on your ownership (duration, new problem or has it been this way since you bought it) could be helpful too.

Cold start is done by the injector at the dead-center front of the plenum; it's controlled by a thermo-time switch, only runs for a few seconds, and is independant of the pressures that run the main injection.
The control pressure regulator (warm-up regulator) controls the CIS main pressure from cold to warm as well enrichment for full throttle operation.
Get all the vac leaks fixed before you dig deeper into the injection also.

More post with pics/tips to follow..

Porche928EURO · 03-17-2005, 06:33 PM

this Problem has just recently started... the Fuel filter looks reasonably new..... the fuel accumulator looks like original equipment...
the Cat I do not think is the problem as this was like one daythe car runs great and the next day I have the scenario as described above......

But the first thing I was going to do is repair all of he vaccum leaks for sure..... which vary well be the condition causing what is going on..

928ram · 03-17-2005, 06:35 PM

Here's a pic of the control pressure regulator, the control pressures are tested by hooking a special gauge set with adapters where these two lines are.
What you need to check 1st: The fittings with the arrows in the pic need to be removed, and underneath you'll find a screen. Check this screen for debris and clean if needed. The screen *can* be removed with a needle or dental pick type devise to be cleaned but is very fragile, so if it doesn't come out use a spray carb cleaner to blow the debris out.

Porche928EURO · 03-17-2005, 06:39 PM

Only one gauge... As I know exactly what you are reffering too... and thank you..
What kind of gauge? what scale?
So basicaly install the gauge in series with the right thread adapter?
What reading should I get? if all is well?
I know that vaccum line is new..
I will have to remove the intake runners to replace some of the faulty vaccum lines... etc........

928ram · 03-17-2005, 06:49 PM

Here's a pic of the fuel distributor:

At location "B" (fuel in from tank/pump), remove the fuel line first then unscrew the second fitting from the fuel distributor.
This fitting contains another screen, just toss the fitting in carb cleaner or laquer thinner (my personal fave) and soak out any schmooey that may have collected in their. It's a very fine and fragile screen; I use an artist's brush with soft bristles if I need to dislodge any specs from there. You'll also need strong light to see if you gotten it clear.

928ram · 03-17-2005, 07:14 PM

The test gauge comes in a set that includes the gauge, adapters, lines, and a valve. I read somewhere that JCwhitney carries a set for around $60, but I'd assume that to be the lowest of quality. Check the Pelican Parts main page to see if they carry a real German-made one (might be under 911). As far as I know, the gauge set is the same for all applications of the CIS system.
I've alway had my pressure tests done at a competent VW shop that used to be local to me.
You don't state whether your car is the 4.5 or 4.7 "S", but the lit I have here gives the same values for both; pressures are in Bars (not sure of the conversion to PSI)
Here's the specs:

Control pressure warm, without vacuum, with engine off and fuel pump running (relay bridged)..........3.0 bar +/- .2 bar
Control pressure with car running at idle speed, with vacuum connected.............................3.6 bar +/- .2 bar
System pressure test value..............5.5-5.8 bar
System pressure adjusting value.......5.3-5.5 bar

With that you've fallen out of my scope of been-there, but as I recall from watching it done the guage is set up on the control pressure regulator for both tests, and the valve that comes with the gauge is open for one test, closed for the other.

Porche928EURO · 03-17-2005, 07:18 PM

Ahhhh My car is a 4.5L 230 horse NON S

carmen78sc · 03-22-2005, 12:39 PM

Does this behavior occur when the car's cold, hot, or both? I used to have this problem on my old '79 only when restarting a warm motor. The fuel accumulator wasn't keeping pressure, allowing vapor lock in the injector lines. Your '80 has a different FI setup, though.