Please help interpret CIS troubleshooting results
 

Hi folks. Yes, another CIS problem. Hopefully I have done all that you in the know need to have to help. I followed the thread CIS Troubleshooting for Dummies and I can't thank tirwin enough. His thread was invaluable!

Symptoms: Warm start problems. Car had CIS rebuilt in 9/08 (including NEW WUR) and has run without issue till last week.

Getting ready for DE, I replaced the rear wheel bearings and went for a test drive. Car felt good so I went for a spirited drive for about 30 minutes or so. Temperature reached 180. Came back and left car in driveway so I could clean up my garage. Then had a beer. Went to pull car in maybe two hours later - no start.

Because the car ran so well ( and I could get it started as described below) I decided to go ahead and go the the track (5 hour drive from my house). Cold starting is not a problem at all. First session of the day, no problem. We had a total of 4, 20 minute sessions each day on Saturday and Sunday. For sessions 2, 3 and 4 of each day I had to remove air cleaner, turn key to on, lift sensor plate to pressurize system, start car, rough idle for 15 seconds - run hard on the track. Couldn't wipe grin from face. :cool:

Seems like maybe a bad check valve in the fuel pump, although it is not that old. I know, still could be bad.


1980 US Spec 911SC
Stock except for back dated heat exchangers
I don't think I have a lambda sensor, but could be wrong
WUR .072
Ambient temp 70 F / 21 C
WUR Resistance 9.1 ohms
System pressure 5 Bar
Cold control pressure 2.1 Bar
Warm control pressure - maxed out at just under 3 minutes - 3.6 Bar
Residual pressure - 0 - no pressure retained once pump was shut off.

I did notice when checking system pressure that I had some fuel leaking from at least one port in the fuel distributor. I got my 13mm socket and was able to tighten two bolts. No more leak. I was thinking that might be the problem till I saw no residual pressure. Certainly could be a factor though.

Now I am back to thinking check valve. If it is bad, is there an inline check valve that can be installed instead of replacing the pump?

Thanks for all your help guys, especially tirwin.

Refer to Wacko's post about check valve......
 

Garmo,

Read his (Wacko) recent post about FP check valve. I gave him a detail procedure to test his residual pressure which I believe is your problem too. Keep us posted.

Tony

Thanks Tony. I'll check it out.

Wouldn't the accumulator maintain pressure to the fuel distributor?

WUR out of spec........
 

Garmo,

Aside from the no residual fuel pressure, your WUR-072 is out spec. At 70°F, your WUR resistance should read about 25 - 26 Ohms. And that's the reason why you could get the WCP of 3.6 bar under three (3) mins. This would be a major problem when the weather gets colder. Could you confirm if you are using the ECU/OXS? Thanks.

Tony

Good news guys. Problem seems to be solved. Bad o-ring on my primary pressure regulator. Thanks for the help form Tony and tirwin.

In my little town I simply cannot find the fitting I need to adapt my pressure tester to my fuel accumulator so I could not verify the fuel pump check valve or the accumulator. I happened to have an extra check valve so I put it in - no change. Checked the pressure regulator and found about 75% of the oring. Had one from an old CIS system and poof - problem seems to be solved.

Its a good day!

Happy father's day to y'all.