BBX

I bought the fuel pressure tester today from Harbor Freight (along with a shopping cart full of junk that I was already contemplating returning on the way home.)
Well the extra junk was a must since Danglerb offered up a great 20% off coupon!

To get to the point,
Can someone write up how to check the fuel pressure before and after the fuel distributor on a CIS car and tell what the pressure should be?

This would help a lot of people in the future!

RicerSchnitzzle

THe BF kit does not have the correct connectors for the CIS system. Sorry. I Have a gauge permanently mounted before the CIS which shows system pressure, should be about 75psi. I also have one on ther control pressure line to the top of the CIS distro. Pressure varies on vacuum once warmed up.

There is no way to adjust main system pressure with out changing the regulator spring set on the distro. I wouldn't mess with it unless you think it's bad. Then change with OEM only.

Here's a walk through on pelican:
http://www.pelicanparts.com/911/tech..._Bosch_CIS.htm

docmirror

Strange, I was gonna do this soon, so here's a good time.

The pressures of the CIS are the critical part of making it run right, unfortunately, there's not much in the way of adjustment.

As with any work involving fuel, have an extinguisher ready, and don't let fittings leak.

1. The hose set should have a closure valve, and the fittings for Bosch fuel inlet. Locate that, and close it.
2. Remove the air cleaner, and locate the CIS head at the rear of the engine in the V. You will see 9 solid lines running off the top of the head. Locate the one in the center. Using a 6pt thin socket, loosen that nut holding the center line.
3. As you remove the banjo fitting, there will be two crush washers, one ea on top and bottom of the banjo fitting, don't loose them.
4. Follow that line forward under the intake, to the warm up regulator. There are two connections on the WUR. Remove the line from the other end of the CIS head. That line can stay in place laying loose below the intake.
5. Connect the hose of the gauge set end away from the closure valve to the WUR using the banjo fitting. Connect the hose end with the closure to the center hole of the CIS head. The fuel will be flowing from the WUR, to the head, through the hose, the tee valve to gauge, through the closure valve, and then to the hose again, and finally to the CIS head.
6. With the valve closed, jump the fuel pump relay, and listen for the fuel pump to run. Key remains off. The gauge should read at least 75Lbs, and not more than about 90Lbs. Remove the fuel pump jumper.
7. Watch the gauge as the jumper is removed. The pressure should not drop too fast. It should retain > 70Lbs for about a minute.
8. Open the valve, and start the engine. The gauge should read about 55Lbs when the engine is cold. This will slowly decrease to about 42Lbs as the car warms up. The low limits can be found in the Bosch book, but these are pretty close.

If your pressures are off, the WUR and the CIS head do have adjustments, but they are kind of tricky. This will give you a good start on checking this critical aspect of the CIS cars.

BBX

The pressure was perfect 75-77lbs between the top of the f.d. line and the WUR. It also holds pressure for quite a while.

So now what? The car will start but not run. Where else should I check?

jpitman2

From my experience, with the valve open (allowing fuel from dist head to run to WUR), cold control pressure should be down around 20psi(temp dependant - see charts in WSM), allowing mixture to richen enough to start. As it warms the pressure should rise to a max of ~45psi. Even if you do seem to get a stable ~45psi with stationery running up to temp, you will need to do a drive around the block to ensure that it doesnt go any higher with driving lifting the temperature - mine once climbed to 60psi and lost almost all power. I have done a doco with pics that should be findable somewhere here, or on landsharkoz, showing the insides of the WUR, and my experiences with them. The small brass aguze filters inside can clog with debris and cause high control pressures - some remove them. The long term solution to this is to DRIVE the thing regularly!
Note that if the electrical connector at WUR is left on with ign on, the 12V supply will warm up the WUR and lift control, so for testing cold control you need to disconnect this wire. You need a copy of Ben Watson, Bosh fuel Injection, Amazon orsimilar, $15. This lists all the hot and cold pressures, how to diagnose etc - invaluable for a CIS owner.
jp 83 Euro S AT 52k

Mrmerlin

any pictures of the hose setup?

jpitman2

Sorry , no picture handy.
I do my setup different from Docm.
Undo line INTO WUR(from fuel dist), lift out of way; connect (via adapters as necessary) hose to inlet pipe such that shutoff valve is on OTHER side of gauge; connect other end of hose to the hole in the WUR where the inlet pipe went in. Disconnect electrical connector from WUR so it doesnt heat up until you want it to. Bridge pump relay - I remove the relay and plug a 2 core lead (~6-8 ft) directly into the 30 & 87 sockets, and have a switch on the end so I can turn the pump on/off from the engine bay. With pump running, closed valve shows system pressure, open valve shows control pressure.
HTH

Mrmerlin

Thanks thats a great description

docmirror

If your control and system pressures are ok, doesn't matter where the shutoff valve is, the deal is that both pressures are in the right area.

Since it's winter, if it will start but not run, you are likely running on the cold start valve, which is a completely separate fuel delivery system. When you say it "won't run", does it die completely after 8-10 seconds? Or does it stumble for a while?

If it dies completely but will start again with the key off then on, you are not getting any fuel through the dist head and to the injectors. If it stumbles, it could be a matter of partial clogging on the dist ports, or the injectors or both.

If it dies completely, a dist port cleaning and injector replacement are in your future. If it will stumble, then you can try to adjust the mixture a bit. 3mm allen in a port on the dist which moves the armature. Go very slow with adjustments. Left/CCW is lean, right/CW is rich.

See step 6 for location: https://rennlist.com/how-tos/a/porsc...gh-idle-376958

Some 928s have a spring loaded screw settting there, and you need to insert the tool, and push down to engage the threaded pin. Some have a plug which needs to be removed, and some have just the 3mm threaded adjustment pin.

Mrmerlin

Hi Doc you might be answering a question from 2009.

I just got a 1979 928 auto and it starts right up and will run at fast idle for about 30 seconds,
then the idle will come down to about 1100 and for about 6 mins as it warms up the idle gets lower and lower eventually the engine dies,
and it will crank all day but not restart.
I have to let the engine cool off to cold beforte it will run again.
It appears that a new WUR was installed and I just put in a new green wire, i have a set of gauges on order from Roger ,
I have no way to test the operating pressures till the CIS test kit gets here.

docmirror

Yup, wrong reply.

check you have the right WUR. If it's the right PN, you'll have to go by the control, then system pressure changes. Having said that, try turning the mixture screw a little richer to keep it running. If you have one of those Gunson colortune deals, you can look at the mixture color as it warms.

gbgastowers

gbgastowers

ROG100

I stock the correct pressure test kit for our CIS cars - $135

jpitman2

Mrmerlin, Can you tell if its dying rich, by a sooty exhaust? If so it sounds like low control pressure, which is unusual, as mostly they go lean with a clogged WUR causing high control pressure. Or maybe the temp-time sensor that controls the cold start injector has failed - try pulling the connector off the time-temp switch. Its only supposed to be powered while cranking, but anything is possible.
jp 83 Euro S AT 57k